Primordial anisotropies from cosmic strings during inflation [CEA]

http://arxiv.org/abs/1703.05714

In this work we study the imprints of a primordial cosmic string on inflationary power spectrum. Cosmic string induces two distinct contributions on curvature perturbations power spectrum. The first type of correction respects the translation invariance while violating isotropy. This generates quadrupolar statistical anisotropy in CMB maps which is constrained by the Planck data. The second contribution breaks both homogeneity and isotropy, generating a dipolar power asymmetry in variance of temperature fluctuations with its amplitude falling on small scales. We show that the strongest constraint on the tension of string is obtained from the quadrupolar anisotropy and argue that the mass scale of underlying theory responsible for the formation of string can not be much higher than the GUT scale. The predictions of string for the diagonal and off-diagonal components of CMB angular power spectrum are presented.

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S. Jazayeri, A. Sadr and H. Firouzjahi
Fri, 17 Mar 17
3/50

Comments: 25 pages, 6 figures

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Constraining holographic cosmology using Planck data [CEA]

http://arxiv.org/abs/1703.05385

Holographic cosmology offers a novel framework for describing the very early Universe in which cosmological predictions are expressed in terms of the observables of a three dimensional quantum field theory (QFT). This framework includes conventional slow-roll inflation, which is described in terms of a strongly coupled QFT, but it also allows for qualitatively new models for the very early Universe, where the dual QFT may be weakly coupled. The new models describe a universe which is non-geometric at early times. While standard slow-roll inflation leads to a (near-)power-law primordial power spectrum, perturbative superrenormalizable QFT’s yield a new holographic spectral shape. Here, we compare the two predictions against cosmological observations. We use CosmoMC to determine the best fit parameters, and MultiNest for Bayesian Evidence, comparing the likelihoods. We find that the dual QFT should be non-perturbative at the very low multipoles ($l \lesssim 30$), while for higher multipoles ($l \gtrsim 30$) the new holographic model, based on perturbative QFT, fits the data just as well as the standard power-law spectrum assumed in $\Lambda$CDM cosmology. This finding opens the door to applications of non-perturbative QFT techniques, such as lattice simulations, to observational cosmology on gigaparsec scales and beyond.

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N. Afshordi, E. Gould and K. Skenderis
Fri, 17 Mar 17
9/50

Comments: 25 pages, 10 figures

Charged massive scalar field configurations supported by a spherically symmetric charged reflecting shell [CL]

http://arxiv.org/abs/1703.05333

The physical properties of bound-state charged massive scalar field configurations linearly coupled to a spherically symmetric charged reflecting shell are studied {\it analytically}. To that end, we solve the Klein-Gordon wave equation for a static scalar field of proper mass $\mu$, charge coupling constant $q$, and spherical harmonic index $l$ in the background of a charged shell of radius $R$ and electric charge $Q$. It is proved that the dimensionless inequality $\mu R<\sqrt{(qQ)^2-(l+1/2)^2}$ provides an upper bound on the regime of existence of the composed charged-spherical-shell-charged-massive-scalar-field configurations. Interestingly, we explicitly show that the {\it discrete} spectrum of shell radii $\{R_n(\mu,qQ,l)\}_{n=0}^{n=\infty}$ which can support the static bound-state charged massive scalar field configurations can be determined analytically. We confirm our analytical results by numerical computations.

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S. Hod
Fri, 17 Mar 17
11/50

Comments: 8 pages

Lectures on the Infrared Structure of Gravity and Gauge Theory [CL]

http://arxiv.org/abs/1703.05448

This is a redacted transcript of a course given by the author at Harvard in spring semester 2016. It contains a pedagogical overview of recent developments connecting the subjects of soft theorems, the memory effect and asymptotic symmetries in four-dimensional QED, nonabelian gauge theory and gravity with applications to black holes. The lectures may be viewed online at https://goo.gl/3DJdOr. Please send typos or corrections to strominger@physics.harvard.edu.

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A. Strominger
Fri, 17 Mar 17
18/50

Comments: 154 pages, 21 figures

Pulsar Timing Constraints on Physics Beyond the Standard Model [CL]

http://arxiv.org/abs/1703.05331

We argue that massive quantum fields source low-frequency long-wavelength metric fluctuations through the quantum fluctuations of their stress-energy, given reasonable assumptions about the analytic structure of its correlators. This can be traced back to the non-local nature of the gauge symmetry in General Relativity, which prevents an efficient screening of UV scales (what we call the cosmological non-constant problem). We define a covariant and gauge-invariant observable which probes line-of-sight spacetime curvature fluctuations on an observer’s past lightcone, and show that current pulsar timing data constrains any massive particle to $m\lesssim 600$ GeV. This astrophysical bound severely limits the possibilities for physics beyond the standard model below the scale of quantum gravity.

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N. Afshordi, H. Kim and E. Nelson
Fri, 17 Mar 17
20/50

Comments: 5 pages, 2 figures; comments welcome

Secluded and Flipped Dark Matter and Stueckelberg Extensions of the Standard Model [CL]

http://arxiv.org/abs/1703.05275

We consider here three dark matter models with the gauge symmetry of the standard model plus an additional local $U(1)_D$ factor. One model is secluded and two models are flipped. All of these models include one dark fermion and one vector boson that attains mass through the Stueckelberg mechanism. We show that the flipped models provide examples dark matter composed of “least interacting particles” (LIPs). Such particles are therefore compatible with the constraints obtained from both laboratory measurements and astrophysical observations.

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E. Fortes, V. Pleitez and F. Stecker
Fri, 17 Mar 17
37/50

Comments: 6 pages, no figures

Dirac states of an electron in a circular intense magnetic field [HEAP]

http://arxiv.org/abs/1703.05193

Neutron-star magnetospheres are structured by very intense magnetic fields extending from 100 to 10 5 km traveled by very energetic electrons and positrons with Lorentz factors up to $\sim$ 10 7. In this context, particles are forced to travel almost along the magnetic field with very small gyro-motion, potentially reaching the quantified regime. We describe the state of Dirac particles in a locally uniform, constant and curved magnetic field in the approximation that the Larmor radius is very small compared to the radius of curvature of the magnetic field lines. We obtain a result that admits the usual relativistic Landau states as a limit of null curvature. We will describe the radiation of these states, that we call quantum curvature or synchro-curvature radiation, in an upcoming paper.

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G. Voisin, S. Bonazzola and F. Mottez
Thu, 16 Mar 17
32/92

Comments: N/A

General dynamical properties of cosmological models with nonminimal kinetic coupling [CL]

http://arxiv.org/abs/1703.04966

We consider cosmological dynamics in the theory of gravity with the scalar field possessing the nonminimal kinetic coupling to curvature given as $\eta G^{\mu\nu}\phi_{,\mu}\phi_{,\nu}$, where $\eta$ is an arbitrary coupling parameter, and the scalar potential $V(\phi)$ which assumed to be as general as possible. With an appropriate dimensionless parameterization we represent the field equations as an autonomous dynamical system which contains ultimately only one arbitrary function $\chi (x)= 8 \pi G |\eta| V(x/\sqrt{8 \pi G})$. Then, assuming the rather general properties of $\chi(x)$, we analyze stationary points and their stability, as well as all possible asymptotical regimes of the dynamical system. It has been shown that for a broad class of $\chi(x)$ there exist attractors representing three accelerated regimes of the Universe evolution, including de Sitter expansion (or late-time inflation), the Little Rip scenario, and the Big Rip scenario. As the specific examples, we consider a power-law potential $V(\phi)=M^4(\phi/\phi_0)^\alpha$, Higgs-like potential $V(\phi)=\frac{\lambda}{4}(\phi^2-\phi_0^2)^2$, and exponential potential $V(\phi)=M^4 e^{-\phi/\phi_0}$.

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J. Matsumoto and S. Sushkov
Thu, 16 Mar 17
65/92

Comments: 26 pages, 3 figures, 3 tables

Massive Fields as Systematics for Single Field Inflation [CEA]

http://arxiv.org/abs/1703.04477

During inflation, massive fields can contribute to the power spectrum of curvature perturbation via a dimension-5 operator. This contribution can be considered as a bias for the program of using $n_s$ and $r$ to select inflation models. Even the dimension-5 operator is suppressed by $\Lambda = M_p$, there is still a significant shift on the $n_s$-$r$ diagram if the massive fields have $m\sim H$. On the other hand, if the heavy degree of freedom appear only at the same energy scale as the suppression scale of the dimension-5 operator, then significant shift on the $n_s$-$r$ diagram takes place at $m=\Lambda \sim 70H$, which is around the inflationary time-translation symmetry breaking scale. Hence, the systematics from massive fields pose a greater challenge for future high precision experiments for inflationary model selection. This result can be thought of as the impact of UV sensitivity to inflationary observables.

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H. Jiang and Y. Wang
Tue, 14 Mar 17
11/74

Comments: 11 pages, 3 figures

Nonlinear Resonant Oscillation of Gravitational Potential Induced by Ultralight Axion in $f(R)$ Gravity [CEA]

http://arxiv.org/abs/1703.03589

We study the ultralight axion dark matter with mass around $10^{-22}$ eV in $f(R)$ gravity which might resolve the dark energy problem. In particular, we focus on the fact that the pressure of the axion field oscillating in time produces oscillations of gravitational potentials. We show that the oscillation of the gravitational potential is sensitive to the model of gravity. Remarkably, we find that the detectability of the oscillation through the gravitational wave detectors can be significantly enhanced due to the nonlinear resonance between the ultralight axion and the scalaron.

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A. Aoki and J. Soda
Mon, 13 Mar 17
4/48

Comments: 19 pages, 4 figures

Effective Description of Higher-Order Scalar-Tensor Theories [CL]

http://arxiv.org/abs/1703.03797

Most existing theories of dark energy and/or modified gravity, involving a scalar degree of freedom, can be conveniently described within the framework of the Effective Theory of Dark Energy, based on the unitary gauge where the scalar field is uniform. We extend this effective approach by allowing the Lagrangian in unitary gauge to depend on the time derivative of the lapse function. Although this dependence generically signals the presence of an extra scalar degree of freedom, theories that contain only one propagating scalar degree of freedom, in addition to the usual tensor modes, can be constructed by requiring the initial Lagrangian to be degenerate. Starting from a general quadratic action, we derive the dispersion relations for the linear perturbations around Minkowski and a cosmological background. Our analysis directly applies to the recently introduced Degenerate Higher-Order Scalar-Tensor (DHOST) theories. For these theories, we find that one cannot recover a Poisson-like equation in the static linear regime except for the subclass that includes the Horndeski and so-called “beyond Horndeski” theories. We also discuss Lorentz-breaking models inspired by Horava gravity.

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D. Langlois, M. Mancarella, K. Noui, et. al.
Mon, 13 Mar 17
12/48

Comments: N/A

Exotic Compact Objects and How to Quench their Ergoregion Instability [CL]

http://arxiv.org/abs/1703.03696

Gravitational-wave astronomy can give us access to the structure of black holes, potentially probing microscopic or even Planckian corrections at the horizon scale, as those predicted by some quantum-gravity models of exotic compact objects. A generic feature of these models is the replacement of the horizon by a reflective surface. Objects with these properties are prone to the so-called ergoregion instability when they spin sufficiently fast. We investigate in detail a simple model consisting of scalar perturbations of a Kerr geometry with a reflective surface near the horizon. The instability depends on the spin, on the compactness, and on the reflectivity at the surface. The instability time scale increases logarithmically in the black-hole limit but, for a perfectly reflecting object, this is not enough to prevent the instability from occurring on dynamical time scales. However, we find that an absorption rate at the surface as small as 0.4% (reflectivity coefficient as large as $|{\cal R}|^2=0.996$) is sufficient to quench the instability completely. Our results suggest that exotic compact objects are not necessarily ruled out by the ergoregion instability.

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E. Maggio, P. Pani and V. Ferrari
Mon, 13 Mar 17
37/48

Comments: 10 pages, 5 figures

Sourcing Dark Matter and Dark Energy from $α$-attractors [CL]

http://arxiv.org/abs/1703.03295

Recently, Kallosh and Linde have drawn attention to a new family of superconformal inflationary potentials, subsequently called $\alpha$-attractors. The $\alpha$-attractor family can interpolate between a large class of inflationary models. It also has an important theoretical underpinning within the framework of supergravity. We demonstrate that the $\alpha$-attractors have an even wider appeal since they may describe dark matter and perhaps even dark energy. The dark matter associated with the $\alpha$-attractors, which we call $\alpha$-dark matter ($\alpha$DM), shares many of the attractive features of fuzzy dark matter, with $V(\varphi) = \frac{1}{2}m^2\varphi^2$, while having none of its drawbacks. Like fuzzy dark matter, $\alpha$DM can have a large Jeans length which could resolve the cusp-core and substructure problems faced by standard cold dark matter. $\alpha$DM also has an appealing tracker property which enables it to converge to the late-time dark matter asymptote, $\langle w\rangle \simeq 0$, from a wide range of initial conditions. It thus avoids the enormous fine-tuning problems faced by the $m^2\varphi^2$ potential in describing dark matter.

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S. Mishra, V. Sahni and Y. Shtanov
Fri, 10 Mar 17
50/52

Comments: 40 pages, 22 figures

Instabilities in Mimetic Matter Perturbations [CL]

http://arxiv.org/abs/1703.02923

We study cosmological perturbations in mimetic matter scenario with a general higher derivative function. We show that the model suffers from the ghost and the gradient instabilities. We perform the analysis in both comoving and Newtonian gauges and confirm that the Hamiltonians and the associated instabilities are consistent with each other in both gauges. The existence of instabilities is independent of the specific form of higher derivative function which generates gradients for mimetic field perturbations. It is verified that these instabilities are not associated with the higher derivative instabilities such as the Ostrogradsky ghost.

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H. Firouzjahi, M. Gorji and A. Mansoori
Thu, 9 Mar 17
8/54

Comments: N/A

Inflationary Dynamics with a Smooth Slow-Roll to Constant-Roll Era Transition [CL]

http://arxiv.org/abs/1703.02853

In this paper we investigate the implications of having a varying second slow-roll index on the canonical scalar field inflationary dynamics. We shall be interested in cases that the second slow-roll can take small values and correspondingly large values, for limiting cases of the function that quantifies the variation of the second slow-roll index. As we demonstrate, this can naturally introduce a smooth transition between slow-roll and constant-roll eras. We discuss the theoretical implications of the mechanism we introduce and we use various illustrative examples in order to better understand the new features that the varying second slow-roll index introduces. In the examples we will present, the second slow-roll index has exponential dependence on the scalar field, and in one of these cases, the slow-roll era corresponds to a type of $\alpha$-attractor inflation. Finally, we briefly discuss how the combination of slow-roll and constant-roll may lead to non-Gaussianities in the primordial perturbations.

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S. Odintsov and V. Oikonomou
Thu, 9 Mar 17
33/54

Comments: N/A

Reconstruction of extended inflationary potentials for attractors [CL]

http://arxiv.org/abs/1703.02220

We give the procedure to reconstruct the extended inflationary potentials for general scalar-tensor theory of gravity and use the $\alpha$ attractor and the constant slow-roll model as examples to show how to reconstruct the class of extended inflationary potentials in the strong coupling limit. The class of extended inflationary potentials have the same attractor in the strong coupling limit, and the reconstructed extended inflationary potentials are consistent with the observational constraints. We also derive the condition on the coupling constant $\xi$ for satisfying the strong coupling.

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Q. Gao and Y. Gong
Thu, 9 Mar 17
41/54

Comments: 12 pages, 3 figures

Über-Gravity and the Cosmological Constant Problem [CL]

http://arxiv.org/abs/1703.02052

Recently, the idea of taking ensemble average over gravity models has been introduced. Based on this idea, we study the ensemble average over (effectively) all the gravity models dubbing the name \”ubergravity. The \”ubergravity has interesting universal properties, independent from the choice of basis: $i)$ it mimics Einstein-Hilbert gravity for high-curvature regime, $ii)$ it predicts stronger gravitational force for an intermediate-curvature regime, $iii)$ surprisingly, for low-curvature regime, i.e. $R<R_0$ where $R$ is Ricci scalar and $R_0$ is a given scale, the Lagrangian vanishes automatically and $iiii)$ there is a sharp transition between low- and intermediate-curvature regimes at $R=R_0$. We show that the \”ubergravity response is robust to any value of the vacuum energy, $\rho_{vac}$. This means the response to any non-vanishing value of $\rho_{vac}$ gives an exact deSitter solution where $R_0$ plays the role of the cosmological constant. Consequently, $R_0$ should be fixed by the observations and there is no need to fine-tune the cosmological constant.

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N. Khosravi
Wed, 8 Mar 17
21/60

Comments: 5 pages, 4 figures, comments are welcomed

Unitary NEC violation in P(X) cosmologies [CL]

http://arxiv.org/abs/1703.00025

A non-singular cosmological bounce in the Einstein frame can only take place if the Null Energy Condition (NEC) is violated. We explore situations where a single scalar field drives the NEC violation and derive the constraints imposed by demanding tree level unitarity on a cosmological background. We then focus on the explicit constraints that arise in P(X) theories and show that constraints from perturbative unitarity make it impossible for the NEC violation to occur within the region of validity of the effective field theory without also involving irrelevant operators that arise at a higher scale that would enter from integrating out more massive degrees of freedom. Within the context of P(X) theories we show that including such operators allows for a bounce that does not manifestly violate tree level unitarity, but at the price of either imposing a shift symmetry or involving technically unnatural small operator coefficients within the low-energy effective field theory.

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C. Rham and S. Melville
Wed, 8 Mar 17
51/60

Comments: 35 pages, 1 figure

Scalar and vector Galileons [CL]

http://arxiv.org/abs/1703.01884

An alternative for the construction of fundamental theories is the introduction of Galileons. These are fields whose action leads to non higher than second-order equations of motion. As this is a necessary but not sufficient condition to make the Hamiltonian bounded from below, as long as the action is not degenerate, the Galileon construction is a way to avoid pathologies both at the classical and quantum levels. Galileon actions are, therefore, of great interest in many branches of physics, specially in high energy physics and cosmology. This proceedings contribution presents the generalities of the construction of both scalar and vector Galileons following two different but complimentary routes.

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Y. Rodriguez and A. Navarro
Tue, 7 Mar 17
2/66

Comments: LaTeX file in jpconf style, 12 pages, no figures. To be published in Journal of Physics: Conference Series as the proceedings of the 70&70 Classical and Quantum Gravitation Party: Meeting with Two Latin American Masters on Theoretical Physics (Cartagena de Indias – Colombia, 28th-30th September, 2016)

Massive Galileon Positivity Bounds [CL]

http://arxiv.org/abs/1702.08577

The EFT coefficients in any gapped, scalar, Lorentz invariant field theory must satisfy positivity requirements if there is to exist a local, analytic Wilsonian UV completion. We apply these bounds to the tree level scattering amplitudes for a massive Galileon. The addition of a mass term, which does not spoil the non-renormalization theorem of the Galileon and preserves the Galileon symmetry at loop level, is necessary to satisfy the lowest order positivity bound. We further show that a careful choice of successively higher derivative corrections are necessary to satisfy the higher order positivity bounds. There is then no obstruction to a local UV completion from considerations of tree level 2-to-2 scattering alone. To demonstrate this we give an explicit example of such a UV completion.

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C. Rham, S. Melville, A. Tolley, et. al.
Tue, 7 Mar 17
26/66

Comments: 31 pages

Black hole acoustics in the minimal geometric deformation of a de Laval nozzle [CL]

http://arxiv.org/abs/1703.01528

The correspondence between sound waves, in a de Laval propelling nozzle, and quasinormal modes emitted by brane-world black holes deformed by a 5D bulk Weyl fluid are here explored and scrutinised. The analysis of sound waves patterns in a de Laval nozzle at a laboratory, reciprocally, is here shown to provide relevant data about the 5D bulk Weyl fluid and its on-brane projection, comprised by the minimal geometrically deformed compact stellar distribution on the brane. Acoustic perturbations of the gas fluid flow in the de Laval nozzle are proved to coincide to the quasinormal modes of black holes solutions deformed by the 5D Weyl fluid, in the geometric deformation procedure. Hence, in a phenomenological E\”otv\”os-Friedmann fluid brane-world model, the realistic shape of a de Laval nozzle is derived and its consequences studied.

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R. Rocha
Tue, 7 Mar 17
32/66

Comments: 7 pages, 3 figures

Higher Derivative Field Theories: Degeneracy Conditions and Classes [CL]

http://arxiv.org/abs/1703.01623

We provide a full analysis of ghost free higher derivative field theories with coupled degrees of freedom. Assuming the absence of gauge symmetries, we derive the degeneracy conditions in order to evade the Ostrogradsky ghosts, and analyze which (non)trivial classes of solutions this allows for. It is shown explicitly how Lorentz invariance avoids the propagation of “half” degrees of freedom. Moreover, for a large class of theories, we construct the field redefinitions and/or (extended) contact transformations that put the theory in a manifestly first order form. Finally, we identify which class of theories cannot be brought to first order form by such transformations.

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M. Crisostomi, R. Klein and D. Roest
Tue, 7 Mar 17
34/66

Comments: 26 pages, 1 figure

Cosmological Dynamics of D-BIonic and DBI Scalar Field and Coincidence Problem of Dark Energy [CL]

http://arxiv.org/abs/1703.01745

We study the cosmological dynamics of D-BIonic and DBI scalar field, which is coupled to matter fluid. For the exponential potential and the exponential couplings, we find a new analytic scaling solution yielding the accelerated expansion of the Universe. Since it is shown to be an attractor for some range of the coupling parameters, the density parameter of matter fluid can be the observed value, as in the coupled quintessence with a canonical scalar field. Contrary to the usual coupled quintessence, where the value of matter couple giving observed density parameter is too large to satisfy observational constraint from CMB, we show that the D-BIonic theory can give similar solution with much smaller value of matter coupling. As a result, together with the fact that the D-BIonic theory has a screening mechanism, the D-BIonic theory can solve the so-called coincidence problem as well as the dark energy problem.

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S. Panpanich, K. Maeda and S. Mizuno
Tue, 7 Mar 17
39/66

Comments: 15 pages, 7 figures

COSMOS-$e'$- soft Higgsotic attractors [CL]

http://arxiv.org/abs/1703.01750

In this work, we have developed an elegant algorithm to study the cosmological consequences from a huge class of quantum field theories (i.e. superstring theory, supergravity, extra dimensional theory, modified gravity etc.), which are equivalently described by soft attractors in the effective field theory framework. In this description we have restricted our analysis for two scalar fields – dilaton and Higgsotic fields minimally coupled with Einstein gravity, which can be generalized for any arbitrary number of scalar field contents with generalized non-canonical and non-minimal interactions. We have explicitly used $R^2$ gravity, from which we have studied the attractor and non-attractor phase by exactly computing two point, three point and four point correlation functions from scalar fluctuations using In-In (Schwinger-Keldysh) and $\delta {\cal N}$ formalism. We have also presented theoretical bounds on the amplitude, tilt and running of the primordial power spectrum, various shapes (equilateral, squeezed, folded kite or counter collinear) of the amplitude as obtained from three and four point scalar functions, which are consistent with observed data. Also the results from two point tensor fluctuations and field excursion formula are explicitly presented for attractor and non-attractor phase. Further, reheating constraints, scale dependent behaviour of the couplings and the dynamical solution for the dilaton and Higgsotic fields are also presented. New sets of consistency relations between two, three and four point observables are also presented, which shows significant deviation from canonical slow roll models. Additionally, three possible theoretical proposals have presented to overcome the tachyonic instability at the time of late time acceleration. Finally, we have also provided the bulk interpretation from the three and four point scalar correlation functions for completeness.

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S. Choudhury
Tue, 7 Mar 17
47/66

Comments: 221 pages, 37 figures, 6 tables

Generalized $α$-attractor models from elementary hyperbolic surfaces [CL]

http://arxiv.org/abs/1703.01650

We consider generalized $\alpha$-attractor models whose scalar potentials are globally well-behaved and whose scalar manifolds are elementary hyperbolic surfaces. Beyond the Poincare disk $\mathbb{D}$, such surfaces include the hyperbolic punctured disk $\mathbb{D}^\ast$ and the hyperbolic annuli $\mathbb{A}(R)$ of modulus $\mu=2\log R>0$. For each elementary surface, we discuss its decomposition into canonical end regions and give an explicit construction of the embedding into the Kerekjarto-Stoilow compactification (which in all cases is the unit sphere), showing how this embedding allows for a universal treatment of globally well-behaved scalar potentials upon expanding their extension in real spherical harmonics. For certain simple but natural choices of extended potentials, we compute scalar field trajectories by projecting numerical solutions of the lifted equations of motion from the Poincare half-plane through the uniformization map, thus illustrating the rich cosmological dynamics of such models.

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M. Babalic and C. Lazaroiu
Tue, 7 Mar 17
58/66

Comments: 36 pages

Thermal Inflation with a Thermal Waterfall Scalar Field Coupled to a Light Spectator Scalar Field [CL]

http://arxiv.org/abs/1702.08855

A new model of thermal inflation is introduced, in which the mass of the thermal waterfall field is dependent on a light spectator scalar field. Using the $\delta N$ formalism, the “end of inflation” scenario is investigated in order to ascertain whether this model is able to produce the dominant contribution to the primordial curvature perturbation. A multitude of constrains are considered so as to explore the parameter space, with particular emphasis to key observational signatures. For natural values of the parameters, the model is found to yield a sharp prediction for the scalar spectral index and its running, well within the current observational bounds.

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K. Dimopoulos, D. Lyth and A. Rumsey
Mon, 6 Mar 17
6/47

Comments: 14 pages, 4 figures

The Linear Point: A cleaner cosmological standard ruler [CEA]

http://arxiv.org/abs/1703.01275

We show how a characteristic length scale imprinted in the galaxy 2-point correlation function, dubbed the “linear point”, can serve as a comoving cosmological standard ruler. In contrast to the Baryon Acoustic Oscillation peak location, this scale is constant in redshift and it is not affected by non-linear effects to within $0.5$ percent precision. We measure the location of the linear point in the galaxy correlation function of the LOWZ and CMASS samples from the Twelfth Data Release (DR12) of the Baryon Oscillation Spectroscopic Survey (BOSS) collaboration. We combine our linear point measurement with Cosmic Microwave Background constraints from the Planck satellite to estimate the isotropic-volume distance $D_{V}(z)$ without relying on a model-template or reconstruction method. We find $D_V(0.32)=1241\pm 50$ Mpc and $D_V(0.57)=2060\pm 33$ Mpc respectively, which are consistent with the quoted values from the BOSS collaboration. This remarkable result suggests that all the distance information contained in the Baryon Acoustic Oscillations can be conveniently compressed into the single length associated with the linear point.

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S. Anselmi, G. Starkman, P. Corasaniti, et. al.
Mon, 6 Mar 17
24/47

Comments: 4 pages, 1 figure

Cosmological Perturbations in the 5D Holographic Big Bang Model [CEA]

http://arxiv.org/abs/1703.00954

The 5D Holographic Big Bang is a novel model for the emergence of the early universe out of a 5D collapsing star (an apparent white hole), in the context of Dvali-Gabadadze-Porrati (DGP) cosmology. The model does not have a big bang singularity, and yet can address cosmological puzzles that are traditionally solved within inflationary cosmology. In this paper, we compute the exact power spectrum of cosmological curvature perturbations due to the effect of a thin atmosphere accreting into our 3-brane. The spectrum is scale-invariant on small scales and red on intermediate scales, but becomes blue on scales larger than the height of the atmosphere. While this behaviour is broadly consistent with the non-parametric measurements of the primordial scalar power spectrum, it is marginally disfavoured relative to a simple power law (at 2.7$\sigma$ level). Furthermore, we find that the best fit nucleation temperature of our 3-brane is at least 3 orders of magnitude larger than the 5D Planck mass, suggesting an origin in a 5D quantum gravity phase.

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N. Altamirano, E. Gould, N. Afshordi, et. al.
Mon, 6 Mar 17
33/47

Comments: 21 pages, 4 figures, 2 tables

Quintessential Inflation with $α$-attractors [CL]

http://arxiv.org/abs/1703.00305

A novel approach to quintessential inflation model building is studied, within the framework of $\alpha$-attractors, motivated by supergravity theories. Inflationary observables are in excellent agreement with the latest CMB observations, while quintessence explains the dark energy observations without any fine-tuning. The model is kept intentionally minimal, avoiding the introduction of many degrees of freedom, couplings and mass scales. In stark contrast to $\Lambda$CDM, for natural values of the parameters, the model attains transient accelerated expansion, which avoids the future horizon problem, while it maintains the field displacement mildly sub-Planckian such that the flatness of the quintessential tail is not lifted by radiative corrections and violations of the equivalence principle (fifth force) are under control. In particular, the required value of the cosmological constant is near the eletroweak scale. Attention is paid to the reheating of the Universe, which avoids gravitino overproduction and respects nucleosynthesis constraints. Kination is treated in a model independent way. A spike in gravitational waves, due to kination, is found not to disturb nucleosynthesis as well.

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K. Dimopoulos and C. Owen
Mon, 6 Mar 17
47/47

Comments: 19 pages, 4 figures

Phases of New Physics in the BAO Spectrum [CEA]

http://arxiv.org/abs/1703.00894

We show that the phase of the spectrum of baryon acoustic oscillations (BAO) is immune to the effects of nonlinear evolution. This suggests that any new physics that contributes to the initial phase of the BAO spectrum, such as extra light species in the early universe, can be extracted reliably at late times. We provide three arguments in support of our claim: First, we point out that a phase shift of the BAO spectrum maps to a characteristic sign change in the real space correlation function and that this feature cannot be generated or modified by nonlinear dynamics. Second, we confirm this intuition through an explicit computation, valid to all orders in cosmological perturbation theory. Finally, we provide a nonperturbative argument using general analytic properties of the linear response to the initial oscillations. Our result motivates measuring the phase of the BAO spectrum as a robust probe of new physics.

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D. Baumann, D. Green and M. Zaldarriaga
Fri, 3 Mar 17
44/62

Comments: 21 pages, 3 figures

Self-similar accretion in thin disks around near-extremal black holes [HEAP]

http://arxiv.org/abs/1703.00022

Near-maximally spinning black holes display conformal symmetry in their near-horizon region, which is therefore the locus of critical phenomena. In this paper we revisit the Novikov-Thorne accretion thin disk model and find a new self-similar radiation-dominated solution in the extremely high spin regime. Motivated by the self-consistency of the model, we require that matter flows at the sound speed at the innermost stable orbit (ISCO). We observe that, when the disk pressure is dominated by radiation at the ISCO, which occurs for the best-fit Novikov-Thorne model of GRS 1915+105, the Shakura-Sunyaev viscosity parameter can be expressed in terms of the spin, mass accretion rate and radiative efficiency. We quantitatively describe how the exact thin disk solution approaches the self-similar solution in the vicinity of the ISCO and for increasing spins.

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G. Compere and R. Oliveri
Thu, 2 Mar 17
7/44

Comments: 13 pages, 6 figures, to be submitted to MNRAS

The Gravitational Wave Physics [CL]

http://arxiv.org/abs/1703.00187

The direct detection of gravitational wave by LIGO indicates the coming of the era of gravitational wave astronomy and gravitational wave cosmology. It is expected that more and more gravitational wave events will be detected by currently existing and planed gravitational wave detectors. The gravitational waves open a new window to explore the Universe and various mysteries will be disclosed through the gravitational wave detection, combined with other cosmological probes. The gravitational wave physics is not only related to gravitation theory, but also is closely tied to fundamental physics, cosmology and astrophysics. In this review article, three kinds of sources of gravitational waves and relevant physics will be discussed, namely gravitational waves produced during the inflation and preheating phases of the Universe, the gravitational waves produced during the first order phase transition as the Universe cools down and the gravitational waves from the three phases: inspiral, merger and ringdown of a compact binary system, respectively. We will also discuss the gravitational waves as a standard siren to explore the evolution of the Universe.

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R. Cai, Z. Cao, Z. Guo, et. al.
Thu, 2 Mar 17
29/44

Comments: 37 pages, 7 figures, invited review for National Science Review

Photonic Chiral Vortical Effect [CL]

http://arxiv.org/abs/1702.08886

Circularly polarized photons have the Berry curvature in the semiclassical regime. Based on the kinetic equation for such chiral photons, we derive the (non)equilibrium expression of the photon current in the direction of the vorticity. We briefly discuss the relevance of this “photonic chiral vortical effect” in pulsars and rotating massive stars and its possible realization in semiconductors.

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N. Yamamoto
Wed, 1 Mar 17
7/67

Comments: 9 pages

Photon-Axion Conversion, Magnetic Field Configuration and Polarization of Photons [CEA]

http://arxiv.org/abs/1702.08843

We study the evolution of photon polarization during the photon-axion conversion process with focusing on the magnetic field configuration dependence. Most previous studies have been carried out in a conventional model where a network of magnetic domains is considered and each domain has a constant magnetic field. We investigate a more general model where a network of domains is still assumed, but each domain has a helical magnetic field. We find that the asymptotic behavior does not depend on the configuration of magnetic fields. Remarkably, we analytically obtain the asymptotic values of the variance of polarization in the conventional model. When the helicity is small, we show that there appears the damped oscillating behavior in the early stage of evolution. Moreover, we see that the constraints on the axion coupling and the cosmological magnetic fields using polarization observations are affected by the magnetic field configuration. This is because the different transient behavior of polarization dynamics is caused by the different magnetic field configuration.

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E. Masaki, A. Aoki and J. Soda
Wed, 1 Mar 17
18/67

Comments: 26 pages, 7 figures

Cosmic strings and other topological defects in nonscaling regimes [CEA]

http://arxiv.org/abs/1702.08453

Cosmic strings are topological defects possibly formed in the early Universe, which may be observable due to their gravitational effects on the cosmic microwave background radiation or gravitational wave experiments. To this effect it is important to quantitatively ascertain the network properties, including their density, velocity or the number of strings present, at the various epochs in the observable Universe. Attempts to estimate these numbers often rely on simplistic approximations for the string parameters, such as assuming that the network is scaling. However, in cosmological models containing realistic amounts of radiation, matter and dark energy a string network is never exactly scaling. Here we use the velocity-dependent one-scale model for the evolution of a string network to better quantify how these networks evolve. In particular we obtain new approximate analytic solutions for the behavior of the network during the radiation-to-matter and matter-to-acceleration transitions (assuming, in the latter case, the canonical $\Lambda$ cold dark matter model), and numerically calculate the relevant quantities for a range of possible dark energy models.

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R. Azevedo and C. Martins
Wed, 1 Mar 17
27/67

Comments: 10 pages, 5 figures

Inflaton Condensate Fragmentation: Analytical Conditions and Application to $α$-Attractor Models [CEA]

http://arxiv.org/abs/1702.08777

We study the stability of an inflaton condensate in the presence of an attractive inflaton self-interaction, in order to determine analytical conditions on the self-interaction couplings under which the condensate undergoes fragmentation. As an application of our results, we consider the stability of the inflaton condensate in E-model and T-model $\alpha$-attractor inflation. We show that the stability of the condensate depends upon the value of $\alpha$. For the E-model with $q = 1$, the condensate is unstable for $\alpha \lesssim 0.16$, while for the T-model with $q = 1$ it is unstable for $\alpha \lesssim 10^{-4}$. In these cases it is expected that inflation will be followed by an oscillon-dominated era.

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J. Kim and J. McDonald
Wed, 1 Mar 17
30/67

Comments: 4 pages

Shapes and features of the primordial bispectrum [CEA]

http://arxiv.org/abs/1702.08756

We offer a new approach to analyse the appearance of features in the primordial bispectrum that justifies the search of oscillating patterns modulated by orthogonal and local templates in the cosmic microwave background data. By studying the dynamics of the primordial curvature perturbation during inflation, we find that the couplings parametrising cubic self-interactions, responsible for features, can be expressed as functions of the bispectrum along specific directions in momentum space. As a result, we find a general expression describing departures from scale invariance in the bispectrum telling us how these appear modulated by different classes of shapes. On one hand, this result allows us to relate features appearing in different shapes in a unique way, such that if they are observed in a particular shape, they have to spread to others obeying certain rules. On the other hand, it serves as a tool to produce new templates of features in the bispectrum modulated by shapes that so far have not been considered to analyse data.

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J. Gong, G. Palma and S. Sypsas
Wed, 1 Mar 17
51/67

Comments: 16 pages, 3 figures, 1 table

Cosmology in beyond-generalized Proca theories [CL]

http://arxiv.org/abs/1702.08610

The beyond-generalized Proca theories are the extension of second-order massive vector-tensor theories (dubbed generalized Proca theories) with two transverse vector modes and one longitudinal scalar besides two tensor polarizations. Even with this extension, the propagating degrees of freedom remain unchanged on the isotropic cosmological background without an Ostrogradski instability. We study the cosmology in beyond-generalized Proca theories by paying particular attention to the dynamics of late-time cosmic acceleration and resulting observational consequences. We derive conditions for avoiding ghosts and instabilities of tensor, vector, scalar perturbations and discuss viable parameter spaces in concrete models allowing the dark energy equation of state smaller than $-1$. The propagation speeds of those perturbations are subject to modifications beyond the domain of generalized Proca theories. There is a mixing between scalar and matter sound speeds, but such a mixing is suppressed during most of the cosmic expansion history without causing a new instability. On the other hand, we find that derivative interactions arising in beyond-generalized Proca theories give rise to important modifications to the cosmic growth history. The growth rate of matter perturbations can be compatible with the redshift-space distortion data due to the realization of gravitational interaction weaker than that in generalized Proca theories. Thus, it is possible to distinguish the dark energy model in beyond-generalized Proca theories from the counterpart in generalized Proca theories as well as from the $\Lambda$CDM model.

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S. Nakamura, R. Kase and S. Tsujikawa
Wed, 1 Mar 17
53/67

Comments: 20 pages, 9 figures

On the cosmological (in)viability of $f(R,T)$ gravity [CL]

http://arxiv.org/abs/1702.07710

Among many alternative gravitational theories to General Relativity (GR), $f(R,T)$ gravity (where $R$ is the Ricci scalar and $T$ the trace of the energy-momentum tensor) has been widely studied recently. By adding a matter contribution to the gravitational Lagrangian, $f(R,T)$ theories have become an interesting extension to GR displaying a broad phenomenology in astrophysics and cosmology. In this paper, we discuss however the difficulties appearing in explaining a viable and realistic cosmology within the $f(R,T)$ class of theories. Our results challenge the viability of $f(R,T)$ as an alternative modification of gravity.

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H. Velten and T. Carames
Wed, 1 Mar 17
60/67

Comments: 8 pages, 6 figures

Nonlocally interacting metrics and cosmic acceleration [CL]

http://arxiv.org/abs/1702.08908

We propose a simple, nonlocal modification to general relativity (GR) on large scales, which provides a model of late-time cosmic acceleration in the absence of a cosmological constant and with the same number of free parameters as in standard cosmology. The model is constructed by adding to the gravity sector an extra spin-2 field interacting nonlocally with the physical metric coupled to matter. The model is inspired by the simplest form of the Deser-Woodard (DW) model, $\alpha R\frac{1}{\Box}R$, with one of the Ricci scalars replaced by the one associated with the extra metriclike field. We study cosmic expansion histories, and demonstrate that this new model can provide background expansions consistent with observations, in contrast to the simple DW model. We also compare the cosmology of the model to that of the Maggiore-Mancarella (MM) model, $m^2R\frac{1}{\Box^2}R$, and demonstrate that the viable cosmic histories follow the standard-model evolution more closely compared to the MM model. In addition, we show that the consistency conditions on the proposed model of nonlocally interacting metrics render it effectively equivalent to a single-metric model where gravity is modified in the infrared by adding a simple term of the form $m^2\frac{1}{\Box}R$, with $m$ being a constant of the order of the Hubble expansion rate today. We further demonstrate that the model possesses the same number of physical degrees of freedom as in GR. Finally, we discuss the appearance of ghosts in the local formulation of the model, and argue that they are unphysical and harmless to the theory, keeping the physical degrees of freedom healthy.

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V. Vardanyan, Y. Akrami, L. Amendola, et. al.
Wed, 1 Mar 17
67/67

Comments: 28 pages, 6 figures

$R+αR^n$ Inflation in higher-dimensional Space-times [CL]

http://arxiv.org/abs/1702.08311

We generalise Starobinsky’s model of inflation to space-times with $D>4$ dimensions, where $D-4$ dimensions are compactified on a suitable manifold. The $D$-dimensional action features Einstein-Hilbert gravity, a higher-order curvature term, a cosmological constant, and potential contributions from fluxes in the compact dimensions. The existence of a stable flat direction in the four-dimensional EFT implies that the power of space-time curvature, $n$, and the rank of the compact space fluxes, $p$, are constrained via $n=p=D/2$. Whenever these constraints are satisfied, a consistent single-field inflation model can be built into this setup, where the inflaton field is the same as in the four-dimensional Starobinsky model. The resulting predictions for the CMB observables are nearly indistinguishable from those of the latter.

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S. Otero, F. Pedro and C. Wieck
Tue, 28 Feb 17
40/69

Comments: 15 pages, 1 figure

General Relativity from Causality [CL]

http://arxiv.org/abs/1702.07720

We study large families of theories of interacting spin 2 particles from the point of view of causality. Although it is often stated that there is a unique Lorentz invariant effective theory of massless spin 2, namely general relativity, other theories that utilize higher derivative interactions do in fact exist. These theories are distinct from general relativity, as they permit any number of species of spin 2 particles, are described by a much larger set of parameters, and are not constrained to satisfy the equivalence principle. We consider the leading spin 2 couplings to scalars, fermions, and vectors, and systematically study signal propagation in all these other families of theories. We find that most interactions directly lead to superluminal propagation of either a spin 2 particle or a matter particle, and interactions that are subluminal generate other interactions that are superluminal. Hence, such theories of interacting multiple spin 2 species have superluminality, and by extension, acausality. This is radically different to the special case of general relativity with a single species of minimally coupled spin 2, which leads to subluminal propagation from sources satisfying the null energy condition. This pathology persists even if the spin 2 field is massive. We compare these findings to the analogous case of spin 1 theories, where higher derivative interactions can be causal. This makes the spin 2 case very special, and suggests that multiple species of spin 2 is forbidden, leading us to general relativity as essentially the unique internally consistent effective theory of spin 2.

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M. Hertzberg and M. Sandora
Tue, 28 Feb 17
42/69

Comments: 30 pages, 4 figures, 1 table

Anisotropic power-law inflation in a two-scalar-field model with a mixed kinetic term [CL]

http://arxiv.org/abs/1702.08308

We examine whether an extended scenario of a two-scalar-field model, in which a mixed kinetic term of canonical and phantom scalar fields is involved, admits the Bianchi type I metric, which is homogeneous but anisotropic spacetime, as its power-law solutions. Then we analyze the stability of the anisotropic power-law solutions to see whether these solutions respect the cosmic no-hair conjecture or not during the inflationary phase. In addition, we will also investigate a special scenario, where the pure kinetic terms of canonical and phantom fields disappear altogether in field equations, to test again the validity of cosmic no-hair conjecture. As a result, the cosmic no-hair conjecture always holds in both these scenarios due to the instability of the corresponding anisotropic inflationary solutions.

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T. Do and S. Nguyen
Tue, 28 Feb 17
46/69

Comments: 19 pages, no figures. Accepted for publication in International Journal of Modern Physics D

Memory in de Sitter space and BMS-like supertranslations [CL]

http://arxiv.org/abs/1702.06928

It is well known that the memory effect in flat spacetime is parametrized by the BMS supertranslation. We investigate the relation between the memory effect and diffeomorphism in de Sitter spacetime. We find that gravitational memory is parametrized by a BMS-like supertranslation in the static patch of de Sitter spacetime. While we do not find a diffeomorphism that corresponds to gravitational memory in the Poincare/cosmological patch, we show that we can perform a boost to bring the null related events within the static patch and apply our results. Our method does not need to assume the separation between the source and the detector to be small compared with the Hubble radius, and can potentially be applicable to other FLRW universes, as well as “ordinary memory” mediated by massive messenger particles.

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Y. Hamada, M. Seo and G. Shiu
Tue, 28 Feb 17
69/69

Comments: 21 pages, 3 figures

Gauss-Bonnet Chern-Simons gravitational wave leptogenesis [CL]

http://arxiv.org/abs/1702.07689

The gravitational Chern-Simons term coupled to an evolving axion is known to generate lepton number through the gravitational anomaly. We examine this leptogenesis scenario in the presence of the Gauss-Bonnet term over and above the gravitational Chern-Simons term. We find that the lepton production can be exponentially enhanced. The Gauss-Bonnet term creates CP-violating instability of gravitational waves that may appear transiently after inflation, and during the period of instability elliptically polarized gravitational waves are exponentially amplified at sub-horizon scales. This instability does not affect the spectrum of the cosmic microwave background as it occurs at much shorter length scales. In a typical scenario based on natural inflation, the observed baryon asymmetry of the Universe corresponds to the UV cutoff scale at $10^{14-16}$ GeV.

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S. Kawai and J. Kim
Mon, 27 Feb 17
1/49

Comments: 5 pages, 2 figures

Dirac-Bergmann Constraints in Physics: Singular Lagrangians, Hamiltonian Constraints and the Second Noether Theorem [CL]

http://arxiv.org/abs/1702.07598

There is a review of the main mathematical properties of system described by singular Lagrangians and requiring Dirac-Bergmann theory of constraints at the Hamiltonian level. The following aspects are discussed:
i) the connection of the rank and eigenvalues of the Hessian matrix in the Euler-Lagrange equations with the chains of first and second class constraints;
ii) the connection of the Noether identities of the second Noether theorem with the Hamiltonian constraints;
iii) the Shanmugadhasan canonical transformation for the identification of the gauge variables and for the search of the Dirac observables, i.e. the quantities invariant under Hamiltonian gauge transformations.
Review paper for a chapter of a future book.

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L. Lusanna
Mon, 27 Feb 17
23/49

Comments: 38 pages

Dirac-Bergmann Constraints in Relativistic Physics: Non-Inertial Frames, Point Particles, Fields and Gravity [CL]

http://arxiv.org/abs/1702.07595

There is a review of the physical theories needing Dirac-Bergmann theory of constraints at the Hamiltonian level due to the existence of gauge symmetries. It contains:
i) the treatment of systems of point particles in special relativity both in inertial and non-inertial frames with a Wigner-covariant way of eliminating relative times in relativistic bound states;
ii) the description of the electro-magnetic field in relativistic atomic physics and of Yang-Mills fields in absence of Gribov ambiguity in particle physics;
iii) the identification of the inertial gauge variables and of the physical variables in canonical ADM tetrad gravity in presence of the electro-magnetic field and of charged scalar point particles in asymptotically Minkowskian space-times without super-translations by means of a Shanmugadhasan canonical transformation to a York canonical basis adapted to ten of the 14 first-class constraints and the definition of the Hamiltonian Post-Minkowskian weak field limit.
Review paper for a chapter of a future book

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L. Lusanna
Mon, 27 Feb 17
40/49

Comments: 30 pages. arXiv admin note: substantial text overlap with arXiv:1108.3224, arXiv:1205.2481

Quantum Circuit Cosmology: The Expansion of the Universe Since the First Qubit [CL]

http://arxiv.org/abs/1702.06959

We consider cosmological evolution from the perspective of quantum information. We present a quantum circuit model for the expansion of a comoving region of space, in which initially-unentangled ancilla qubits become entangled as expansion proceeds. We apply this model to the comoving region that now coincides with our Hubble volume, taking the number of entangled degrees of freedom in this region to be proportional to the de Sitter entropy. The quantum circuit model is applicable for at most 140 $e$-folds of inflationary and post-inflationary expansion: we argue that no geometric description was possible before the time $t_1$ when our comoving region was one Planck length across, and contained one pair of entangled degrees of freedom. This approach could provide a framework for modeling the initial state of inflationary perturbations.

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N. Bao, C. Cao, S. Carroll, et. al.
Fri, 24 Feb 17
11/50

Comments: 12 pages, 1 figure. Including appendix

BRS structure of Simple Model of Cosmological Constant and Cosmology [CL]

http://arxiv.org/abs/1702.07063

In arXiv:1601.02203, a simple model has been proposed in order to solve one of the problems related with the cosmological constant. The model is given by a topological field theory and the model has an infinite numbers of the BRS symmetries. The BRS symmetries are, however, spontaneously broken in general. In this paper, we investigate the BRS symmetry in more details and show that there is one and only one BRS symmetry which is not broken and the unitarity can be guaranteed. In the model, the quantum problem of the vacuum energy, which may be identified with the cosmological constant, reduces to the classical problem of the initial condition. In this paper, we investigate the cosmology given by the model and specify the region of the initial conditions which could be consistent with the evolution of the universe. We also show that there is a stable solution describing the de Sitter space-time, which may explain the accelerating expansion in the current universe.

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T. Mori, D. Nitta and S. Nojiri
Fri, 24 Feb 17
31/50

Comments: LaTeX 10 pages, 3 figures

Fifty years of cosmological particle creation [CL]

http://arxiv.org/abs/1702.07132

In the early sixties Leonard Parker discovered that the expansion of the universe can create particles out of the vacuum, opening a new and fruitfull field in physics. We give a historical review in the form of an interview that took place during the Conference ERE2014 (Valencia 1-5, September, 2014).

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L. Parker and J. Navarro-Salas
Fri, 24 Feb 17
35/50

Comments: 8 pages