The effect upon neutrinos of core-collapse supernova accretion phase turbulence [HEAP]

During the accretion phase of a core-collapse supernovae, large amplitude turbulence is generated by the combination of the standing accretion shock instability and convection driven by neutrino heating. The turbulence directly affects the dynamics of the explosion, but there is also the possibility of an additional, indirect, feedback mechanism due to the effect turbulence can have upon neutrino flavor evolution and thus the neutrino heating. In this paper we consider the effect of turbulence during the accretion phase upon neutrino evolution, both numerically and analytically. Adopting representative supernova profiles taken from the accretion phase of a supernova simulation, we find the numerical calculations exhibit no effect from turbulence. We explain this absence using two analytic descriptions: the Stimulated Transition model and the Distorted Phase Effect model. In the Stimulated Transition model turbulence effects depend upon six different lengthscales, and three criteria must be satisfied between them if one is to observe a change in the flavor evolution due to Stimulated Transition. We further demonstrate that the Distorted Phase Effect depends upon the presence of multiple semi-adiabatic MSW resonances or discontinuities that also can be expressed as a relationship between three of the same lengthscales. When we examine the supernova profiles used in the numerical calculations we find the three Stimulated Transition criteria cannot be satisfied, independent of the form of the turbulence power spectrum, and that the same supernova profiles lack the multiple semi-adiabatic MSW resonances or discontinuities necessary to produce a Distorted Phase Effect. Thus we conclude that even though large amplitude turbulence is present in supernova during the accretion phase, it has no effect upon neutrino flavor evolution.

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J. Kneller and M. Reyes
Fri, 24 Feb 17

Comments: N/A

Fifty years of cosmological particle creation [CL]

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

Comments: 8 pages

Measurement of Anisotropy and Search for UHECR Sources [HEAP]

Ultra-high energy cosmic rays (UHECRs) are particles, likely protons and/or nuclei, with energies up to $10^{20}$ eV that are observed through the giant air showers they produce in the atmosphere. These particles carry the information on the most extreme phenomena in the Universe. At these energies, even charged particles could be magnetically rigid enough to keep track of, or even point directly to, the original positions of their sources on the sky. The discovery of anisotropy of UHECRs would thus signify opening of an entirely new window onto the Universe. With the construction and operation of the new generation of cosmic ray experiments — the Pierre Auger Observatory in the Southern hemisphere and the Telescope Array in the Northern one — the study of these particles, the most energetic ever detected, has experienced a jump in statistics as well as in the data quality, allowing for a much better sensitivity in searching for their sources. In this review, we summarize the searches for anisotropies and the efforts to identify the sources of UHECRs which have been carried out using these new data.

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O. Deligny, K. Kawata and P. Tinyakov
Fri, 24 Feb 17

Comments: 29 pages, 14 figures, accepted for publication in Prog. Theor. Exp. Phys

The electron plus positron spectrum from annihilation of Kaluza-Klein dark matter in the Galaxy [HEAP]

The lightest Kaluza-Klein particle (LKP), which appears in the theory of universal extra dimensions, is one of good candidates for cold dark matter (CDM). When LKP pairs annihilate around the center of the Galaxy where CDM is concentrated, there are some modes which produce electrons and positrons as final products, and we categorize them into two components. One of them is the “Line” component, which directly annihilates into electron–positron pair. Another one is the “Continuum” component, which consists of secondarily produced electrons and positrons via some decay modes. Before reaching Earth, directions of electrons and positrons are randomized by the Galactic magnetic field, and their energies are reduced by energy loss mechanisms. We assume the LKP is in the mass range from 300 GeV to 1500 GeV. We calculate the electron plus positron spectrum after propagation in the Galactic halo to Earth, and we analyze the resulting spectrum and positron fraction. We also point out that the energy dependence of observed positron fraction is well reproduced by the mixture of “line” and “continuum” components. We can fit the electron plus positron spectrum and the positron fraction by assuming appropriate boost factors describing dark matter concentration in the Galactic halo. However, it is difficult to explain both the electron plus positron spectrum and the positron fraction by a single boost factor, if we take account of observational data obtained by AMS-02 only.

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S. Tsuchida and M. Mori
Thu, 23 Feb 17

Comments: 13 pages, 5 figures: Accepted for publication in the International Journal of Modern Physics D

The Core-Collapse Supernova Explosion Mechanism [SSA]

The explosion mechanism of core-collapse supernovae is a long-standing problem in stellar astrophysics. We briefly outline the main contenders for a solution and review recent efforts to model core-collapse supernova explosions by means of multi-dimensional simulations. We discuss several suggestions for solving the problem of missing or delayed neutrino-driven explosions in three-dimensional supernova models, including — among others — variations in the microphysics and large seed perturbations in convective burning shells. Focusing on the neutrino-driven mechanism, we summarise currents efforts to predict supernova explosion and remnant properties based on first-principle models and on more phenomenological approaches.

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B. Muller
Thu, 23 Feb 17

Comments: Invited review to appear in the International Astronomical Union Proceedings Serie (IAU Symposium 329, “The Lives and Death Throes of Massive Stars”). 8 pages, 2 figures

Positivity Bounds for Scalar Theories [CL]

Assuming the existence of a local, analytic, unitary UV completion in a Poincar\'{e} invariant scalar field theory with a mass gap, we derive an infinite number of positivity requirements using the known properties of the amplitude at and away from the forward scattering limit. These take the form of bounds on combinations of the pole subtracted scattering amplitude and its derivatives. In turn, these positivity requirements act as constraints on the operator coefficients in the low energy effective theory. For certain theories these constraints can be used to place an upper bound on the mass of the next lightest state that must lie beyond the low energy effective theory if such a UV completion is to ever exist.

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C. Rham, S. Melville, A. Tolley, et. al.
Thu, 23 Feb 17

Comments: 5 pages

Supernova neutrinos: fast flavor conversions near the core [CL]

Neutrino flux streaming from a supernova can undergo rapid flavor conversions almost immediately above the core. Focusing on this region, we study these fast conversions using a linear stability analysis. We find that, for realistic angular distributions of neutrinos, fast conversions can occur within a few nanoseconds in regions just above the neutrinosphere. Our results also show that neutrinos travelling towards the core make fast conversions more rapid. These conversions, if they exist, can have significant implications for supernova explosion mechanism and nucleosynthesis.

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M. Sen
Thu, 23 Feb 17

Comments: Presented at the XXII DAE-BRNS HEP Symposium. Proceedings to appear in European Physics Journal C