Understanding the spectral hardenings and radial distribution of Galactic cosmic rays and Fermi diffuse gamma-rays with spatially-dependent propagation [HEAP]


Recent direct measurements of Galactic cosmic ray spectra by balloon/space-borne detectors reveal spectral hardenings of all major nucleus species at rigidities of a few hundred GV. The all-sky diffuse gamma-ray emissions measured by the Fermi Large Area Telescope also show spatial variations of the intensities and spectral indices of cosmic rays. These new observations challenge the traditional simple acceleration and/or propagation scenario of Galactic cosmic rays. In this work we propose a spatially-dependent diffusion scenario to explain all these phenomena. The diffusion coefficient is assumed to be anti-correlated with the source distribution, which is a natural expectation from the charged particle transportation in turbulent magnetic field. The spatially-dependent diffusion model also gives a lower level of anisotropies of cosmic rays, which are consistent with observations by underground muons and air shower experiments. The spectral variations of cosmic rays across the Galaxy can be properly reproduced by this model.

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Y. Guo and Q. Yuan
Fri, 19 Jan 18

Comments: N/A

Multi-TeV flares from the nearest Blazar Markarian 421 and their origin [HEAP]


Markarian 421 is a high-peaked BL Lac object and has undergone many major outbursts since its discovery in 1992. Through dedicated multiwavelength observations, Markarian 421 has been studied intensively and several major multi-TeV flares have been observed by Cherenkov telescope arrays. The major outbursts of April 2004 observed by Whipple telescopes and of February 2010 by HESS telescopes are explained well in this work by using the photohadronic model. To account for the attenuation of these high energy gamma-rays by the extragalactic background light, we use template EBL models. During different epochs of flaring the calculated intrinsic fluxes are not the same due to the change in the power-law dependence of the seed photon densities in the tail region of the SSC band. Our results show that the contemporaneous multiwavelength observations, particularly in the tail region of the SSC band of the source is important to explain the flaring phenomena.

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S. Sahu, A. Leon, S. Nagataki, et. al.
Fri, 19 Jan 18

Comments: 15 pages, 6 figures

Modulus D-term Inflation [CL]


We propose a new model of single-field D-term inflation in supergravity, where the inflation is driven by a single modulus field which transforms non-linearly under the U(1) gauge symmetry. One of the notable features of our modulus D-term inflation scenario is that the global U(1) remains unbroken in the vacuum and hence our model is not plagued by the cosmic string problem which can exclude most of the conventional D-term inflation models proposed so far due to the CMB observations.

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K. Kadota, T. Kobayashi, I. Saga, et. al.
Fri, 19 Jan 18

Comments: 15 pages, 5 figures

Vacuum Polarization and Photon Propagation in an Electromagnetic Plane Wave [CL]


The QED vacuum polarization in external monochromatic plane-wave electromagnetic fields is calculated with spatial and temporal variations of the external fields being taken into account. We develop a perturbation theory to calculate the induced electromagnetic current that appears in the Maxwell equations, based on Schwinger’s proper-time method, and combine it with the so-called gradient expansion to handle the variation of external fields perturbatively. The crossed field, i.e., the long wavelength limit of the electromagnetic wave is first considered. The eigenmodes and the refractive indices as the eigenvalues associated with the eigenmodes are computed numerically for the probe photon propagating in some particular directions. In so doing, no limitation is imposed on the field strength and the photon energy unlike previous studies. It is shown that the real part of the refractive index becomes less than unity for strong fields, the phenomenon that has been known to occur for high-energy probe photons. We then evaluate numerically the lowest-order corrections to the crossed-field resulting from the field variations in space and time. It is demonstrated that the corrections occur mainly in the imaginary part of the refractive index.

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A. Yatabe and S. Yamada
Thu, 18 Jan 18

Comments: 50 pages, 17 figures, accepted for publication in Progress of Theoretical and Experimental Physics

Initial conditions for Inflation in an FRW Universe [CL]


We examine the class of initial conditions which give rise to inflation. Our analysis is carried out for several popular models including: Higgs inflation, Starobinsky inflation, chaotic inflation, axion monodromy inflation and non-canonical inflation. In each case we determine the set of initial conditions which give rise to sufficient inflation, with at least $60$ e-foldings. A phase-space analysis has been performed for each of these models and the effect of the initial inflationary energy scale on inflation has been studied numerically. This paper discusses two scenarios of Higgs inflation: (i) the Higgs is coupled to the scalar curvature, (ii) the Higgs Lagrangian contains a non-canonical kinetic term. In both cases we find Higgs inflation to be very robust since it can arise for a large class of initial conditions. One of the central results of our analysis is that, for plateau-like potentials associated with the Higgs and Starobinsky models, inflation can be realized even for initial scalar field values which lie close to the minimum of the potential. This dispels a misconception relating to plateau potentials prevailing in the literature. We also find that inflation in all models is more robust for larger values of the initial energy scale.

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S. Mishra, V. Sahni and A. Toporensky
Wed, 17 Jan 18

Comments: 46 pages, 29 figures

Neutrino masses and their ordering: Global Data, Priors and Models [CL]


We present a Bayesian analysis of the combination of current neutrino oscillation, neutrinoless double beta decay and CMB observations. Our major goal is to carefully investigate the possibility to single out one neutrino mass ordering, Normal Ordering or Inverted Ordering, with current data. Two possible parametrizations (three neutrino masses versus the lightest neutrino mass plus the two oscillation mass splittings) and priors (linear versus logarithmic) are examined. We find that the preference for NO is only driven by neutrino oscillation data. Moreover, the values of the Bayes factor indicate that the evidence for NO is strong only when the scan is performed over the three neutrino masses with logarithmic priors; for every other combination of parameterization and prior, the preference for NO is only weak. As a by-product of our Bayesian analyses, we are able to a) compare the Bayesian bounds on the neutrino mixing parameters to those obtained by means of frequentist approaches, finding a very good agreement; b) determine that the lightest neutrino mass plus the two mass splittings parametrization, motivated by the physical observables, is strongly preferred over the three neutrino mass eigenstates scan and c) find that there is a weak-to-moderate preference for logarithmic priors. These results establish the optimal strategy to successfully explore the neutrino parameter space, based on the use of the oscillation mass splittings and a logarithmic prior on the lightest neutrino mass. We also show that the limits on the total neutrino mass $\sum m_\nu$ can change dramatically when moving from one prior to the other. These results have profound implications for future studies on the neutrino mass ordering, as they crucially state the need for self-consistent analyses which explore the best parametrization and priors, without combining results that involve different assumptions.

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S. Gariazzo, M. Archidiacono, P. Salas, et. al.
Wed, 17 Jan 18

Comments: 21 pages, 5 figures, 6 tables

Absolute stability window and upper bound on the magnetic field strength in a strongly magnetized strange quark star [CL]


Magnetized strange quark stars, composed of strange quark matter (SQM) and self-bound by strong interactions, can be formed if the energy per baryon of magnetized SQM is less than that of the most stable $^{56}$Fe nucleus under the zero external pressure and temperature. Utilizing the MIT bag model description of magnetized SQM under charge neutrality and beta equilibrium conditions, the corresponding absolute stability window in the parameter space of the theory is determined. It is shown that there exists the maximum magnetic field strength allowed by the condition of absolute stability of magnetized SQM. The value of this field, $H\sim3\cdot10^{18}$ G, represents the upper bound on the magnetic field strength which can be reached in a strongly magnetized strange quark star.

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A. Isayev
Wed, 17 Jan 18

Comments: 9 pages, 2 figures. arXiv admin note: text overlap with arXiv:1501.07772