Thermal Dark Matter Below an MeV [CL]

We consider a class of models in which thermal dark matter is lighter than an MeV. If dark matter thermalizes with the Standard Model below the temperature of neutrino-photon decoupling, equilibration and freeze-out cools and heats the Standard Model bath comparably, alleviating constraints from measurements of the effective number of neutrino species. We demonstrate this mechanism in a model consisting of fermionic dark matter coupled to a light scalar mediator. Thermal dark matter can be as light as a few keV, while remaining compatible with existing cosmological and astrophysical observations. This framework motivates new experiments in the direct search for sub-MeV thermal dark matter and light force carriers.

Read this paper on arXiv…

A. Berlin and N. Blinov
Fri, 23 Jun 17

Comments: 5 pages, 4 figures

Wormholes and masses for Goldstone bosons [CL]

There exist non-trivial stationary points of the Euclidean action for an axion particle minimally coupled to Einstein gravity, dubbed wormholes. They explicitly break the continuos global shift symmetry of the axion in a non-perturbative way, and generate an effective potential that may compete with QCD depending on the value of the axion decay constant. In this paper, we explore both theoretical and phenomenological aspects of this issue. On the theory side, we address the problem of stability of the wormhole solutions, and we show that the spectrum of the quadratic action features only positive eigenvalues. On the phenomenological side, we discuss, beside the obvious application to the QCD axion, relevant consequences for models with ultralight dark matter, black hole superradiance, and the relaxation of the electroweak scale. We conclude discussing wormhole solutions for a generic coset and the potential they generate.

Read this paper on arXiv…

R. Alonso and A. Urbano
Fri, 23 Jun 17

Comments: 50 pages, 15 figures

High-Energy Gamma Rays and Neutrinos from Nearby Radio Galaxies [HEAP]

Multi-messenger data suggest that radio galaxies (i.e. non-blazar active galaxies) are perhaps the most likely class of sources for the diffuse flux of high-energy neutrinos reported by the IceCube Collaboration. In this study, we consider the gamma-ray spectrum observed from four nearby radio galaxies (Centaurus A, PKS 0625-35, NGC 1275 and IC 310) and constrain the intensity and spectral shape of the emission injected from these sources, accounting for the effects of attenuation and contributions from electromagnetic cascades (initiated both within the radio galaxy itself and during extragalactic propagation). Assuming that this gamma-ray emission is generated primarily through the interactions of cosmic-ray protons with gas, we calculate the neutrino flux predicted from each of these sources. Although this scenario is consistent with the constraints published by the IceCube and ANTARES Collaborations, the predicted fluxes consistently fall within an order of magnitude of the current point source sensitivity. The prospects appear very encouraging for the future detection of neutrino emission from the nearest radio galaxies.

Read this paper on arXiv…

C. Blanco and D. Hooper
Fri, 23 Jun 17

Comments: 28 pages, 17 figures

Effect of collisions on neutrino flavor inhomogeneity in the early universe [CL]

We investigate the stability, with respect to spatial inhomogeneity, of a two-dimensional dense neutrino gas. The system exhibits growth of seed inhomogeneity due to nonlinear coherent neutrino self-interactions. In the absence of incoherent collisional effects, we observe a dependence of this instability growth rate on the neutrino mass spectrum: the normal neutrino mass hierarchy exhibits spatial instability over a larger range of neutrino number density compared to that of the inverted case. We further consider the effect of elastic incoherent collisions of the neutrinos with a static background of heavy, nucleon-like scatterers. At small scales, the growth of flavor instability can be suppressed by collisions. At large length scales we find, perhaps surprisingly, that for inverted neutrino mass hierarchy incoherent collisions fail to suppress flavor instabilities, independent of the coupling strength.

Read this paper on arXiv…

V. Cirigliano, M. Paris and S. Shalgar
Fri, 23 Jun 17

Comments: 10 pages, 6 figures

Dark Matter, Neutrino mass, Cutoff for Cosmic-Ray Neutrino, and Higgs Boson Invisible Decay from a Neutrino Portal Interaction [CL]

We study an effective theory beyond the standard model (SM) where either of two additional gauge singlets, a Majorana fermion and a real scalar, constitute all or some fraction of dark matter. The only additional interaction to the SM is via a dimension-five lepton number preserving operator: a neutrino portal interaction. We point out that this interaction (i) generates the neutrino mass radiatively, (ii) gives a cutoff for the cosmic-ray neutrino, and (iii) induces the testable Higgs boson invisible decay in the future lepton colliders, such as the CEPC, ILC, and CLIC. In particular, there are two correlated phenomena. If the dark matter is detected in XENON1T, XENONnT, LZ, DARWIN, or PandaX in future, the Higgs invisible decay is within the reach of the future lepton colliders. If a high energy cutoff of cosmic-ray neutrino, which may account for the non-detection of GZK neutrinos or Glashow resonance, is generated due to its annihilation with the cosmic background neutrino, the Higgs invisible decay can be searched for in these colliders. Moreover, the scale for one of the neutrino masses is predicted. The UV completion and the fine tuning, as well as the constraints from collider physics, cosmology, and astronomy are discussed.

Read this paper on arXiv…

W. Yin
Thu, 22 Jun 17

Comments: 21 pages, 5 figures

Linear scale bounds on dark matter–dark radiation interactions and connection with the small scale crisis of cold dark matter [CEA]

One of the open questions in modern cosmology is the small scale crisis of the cold dark matter paradigm. Increasing attention has recently been devoted to self-interacting dark matter models as a possible answer. However, solving the so-called “missing satellites” problem requires in addition the presence of an extra relativistic particle (dubbed dark radiation) scattering with dark matter in the early universe. Here we investigate the impact of different theoretical models devising dark matter dark radiation interactions on large scale cosmological observables. We use cosmic microwave background data to put constraints on the dark radiation component and its coupling to dark matter. We find that the values of the coupling allowed by the data imply a cut-off scale of the halo mass function consistent with the one required to match the observations of satellites in the Milky Way.

Read this paper on arXiv…

M. Archidiacono, S. Bohr, S. Hannestad, et. al.
Thu, 22 Jun 17

Comments: 7 pages, 4 figures. Comments welcome

Constraining sterile neutrino and dark energy with the latest cosmological observations [CEA]

We investigate how the dark energy properties change the cosmological limits on sterile neutrino parameters by using recent cosmological observations. We consider the simplest dynamical dark energy models, the $w$CDM model and the holographic dark energy (HDE) model to make an analysis. The cosmological observations used in this work include the Planck 2015 temperature and polarization data, the baryon acoustic oscillation data, the type Ia supernova data, the Hubble constant direct measurement data, and the CMB lensing measurement. We find that, $m_{\nu,{\rm{sterile}}}^{\rm{eff}}<0.2675$ eV and $N_{\rm eff}<3.5718$ for $\Lambda$CDM cosmology, $m_{\nu,{\rm{sterile}}}^{\rm{eff}}<0.5313$ eV and $N_{\rm eff}<3.5008$ for $w$CDM cosmology, and $m_{\nu,{\rm{sterile}}}^{\rm{eff}}<0.1989$ eV and $N_{\rm eff}<3.6701$ for HDE cosmology, under the constraints of the combination of these data. Thus, without the addition of measurements of growth of structure, only upper limits on both $m_{\nu,{\rm{sterile}}}^{\rm{eff}}$ and $N_{\rm eff}$ can be derived, indicating that no evidence of the existence of a sterile neutrino with eV-scale mass is found in this analysis. Moreover, compared to the $\Lambda$CDM model, in the $w$CDM model the limit on $m_{\nu,{\rm{sterile}}}^{\rm{eff}}$ becomes much looser, but in HDE model the limit becomes much tighter. Therefore, the dark energy properties could significantly impact the constraint limits on sterile neutrino parameters. Furthermore, we also show that, compared to the $\Lambda$CDM cosmology, the dynamical dark energy cosmology with sterile neutrinos can relieve the tension between the Planck observation and the direct measurement of $H_0$ much better.

Read this paper on arXiv…

L. Feng, J. Zhang and X. Zhang
Thu, 22 Jun 17

Comments: 17 pages, 5 figures. arXiv admin note: substantial text overlap with arXiv:1703.04884