arXiv subjects

German A. Gomez-Vargas

Publications and source records attributed to German A. Gomez-Vargas.

9 recordsLinked to original sources

arXiv2020

MeV-GeV $γ$-ray telescopes probing gravitino LSP with coexisting axino NLSP as dark matter in the $μν$SSM

In $R$-parity violating supersymmetry, the gravitino as the lightest supersymmetric particle (LSP) is a good candidate for dark matter, with the interesting characteristic to be detectable through $γ$-ray telescopes. We extend this analysis considering an axino next-to-LSP (NLSP) as a coexisting dark matter particle contributing with a detectable signal in the $γ$-ray spectrum. The analysis is carried out in the framework of the $μν$SSM, which solves the $μ$ problem reproducing simultaneously neutrino data only with the addition of right-handed neutrinos. We find that important regions of the parameter space can be tested by future MeV-GeV $γ$-ray telescopes through the line signal coming from the decay of the axino NLSP into photon-neutrino. In a special region, a double-line signal from axino NLSP and gravitino LSP is possible with both contributions detectable.

hep-ph↗

arXiv2020

MeV-GeV $γ$-ray telescopes probing axino LSP/gravitino NLSP as dark matter in the $μν$SSM

Axino and gravitino are promising candidates to solve the dark matter (DM) problem in the framework of supersymmetry. In this work, we assume that the axino is the lightest supersymmetric particle (LSP), and therefore contributes to DM. In the case of R-parity violating models, the axino can decay into a neutrino-photon pair with a lifetime much longer than the age of the Universe, yielding a potentially detectable signal. Interestingly, a gravitino next-to-LSP (NLSP) can live enough as to contribute to the relic density. We study both scenarios, only axino LSP as DM, and axino LSP with gravitino NLSP as DM. We carry out the analysis in the context of the $μν$SSM, which solves the $μ$ problem and reproduces neutrino data, only adding couplings involving right-handed neutrinos. In particular, we perform a complete analysis of the relevant parameter space of the model considering constraints from neutrino physics, cosmological observations, and $γ$-ray detection. We find that the axino or the gravitino can produce a signal detectable by future MeV-GeV $γ$-ray telescopes. In addition, in a parameter region where we get a well-tempered mixture of both particles, a double-line signal arises as a smoking gun.

hep-ph↗

arXiv2017

Search for sharp and smooth spectral signatures of $μν$SSM gravitino dark matter with Fermi-LAT

The $μν$SSM solves the $μ$ problem of supersymmetric models and reproduces neutrino data, simply using couplings with right-handed neutrinos $ν$'s. Given that these couplings break explicitly $R$ parity, the gravitino is a natural candidate for decaying dark matter in the $μν$SSM. In this work we carry out a complete analysis of the detection of $μν$SSM gravitino dark matter through $γ$-ray observations. In addition to the two-body decay producing a sharp line, we include in the analysis the three-body decays producing a smooth spectral signature. We perform first a deep exploration of the low-energy parameter space of the $μν$SSM taking into account that neutrino data must be reproduced. Then, we compare the $γ$-ray fluxes predicted by the model with Fermi-LAT observations. In particular, with the 95$\%$ CL upper limits on the total diffuse extragalactic $γ$-ray background using 50 months of data, together with the upper limits on line emission from an updated analysis using 69.9 months of data. For standard values of bino and wino masses, gravitinos with masses larger than about 4 GeV, or lifetimes smaller than $10^{28}$ s, produce too large fluxes and are excluded as dark matter candidates. However, when limiting scenarios with large and close values of the gaugino masses are considered, the constraints turn out to be less stringent, excluding masses larger than 17 GeV and lifetimes smaller than $4\times 10^{25}$ s.

hep-ph↗

arXiv2015

Confronting recent AMS-02 positron fraction and Fermi-LAT Extragalactic Gamma-Ray Background measurements with gravitino dark matter

Recent positron flux fraction measurements in cosmic-rays (CR) made by the AMS-02 satellite confirm and extends the evidence on the existence of a new (yet unknown) source of high energy positrons. To explain this excess, we use the gravitino of bilinear R-parity violating SUSY models as a decaying Dark Matter candidate, as the source of those high energy particles. Being a long lived weak-interacting and spin 3/2 particle, it offers several particularities which makes it an attractive candidate. We compute the electron, positron and $γ$-ray\ fluxes produced by each gravitino decay channel at the Earth. Combining the flux from the different decay modes we can fit AMS-02 measurements of the positron fraction, as well as the electron and positron fluxes, with a gravitino mass in the range $1-2$ TeV and lifetimes of $\sim 1.0-0.8\times 10^{26}$ s. . Then, we study the viability of these scenarios through their implications in $γ$-ray observations. We set limits on the gravitino lifetime using the Extragalactic $γ$-ray Background recently reported by the {\it Fermi}-LAT Collaboration and a state-of-the-art model of its known contributors. These limits exclude the gravitino parameter space which provides an acceptable explanation of the AMS-02 data. Therefore, we conclude that the gravitino of bilinear R-parity violating models is ruled out as the unique primary source of electrons and positrons needed to explain the rise in the positron fraction.

hep-ph↗

arXiv2015

Strong Optimized Conservative Fermi-LAT Constraints on Dark Matter Models from the Inclusive Photon Spectrum

We set conservative, robust constraints on the annihilation and decay of dark matter into various Standard Model final states under various assumptions about the distribution of the dark matter in the Milky Way halo. We use the inclusive photon spectrum observed by the Fermi Gamma-ray Space Telescope through its main instrument, the Large-Area Telescope (LAT). We use simulated data to first find the "optimal" regions of interest in the gamma-ray sky, where the expected dark matter signal is largest compared with the expected astrophysical foregrounds. We then require the predicted dark matter signal to be less than the observed photon counts in the a priori optimal regions. This yields a very conservative constraint as we do not attempt to model or subtract astrophysical foregrounds. The resulting limits are competitive with other existing limits, and, for some final states with cuspy dark-matter distributions in the Galactic Center region, disfavor the typical cross section required during freeze-out for a weakly interacting massive particle (WIMP) to obtain the observed relic abundance.

hep-ph↗

arXiv2014

Search for 100 MeV to 10 GeV gamma-ray lines in the Fermi-LAT data and implications for gravitino dark matter in the $μν$SSM

Dark matter decay or annihilation may produce monochromatic signals in the gamma-ray energy range. In this work we argue that there are strong theoretical motivations for studying these signals in the framework of gravitino dark matter decay and we perform a search for gamma-ray spectral lines from 100\,MeV to 10\,GeV with Fermi-LAT data. In contrast to previous line searches at higher energies, the sensitivity of the present search is dominated by systematic uncertainties across most of the energy range considered. We estimate the size of systematic effects by analysing the flux from a number of control regions, and include the systematic uncertainties consistently in our fitting procedure. We have not observed any significant signals and present model-independent limits on gamma-ray line emission from decaying and annihilating dark matter. We apply the former limits to the case of the gravitino, a well-known dark matter candidate in supersymmetric scenarios. In particular, the $R$-parity violating "$μ$ from $ν$" Supersymmetric Standard Model ($μν$SSM) is an attractive scenario in which including right-handed neutrinos solves the $μ$ problem of the Minimal Supersymmetric Standard Model while simultaneously explaining the origin of neutrino masses. At the same time, the violation of $R$-parity renders the gravitino unstable and subject to decay into a photon and a neutrino. As a consequence of the limits on line emission, $μν$SSM gravitinos with masses larger than about 5\,GeV, or lifetimes smaller than about $10^{28}$\,s, are excluded at 95% confidence level as dark matter candidates.

astro-ph.HE↗

arXiv2014

Are we really seeing dark matter signals from the Milky Way center?

The center of the Milky Way is one of the most interesting regions of the $γ$-ray sky because of the potential for indirect dark matter (DM) detection. It is also complicated due to the many sources and uncertainties associated with the diffuse $γ$-ray emission. Many independent groups have claimed a DM detection in the data collected by the Large Area Telescope on board the Fermi $γ$-ray Satellite from the inner Galaxy region at energies below 10 GeV. However, an exotic signal needs to be disentangled from the data using a model of known $γ$-ray emitters, i.e. a background model. We point out that deep understanding of background ingredients and their main uncertainties is of capital importance to disentangle a dark matter signal from the Galaxy center.

hep-ph↗

arXiv2014

Searching for Dark Matter Annihilation in the Smith High-Velocity Cloud

Recent observations suggest that some high-velocity clouds may be confined by massive dark matter halos. In particular, the proximity and proposed dark matter content of the Smith Cloud make it a tempting target for the indirect detection of dark matter annihilation. We argue that the Smith Cloud may be a better target than some Milky Way dwarf spheroidal satellite galaxies and use gamma-ray observations from the Fermi Large Area Telescope to search for a dark matter annihilation signal. No significant gamma-ray excess is found coincident with the Smith Cloud, and we set strong limits on the dark matter annihilation cross section assuming a spatially-extended dark matter profile consistent with dynamical modeling of the Smith Cloud. Notably, these limits exclude the canonical thermal relic cross section ($\sim 3\times10^{-26}{\rm cm}^{3}{\rm s}^{-1}$) for dark matter masses $\lesssim 30$ GeV annihilating via the $b \bar b$ or $τ^{+}τ^{-}$ channels for certain assumptions of the dark matter density profile; however, uncertainties in the dark matter content of the Smith Cloud may significantly weaken these constraints.

astro-ph.HE↗

arXiv2013

Constraints on WIMP Annihilation for Contracted Dark Matter in the Inner Galaxy with the Fermi-LAT

We derive constraints on parameters of generic dark matter candidates by comparing theoretical predictions with the gamma-ray emission observed by the Fermi-LAT from the region around the Galactic Center. Our analysis is conservative since it simply requires that the expected dark matter signal does not exceed the observed emission. The constraints obtained in the likely case that the collapse of baryons to the Galactic Center is accompanied by the contraction of the dark matter are strong. In particular, we find that for bb and τ+τ- or W+W- dark matter annihilation channels, the upper limits on the annihilation cross section imply that the thermal cross section is excluded for a Weakly Interacting Massive Particle (WIMP) mass smaller than about 700 and 500 GeV, respectively. For the μ+ μ- channel, where the effect of the inverse Compton scattering is important, depending on models of the Galactic magnetic field the exclusion of the thermal cross-section is for a WIMP mass smaller than about 150 to 400 GeV. The upper limits on the annihilation cross section of dark matter particles obtained are two orders of magnitude stronger than without contraction. In the latter case our results are compatible with the upper limits from the Galactic halo analysis reported by the Fermi-LAT collaboration for the case in which the same conservative approach without modeling of the astrophysical background is employed.

astro-ph.HE↗