Decaying Gravitino Dark Matter Research Articles

Trans-Planckian censorship and inflation in grand unified theories

The recently proposed trans-Planckian censorship conjecture (TCC) amounts to the claim that inflation models with an inflationary energy scale larger than Λinfmax∼109GeV belong to the swampland, i.e., cannot be embedded into a consistent theory of quantum gravity. In this paper, we point out that this constraint can be readily satisfied in D-term hybrid inflation (DHI), which is a well-motivated inflation scenario in the context of supersymmetric grand unification. In DHI, the amplitude of the primordial scalar power spectrum originates from a Fayet–Iliopoulos term of the order of the unification scale, ξ∼1016GeV. At the same time, the TCC results in an upper bound on the corresponding gauge coupling constant of gmax∼10−14. We are able to show that this constraint translates into an upper bound on the gravitino mass of m3/2max∼10MeV, which opens the possibility that dark matter is accounted for by thermally produced gravitinos, if the reheating temperature is close to Treh∼100TeV. Interestingly enough, a somewhat similar gravitino mass range has recently been derived in a model that aims at explaining dark energy in terms of axion quintessence and resolving the Hubble tension by means of decaying gravitino dark matter.

AMS-02 antiprotons from annihilating or decaying dark matter

Recently the AMS-02 experiment reported an excess of cosmic ray antiprotons over the expected astrophysical background. We interpret the excess as a signal from annihilating or decaying dark matter and find that the observed spectrum is well fitted by adding contributions from the annihilation or decay of dark matter with mass of O(TeV) or larger. Interestingly, Wino dark matter with mass of around 3 TeV, whose thermal relic abundance is consistent with present dark matter abundance, can explain the antiproton excess. We also discuss the implications for the decaying gravitino dark matter with R-parity violation.

Antiproton Limits on Decaying Gravitino Dark Matter

We report on constraints on the lifetime of decaying gravitino dark matter in models with bilinear R-parity violation derived from observations of cosmic-ray antiprotons with the PAMELA experiment. Performing a scan over a viable set of cosmic-ray propagation parameters we find lower limits ranging from 8 × 1028 s to 6 × 1028 s for gravitino masses from roughly 100GeV to 10 TeV. Comparing these limits to constraints derived from gamma-ray and neutrino observations we conclude that the presented antiproton limits are currently the strongest and most robust limits on the gravitino lifetime in the considered mass range. These constraints correspond to upper limits on the size of the bilinear R-parity breaking parameter in the range of 10−8 to 8 × 10−13.

Search for 100 MeV to 10 GeV γ-ray lines in the Fermi-LAT data and implications for gravitino dark matter in the μνSSM

Dark matter decay or annihilation may produce monochromatic signals in the γ-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 γ-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 γ-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 μνSSM) 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, μνSSM gravitinos with masses larger than about 5 GeV, or lifetimes smaller than about 1028 s, are excluded at 95% confidence level as dark matter candidates.

Constraints on ultracompact minihalos using neutrino signals from gravitino dark matter decay

Ultracompact dark matter minihalos (UCMHs) would be formed during the early universe if there were large density perturbations. If dark matter can decay into particles described by the standard model, such as neutrinos, these objects would become potential astrophysical sources of emission which could be detected by instruments such as IceCube. In this paper, we investigate neutrino signals from nearby UCMHs due to gravitino dark matter decay and compare these signals with the background neutrino flux which is mainly from the atmosphere to obtain constraints on the abundance of UCMHs.

3.5 keV x-ray line from decaying gravitino dark matter

Extremely weakly interacting particles like the gravitino may be stable enough on cosmological time scales to constitute a good dark matter candidate even in the presence of R-parity violation. We consider the possibility that the recently identified 3.5 keV x-ray line can be generated in light gravitino decays to neutrinos and photons. We find that this is indeed possible in loop processes induced by trilinear lepton-number-violating couplings. We show that in order to avoid overproduction of gravitinos, the reheating temperature has to be at most around 100 GeV to 1 TeV. Finally we briefly discuss associated LHC phenomenology due to a relatively light gluino and multijet/multilepton events from R-parity violating decays of neutralinos.

Recent result of the AMS-02 experiment and decaying gravitino dark matter in gauge mediation

The AMS-02 collaboration has recently reported an excess of cosmic-ray positron fractions, which is consistent with previous results at PAMELA and Fermi-LAT experiments. The result indicates the existence of new physics phenomena to provide the origin of the energetic cosmic-ray positron. We pursue the possibility that the enhancement of the positron fraction is due to the decay of gravitino dark matter. We discuss that such a scenario viably fits into the models in which the soft SUSY breaking parameters are dominantly from gauge-mediation mechanism with superparticle masses of around 10 TeV. Our scenario is compatible with ~126 GeV Higgs boson, negative searches for SUSY particles, and non-observation of anomalous FCNC processes. We also point out that the scenario will be tested in near future by measuring the electric dipole moment of the electron and the lepton flavor violating decay of the muon.

Gamma-ray line from radiative decay of gravitino dark matter

We study radiative decay of gravitino dark matter with trilinear R-parity violations. We show that the branching ratio of the decay of gravitino into monochromatic photon can be large enough to explain the observed gamma-ray line from the Galactic centre in the Fermi-LAT data without producing too much continuum gamma-ray and anti-proton flux. This scenario is realized when the mass of sfermions and the trilinear R-parity violating coupling are O(1–10) TeV and O(10−7–10−6) respectively.

Long-lived higgsinos as probes of gravitino dark matter at the LHC

AbstractWe investigate the LHC sensitivity to supersymmetric models with light higgsinos, small R-parity breaking and gravitino dark matter. The limits on decaying gravitino dark matter from gamma-ray searches with the Fermi-LAT put a lower bound on the higgsino-like neutralino NLSP decay length, giving rise to a displaced-vertex collider signature. Using publicly available tools for simulation of signal, background and detector response, we find that higgsinos with masses of 100 – 400 GeV and R-parity violation ofζ~ 10−8– 10−9can show up in the 8 TeV LHC data with 10 – 30 fb−1of integrated luminosity. We demonstrate that in the case of a signal, the higgsino mass can be determined by reconstruction of the dimuon mass edge.

Indirect searches for gravitino dark matter

The gravitino in models with a small violation of R-parity is a well-motivated decaying dark matter candidate that leads to a cosmological scenario that is consistent with big bang nucleosynthesis and thermal leptogenesis. The gravitino lifetime is cosmologically long-lived since its decays are suppressed by the Planck-scale as well as the small R-parity violating parameter. We discuss the signals in different cosmic-ray species coming from the decay of gravitino dark matter, namely gamma rays, positrons, antiprotons, antideuterons and neutrinos. Comparison to cosmic-ray data can be used to constrain the parameters of the model.

Gamma-ray detection from gravitino dark matter decay in the μνSSM

The μνSSM provides a solution to theμ-problem of the MSSM and explains the origin of neutrino massesby simply using right-handed neutrino superfields. Given that R-parity is broken in this model, the gravitino is a natural candidate for dark matter since its lifetime becomes much longer than the age of the Universe.We consider the implications of gravitino dark matter in the μνSSM,analyzing in particular the prospects for detecting gamma rays from decaying gravitinos. If the gravitino explains the whole dark matter component,a gravitino mass larger than 20GeV is disfavored by the isotropic diffuse photon background measurements. On the other hand, a gravitino with a mass range between 0.1−20 GeV gives rise to a signal that might be observed by the FERMI satellite. In this way important regions of the parameter space of the μνSSM can bechecked.

Probing gravitino dark matter with PAMELA and Fermi

We analyse the cosmic-ray signatures of decaying gravitino dark matter in a model-independent way based on an operator analysis. Thermal leptogenesis and universal boundary conditions at the GUT scale restrict the gravitino mass to be below 600 GeV. Electron and positron fluxes from gravitino decays, together with the standard GALPROP background, cannot explain both the PAMELA positron fraction and the electron + positron flux recently measured by Fermi LAT. For gravitino dark matter, the observed fluxes require astrophysical sources. The measured antiproton flux allows for a sizable contribution of decaying gravitinos to the gamma-ray spectrum, in particular a line at an energy below 300 GeV. Future measurements of the gamma-ray flux will provide important constraints on possible signatures of decaying gravitino dark matter at the LHC.

Decaying gravitino dark matter and an upper bound on the gluino mass

We show that, if decaying gravitino dark matter is responsible for the PAMELA and ATIC/PPB-BETS anomalies in the cosmic-ray electron and positron fluxes, both reheating temperature and the gluino mass are constrained from above. In particular, the gluino mass is likely within the reach of LHC, if thermal leptogenesis is the source of the observed baryon asymmetry.

Unstable gravitino dark matter and neutrino flux

The gravitino is a promising supersymmetric dark matter candidatewhich does not require exact R-parity conservation.In fact, even with some small R-parity breaking, gravitinosare sufficiently long-lived to constitute the dark matter of the Universe,while yielding a cosmological scenario consistent with primordialnucleosynthesis and the high reheating temperature required for thermalleptogenesis. In this paper, we compute the neutrino flux from direct gravitinodecay and gauge boson fragmentation in a simple scenario withbilinear R-parity breaking. Our choice of parameters is motivated by a proposed interpretation of anomalies in the extragalactic gamma-ray spectrum and the positron fraction in terms of gravitino dark matter decay. We find that the generated neutrino flux is compatible with present measurements. We also discuss the possibility of detecting these neutrinos in present and future experiments and conclude that it is a challenging task. However, if detected, this distinctive signal might bring significant support to the scenario of gravitinos as decaying dark matter.

Superparticle mass window from leptogenesis and decaying gravitino dark matter

Gravitino dark matter, together with thermal leptogenesis, implies an upper bound on the masses of superparticles. In the case of broken R-parity the constraints from primordial nucleosynthesis are naturally satisfied and decaying gravitinos lead to characteristic signatures in high energy cosmic rays. We analyse the implications for supergravity models with universal boundary conditions at the grand unification scale. Together with low-energy observables one obtains a window of superparticle masses, which will soon be probed at the LHC, and a range of allowed reheating temperatures.

High energy cosmic rays from the decay of gravitino dark matter

We study high energy cosmic rays from the decay of the gravitino dark matter in the framework of supersymmetric model with $R$-parity violation. Even though $R$ parity is violated, the lifetime of the gravitino, which is assumed to be the lightest superparticle, can be longer than the present age of the Universe if $R$-parity violating interactions are weak enough. We have performed a detailed calculation of the fluxes of gamma ray and positron from the decay of the gravitino dark matter. We also discuss the implication of such a scenario to present and future observations of high energy cosmic rays. In particular, we show that the excess of the gamma-ray flux observed by Energetic Gamma Ray Experiment Telescope and the large positron fraction observed by High Energy Antimatter Telescope can be simultaneously explained by the cosmic rays from the decay of the gravitino dark matter.