arXiv subjects

Chiara Arina

Publications and source records attributed to Chiara Arina.

At least 37 records · Page 2Linked to original sources

arXiv2017

Probing Dark Matter Long-lived Mediators with Solar $γ$ rays

We show that solar $γ$-ray observations can provide a complementary probe of Dark Matter in scenarios where the interactions with the Standard Model proceed via long-lived mediators. For illustration we consider a simplified model which provides solar $γ$-ray fluxes observable with the next generation $γ$-ray telescopes, while complying with the existing experimental constraints. Our results suggest that solar $γ$-ray fluxes can be orders of magnitude larger than the ones from the Galactic center, while being subject to low backgrounds.

hep-ph↗

arXiv2017

Solar $γ$-rays as a Complementary Probe of Dark Matter

We show that observations of solar $γ$-rays offer a novel probe of dark matter in scenarios where interactions with the visible sector proceed via a long-lived mediator. As a proof of principle, we demonstrate that there exists a class of models which yield solar $γ$-ray fluxes observable with the next generation of $γ$-ray telescopes, while being allowed by a variety of current experimental constraints. The parameter space allowed by big bang nucleosynthesis and beam dump experiments naturally leads to mediator lifetimes sufficient to produce observable solar $γ$-ray signals. The model allows for solar $γ$-ray fluxes up to orders of magnitude larger compared to dwarf spheroidal galaxies, without reaching equilibrium between dark matter annihilation and capture rate. Our results suggest that solar $γ$-ray observations are complementary, and in some cases superior, to existing and future dark matter detection efforts.

astro-ph.HE↗

arXiv2016

Confronting SUSY models with LHC data via electroweakino production

We investigate multi-lepton signals produced by ElectroWeakino (EWino) decays in the MSSM and the TMSSM scenarios with sfermions, gluinos and non Standard Model Higgses at the TeV scale, being the Bino electroweak-scale dark matter. We recast the present LHC constraints on EWinos for these models and we find that wide MSSM and TMSSM parameter regions prove to be allowed. We forecast the number of events expected in the signal regions of the experimental multi-lepton analyses in the next LHC runs. The correlations among these numbers will help to determine whether future deviations in multi-lepton data are ascribable to the EWinos, as well as the supersymmetric model they originate from.

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arXiv2016

A comprehensive approach to dark matter studies: exploration of simplified top-philic models

Studies of dark matter lie at the interface of collider physics, astrophysics and cosmology. Constraining models featuring dark matter candidates entails the capability to provide accurate predictions for large sets of observables and compare them to a wide spectrum of data. We present a framework which, starting from a model lagrangian, allows one to consistently and systematically make predictions, as well as to confront those predictions with a multitude of experimental results. As an application, we consider a class of simplified dark matter models where a scalar mediator couples only to the top quark and a fermionic dark sector (i.e. the simplified top-philic dark matter model). We study in detail the complementarity of relic density, direct/indirect detection and collider searches in constraining the multi-dimensional model parameter space, and efficiently identify regions where individual approaches to dark matter detection provide the most stringent bounds. In the context of collider studies of dark matter, we point out the complementarity of LHC searches in probing different regions of the model parameter space with final states involving top quarks, photons, jets and/or missing energy. Our study of dark matter production at the LHC goes beyond the tree-level approximation and we show examples of how higher-order corrections to dark matter production processes can affect the interpretation of the experimental results.

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arXiv2016

Constraints on sneutrino dark matter from LHC Run 1

A mostly right-handed sneutrino as the lightest supersymmetric particle (LSP) is an interesting dark matter candidate, leading to LHC signatures which can be quite distinct from those of the conventional neutralino LSP. Using SModelSv1.0.1 for testing the model against the limits published by ATLAS and CMS in the context of so-called Simplified Model Spectra (SMS), we investigate to what extent the supersymmetry searches at Run 1 of the LHC constrain the sneutrino-LSP scenario. Moreover, we discuss the most relevant topologies for which no SMS results are provided by the experimental collaborations but which would allow to put more stringent constraints on sneutrino LSPs. These include, for instance, the mono-lepton signature which should be particularly interesting to consider at Run 2 of the LHC.

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arXiv2015

Monochromatic neutrino lines from sneutrino dark matter

We investigate the possibility of observing monochromatic neutrino lines originating from annihilation of dark matter. We analyse several astrophysical sources with overdensities of dark matter that can amplify the signal. As a case study, we consider mixed left and right handed sneutrino dark matter. We demonstrate that in the physically viable region of the model, one can obtain a prominent monochromatic neutrino line. We propose a search strategy to observe these neutrino lines in future generations of neutrino telescopes that is especially sensitive to dwarf spheroidal galaxies. We demonstrate that the presence of massive black holes in the cores of dwarfs as well as of more massive galaxies substantially boosts any putative signal. In particular, dark matter in dwarf galaxies spiked by IMBH provides a powerful means of probing low annihilation cross-sections well below $10^{-26} \rm cm^3 s^{-1}$ that are otherwise inaccessible by any future direct detection or collider experiment.

astro-ph.HE↗

arXiv2014

Not so Coy Dark Matter explains DAMA (and the Galactic Center excess)

We study a Dirac Dark Matter particle interacting with ordinary matter via the exchange of a light pseudo-scalar, and analyze its impact on both direct and indirect detection experiments. We show that this candidate can accommodate the long-standing DAMA modulated signal and yet be compatible with all exclusion limits at $99_S$ % CL. This result holds for natural choices of the pseudo-scalar-quark couplings (e.g.~flavor-universal), which give rise to a significant enhancement of the Dark Matter-proton coupling with respect to the coupling to neutrons. We also find that this candidate can accommodate the observed 1-3 GeV gamma-ray excess at the Galactic Center and at the same time have the correct relic density today. The model could be tested with measurements of rare meson decays, flavor changing processes, and searches for axion-like particles with mass in the MeV range.

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arXiv2014

Enhanced Line Signals from Annihilating Kaluza-Klein Dark Matter

Monochromatic gamma ray lines have long been known to provide potential smoking gun signals for annihilating dark matter. Here, we demonstrate that the situation is particularly interesting for Kaluza-Klein dark matter because resonant annihilation is generically expected for small, but not necessarily vanishing relative velocities of the annihilating particles. We calculate the contribution from those hitherto neglected resonances and show that the annihilation rate into monochromatic photons can be significantly enhanced, in a way that is much more pronounced than for the associated production of continuum photons. For favorable astrophysical conditions, this leads to promising prospects for the detection of TeV-scale Kaluza-Klein dark matter. We also point out that the situation may be even more interesting in the vicinity of black holes, like the supermassive black hole at the center of our Galaxy, where in principle center-of-mass energies much larger than the rest mass are available. In this case, annihilating Kaluza-Klein dark matter may show the striking and unique signature of several gamma ray lines, with an equidistant spacing corresponding to twice the compactification radius of the extra dimension.

hep-ph↗

arXiv2014

Dark Matter versus h into gamma gamma and h into gamma Z with supersymmetric triplets

The Triplet extension of the MSSM (TMSSM) alleviates the little hierarchy problem and provides a significant enhancement of the loop-induced diphoton rate of the lightest CP-even Higgs h. In this paper we pursue the analysis of the TMSSM Higgs phenomenology by computing for the first time the h into Z + gamma decay. Interestingly we find that the rates of loop-induced decays are correlated and their signal strengths can rise up to 40% - 60% depending on the channel. We furthermore study the dark matter phenomenology of the TMSSM. The lightest neutralino is a good dark matter candidate in two regions. The first one is related to the Higgs and Z resonances and the LSP is mostly Bino. The second one is achieved for a mass larger than 90 GeV and the LSP behaves as the well-tempered neutralino. An advantage of the triplet contribution is that the well-tempered neutralino can be a Bino-Triplino mixture, relieving the problem of achieving M_2 ~ M_1 in unified scenarios. The dark matter constraints strongly affect the Higgs phenomenology, reducing the potential enhancements of the diphoton and of the Z + photon channels by 20% at most. These enhancements are however larger than the MSSM ones. In the near future, complementarity of dark matter direct searches and collider experiments will be crucial to probe most of the parameter space where the neutralino is the dark matter candidate.

hep-ph↗

arXiv2014

Multi-lepton signatures at LHC from sneutrino dark matter

We investigate multi-lepton LHC signals arising from an extension at the grand unification scale of the standard minimal supersymmetric model (MSSM) involving right-handed neutrino superfields. In this framework neutrinos have Dirac masses and the mixed sneutrinos are the lightest supersymmetric particles and hence the dark matter candidates. We analyze the model parameter space in which the sneutrino is a good dark matter particle and has a direct detection cross-section compatible with the LUX bound. Studying the supersymmetric mass spectrum of this region, we find several signatures relevant for LHC, which are distinct from the predictions of the MSSM with neutralino dark matter. For instance two opposite sign and different flavor leptons, three uncorrelated leptons and long-lived staus are the most representative. Simulating both the signal and expected background, we find that the multi-lepton signatures and the long-lived stau are in the reach of the future run of LHC with a luminosity of 100/fb. We point out that if one of these signatures is detected, it might be an indication of sneutrino dark matter.

hep-ph↗

arXiv2014

Bayesian analysis of multiple direct detection experiments

Bayesian methods offer a coherent and efficient framework for implementing uncertainties into induction problems. In this article, we review how this approach applies to the analysis of dark matter direct detection experiments. In particular we discuss the exclusion limit of XENON100 and the debated hints of detection under the hypothesis of a WIMP signal. Within parameter inference, marginalizing consistently over uncertainties to extract robust posterior probability distributions, we find that the claimed tension between XENON100 and the other experiments can be partially alleviated in isospin violating scenario, while elastic scattering model appears to be compatible with the frequentist statistical approach. We then move to model comparison, for which Bayesian methods are particularly well suited. Firstly, we investigate the annual modulation seen in CoGeNT data, finding that there is weak evidence for a modulation. Modulation models due to other physics compare unfavorably with the WIMP models, paying the price for their excessive complexity. Secondly, we confront several coherent scattering models to determine the current best physical scenario compatible with the experimental hints. We find that exothermic and inelastic dark matter are moderatly disfavored against the elastic scenario, while the isospin violating model has a similar evidence. Lastly the Bayes' factor gives inconclusive evidence for an incompatibility between the data sets of XENON100 and the hints of detection. The same question assessed with goodness of fit would indicate a 2 sigma discrepancy. This suggests that more data are therefore needed to settle this question.

hep-ph↗

arXiv2013

Complementarity of direct and indirect Dark Matter detection experiments

We investigate the prospects for reconstructing the mass, spin-independent and spin-dependent cross-sections of Dark Matter particles with a combination of future direct detection experiments such as XENON1T, and the IceCube neutrino telescope in the 86-string configuration including the DeepCore array. We quantify the degree of complementarity between the two experiments by adopting realistic values for their exposure, energy threshold and resolution. Starting from benchmark models arising from a supersymmetric model with 25 free parameters, we show that despite the stringent constraints set by the run with 79 strings, IceCube can help break the degeneracies in the Dark Matter cross-section parameter space, even in the unfortunate case where it fails to discover high energy neutrinos from the Sun. We also discuss how the reconstruction of the Dark Matter particle parameters from the combined data sets is affected by the uncertainties associated with the nuclear structure of the target material in case of spin-dependent scattering and those associated with astrophysical quantities such as the Dark Matter density and velocity distribution.

hep-ph↗

arXiv2013

Co-genesis of Matter and Dark Matter with Vector-like Fourth Generation Leptons

We propose a simple extension of the standard model by adding a fourth generation vector-like lepton doublet and show that if the fourth neutrino is a massive pseudo-Dirac fermion with mass in the few hundred GeV range and mass splitting of about 100 keV, its lighter component can be a viable inelastic dark matter candidate. Its relic abundance is produced by the CP violating out-of-equilibrium decay of the type-II seesaw scalar triplet, which also gives rise to the required baryon asymmetry of the Universe via type-II leptogenesis, thus providing a simultaneous explanation of dark matter and baryon abundance observed today. Moreover, the induced vacuum expectation value of the same scalar triplet is responsible for the sub-eV Majorana masses to the three active neutrinos. A stable fourth generation of neutrinos is elusive at collider, however might be detected by current dark matter direct search experiments.

hep-ph↗

arXiv2012

Chasing a consistent picture for dark matter direct searches

In this paper we assess the present status of dark matter direct searches by means of Bayesian statistics. We consider three particle physics models for spin-independent dark matter interaction with nuclei: elastic, inelastic and isospin violating scattering. We shortly present the state of the art for the three models, marginalising over experimental systematics and astrophysical uncertainties. Whatever the scenario is, XENON100 appears to challenge the detection region of DAMA, CoGeNT and CRESST. The first aim of this study is to rigorously quantify the significance of the inconsistency between XENON100 data and the combined set of detection (DAMA, CoGeNT and CRESST together), performing two statistical tests based on the Bayesian evidence. We show that XENON100 and the combined set are inconsistent at least at 2 sigma level in all scenarios but inelastic scattering, for which the disagreement drops to 1 sigma level. Secondly we consider only the combined set and hunt the best particle physics model that accounts for the events, using Bayesian model comparison. The outcome between elastic and isospin violating scattering is inconclusive, with the odds 2:1, while inelastic scattering is disfavoured with the odds of 1:32 because of CoGeNT data. Our results are robust under reasonable prior assumptions. We conclude that the simple elastic scattering remains the best model to explain the detection regions, since the data do not support extra free parameters. Present direct searches therefore are not able to constrain the particle physics interaction of the dark matter. The outcome of consistency tests implies that either a better understanding of astrophysical and experimental uncertainties is needed, either the dark matter theoretical model is at odds with the data.

hep-ph↗

arXiv2012

Triplet seesaw model: from inflation to asymmetric dark matter and leptogenesis

The nature of dark matter (DM) particles and the mechanism that provides their measured relic abundance are currently unknown. Likewise, the nature of the inflaton is unknown as well. We investigate the triplet seesaw model in an unified picture. At high energy scale, we consider Higgs inflation driven by an admixture of standard model and triplet Higgs fields, both coupled non-minimally to gravity. At intermediate and low energies we investigate vector like fermion doublet DM candidates with a charge asymmetry in the dark sector, which is generated by the same mechanism that provides the baryon asymmetry, namely baryogenesis-via-leptogenesis induced by the decay of scalar triplets. At the same time the model gives rise to neutrino masses in the ballpark of oscillation experiments via type-II seesaw. We then apply Bayesian statistics to infer the model parameters giving rise to the observed baryon asymmetry and DM density, compatibly with inflationary and DM direct detection constraints, updated with the CRESST-II excess, the new XENON100 data release and KIMS exclusion limit.

hep-ph↗

arXiv2012

Unifying darko-lepto-genesis with scalar triplet inflation

We present a scalar triplet extension of the standard model to unify the origin of inflation with neutrino mass, asymmetric dark matter and leptogenesis. In presence of non-minimal couplings to gravity the scalar triplet, mixed with the standard model Higgs, plays the role of inflaton in the early Universe, while its decay to SM Higgs, lepton and dark matter simultaneously generate an asymmetry in the visible and dark matter sectors. On the other hand, in the low energy effective theory the induced vacuum expectation value of the triplet gives sub-eV Majorana masses to active neutrinos. We investigate the model parameter space leading to successful inflation as well as the observed dark matter to baryon abundance. Assuming the standard model like Higgs mass to be at 125-126 GeV, we found that the mass scale of the scalar triplet to be ~ O(10^9) GeV and its trilinear coupling to doublet Higgs is ~ 0.09 so that it not only evades the possibility of having a metastable vacuum in the standard model, but also lead to a rich phenomenological consequences as stated above. Moreover, we found that the scalar triplet inflation strongly constrains the quartic couplings, while allowing for a wide range of Yukawa couplings which generate the CP asymmetries in the visible and dark matter sectors.

hep-ph↗

arXiv2012

Evidence for dark matter modulation in CoGeNT?

We investigate the question of whether the recent modulation signal claimed by CoGeNT is best explained by the dark matter (DM) hypothesis from a Bayesian model comparison perspective. We consider five phenomenological explanations for the data: no modulation signal, modulation due to DM, modulation due to DM compatible with the total CoGeNT rate, and a signal coming from other physics with a free phase but annual period, or with a free phase and a free period. In each scenario, we assign to the free parameters physically motivated priors. We find that while the DM models are weakly preferred to the no modulation model, but when compared to models where the modulation is due to other physics, the DM hypothesis is favoured with odds ranging from 185:1 to 560:1. This result is robust even when astrophysical uncertainties are taken into account and the impact of priors assessed. Interestingly, the odds for the DM model in which the modulation signal is compatible with the total rate against a DM model in which this prior is not implemented is only 5:8, in spite of the former's prediction of a modulation amplitude in the energy range 0.9 to 3.0 keVee that is significantly smaller than the value observed by CoGeNT. Classical hypothesis testing also rules out the null hypothesis of no modulation at the 1.6 sigma to 2.3 sigma level, depending on the details of the alternative. Lastly, we investigate whether anisotropic velocity distributions can help to mitigate the tension between the CoGeNT total and modulated rates, and find encouraging results.

hep-ph↗

arXiv2011

Bayes and present dark matter direct search status

Recently there has been a huge activity in the dark matter direct detection field, with the report of an excess from CoGeNT and CRESST along with the annual modulated signal of DAMA/Libra and the strong exclusion bound from XENON100. We analyse these results within the framework of Bayesian inference and evidence. Indeed Bayesian methods are well suited for marginalizing over experimental systematics and background. We present the results for spin-independent interaction on nucleus with particular attention to the low dark matter mass region and the compatibility between experiments. In the same vein we also investigate the impact of astrophysical uncertainties on the WIMP preferred parameter space within the class of isotropic dark matter velocity distributions.

astro-ph.CO↗