arXiv subjects

Genevieve Belanger

Publications and source records attributed to Genevieve Belanger.

At least 19 recordsLinked to original sources

arXiv2022

Co-scattering in micrOMEGAs: a case study for the singlet-triplet dark matter model

In scenarios with very small dark matter (DM) couplings and small mass splittings between the DM and other dark sector particles, so-called "co-scattering" or "conversion-driven freeze-out" can be the dominant mechanism for DM production. We present the inclusion of this mechanism in micrOMEGAs together with a case study of the phenomenological implications in the fermionic singlet-triplet model. For the latter, we focus on the transition between co-annihilation and co-scattering processes. We observe that co-scattering is needed to describe the thermal behaviour of the DM for very small couplings, opening up a new region in the parameter space of the model. The triplet states are often long-lived in this region; we therefore also discuss LHC constraints from long-lived signatures obtained with SModelS.

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arXiv2021

Recasting direct detection limits within micrOMEGAs and implication for non-standard Dark Matter scenarios

Direct detection experiments obtain 90% upper limits on the elastic scattering cross sections of dark matter with nucleons assuming point-like interactions and standard astrophysical and cosmological parameters. In this paper we provide a recasting of the limits from XENON1T, PICO-60, CRESST-III and DarkSide-50 and include them in micrOMEGAs. The code can then be used to directly impose constraints from these experiments on generic dark matter models under different assumptions about the DM velocity distribution or on the nucleus form factors. Moreover new limits on the elastic scattering cross sections can be obtained in the presence of a light t-channel mediator or of millicharged particles.

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arXiv2020

Status of low mass LSP in SUSY

In this article we review the case for a light ($< m_{h_{125}}/2$) neutralino and sneutrino being a viable Dark Matter (DM) candidate in Supersymmetry(SUSY). To that end we recapitulate, very briefly, three issues related to the DM which impact the discussions : calculation of DM relic density, detection of the DM in Direct and Indirect experiments and creation /detection at the Colliders. In case of SUSY, the results from Higgs and SUSY searches at the colliders also have implications for the DM mass and couplings. In view of the constraints coming from all these sources, the possibility of a light neutralino is all but ruled out for the constrained MSSM : cMSSM. The pMSSM, where the gaugino masses are not related at high scale, is also quite constrained and under tension in case of thermal DM and will be put to very stern test in the near future in Direct Detection (DD) experiments as well as by the LHC analyses. However in the pMSSM with modified cosmology and hence non-thermal DM or in the NMSSM, a light neutralino is much more easily accommodated. A light RH sneutrino is also still a viable DM candidate although it requires extending the MSSM with additional singlet neutrino superfields. All of these possibilities can be indeed tested jointly in the upcoming SUSY-electroweakino and Higgs searches at the HL/HE luminosity LHC, the upcoming experiments for the Direct Detection (DD) and indirect detection for the DM as well as the high precision electron-positron colliders under planning.

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arXiv2020

Dark Matter Abundance from Sequential Freeze-in Mechanism

We present a thorough analysis of the sequential freeze-in mechanism for dark matter production in the early universe. In this mechanism the dark matter relic density results from pair annihilation of mediator particles which are themselves produced by thermal collisions of standard model particles. Below some critical value of the mediator coupling to standard model fields, this sequential channel dominates over the usual freeze-in where dark matter is directly produced from thermal collisions, even when the mediator is not in thermal equilibrium. The latter case requires computing the full non-thermal distribution of the mediators, for which finite temperature corrections are particularly important.

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arXiv2018

Probing CP nature of a mediator in associated production of dark matter with single top quark

We consider associated production of dark matter with single top quark, in a simplified dark matter model with spin-0 mediators. The produced top quark is polarized and the polarization depends on the CP of the mediator. We calculate both the cross-section and top polarization for these processes. We compute angular asymmetries which demonstrate the difference between the polarization expected for the scalar or pseudoscalar mediator. Both the cross section and top polarization are sensitive to the CP property of the mediator, depending on the mediator mass. We find that these polarization asymmetries add value to the determination of the CP property of the mediator particularly in the case of a state with indeterminate CP.

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arXiv2017

The invisible decay of Higgs boson in the context of a thermal and non-thermal relic in MSSM

We study the decay of 125 GeV Higgs boson to light LSP neutralino in the phenomenological minimal supersymmetric standard model in the context of collider searches and astrophysical experiments. We consider the parameter space for light neutralinos that can be probed via the invisible Higgs decays and higgsino searches at the ILC. We consider the cases where the light neutralino is compatible with the observed relic density or where the thermal relic is over-abundant, pointing to non-standard cosmology. In the former case, when the neutralino properties give rise to under-abundant relic density, the correct amount of relic abundance is assumed to be guaranteed by either additional DM particles or by non-thermal cosmology. We contrast these different cases. We assess what astrophysical measurements can be made, in addition to the measurements made at the ILC, which can provide a clue to the nature of the light neutralino. We find that a number of experiments, including Xenon-nT, PICO-250, LZ in conjunction with measurements made at the ILC on invisible Higgs width can pin down the nature of this neutralino, along with its cosmological implications. Additionally, we also point out potential LHC signatures that could be complementary in this region of parameter space.

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arXiv2015

Light stop in the MSSM after LHC Run 1

The discovery of a Higgs boson with a mass of 126 GeV at the LHC when combined with the non-observation of new physics both in direct and indirect searches imposes strong constraints on supersymmetric models and in particular on the top squark sector. The experiments for direct detection of dark matter have provided with yet more constraints on the neutralino LSP mass and its interactions. After imposing limits from the Higgs, flavour and dark matter sectors, we examine the feasibility for a light stop in the context of the pMSSM, in light of current results for stop and other SUSY searches at the LHC. We only require that the neutralino dark matter explains a fraction of the cosmologically measured dark matter abundance. We find that a stop with mass below $\sim$ 500 GeV is still allowed. We further study various probes of the light stop scenario that could be performed at the LHC Run - II either through direct searches for the light and heavy stop, or SUSY searches not currently available in simplified model results. Moreover we study the characteristics of heavy Higgs for the points in the parameter space allowed by all the available constraints and illustrate the region with large cross sections to fermionic or electroweakino channels. Finally we show that nearly all scenarios with a small stop$-$LSP mass difference will be tested by Xenon1T provided the NLSP is a chargino, thus probing a region hard to access at the LHC.

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arXiv2014

The Dark Side of Electroweak Naturalness Beyond the MSSM

Weak scale supersymmetry (SUSY) remains a prime explanation for the radiative stability of the Higgs field. A natural account of the Higgs boson mass, however, strongly favors extensions of the Minimal Supersymmetric Standard Model (MSSM). A plausible option is to introduce a new supersymmetric sector coupled to the MSSM Higgs fields, whose associated states resolve the little hierarchy problem between the third generation squark masses and the weak scale. SUSY also accomodates a weakly interacting cold dark matter (DM) candidate in the form of a stable neutralino. In minimal realizations, the thus-far null results of direct DM searches, along with the DM relic abundance constraint, introduce a level of fine-tuning as severe as the one due to the SUSY little hierarchy problem. We analyse the generic implications of new SUSY sectors parametrically heavier than the minimal SUSY spectrum, devised to increase the Higgs boson mass, on this little neutralino DM problem. We focus on the SUSY operator of smallest scaling dimension in an effective field theory description, which modifies the Higgs and DM sectors in a correlated manner. Within this framework, we show that recent null results from the LUX experiment imply a tree-level fine-tuning for gaugino DM which is parametrically at least a few times larger than that of the MSSM. Higgsino DM whose relic abundance is generated through a thermal freeze-out mechanism remains also severely fine-tuned, unless the DM lies below the weak boson pair-production threshold. As in the MSSM, well-tempered gaugino-Higgsino DM is strongly disfavored by present direct detection results.

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arXiv2013

Probing the flavor violating scalar top quark signal at the LHC

The Large Hadron Collider(LHC) has completed its run at 8 TeV with the experiments ATLAS and CMS having collected about 25 $\rm fb^{-1}$ of data each. Discovery of a light Higgs boson, coupled with lack of evidence for supersymmetry at the LHC so far, has motivated studies of supersymmetry in the context of naturalness with the principal focus being the third generation squarks. In this work, we analyze the prospects of the flavor violating decay mode $\rm \tilde{t}_1\to cχ_{1}^{0}$ at 8 and 13 TeV center of mass energy at the LHC. This channel is also relevant in the dark matter context for the stop-coannihilation scenario, where the relic density depends on the mass difference between the lighter stop quark ($\tilde{t}_1$) and the lightest neutralino($χ_{1}^{0}$) states. This channel is extremely challenging to probe, specially for situations when the mass difference between the lighter stop quark and the lightest neutralino is small. Using certain kinematical properties of signal events we find that the level of backgrounds can be reduced substantially. We find that the prospect for this channel is limited due to the low production cross section for top squarks and limited luminosity at 8 TeV, but at the 13 TeV LHC with 100 $fb^{-1}$ luminosity, it is possible to probe top squarks with masses up to $\sim$ 450 GeV. We also discuss how the sensitivity could be significantly improved by tagging charm jets.

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arXiv2013

LHC constraints on light neutralino dark matter in the MSSM

Light neutralino dark matter can be achieved in the Minimal Supersymmetric Standard Model if staus are rather light, with mass around 100 GeV. We perform a detailed analysis of the relevant supersymmetric parameter space, including also the possibility of light selectons and smuons, and of light higgsino- or wino-like charginos. In addition to the latest limits from direct and indirect detection of dark matter, ATLAS and CMS constraints on electroweak-inos and on sleptons are taken into account using a "simplified models" framework. Measurements of the properties of the Higgs boson at 125 GeV, which constrain amongst others the invisible decay of the Higgs boson into a pair of neutralinos, are also implemented in the analysis. We show that viable neutralino dark matter can be achieved for masses as low as 15 GeV. In this case, light charginos close to the LEP bound are required in addition to light right-chiral staus. Significant deviations are observed in the couplings of the 125 GeV Higgs boson. These constitute a promising way to probe the light neutralino dark matter scenario in the next run of the LHC.

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arXiv2013

Top Polarization in Sbottom Decays at the LHC

We perform a comprehensive analysis of the polarization of the top quarks originating from sbottom-pair production at the LHC, followed by sbottom decays to top+chargino. We study moreover the expected net polarization of top quarks produced in sbottom-to-chargino and stop-to-neutralino decays in scenarios with small chargino - neutralino mass difference, where these decays may be hard to distinguish. We show that, in contrast to top quarks produced via the Standard Model processes, the average polarization of top quarks originating from these SUSY decays can obtain any value between +1 and -1. We further study the effect of this polarization on the top quark decay kinematics. On the one hand this may be used to construct measures of this polarization, on the other hand it may be used to enhance the search reach in certain scenarios. Exploiting top polarization may also prove useful for searches for "natural" SUSY with light higgsinos, which is typically very difficult to detect at the LHC.

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arXiv2012

Testing Minimal Universal Extra Dimensions Using Higgs Boson Searches at the LHC

Large Hadron Collider (LHC) searches for the SM Higgs boson provide a powerful limit on models involving Universal Extra Dimensions (UED) where the Higgs production is enhanced. We have evaluated all one-loop diagrams for Higgs production from gluon fusion and decay to two photons within "minimal" UED (mUED), independently confirming previous results, and we have evaluated enhancement factors for Higgs boson production and decay over the mUED parameter space. Using these we have derived limits on the parameter space, combining data from both ATLAS and CMS collaborations for the most recent 7 TeV and 8 TeV LHC data. We have performed a rigorous statistical combination of several Higgs boson search channels which is important because mUED signatures from the Higgs boson are not universally enhanced. We have found that 1/R < 500 GeV is excluded at 95% CL, while for larger 1/R only a very narrow (\pm1-4 GeV) mass window around m_h = 125 GeV and another window (up to 2 GeV wide for 1/R > 1000 GeV) around m_h = 118 GeV are left. The latter is likely to be excluded as more data becomes available whereas the region around 125 GeV is where the recently discovered Higgs-like particle was observed and therefore where the exclusion limit is weaker. It is worth stressing that mUED predicts an enhancement for all channels for Higgs production by gluon fusion and decay while the vector boson fusion process WW/ZZ -> h -> AA is generically suppressed and WW/ZZ -> h -> WW*/ZZ* is standard. Therefore, as more 8 TeV LHC data becomes available, the information on individual Higgs boson production and decay processes provided by the CMS and ATLAS experiments can be effectively used to favour mUED or exclude it further.

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arXiv2012

Light neutralino dark matter in the MSSM and its implication for LHC searches for staus

It was shown in a previous study that a lightest neutralino with mass below 30 GeV was severely constrained in the minimal supersymmetric standard model (MSSM), unless it annihilates via a light stau and thus yields the observed dark matter abundance. In such a scenario, while the stau is the next-to-lightest supersymmetric particle (NLSP), the charginos and the other neutralinos as well as sleptons of the first two families are also likely to be not too far above the mass bounds laid down by the Large Electron Positron (LEP) collider. As the branching ratios of decays of the charginos and the next-to-lightest neutralino into staus are rather large, one expects significant rates of tau-rich final states in such a case. With this in view, we investigate the same-sign ditau and tri-tau signals of this scenario at the Large Hadron Collider (LHC) for two MSSM benchmark points corresponding to light neutralino dark matter. The associated signal rates for these channels are computed, for the centre-of-mass energy of 14 TeV. We find that both channels lead to appreciable rates if the squarks and the gluino are not too far above a TeV, thus allowing to probe scenarios with light neutralinos in the 14 TeV LHC run with 10-100 fb^{-1}.

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arXiv2012

Mixed sneutrino dark matter in light of the 2011 XENON and LHC results

In the context of supersymmetric models in which small Dirac neutrino masses are generated by supersymmetry breaking, a mainly right-handed (RH) mixed sneutrino can be an excellent cold dark matter (DM) candidate. We perform a global analysis of the Minimal Supersymmetric Standard Model (MSSM)+RH neutrino parameter space by means of Markov Chain Monte Carlo scans. We include all relevant constraints from collider and dark matter searches, paying particular attention to nuclear and astrophysical uncertainties. Two distinct cases can satisfy all constraints: heavy sneutrino DM with mass of order 100 GeV, as well as light sneutrino DM with mass of about 3-6 GeV. We discuss the implications for direct and indirect dark matter searches, as well as for SUSY and Higgs searches at the LHC for both, the light and the heavy sneutrino dark matter case. The light sneutrino case is excluded by the 125-126 GeV Higgs signal.

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arXiv2012

PAMELA and FERMI-LAT limits on the neutralino-chargino mass degeneracy

Searches for Dark Matter (DM) particles with indirect detection techniques have reached important milestones with the precise measurements of the anti-proton and gamma-ray spectra, notably by the PAMELA and FERMI-LAT experiments. While the gamma-ray results have been used to test the thermal Dark Matter hypothesis and constrain the Dark Matter annihilation cross section into Standard Model (SM) particles, the anti-proton flux measured by the PAMELA experiment remains relatively unexploited. Here we show that the latter can be used to set a constraint on the neutralino-chargino mass difference. To illustrate our point we use a Supersymmetric model in which the gauginos are light, the sfermions are heavy and the Lightest Supersymmetric Particle (LSP) is the neutralino. In this framework the W^+ W^- production is expected to be significant, thus leading to large anti-proton and gamma-ray fluxes. After determining a generic limit on the Dark Matter pair annihilation cross section into W^+ W^- from the anti-proton data only, we show that one can constrain scenarios in which the neutralino-chargino mass difference is as large as ~ 20 GeV for a mixed neutralino (and intermediate choices of the anti-proton propagation scheme). This result is consistent with the limit obtained by using the FERMI-LAT data. As a result, we can safely rule out the pure wino neutralino hypothesis if it is lighter than 450 GeV and constitutes all the Dark Matter.

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arXiv2012

The 125 GeV Higgs in the NMSSM in light of LHC results and astrophysics constraints

Recent LHC data suggest an excess in the Higgs decay channels into gamma gamma, W W and Z Z at roughly 125 GeV. The current excess in the diphoton channel is twice that expected from a Standard Model Higgs; whilst this may well change with more statistics, it is interesting to consider the implications should the result persist. Here, we assess whether the NMSSM with a neutralino dark matter candidate could explain this excess when astrophysical constraints (e.g. no overproduction of gamma rays and radio emission in the galaxy, no anomalous excess in the dark matter direct detection experiments and no dark matter overabundance) are imposed on the neutralino. This enables us to disregard unphysical regions of the parameter space even though the Higgs signal is compatible with the observed excess. The result of our analysis is that there are configurations of the parameter space which can explain the signal strength reported by the ATLAS and CMS collaborations for a Higgs mass within the required range. Should the observed signal strength finally be compatible with Standard Model expectations, it would be difficult to distinguish between the discovery of Standard Model Higgs and a SM-like Higgs from the NMSSM, unless one performs dedicated searches of very light Higgs bosons and possibly investigate peculiar signatures of supersymmetric particles. We also propose a new jets + missing E_T signal for the case where the LSP is a singlino-like neutralino.

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arXiv2012

Model-Independent Bounds on Squarks from Monophoton Searches

Supersymmetry with a compressed spectrum could be responsible for the negative results from supersymmetric searches at LHC. Squarks and gluinos well below the TeV scale could have escaped detection since all search channels lose sensitivity when the mass splitting between supersymmetric particles becomes small. Even in this stealthy situation, production of colored particles is probed in processes with supersymmetric particles produced in association with a high-pT photon. We show that searches for missing energy with a monophoton are a powerful tool, and that the 2011 LHC data already surpasses the limits set by LEP and TeVatron in the compressed case. We set a model-independent bound on the mass of any up (down) type squark of 150 (110) GeV, and stronger model-dependent bounds can be set. We also comment on the expected improvement on those bounds in the 2012 LHC run.

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arXiv2012

Assisted freeze-out

We explore a class of dark matter models with two dark matter candidates, only one interacts with the standard model sector. One of the dark matter is thermalized with the assistance of the other stable particle. While both stable particles contribute to the total relic density only one can elastically scatter with nuclei, thus effectively reducing the direct detection rate.

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