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G. Belanger

Publications and source records attributed to G. Belanger.

At least 37 records · Page 2Linked to original sources
arXiv2014

micrOMEGAs4.1: two dark matter candidates

micrOMEGAs is a code to compute dark matter observables in generic extensions of the standard model. This version of micrOMEGAs includes a generalization of the Boltzmann equations to take into account the possibility of two dark matter candidates. The modification of the relic density calculation to include interactions between the two DM sectors as well as semi-annihilation is presented. Both DM signals in direct and indirect detection are computed as well. An extension of the standard model with two scalar doublets and a singlet is used as an example.

hep-ph↗
arXiv2014

Boosting Higgs decays into gamma and a Z in the NMSSM

In this work we present the computation of the Higgs decay into a photon and a $Z^0$ boson at one-loop level in the framework of the Next-to-Minimal Supersymmetric Standard Model (NMSSM). The numerical evaluation of this decay width was performed within the framework of the SloopS code, orginally developped for the Minimal Supersymmetric Standard Model (MSSM) but which was recently extended to deal with the NMSSM. Thanks to the high level of automation of SloopS all contributions from the various sector of the NMSSM are consistently taken into account, in particular the non-diagonal chargino and sfermion contributions. We then explored the NMSSM parameter space, using HiggsBounds and HiggsSignals, to investigate to which extent these signal can be enhanced.

hep-ph↗
arXiv2014

Isospin-violating dark matter from a double portal

We study a simple model that can give rise to isospin-violating interactions of Dirac fermion asymmetric dark matter to protons and neutrons through the interference of a scalar and U(1)$'$ gauge boson contribution. The model can yield a large suppression of the elastic scattering cross section off Xenon relative to Silicon thus reconciling CDMS-Si and LUX results while being compatible with LHC findings on the 126 GeV Higgs, electroweak precision tests and flavour constraints.

hep-ph↗
arXiv2013

Global fit to Higgs signal strengths and couplings and implications for extended Higgs sectors

The most recent LHC data have provided a considerable improvement in the precision with which various Higgs production and decay channels have been measured. Using all available public results from ATLAS, CMS and the Tevatron, we derive for each final state the combined confidence level contours for the signal strengths in the (gluon fusion + ttH associated production) versus (vector boson fusion + VH associated production) space. These "combined signal strength ellipses" can be used in a simple, generic way to constrain a very wide class of New Physics models in which the couplings of the Higgs boson deviate from the Standard Model prediction. Here, we use them to constrain the reduced couplings of the Higgs boson to up-quarks, down-quarks/leptons and vector boson pairs. We also consider New Physics contributions to the loop-induced gluon-gluon and photon-photon couplings of the Higgs, as well as invisible/unseen decays. Finally, we apply our fits to some simple models with an extended Higgs sector, in particular to Two-Higgs-Doublet models of Type I and Type II, the Inert Doublet model, and the Georgi-Machacek triplet Higgs model.

hep-ph↗
arXiv2013

Status of invisible Higgs decays

We analyze the extent to which the LHC and Tevatron results as of the end of 2012 constrain invisible (or undetected) decays of the Higgs boson-like state at ~ 125 GeV. To this end we perform global fits for several cases: 1) a Higgs boson with Standard Model (SM) couplings but additional invisible decay modes; 2) SM couplings to fermions and vector bosons, but allowing for additional new particles modifying the effective Higgs couplings to gluons and photons; 3) no new particles in the loops but tree-level Higgs couplings to the up-quarks, down-quarks and vector bosons, relative to the SM, treated as free parameters. We find that in the three cases invisible decay rates of 23%, 61%, 88%, respectively, are consistent with current data at 95% confidence level (CL). Limiting the coupling to vector bosons, CV, to CV < 1 in case 3) reduces the allowed invisible branching ratio to 56% at 95% CL. Requiring in addition that the Higgs couplings to quarks have the same sign as in the SM, an invisible rate of up to 36% is allowed at 95% CL. We also discuss direct probes of invisible Higgs decays, as well as the interplay with dark matter searches.

hep-ph↗
arXiv2013

micrOMEGAs3.1 : a program for calculating dark matter observables

micrOMEGAs is a code to compute dark matter observables in generic extensions of the standard model. This new version of micrOMEGAs is a major update which includes a generalization of the Boltzmann equations to accommodate models with asymmetric dark matter or with semi-annihilation and a first approach to a generalization of the thermodynamics of the Universe in the relic density computation. Furthermore a switch to include virtual vector bosons in the final states in the annihilation cross sections or relic density computations is added. Effective operators to describe loop-induced couplings of Higgses to two-photons or two-gluons are introduced and reduced couplings of the Higgs are provided allowing for a direct comparison with recent LHC results. A module that computes the signature of DM captured in celestial bodies in neutrino telescopes is also provided. Moreover the direct detection module has been improved as concerns the implementation of the strange "content" of the nucleon. New extensions of the standard model are included in the distribution.

hep-ph↗
arXiv2013

In-flight calibration of the INTEGRAL/IBIS mask

Since the release of the INTEGRAL Offline Scientific Analysis (OSA) software version 9.0, the ghost busters module has been introduced in the INTEGRAL/IBIS imaging procedure, leading to an improvement of the sensitivity around bright sources up to a factor of 7. This module excludes in the deconvolution process the IBIS/ISGRI detector pixels corresponding to the projection of a bright source through mask elements affected by some defects. These defects are most likely associated with screws and glue fixing the IBIS mask to its support. Following these major improvements introduced in OSA 9, a second order correction is still required to further remove the residual noise, now at a level of 0.2-1% of the brightest source in the field of view. In order to improve our knowledge of the IBIS mask transparency, a calibration campaign has been carried out during 2010-2012. We present here the analysis of these data, together with archival observations of the Crab and Cyg X-1, that allowed us to build a composite image of the mask defects and to investigate the origin of the residual noise in the IBIS/ISGRI images. Thanks to this study, we were able to point out a simple modification of the ISGRI analysis software that allows to significantly improve the quality of the images in which bright sources are detected at the edge of the field of view. Moreover, a refinement of the area excluded by the ghost busters module is considered, and preliminary results show improvements to be further tested. Finally, this study indicates further directions to be investigated for improving the ISGRI sensitivity, such as taking into account the thickness of the screws in the mask model or studying the possible discrepancy between the modeled and actual mask element bridges.

astro-ph.IM↗
arXiv2013

Higgs Couplings at the End of 2012

Performing a fit to all publicly available data, we analyze the extent to which the latest results from the LHC and Tevatron constrain the couplings of the Higgs boson-like state at ~ 125 GeV. To this end we assume that only Standard Model (SM) particles appear in the Higgs decays, but tree-level Higgs couplings to the up-quarks, down-quarks and vector bosons, relative to the SM are free parameters. We also assume that the leptonic couplings relative to the SM are the same as for the down-quark, and a custodial symmetry for the V=W,Z couplings. In the simplest approach, the effective Higgs couplings to gluons and photons are computed in terms of the previous parameters. This approach is also applied to Two-Higgs-Doublet Models of Type I and Type II. However, we also explore the possibility that the net Higgs to gluon-gluon and gamma-gamma couplings have extra loop contributions coming from Beyond-the-Standard Model physics. We find that the SM p-value ~ 0.5 is more than 2 sigma away from fits in which: a) there is some non-SM contribution to the gamma-gamma coupling of the Higgs; or b) the sign of the top quark coupling to the Higgs is opposite that of the W coupling. In both these cases p-values ~ 0.9 can be achieved. Since option b) is difficult to realize in realistic models, it would seem that new physics contributions to the effective couplings of the Higgs are preferred.

hep-ph↗
arXiv2012

Top Polarization in Stop Production at the LHC

We survey the expected polarization of the top produced in the decay of a scalar top quark, $\tilde t \rightarrow {\tilde t}χ_i^0, i =1-2$. The phenomenology is quite interesting, since the expected polarization depends both on the mixing in the stop and neutralino sectors and on the mass differences between the stop and the neutralino. We find that a mixed stop behaves almost like a right-handed stop due to the larger hypercharge that enters the stop/top/gaugino coupling and that these polarisation effects disappear, when $m_{\tilde t_1} \approx m_t+m_{\tildeχ^0_i}$. After a discussion on the expected top polarization from the decay of a scalar top quark, we focus on the interplay of polarization and kinematics at the LHC. We discuss different probes of the top polarization in terms of lab-frame observables. We find that these observables faithfully reflect the polarization of the parent top-quark, but also have a non-trivial dependence on the kinematics of the stop production and decay process. In addition, we illustrate the effect of top polarization on the energy and transverse momentum of the decay lepton in the laboratory frame. Our results show that both spectra are softened substantially in case of a negatively polarized top, particularly for a large mass difference between the stop and the neutralino. Thus, the search strategies, and the conclusions that can be drawn from them, depends not just on the mass difference $m_{\tilde t} - m_{\tildeχ_{i}^{0}}$ due to the usual kinematic effects but also on the effects of top polarization on the decay kinematics the extent of which depends in turn on the said mass difference.

hep-ph↗
arXiv2012

Two Higgs Bosons at the Tevatron and the LHC?

The best fit to the Tevatron results in the bb channel and the mild excesses at CMS in the gamma-gamma channel at 136 GeV and in the tau-tau channel above 132 GeV can be explained by a second Higgs state in this mass range, in addition to the one at 125 GeV recently discovered at the LHC. We show that a scenario with two Higgs bosons at 125 GeV and 136 GeV can be consistent with practically all available signal rates, including a reduced rate in the tau-tau channel around 125 GeV as reported by CMS. An example in the parameter space of the general NMSSM is given where, moreover, the signal rates of the 125 GeV Higgs boson in the gamma-gamma channels are enhanced relative to the expectation for a SM Higgs boson of this mass.

hep-ph↗
arXiv2012

Searches for New Physics: Les Houches Recommendations for the Presentation of LHC Results

We present a set of recommendations for the presentation of LHC results on searches for new physics, which are aimed at providing a more efficient flow of scientific information between the experimental collaborations and the rest of the high energy physics community, and at facilitating the interpretation of the results in a wide class of models. Implementing these recommendations would aid the full exploitation of the physics potential of the LHC.

hep-ph↗
arXiv2011

The Higgs boson in the MSSM in light of the LHC

We investigate the expectations for the light Higgs signal in the MSSM in different search channels at the LHC. After taking into account dark matter and flavor constraints in the MSSM with eleven free parameters, we show that the light Higgs signal in the $gammaγ$ channel is expected to be at most at the level of the SM Higgs, while the $h\rightarrow b\bar{b}$ from W fusion and/or the $h \rightarrowτ\barτ$ can be enhanced. For the main discovery mode, we show that a strong suppression of the signal occurs in two different cases: low $M_A$ or large invisible width. A more modest suppression is associated with the effect of light supersymmetric particles. Looking for such modification of the Higgs properties and searching for supersymmetric partners and pseudoscalar Higgs offer two complementary probes of supersymmetry.

hep-ph↗
arXiv2011

The right-handed sneutrino as thermal dark matter in U(1) extensions of the MSSM

We investigate the parameter space of a supersymmetric model with an extended U(1) gauge symmetry in which the RH sneutrino is a thermal dark matter candidate. In this scenario, annihilation of RH sneutrinos proceeds mainly through Higgs or Z' exchange. We find that sneutrinos in the mass range from 50GeV to more than 1 TeV can be consistent with both the WMAP limit and the direct detection upper limits. Powerful constraints from new gauge boson searches at the LHC as well as from $ΔM_s$ are incorporated. Depending on the choice of the U(1) charge, these scenarios will be further probe by direct dark matter searches as well as by Higgs searches at the LHC.

hep-ph↗
arXiv2011

Concurrent X-ray, near-infrared, sub-millimeter, and GeV gamma-ray observations of Sgr A*

The radiative counterpart of the supermassive black hole at the Galactic center (GC), Sgr A*, is subject to frequent flares visible simultaneously in X-rays and near-infrared (NIR). Often, enhanced radio variability from centimeter to sub-millimeter wavelengths is observed to follow these X-ray/NIR eruptions. We present here a multi-wavelength campaign carried out in April 2009, with the aim of characterizing this broadband flaring activity. Concurrent data from the XMM-Newton/EPIC (2-10 keV), VLT/NACO (2.1 microns, 3.8 microns), APEX/LABOCA (870 microns), and Fermi/LAT (0.1-200 GeV) instruments are employed to derive light curves and spectral energy distributions of new flares from Sgr A*. We detected two relatively bright NIR flares both associated with weak X-ray activity, one of which was followed by a strong sub-mm outburst 200 min later. Photometric spectral information on a NIR flare was obtained for the first time with NACO giving a power-law photon index alpha=-0.4\pm0.3. The first attempt to detect flaring activity from the Fermi GC source 1FGL J1745.6-2900 is also reported. NIR, X-ray, and sub-mm flares are finally modeled in the context of non-thermal emission processes. It is found that the simplest scenario involving a single expanding plasmoid releasing synchrotron NIR/sub-mm and synchrotron self-Compton X-ray radiation is inadequate to reproduce the data, but suggestions to reconcile the basic elements of the theory and the observations are proposed.

astro-ph.HE↗
arXiv2010

Dark matter in UED : the role of the second KK level

We perform a complete calculation of the relic abundance of the KK-photon LKP in the universal extra dimension model including all coannihilation channels and all resonances. We show that the production of level 2 particles which decay dominantly into SM particles contribute significantly to coannihilation processes involving level 1 KK-leptons. As a result the preferred dark matter scale is increased to $R^{-1}=1.3$~TeV. A dark matter candidate at or below the TeV scale can only be found in the non-minimal model by reducing the mass splittings between the KK-particles and the LKP. The LKP nucleon scattering cross section is typically small, $σ< 10^{-10}$~pb, unless the KK-quarks are nearly degenerate with the LKP.

hep-ph↗
arXiv2010

Indirect search for dark matter with micrOMEGAs2.4

We present a new module of micrOMEGAs devoted to the computation of indirect signals from dark matter annihilation in any new model with a stable weakly interacting particle. The code provides the mass spectrum, cross-sections, relic density and exotic fluxes of gamma rays, positrons and antiprotons. The propagation of charged particles in the Galactic halo is handled with a new module that allows to easily modify the propagation parameters.

hep-ph↗
arXiv2010

Light mixed sneutrinos as thermal dark matter

In supersymmetric models with Dirac neutrino masses, a left-right mixed sneutrino can be a viable dark matter candidate. We examine the MSSM+$\tildeν_R$ parameter space where this is the case with particular emphasis on light sneutrinos with masses below 10 GeV. We discuss implications for direct and indirect dark matter searches, including the relevant uncertainties, as well as consequences for collider phenomenology.

hep-ph↗