arXiv subjects

Leszek Roszkowski

Publications and source records attributed to Leszek Roszkowski.

At least 55 records · Page 3Linked to original sources

arXiv2014

Reconstructing CMSSM parameters at the LHC with $\sqrt{s}=14$ TeV via the golden decay channel

We identify a benchmark point in the CMSSM's heavy stau-coannihilation region, which is favored by experiments, and demonstrate that it could be accessible to the LHC at $\sqrt{s}=14$ TeV with 300/fb of integrated luminosity via a golden decay measurement. With Monte-Carlo, we simulate sparticle production and subsequent golden decay at the event level and perform pseudo-measurements of sparticle masses from kinematic endpoints in invariant mass distributions. We find that two lightest neutralino masses and the first and second generation left-handed slepton and squark masses could be rather precisely measured with correlated uncertainties. We investigate whether from such measurements one could determine the CMSSM's Lagrangian parameters by including a likelihood from our pseudo-measurements of sparticle masses in a Bayesian analysis of the CMSSM's parameter space. We find that the CMSSM's parameters can be accurately determined, with the exception of the common trilinear parameter. Experimental measurements of the relic density by Planck and the Higgs boson's mass slightly improve this determination, especially for the common trilinear parameter. Finally, within our benchmark scenario, we show that the neutralino dark matter will be accessible to direct searches in future one tonne detectors.

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arXiv2014

Dark matter production in the early Universe: beyond the thermal WIMP paradigm

Increasingly stringent limits from LHC searches for new physics, coupled with lack of convincing signals of weakly interacting massive particle (WIMP) in dark matter searches, have tightly constrained many realizations of the standard paradigm of thermally produced WIMPs as cold dark matter. In this article, we review more generally both thermally and non-thermally produced dark matter (DM). One may classify DM models into two broad categories: one involving bosonic coherent motion (BCM) and the other involving WIMPs. BCM and WIMP candidates need, respectively, some approximate global symmetries and almost exact discrete symmetries. Supersymmetric axion models are highly motivated since they emerge from compelling and elegant solutions to the two fine-tuning problems of the Standard Model: the strong CP problem and the gauge hierarchy problem. We review here non-thermal relics in a general setup, but we also pay particular attention to the rich cosmological properties of various aspects of mixed SUSY/axion dark matter candidates which can involve both WIMPs and BCM in an interwoven manner. We also review briefly a panoply of alternative thermal and non-thermal DM candidates.

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arXiv2014

Neutralino and gravitino dark matter with low reheating temperature

We examine a scenario in which the reheating temperature $T_R$ after inflation is so low that it is comparable to, or lower than, the freeze out temperature of ordinary WIMPs. In this case the dark matter relic abundance is reduced, thus relaxing the impact of the usually strong constraint coming from the requirement that the universe does not overclose. We first re-examine the dynamics of freezeout during reheating. Next we apply a Bayesian approach to study the parameter space of the MSSM with ten free parameters, the CMSSM and the singlino-dominated regions of the NMSSM. In each case we find dramatic departures from the usually considered regime of high $T_R$, with important implications for direct detection dark matter searches. In the MSSM we examine WIMP mass range up to ~5 TeV, and find regions of bino dark matter over the whole mass range, and of higgsino dark matter with mass over a similar range but starting from the ~1 TeV value of the standard high $T_R$ scenario. We show that the prospects for bino detection strongly depend on $T_R$, while the higgsino is for the most part detectable by future one-tonne detectors. The wino, which is excluded in the standard scenario, becomes allowed again if its mass is roughly above 3.5 TeV, and can be detectable. In the CMSSM, the bino and higgsino mass ranges become more constrained although detection prospects remain similar. In the Next-to-MSSM at low enough $T_R$ wide ranges of singlino-dominated parameter space of the model become cosmologically allowed. We also study the contribution to the DM relic density from direct and cascade decays of the inflaton. Finally, we consider the case of a gravitino as dark matter. We find strong bounds from overclosure and Big Bang Nucleosynthesis, and derive lower limits on $T_R$ which depend on the gravitino mass and on the nature of the lightest ordinary superpartner.

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arXiv2014

Low fine tuning in the MSSM with higgsino dark matter and unification constraints

We examine the issue of fine tuning in the MSSM with GUT-scale boundary conditions. We identify specific unification patterns and mass relations that can lead to a significant lowering of the fine tuning due to gauginos, scalars, and the μ parameter, relative to the simplest unification conditions. We focus on a phenomenologically interesting region that is favored by the Higgs mass and the relic density where the dark matter is a nearly pure higgsino with mass given by μ~1 TeV while the scalars and gauginos have masses in the multi-TeV regime. There, we find that the fine tuning can be reduced to the level of a few percent. Despite the gluino mass in the ballpark of 2 TeV, resulting mass spectra will be hard to explore at the LHC, but good prospects for detection come from dark matter direct detection experiments. Finally, we demonstrate with a specific example how the conditions and mass relations giving low fine tuning can originate in the context of supergravity and Grand Unified Theories.

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arXiv2013

Simultaneous enhancement in gamma.gamma, b.b-bar and tau+.tau- rates in the NMSSM with nearly degenerate scalar and pseudoscalar Higgs bosons

We propose an experimental test of a scenario in the Next-to-Minimal Supersymmetric Standard Model in which both the lightest scalar and the lightest pseudoscalar Higgs bosons have masses around 125 GeV. The pseudoscalar can contribute significantly to the gamma.gamma rate at the LHC due to light Higgsino-like charginos in its effective one-loop coupling to two photons. Such charginos are obtained for small values of the mu_eff parameter which also results in enhanced b.b-bar and tau+.tau- rates compared to those expected for a Standard Model Higgs boson. This scenario should result in a clear discrepancy between the observed rates in these three decay channels and those in the WW and ZZ channels, since the pseudoscalar does not couple to the W and Z bosons. However, in the dominant gluon fusion production mode the pseudoscalar will stay hidden behind the SM-like scalar Higgs boson and in order for it to be observable the associated b.b-bar.h production mode has to be considered, the cross section for which is tiny in the Standard Model but tan.beta-enhanced in supersymmetry. We analyze the constrained NMSSM with non-universal Higgs sector parameters and identify regions of its parameter space where the lightest pseudoscalar with mass around 125 GeV and strongly enhanced gamma.gamma (up to 60%), b.b-bar and tau+.tau- rates in the b.b-bar.h mode can be obtained.

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arXiv2013

Dark matter and collider signatures of the MSSM

We explore the MSSM with 9 free parameters (p9MSSM) that have been selected as a minimum set that allows an investigation of neutralino dark matter and collider signatures while maintaining consistency with several constraints. These include measurement of the dark matter relic density from PLANCK, main properties of the discovered Higgs boson, LHC direct SUSY searches, recent evidence for a Standard Model-like BR(Bs -> μ+ μ-), and the measurement of δ(g-2), plus a number of other electroweak and flavor physics constraints. We perform a simulation of two LHC direct SUSY searches at sqrt(s)=8 TeV: the CMS inclusive α_T search for squarks and gluinos and the CMS electroweak production search with 3l+E_T^miss in the final state. We use the latter to identify the regions of the parameter space, consistent at 2σ with δ(g-2), that are not excluded by the direct limits from the electroweak production. We find that they correspond to a neutralino mass in the window 200 GeV<m_χ<500 GeV. We also implement the likelihood for the XENON100 exclusion bound, in which we consider for the first time the impact of a recent determination of the Σ_{πN} term from CHAOS data, Σ_{πN}=43\pm12 MeV. We show that in light of this measurement, the present statistical impact of the XENON100 bound is greatly reduced, although future sensitivities of the LUX and XENON1T experiments will have decisive impact on the mixed bino/higgsino composition of the neutralino. We point out some tension between the constraints from δ(g-2) and XENON100. Finally, we present prospects for various indirect searches of dark matter, namely γ-ray fluxes from dSphs and the Galactic Center at Fermi-LAT, and the positron flux at AMS02. We also show the 5-year sensitivity on the spin-dependent neutralino-proton cross section due to neutrino fluxes from the Sun at IceCube.

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arXiv2013

Review of axino dark matter

We review the status of axino dark matter. Two hierarchy problems, the strong CP problem and the gauge hierarchy problem, have led to introducing into particle physics a spontaneously broken global Peccei-Quinn symmetry and a softly broken supersymmetry, respectively. Combining them implies the presence of not only an axion, but also of its scalar component, saxion, and their fermionic partner, axino. Among these, the axion and the axino are attractive dark matter candidates. Various possibilities for the axino as dark matter are discussed.

astro-ph.CO↗

arXiv2013

Two ultimate tests of constrained supersymmetry

We examine the prospects of using two alternative and complementary ways to explore the regions that are favored by global constraints in two simple unified supersymmetric models: the CMSSM and the NUHM. First, we consider BR(Bs->μμ), which has recently been for the first time measured by LHCb. In the CMSSM we show that ultimate, but realistic, improvement in the determination of the observable to about 5-10% around the Standard Model value would strongly disfavor the A-funnel region, while not affecting much the other favored regions. Second, we show that all the favored regions of the CMSSM will be, for the most part, sensitive to direct dark matter searches in future one-tonne detectors. A signal at low WIMP mass (<=450 GeV) and low spin-independent cross section would then strongly favor the stau coannihilation region while a signal at higher WIMP mass (~800 GeV to ~1.2 TeV) would clearly point to the region where the neutralino is higgsino-like with mass ~1 TeV. A nearly complete experimental testing of the CMSSM over multi-TeV ranges of superpartner masses, far beyond the reach of direct SUSY searches at the LHC, can therefore be achievable. In the NUHM, in contrast, similar favored regions exist but a sample study reveals that even a precise determination of BR(Bs->μμ) would have a much less constraining power on the model, including the A-funnel region. On the other hand, this could allow one to, by detecting in one-tonne detectors a signal for 500 GeV<m_χ<800 GeV, strongly disfavor the CMSSM.

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arXiv2013

The Constrained NMSSM with a 126 GeV Higgs boson: A global analysis

We present the first global analysis of the Constrained NMSSM that investigates the impact of the recent discovery of a 126 GeV Higgs-like boson, of the observation of a signal for BR(B_s->μ^+μ^-), and of constraints on supersymmetry from ~5/fb of data accumulated at the LHC, as well as of other relevant constraints from colliders, flavor physics and dark matter. We consider three possible cases, assuming in turn that the discovered Higgs boson is: i) the lightest Higgs boson of the model; ii) the next-to-lightest Higgs boson; and iii) a combination of both roughly degenerate in mass. The likelihood function for the Higgs signal uses signal rates in the γγ and ZZ --> 4l channels, while that for the Higgs exclusion limits assumes decay through the γγ, ττ, ZZ and W^+W^- channels. In all cases considered we identify the 68% and 95% credible posterior probability regions in a Bayesian approach. We find that, when the constraints are applied with their respective uncertainties, the first case shows strong CMSSM-like behavior, with the stau coannihilation region featuring highest posterior probability, the best-fit point, a correct mass of the lightest Higgs boson and the lighter stop mass in the ballpark of 1 TeV. The second and the third cases, on the other hand, while allowed are disfavored by the constraints from direct detection of dark matter and from BR(B_s->μ^+μ^-). Without the anomalous magnetic moment of the muon the fit improves considerably, especially for negative effective μ parameter. We discuss how the considered scenarios could be tested furtherly at the LHC and in dark matter searches.

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arXiv2013

Gravitino dark matter with constraints from Higgs boson mass and sneutrino decays

We investigate gravitino dark matter produced thermally at high temperatures and in decays of a long-lived sneutrino. We consider the Non-Universal Higgs Model and a generalized gauge mediation model, and in each case identify sneutrino LOSP regions of the parameter space consistent with the mass of the Higgs-like boson observed at the LHC. We apply relevant collider and cosmological bounds, including constraints from Big Bang Nucleosynthesis and from warm dark matter on large scale structures. Generally, we find allowed values of the reheating temperature TR below 10^9 GeV, i.e. somewhat smaller than the values needed for thermal leptogenesis, even with a conservative lower bound of 122 GeV on the Higgs mass. Requiring mass values closer to 126 GeV implies TR below 10^7 GeV and the gravitino mass less than 10 GeV.

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arXiv2013

Bayesian Implications of Current LHC Supersymmetry and Dark Matter Detection Searches for the Constrained MSSM

We investigate the impact of recent limits from LHC searches for supersymmetry and from direct and indirect searches for dark matter on global Bayesian inferences of the parameter space of the Constrained Minimal Supersymmetric Standard Model (CMSSM). In particular we apply recent exclusion limits from the CMS α_T analysis of 1.1/fb of integrated luminosity, the current direct detection dark matter limit from XENON100, as well as recent experimental constraints on γ-ray fluxes from dwarf spheroidal satellite galaxies of the Milky Way from the FermiLAT telescope, in addition to updating values for other non-LHC experimental constraints. We extend the range of scanned parameters to include a significant fraction of the focus point/hyperbolic branch region. While we confirm earlier conclusions that at present LHC limits provide the strongest constraints on the model's parameters, we also find that when the uncertainties are not treated in an excessively conservative way, the new bounds from dwarf spheroidal have the power to significantly constrain the focus point/hyperbolic branch region. Their effect is then comparable, if not stronger, to that from XENON100. We further analyze the effects of one-year projected sensitivities on the neutrino flux from the Sun in the 86-string IceCube+DeepCore configuration at the South Pole. We show that data on neutrinos from the Sun, expected for the next few months at IceCube and DeepCore, have the potential to further constrain the same region of parameter space independently of the LHC and can yield additional investigating power for the model.

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arXiv2012

Constrained MSSM favoring new territories: The impact of new LHC limits and a 125 GeV Higgs boson

We present an updated and extended global analysis of the Constrained MSSM (CMSSM) taking into account new limits on supersymmetry from ~5/fb data sets at the LHC. In particular, in the case of the razor limit obtained by the CMS Collaboration we simulate detector efficiency for the experimental analysis and derive an approximate but accurate likelihood function. We discuss the impact on the global fit of a possible Higgs boson with mass near 125 GeV, as implied by recent data, and of a new improved limit on BR(B_s->μμ). We identify high posterior probability regions of the CMSSM parameters as the stau-coannihilation and the A-funnel region, with the importance of the latter now being much larger due to the combined effect of the above three LHC results and of dark matter relic density. We also find that the focus point region is now disfavored. Ensuing implications for superpartner masses favor even larger values than before, and even lower ranges for dark matter spin-independent cross section, σ^{SI}_p<10^{-9} pb. We also find that relatively minor variations in applying experimental constraints can induce a large shift in the location of the best-fit point. This puts into question the robustness of applying the usual chisquare approach to the CMSSM. We discuss the goodness-of-fit and find that, while it is difficult to calculate a p-value, the g-2 constraint makes, nevertheless, the overall fit of the CMSSM poor. We consider a scan without this constraint, and we allow μ to be either positive or negative. We find that the global fit improves enormously for both signs of μ, with a slight preference for μ<0 caused by a better fit to BR(b->sγ) and BR(B_s->μμ).

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arXiv2012

Axino Cold Dark Matter Revisited

Axino arises in supersymmetric versions of axion models and is a natural candidate for cold or warm dark matter. Here we revisit axino dark matter produced thermally and non-thermally in light of recent developments. First we discuss the definition of axino relative to low energy axion one for several KSVZ and DFSZ models of the axion. Then we review and refine the computation of the dominant QCD production in order to avoid unphysical cross-sections and, depending on the model, to include production via SU(2) and U(1) interactions and Yukawa couplings.

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arXiv2012

Bayesian Implications of Current LHC and XENON100 Search Limits for the Constrained MSSM

The CMS Collaboration has released the results of its search for supersymmetry, by applying an alphaT method to 1.1/fb of data at 7 TeV. The null result excludes (at 95% CL) a low-mass region of the Constrained MSSM's parameter space that was previously favored by other experiments. Additionally, the negative result of the XENON100 dark matter search has excluded (at 90% CL) values of the spin-independent scattering cross sections sigma^SI_p as low as 10^-8 pb. We incorporate these improved experimental constraints into a global Bayesian fit of the Constrained MSSM by constructing approximate likelihood functions. In the case of the alphaT limit, we simulate detector efficiency for the CMS alphaT 1.1/fb and validate our method against the official 95% CL contour. We identify the 68% and 95% credible posterior regions of the CMSSM parameters, and also find the best-fit point. We find that the credible regions change considerably once a likelihood from alphaT is included, in particular the narrow light Higgs resonance region becomes excluded, but the focus point/horizontal branch region remains allowed at the 1sigma level. Adding the limit from XENON100 has a weaker additional effect, in part due to large uncertainties in evaluating sigma^SI_p, which we include in a conservative way, although we find that it reduces the posterior probability of the focus point region to the 2sigma level. The new regions of high posterior favor squarks lighter than the gluino and all but one Higgs bosons heavy. The dark matter neutralino mass is found in the range 250 GeV <~ m_Chi1 <~ 343 GeV (at 1sigma) while, as the result of improved limits from the LHC, the favored range of sigma^SI_p is pushed down to values below 10^{-9} pb. We highlight tension between (g-2)_mu and BR(b->sg), which is exacerbated by including the alphaT limit; each constraint favors a different region of the CMSSM's mass parameters.

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arXiv2011

Next-to-Minimal Supersymmetric Model Higgs Scenarios for Partially Universal GUT Scale Boundary Conditions

We examine the extent to which it is possible to realize the NMSSM "ideal Higgs" models espoused in several papers by Gunion et al in the context of partially universal GUT scale boundary conditions. To this end we use the powerful methodology of nested sampling. We pay particular attention to whether ideal-Higgs-like points not only pass LEP constraints but are also acceptable in terms of the numerous constraints now available, including those from the Tevatron and $B$-factory data, $(g-2)_μ$ and the relic density $Ωh^2$. In general for this particular methodology and range of parameters chosen, very few points corresponding to said previous studies were found, and those that were found were at best $2σ$ away from the preferred relic density value. Instead, there exist a class of points, which combine a mostly singlet-like Higgs with a mostly singlino-like neutralino coannihilating with the lightest stau, that are able to effectively pass all implemented constraints in the region $80<m_h<100$. It seems that the spin-independent direct detection cross section acts as a key discriminator between ideal Higgs points and the hard to detect singlino-like points.

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arXiv2011

Is light neutralino as dark matter still viable?

Motivated by the recent re-confirmation by CoGENT of the low-energy excess of events observed last year, and the recent improved limits from the XENON-100 experiment that are in contention with the CoGENT data, we re-examine the low mass neutralino region of the Minimal Supersymmetric Standard Model and of the Next-to-Minimal Supersymmetric Standard Model, both without assuming gaugino mass unification. We make several focused scans for each model, determining conservative constraints on input parameters. We then determine how these constraints are made increasingly stringent as we re-invoke our experimental constraints involving the dark matter relic abundance, collider constraints from LEP and the Tevatron, and then from flavour physics, as a series of successive 2 sigma hard cuts. We find that for both models, when all relevant constraints are applied in this fashion, we do not generate neutralino LSPs that possess a spin-independent scattering cross section in excess of 10^-5 pb and a mass ~7 GeV < m_chi < ~9 GeV that is necessary in order to explain the CoGENT observations.

astro-ph.CO↗

arXiv2010

The impact of propagation uncertainties on the potential Dark Matter contribution to the Fermi LAT mid-latitude gamma-ray data

We investigate the extent to which the uncertainties associated with the propagation of Galactic cosmic rays impact upon estimates for the gamma-ray flux from the mid-latitude region. We consider contributions from both standard astrophysical background (SAB) processes as well as resolved point sources. We have found that the uncertainties in the total gamma-ray flux from the mid-latitude region relating to propagation parameter values consistent with local B/C and Be10/Be9 data dominate by 1-2 orders of magnitude. These uncertainties are reduced to less than an order of magnitude when the normalisations of the SAB spectral components are fitted to the corresponding Fermi LAT data. We have found that for many propagation parameter configurations (PPCs) our fits improve when an extragalactic background (EGB) component is simultaneously fitted to the data. We also investigate the improvement in our fits when a flux contribution from neutralino dark matter (DM), described by the Minimal Supersymmetric Standard Model, was simultaneously fitted to the data. We consider three representative cases of neutralino DM for both Burkert and Einasto DM density profiles, in each case simultaneously fitting a boost factor of the DM contribution together with the SAB and EGB components. We have found that for several PPCs there are significant improvements in our fits, yielding both substantial EGB and DM components, where for a few of these PPCs the best-fit EGB component is consistent with recent estimates by the Fermi Collaboration.

astro-ph.HE↗

arXiv2009

A Re-analysis of Gravitino Dark Matter in the Constrained MSSM

We re-consider the gravitino as dark matter in the framework of the Constrained MSSM. We include several recently suggested improvements on: (i) the thermal production of gravitinos, (ii) the calculation of the hadronic spectrum from NLSP decay and (iii) the BBN calculation including stau bound-state effects. In most cases we find an upper bound on the reheating temperature $\treh\lsim {\rm a few}\times 10^7\gev$ from over-production of $^6{\rm Li}$ from bound state effects. We also find an upper limit on the stau lifetime of $3\times10^4 \sec$, which is nearly an order of magnitude larger than the simple limit $5\times 10^3 \sec$ often used to avoid the effect of bound-state catalysis. The bound on $\treh$ is relaxed to $\lsim {\rm a few}\times 10^8\gev$ when we use a more conservative bound on ${^6}{\rm Li}/{^7}{\rm Li}$, in which case a new region at small stau mass at $\sim 100\gev$ and much longer lifetimes opens up. Such a low stau mass region can be easily tested at the LHC.

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