arXiv subjects

S. S. AbdusSalam

Publications and source records attributed to S. S. AbdusSalam.

12 recordsLinked to original sources

arXiv2023

The MSSM compatibility with the limit on electron electric dipole moment

The minimal supersymmetric standard model (MSSM) particles can generate loop-level radiative corrections that contribute to the electric dipole moment (EDM) of an electron. The upper bound on the EDM can therefore be used for delineating the MSSM parameters space. We use this setting to describe a direction of particle physics phenomenology research -- the global fits of particle physics models beyond the standard model. This is done within the context of the MSSM phenomenology framework with thirty free parameters (MSSM30). Using samples of MSSM30 parameter-space points constrained with the latest bound on the electron EDM, we show that Arg(mu M2) is the most constrained MSSM CP-violating phase. The EDM-compatible parameter regions feature multi-TeV pseudoscalar Higgs bosons and relatively lower "tan beta" values compared to previous analyses.

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arXiv2021

Majorana phases in high-scale mixings unification hypotheses

For addressing the remarkable difference between neutrino and quark mixings, high-scale mixings relations (HSMR) or unification (HSMU) hypothe\ ses were proposed. These phenomenology frameworks have been explored with respect to bounds from neutrino oscillations and relevant cosmologic\ al data. However there are caveats with regards to assessing the hypotheses' compatibility with data in a statistically robust and convergent \ manner because most analysis employ a few sample of points in model parameters' space. A remedy could be achieved by using Bayesian algorithms\ for the parameters' space exploration. Using this approach, we made global fits of the HSMU and HSMR models to data and find compatible param\ eter regions, including for Majorana phases. The posterior samples could be used for studying correlations between neutrino observables and pr\ ospects for updates of related experiments.

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arXiv2018

30 parameter version of the MSSM in light of the $B_s\rightarrowμ^+μ^-$ observation

The R-parity conserving MSSM in light of the decay $B_s\rightarrowμ^+μ^-$ with near-SM branching ratio is an interesting platform for studying the complementarity between direct and indirect searches for beyond the SM physics. Based on this, we have analysed the possible impact of the $B_s\rightarrowμ^+μ^-$ observation on the posterior sample from the global fit of a 30-parameter MSSM (MSSM-30), and the related Wilson Coefficients. The MSSM-30 is a systematically constructed, symmetry-guided, MSSM parametrization, as opposed to the traditional frames (e.g. pMSSM) with crude treatment of flavor violation parameters. This paper illustrates why phenomenological frames like the MSSM-30 should be preferred to study flavor physics. For the current and future B-physics experimental precision, such a consideration is crucial for suitably assessing supersymmetric contributions to flavor observables.

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arXiv2017

Light and compressed gluinos at the LHC via string theory

In this article, we show that making global fits of string theory model parameters to data is an interesting mechanism for probing, mapping and forecasting connections of the theory to real world physics. We considered a large volume scenario (LVS) with D3-branes matter fields and supersymmetry breaking. A global fit of the parameters to low energy data shows that the set of LVS models are associated with light gluinos which are quasi-degenerate with the neutralinos and charginos they can promptly decay into and thus possibly hidden to current LHC gluino search strategies.

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arXiv2016

Where to look for natural supersymmetry

Why is natural supersymmetry neither detected nor ruled-out to date? To answer this question we use the Bayesian approach where the emphasis on finding prior-independent features within broader and minimally biased frames is taken as the guiding principle. The 20-parameter minimal supersymmetric standard model (MSSM) fits to subjective naturalness indicate the existence of a prior-independent upper bound on the pseudoscalar Higgs boson mass $m_A$ as a function of $\tan β$, the ratio of the vacuum expectation values of the MSSM Higgs doublets. For a 30-parameter MSSM this implies that $m_A \lesssim 3$ TeV and $\tan β\lesssim 25$ at 95\% Bayesian confidence. Removing the contradictory subjectiveness within the electroweak fine-tuning measure leads to finding the naturalness line, $m_A \sim \frac{1}{\sqrt{2}} \, m_Z \, \tan β,$ that reduces by one the number of MSSM Higgs sector free parameters.

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arXiv2015

MFV Reductions of MSSM Parameter Space

The 100+ free parameters of the minimal supersymmetric standard model (MSSM) make it computationally difficult to compare systematically with data, motivating the study of specific parameter reductions such as the cMSSM and pMSSM. Here we instead study the reductions of parameter space implied by using minimal flavour violation (MFV) to organise the R-parity conserving MSSM, with a view towards systematically building in constraints on flavour-violating physics. Within this framework the space of parameters is reduced by expanding soft supersymmetry-breaking terms in powers of the Cabibbo angle, leading to a 24-, 30- or 42-parameter framework (which we call MSSM-24, MSSM-30, and MSSM-42 respectively), depending on the order kept in the expansion. We provide a Bayesian global fit to data of the MSSM-30 parameter set to show that this is manageable with current tools. We compare the MFV reductions to the 19-parameter pMSSM choice and show that the pMSSM is not contained as a subset. The MSSM-30 analysis favours a relatively lighter TeV-scale pseudoscalar Higgs boson and $\tan β\sim 10$ with multi-TeV sparticles.

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arXiv2012

Benchmark Models, Planes, Lines and Points for Future SUSY Searches at the LHC

We define benchmark models for SUSY searches at the LHC, including the CMSSM, NUHM, mGMSB, mAMSB, MM-AMSB and p19MSSM, as well as models with R-parity violation and the NMSSM. Within the parameter spaces of these models, we propose benchmark subspaces, including planes, lines and points along them. The planes may be useful for presenting results of the experimental searches in different SUSY scenarios, while the specific benchmark points may serve for more detailed detector performance tests and comparisons. We also describe algorithms for defining suitable benchmark points along the proposed lines in the parameter spaces, and we define a few benchmark points motivated by recent fits to existing experimental data.

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arXiv2011

Can the LHC rule out the MSSM ?

If supersymmetry (SUSY) exists in nature and is a solution to the hierarchy problem then it should be detectable at the TeV energy scale which the large hadron collider (LHC) is now exploring. One of the main goals of the LHC is the discovery or exclusion of the R-parity conserving minimal supersymmetric standard model (MSSM). So far, the SUSY search results are presented in the context of the constrained MSSM and other specific simplified SUSY models. A model-independent analysis necessarily relies on the trigger-system of the LHC detectors. By using the posterior samples of a 20-parameter MSSM, the phenomenological MSSM, from a fit to indirect collider and cosmological data we find that there is a significant volume in the MSSM parameter space that would escape the standard trigger-systems of the detectors. As such, in the absence of discovery in the current and future LHC runs, it would be difficult if not impossible to exclude the MSSM unless some dedicated and special triggers are commissioned or a Higgs boson with mass as predicted by the supersymmetric models is not found.

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arXiv2011

Cold Dark Matter Hypotheses in the MSSM

We perform a Bayesian model selection analysis in the the R-parity conserving MSSM to compare two different assumptions: whether the lightest neutralinos make all or only part of the cold dark matter. This corresponds to either imposing full WMAP relic density limits or just its upper bound for constraining the MSSM parameters. We consider several realisations of the MSSM, namely, three GUT-scale SUSY breaking scenarios with a handful of parameters corresponding to the CMSSM, anomaly mediation and the large volume string scenarios as well as the weak-scale 25-parameter phenomenological MSSM (pMSSM). The results give a data-based quantitative evidence for a multicomponent cold dark matter. The pMSSM posterior samples indicate that the choice of imposing full WMAP limits or just its upper bound affects mostly the gaugino-higgsino content of the neutralino and, against naive expectations, essentially not any other sector.

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arXiv2010

Selecting a Model of Supersymmetry Breaking Mediation

We study the problem of selecting between different mechanisms of supersymmetry breaking in the Minimal Supersymmetric Standard Model using current data. We evaluate the Bayesian evidence of four supersymmetry breaking scenarios: mSUGRA, mGMSB, mAMSB and moduli mediation. The results show a strong dependence on the dark matter assumption. Using the inferred cosmological relic density as an upper bound, minimal anomaly mediation is at least moderately favoured over the CMSSM. Our fits also indicate that evidence for a positive sign of the mu parameter is moderate at best. We present constraints on the anomaly and gauge mediated parameter spaces and some previously unexplored aspects of the dark matter phenomenology of the moduli mediation scenario. We use sparticle searches, indirect observables and dark matter observables in the global fit and quantify robustness with respect to prior choice. We quantify how much information is contained within each constraint.

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arXiv2010

Fitting the Phenomenological MSSM

We perform a global Bayesian fit of the phenomenological minimal supersymmetric standard model (pMSSM) to current indirect collider and dark matter data. The pMSSM contains the most relevant 25 weak-scale MSSM parameters, which are simultaneously fit using `nested sampling' Monte Carlo techniques in more than 15 years of CPU time. We calculate the Bayesian evidence for the pMSSM and constrain its parameters and observables in the context of two widely different, but reasonable, priors to determine which inferences are robust. We make inferences about sparticle masses, the sign of the $μ$ parameter, the amount of fine tuning, dark matter properties and the prospects for direct dark matter detection without assuming a restrictive high-scale supersymmetry breaking model. We find the inferred lightest CP-even Higgs boson mass as an example of an approximately prior independent observable. This analysis constitutes the first statistically convergent pMSSM global fit to all current data.

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arXiv2008

Bayesian Selection of sign(mu) within mSUGRA in Global Fits Including WMAP5 Results

We study the properties of the constrained minimal supersymmetric standard model (mSUGRA) by performing fits to updated indirect data, including the relic density of dark matter inferred from WMAP5. In order to find the extent to which mu < 0 is disfavoured compared to mu > 0, we compare the Bayesian evidence values for these models, which we obtain straightforwardly and with good precision from the recently developed multi-modal nested sampling ('MultiNest') technique. We find weak to moderate evidence for the mu > 0 branch of mSUGRA over mu < 0 and estimate the ratio of probabilities to be P(mu > 0)/P(mu < 0) = 6-61 depending on the prior measure and range used. There is thus positive (but not overwhelming) evidence that mu > 0 in mSUGRA. The MultiNest technique also delivers probability distributions of parameters and other relevant quantities such as superpartner masses. We explore the dependence of our results on the choice of the prior measure used. We also use the Bayesian evidence to quantify the consistency between the mSUGRA parameter inferences coming from the constraints that have the largest effects: (g-2)_mu, BR(b -> s gamma) and cold dark matter (DM) relic density Omega_{DM}h^2.

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