arXiv subjects

Nausheen R. Shah

Publications and source records attributed to Nausheen R. Shah.

At least 19 recordsLinked to original sources

arXiv2026

Gedanken Experiments of Entanglement in Particle Physics: Interactions, Operators and Bell Inequalities in Flavor Space

In this article we explore ideas from quantum entanglement which can be meaningfully formulated and tested in the collider environment. We propose Bell-type inequalities as operator-level diagnostics of quantum incompatibility in particle-physics systems. We construct flavor operators associated with mass identification, flavor change, and charged-current weak mixing which arise from fundamental interactions in the Standard Model. We treat these interactions as alternative measurement settings in a Gendanken experiment. For entangled two-particle states, these operators generate nontrivial correlations that violate Bell-type bounds, excluding non-contextual local descriptions under the stated assumptions. These violations arise from the algebraic structure of the operators rather than from kinematic correlations or exotic dynamics. We discuss how the predicted correlation patterns may be probed with experimental data, clarifying the scope and limitations of Bell-type reasoning in particle physics.

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arXiv2026

The Deconstruction of Flavor in the Privately Democratic Higgs Sector

The Standard Model (SM) of particle physics fails to explain the observed hierarchy in fermion masses or the origin of fermion-flavor structure. We construct a model to explain these observations in the quark sector. We introduce a spectrum of new particles consisting of six of each -- massive singlet vector-like quarks (VLQs), singlet scalars, and SU(2)-doublet scalars. SM quark masses are generated when the neutral components of the SU(2)-doublet scalars acquire non-zero vacuum expectation values (VEVs). We impose global symmetries to ensure that Yukawa couplings stay roughly flavor diagonal and democratic (of the same order), as well as to suppress tree-level flavor-changing neutral currents. Quark-mass hierarchy then follows from a hierarchy in scalar VEVs. The singlet scalars also acquire weak-scale VEVs. Together with the VLQs, they act as messengers between different generations of quarks in the SM. These messenger particles are responsible for generating the elements of the Cabibbo-Kobayashi-Masakawa (CKM) matrix which depend on the ratios of the singlet VEVs and VLQ masses. Constructed this way, the CKM matrix is found to be \emph{independent} of the SM fermion masses. Using the measured values of the CKM matrix elements and assuming order-one couplings, we derive constraints on the masses of the VLQs and discuss prospects for probing our model in the near future.

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arXiv2024

Benchmark Lines and Planes for Higgs-to-Higgs Decays in the NMSSM

A number of benchmark scenarios for NMSSM Higgs boson searches via Higgs-to-Higgs decays at the LHC have been proposed by the NMSSM Subgroup of the LHC HWG3. Some of them are already in use by the ATLAS and CMS collaborations for the interpretation of their results from Run 2. In this document we summarize the theory setup, the underlying procedures and reproduce the benchmark scenarios in table form.

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arXiv2023

Lighting up the LHC with Dark Matter

We show that simultaneously explaining dark matter and the observed value of the muon's magnetic dipole moment may lead to yet unexplored photon signals at the LHC. We consider the Minimal Supersymmetric Standard Model with electroweakino masses in the few-to-several hundred GeV range, and opposite sign of the Bino mass parameter with respect to both the Higgsino and Wino mass parameters. In such region of parameter space, the spin-independent elastic scattering cross section of a Bino-like dark matter candidate in direct detection experiment is suppressed by cancellations between different amplitudes, and the observed dark matter relic density can be realized via Bino-Wino co-annihilation. Moreover, the observed value of the muon's magnetic dipole moment can be explained by Bino and Wino loop contributions. Interestingly, "radiative" decays of Wino-like neutralinos into the lightest neutralino and a photon are enhanced, whereas decays into leptons are suppressed. While these decay patterns weaken the reach of multi-lepton searches at the LHC, the radiative decay opens a new window for probing dark matter at the LHC through the exploration of parameter space regions beyond those currently accessible. To complement the current electroweakino searches, we propose searching for a single (soft) photon plus missing transverse energy, accompanied by a hard initial state radiation jet.

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arXiv2022

Report of the Topical Group on Physics Beyond the Standard Model at Energy Frontier for Snowmass 2021

This is the Snowmass2021 Energy Frontier (EF) Beyond the Standard Model (BSM) report. It combines the EF topical group reports of EF08 (Model-specific explorations), EF09 (More general explorations), and EF10 (Dark Matter at Colliders). The report includes a general introduction to BSM motivations and the comparative prospects for proposed future experiments for a broad range of potential BSM models and signatures, including compositeness, SUSY, leptoquarks, more general new bosons and fermions, long-lived particles, dark matter, charged-lepton flavor violation, and anomaly detection.

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arXiv2022

Early-Universe Model Building

Theoretical investigations into the evolution of the early universe are an essential part of particle physics that allow us to identify viable extensions to the Standard Model as well as motivated parameter space that can be probed by various experiments and observations. In this white paper, we review particle physics models of the early universe. First, we outline various models that explain two essential ingredients of the early universe (dark matter and baryon asymmetry) and those that seek to address current observational anomalies. We then discuss dynamics of the early universe in models of neutrino masses, axions, and several solutions to the electroweak hierarchy problem. Finally, we review solutions to naturalness problems of the Standard Model that employ cosmological dynamics.

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arXiv2022

Higgs alignment and novel $CP$-Violating observables in two-Higgs-doublet models

Null results from searches for new physics at the Large Hadron Collider (LHC) tend to enforce the belief that new particles must be much heavier than the weak scale. We undertake a systematic study of the interplay between Higgs alignment and $CP$-violation in complex two-Higgs-doublet models, which enables us to construct a $CP$-violating scenario where new Higgs bosons are close to the weak scale after including stringent constraints from the electric dipole moment and measurements at the LHC. In addition, we propose a novel potential signal of $CP$-violation in the Higgs-to-Higgs decays, $h_3\to h_2 h_1$, where $h_3, h_2$, and $h_1$ are the heaviest, second heaviest and the Standard Model-like neutral Higgs bosons, respectively. The decay could manifest itself in triple boson final states in $h_1h_1h_1$ and $h_1h_1Z$, which are quite distinct and provide unique venues for new measurements at the LHC.

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arXiv2022

The Tiny (g-2) Muon Wobble from Small-$μ$ Supersymmetry

A new measurement of the muon anomalous magnetic moment has been reported by the Fermilab Muon g-2 collaboration and shows a $4.2σ$ departure from the most precise and reliable calculation of this quantity in the Standard Model. Assuming that this discrepancy is due to new physics, we concentrate on a simple supersymmetric model that also provides a dark matter explanation in a previously unexplored region of supersymmetric parameter space. Such interesting region can realize a Bino-like dark matter candidate compatible with all current direct detection constraints for small to moderate values of the Higgsino mass parameter $|μ|$. This in turn would imply the existence of light additional Higgs bosons and Higgsino particles within reach of the high-luminosity LHC and future colliders. We provide benchmark scenarios that will be tested in the next generation of direct dark matter experiments and at the LHC.

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arXiv2021

Nucleation is More than Critical -- A Case Study of the Electroweak Phase Transition in the NMSSM

Electroweak baryogenesis is an attractive mechanism to generate the baryon asymmetry of the Universe via a strong first order electroweak phase transition. We compare the phase transition patterns suggested by the vacuum structure at the critical temperatures, at which local minima are degenerate, with those obtained from computing the probability for nucleation via tunneling through the barrier separating local minima. Heuristically, nucleation becomes difficult if the barrier between the local minima is too high, or if the distance (in field space) between the minima is too large. As an example of a model exhibiting such behavior, we study the Next-to-Minimal Supersymmetric Standard Model, whose scalar sector contains two SU(2) doublets and one gauge singlet. We find that the calculation of the nucleation probabilities prefers different regions of parameter space for a strong first order electroweak phase transition than the calculation based solely on the critical temperatures. Our results demonstrate that analyzing only the vacuum structure via the critical temperatures can provide a misleading picture of the phase transition patterns, and, in turn, of the parameter space suitable for electroweak baryogenesis.

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arXiv2020

Personal Ultraviolet Respiratory Germ Eliminating Machine (PUR$\diamond$GEM) for COVID-19

The current COVID-19 pandemic has highlighted the need for cheap reusable personal protective equipment. The disinfection properties of Ultraviolet (UV) radiation in the 200-300 nm have been long known and documented. Many solutions using UV radiation, such as cavity disinfection and whole room decontamination between uses, are in use in various industries, including healthcare. Here we propose a portable wearable device which can safely, efficiently and economically, continuously disinfect inhaled/exhaled air using UV radiation with possible 99.99% virus elimination. We utilize UV radiation in the 260 nm range where no ozone is produced, and because of the self-contained UV chamber, there would be no UV exposure to the user. We have optimized the cavity design such that an amplification of 10-50 times the irradiated UV power may be obtained. This is crucial in ensuring enough UV dosage is delivered to the air flow during breathing. Further, due to the turbulent nature of airflow, a series of cavities is proposed to ensure efficient actual disinfection. The Personal Ultraviolet Respiratory Germ Eliminating Machine (PUR$\diamond$GEM) can be worn by people or attached to devices such as ventilator exhausts/intakes, or be used free-standing as a portable local air disinfection unit, offering modularity with multiple avenues of usage. Patent pending.

physics.med-ph↗

arXiv2020

Personal Ultraviolet Respiratory Germ Eliminating Machine (PUR$\diamond$GEM) for COVID-19: Prototype Development

In this article we detail the prototype development of the Personal Ultraviolet Respiratory Germ Eliminating Machine(PUR$\diamond$GEM) to safely, efficiently and economically, continuously disinfect inhaled/exhaled air using Ultraviolet (UV) radiation with possible 99.99% virus elimination. The PUR$\diamond$GEM consists of a series of UV disinfection chambers through which constant airflow is maintained via fans. A minimum air flow rate of $\sim20-30$ L/min is sufficient to keep CO$_2$ levels $\lesssim$ 0.5% in the hood/helmet. We validated that using easily available PTFE wrap, a factor of $\sim 18$ enhancement in UV power can be obtained in our spherical chambers. Detailed analysis is presented for the air travel time distributions through the cavities, and the expectation value for actual pathogen elimination is computed. We provide the scaling of pathogen elimination with the number of cavities in series, reflective enhancement, UV source power, sphere radius and airflow rate. We show that disinfection greater than 4-log is achievable for a series of three or more spheres. We 3D printed our prototype, consisting of two spheres of 10 cm diameter each in series for each direction of disinfection. Using UVC LEDs emitting $\sim$ 40 mW of power each with an airflow rate of 30 L/min, actual SARS-COV2 virus elimination of $\sim$ 98% is expected. While not manually feasible to construct smaller spheres in the lab, smaller cavities can be commercially manufactured, leading to significantly higher actual pathogen elimination, as well as reducing fingerprint and cost of cavity manufacture. Patent pending.

physics.med-ph↗

arXiv2019

Benchmark Suggestions for Resonant Double Higgs Production at the LHC for Extended Higgs Sectors

In this note we present benchmark scenarios for resonant double Higgs production at the $13\,$TeV LHC in the 2HDM+S model and the $Z_3$ Next-to-Minimal Supersymmetric Standard Model (NMSSM), which may be accessible with 300 fb$^{-1}$ of data. The NMSSM Higgs sector can be mapped onto the 2HDM+S. We show benchmark points and relevant parameter planes in the 2HDM+S for three sets of signatures: ($A\to h_{125} a, ~H\to h_{125} h)$, ($A\to a h, H\to hh, H\to aa)$, and ($H\to h_{125}h_{125}$). The first two signatures are optimized in what we call $Z$-Phobic scenarios where $H/A$ decays into final states with $Z$ bosons are suppressed. The last signature, $h_{125}$ pair production, is directly proportional to the misalignment of $h_{125}$ with the interaction state sharing the couplings of a SM Higgs boson, and hence is presented in the Max Misalignment scenario. We also present two NMSSM benchmark points for the ($A\to h_{125} a, ~H\to h_{125} h)$ signatures. The benchmark scenarios presented here are based on Refs. [1,2].

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arXiv2019

The Return of the WIMP: Missing Energy Signals and the Galactic Center Excess

In a recent work, we emphasized that an excess in tri-lepton events plus missing energy observed by the ATLAS experiment at the LHC could be interpreted as a signal of low energy supersymmetry. In such a scenario the lightest neutralino mass is approximately $m_χ\simeq 60$ GeV and the direct Dark Matter detection cross section is naturally below the current bound. In this work we present simple extensions of this scenario that lead to an explanation of the gamma ray excess at the center of the galaxy observed by Fermi-LAT, as well as the anti-proton excess observed by AMS-02. These extensions include the addition of a small CP violating phase in the neutralino sector or the addition of a light CP-odd Higgs scalar. Our study is of special relevance in view of a recent analysis that casts doubt on the previously accepted preference for mili-second pulsars as the origin of the galactic center excess.

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arXiv2019

A $\pmbν$ Solution to the Strong CP Problem

We present a new solution to the strong CP problem in which the imaginary component of the up quark mass, $\mathcal{I}[m_u]$, acquires a tiny, but non-vanishing value. This is achieved via a Dirac seesaw mechanism, which is also responsible for the generation of the small neutrino masses. Consistency with the observed value of the up quark mass is achieved via instanton contributions arising from QCD-like interactions. In this framework, the value of the neutron electric dipole moment is directly related to $\mathcal{I}[m_u]$, which, due to its common origin with the neutrino masses, implies that the neutron electric dipole moment is likely to be measured in the next round of experiments. We also present a supersymmetric extension of this Dirac seesaw model to stabilize the hierarchy among the scalar mass scales involved in this new mechanism.

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arXiv2019

The NMSSM is within Reach of the LHC: Mass Correlations & Decay Signatures

The Next-to-Minimal Supersymmetric Standard Model (NMSSM), the singlet extension of the MSSM which fixes many of the MSSM's shortcomings, is shown to be within reach of the upcoming runs of the Large Hadron Collider (LHC). A systematic treatment of the various Higgs decay channels and their interplay has been lacking due to the seemingly large number of free parameters in the NMSSM's Higgs sector. We demonstrate that due to the SM-like nature of the observed Higgs boson, the NMSSM's Higgs and neutralino sectors have highly correlated masses and couplings and can effectively be described by four physically intuitive parameters: the physical masses of the two CP-odd states and their mixing angle, and $\tanβ$, which plays a minor role. The heavy Higgs bosons in the NMSSM have large branching ratios into pairs of lighter Higgs bosons or a light Higgs and a $Z$ boson. Search channels arising via these Higgs cascades are unique to models like the NMSSM with a Higgs sector larger than that of the MSSM. In order to cover as much of the NMSSM parameter space as possible, one must combine conventional search strategies employing decays of the additional Higgs bosons into pairs of SM particles with Higgs cascade channels. We demonstrate that such a combination would allow a significant fraction of the viable NMSSM parameter space containing additional Higgs bosons with masses below 1 TeV to be probed at future runs of the LHC.

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arXiv2018

The Higgs and WIMP DM Lamp Posts for New Weak Scale Physics: EFT Perspectives and the NMSSM

I will show, via effective field theory (EFT) techniques, that obtaining an observationally consistent relic density while evading stringent direct detection limits and maintaining $h_{125}$ phenomenology in an extended Higgs sector can be easily achieved. I will then map such an EFT to the low energy limit of the NMSSM with the Higgsinos integrated out. Both the singlino and the singlet-like CP-odd and even scalars in the NMSSM may play a relevant role in such a scenario, while being difficult to probe via conventional searches. The singlet sector of the general NMSSM can be mapped on to a 2HDM+S, and I will discuss prospects of probing this at the LHC using signatures such as mono-Higgs and mono-Z. This proceeding is mostly based on Refs. arXiv:1712.09873 and arXiv:1808.02667.

hep-ph↗

arXiv2018

Two Higgs Doublets and a Complex Singlet: Disentangling the Decay Topologies and Associated Phenomenology

We present a systematic study of an extension of the Standard Model (SM) with two Higgs doublets and one complex singlet (2HDM+S). In order to gain analytical understanding of the parameter space, we re-parameterize the 27 parameters in the Lagrangian by quantities more closely related to physical observables: physical masses, mixing angles, trilinear and quadratic couplings, and vacuum expectation values. Embedding the 125\,GeV SM-like Higgs boson observed at the LHC places stringent constraints on the parameter space. In particular, the mixing of the SM-like interaction state with the remaining states is severely constrained, requiring approximate alignment without decoupling in the region of parameter space where the additional Higgs bosons are light enough to be accessible at the LHC. In contrast to 2HDM models, large branching ratios of the heavy Higgs bosons into two lighter Higgs bosons or a light Higgs and a $Z$ boson, so-called Higgs cascade decays, are ubiquitous in the 2HDM+S. Using currently available limits, future projections, and our own collider simulations, we show that combining different final states arising from Higgs cascades would allow to probe most of the interesting region of parameter space with Higgs boson masses up to 1\,TeV at the LHC with $L=3000\,{\rm fb}^{-1}$ of data.

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arXiv2018

Supersymmetry and LHC Missing Energy Signals

Current analyses of the LHC data put stringent bounds on strongly interacting supersymmetric particles, restricting the masses of squarks and gluinos to be above the TeV scale. However, the supersymmetric electroweak sector is poorly constrained. In this article we explore the consistency of possible LHC missing energy signals with the broader phenomenological structure of the electroweak sector in low energy supersymmetry models. As an example, we focus on the newly developed Recursive Jigsaw Reconstruction analysis by ATLAS, which reports interesting event excesses in channels containing di-lepton and tri-lepton final states plus missing energy. We show that it is not difficult to obtain compatibility of these LHC data with the observed dark matter relic density, the bounds from dark matter direct detection experiments, and the measured anomalous magnetic moment of the muon. We provide analytical expressions which can be used to understand the range of gaugino masses, the value of the Higgsino mass parameter, the heavy Higgs spectrum, the ratio of the Higgs vacuum expectation values $\tan β$, and the slepton spectrum obtained in our numerical analysis of these observables.

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