Determining the space-time structure of bottom-quark couplings to spin-zero particles

We present a general argument that highlights the difficulty of determining the space-time structure of the renormalizable bottom quark Yukawa interactions of the Standard Model Higgs boson, or for that matter of any hypothetical spin-zero particle, at high energy colliders. The essence of the argument is that, it is always possible, by chiral rotations, to transform between scalar and pseudoscalar Yukawa interactions without affecting the interactions of bottom quarks with SM gauge bosons. Since these rotations affect only the $b$-quark mass terms in the Standard Model Lagrangian, any differences in observables for scalar versus pseudoscalar couplings vanish when $m_b \rightarrow 0$, and are strongly suppressed in high energy processes involving the heavy spin-zero particle where the $b$-quarks are typically relativistic. We show, however, that the energy dependence of, for instance, $e^+e^- \rightarrow b\bar{b} X$ (here $X$ denotes the spin-zero particle) close to the reaction threshold may serve to provide a distinction between the scalar versus pseudoscalar coupling at electron-positron colliders that are being proposed, provided that the $Xb\bar{b}$ coupling is sizeable. We also note that while various kinematic distributions for $t \bar{t} h$ are indeed sensitive to the space-time structure of the top Yukawa coupling, for a spin-0 particle $X$ of an arbitrary mass, the said sensitivity is lost if $m_{X} >> m_t$.Comment: 18 [ages, 6 figure

Signals for R-parity-violating Supersymmetry at a 500 GeV e+ e- Collider

We investigate the production of charginos and neutralinos at a 500 GeV e^+e^- collider (NLC) and study their decays to the lightest neutralino, which then decays into multi-fermion final states through couplings which do not conserve R-parity. These couplings are assumed to affect only the decay of the lightest neutralino. Detailed analyses of the possible signals and backgrounds are performed for five selected points in the parameter space.Comment: 42 pages, LaTeX, 12 postscript figure

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.Comment: 54 pages, minor changes in the text, to appear in JHE

Looking for an Invisible Higgs Signal at the LHC

While the recent discovery of a Higgs-like boson at the LHC is an extremely important and encouraging step towards the discovery of the {\it complete} standard model(SM), the current information on this state does not rule out possibility of beyond standard model (BSM) physics. In fact the current data can still accommodate reasonable values of the branching fractions of the Higgs into a channel with `invisible' decay products, such a channel being also well motivated theoretically. In this study we revisit the possibility of detecting the Higgs in this invisible channel for both choices of the LHC energies, 8 and 14 TeV, for two production channels; vector boson fusion(VBF) and associated production($ZH$). In the latter case we consider decays of the $Z$ boson into a pair of leptons as well as a $b \bar b$ pair. For the VBF channel the sensitivity is found to be more than $5 \sigma$ at both the energies up to an invisible branching ratio ${\cal B}r_{invis} \sim 0.80$, with luminosities $\sim 20/30 {\rm fb}^{-1}$. The sensitivity is further extended to values of ${\cal B}r_{invis} \sim 0.25$ for $300 {\rm fb}^{-1}$ at 14 TeV. However the reach is found to be more modest for the $ZH$ mode with leptonic final state; with about $3.5 \sigma$ for the planned luminosity at 8 TeV, reaching $8 \sigma$ only for 14 TeV for $50 {\rm fb}^{-1}$. In spite of the much larger branching ratio of the $Z$ into a $b \bar b$ channel compared to the dilepton case, the former channel, can provide useful reach upto {\cal B}r_{invis} \gsim 0.75, only for the higher luminosity ($300{\rm fb}^{-1}$) option using jet-substructure and jet clustering methods for $b$-jet identification.Comment: 20 pages, 1 figure. 95 % confidence level limits on invisible Higgs branching ratio for various channels added, typos corrected, text slightly modified, references updated to cover an exhaustive list of Higgs cross section calculations, conclusion remains unchanged.Version accepted for publication at PL

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 $\rm \tilde{t}_1\to c\chi_{1}^{0}$ 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($\chi_{1}^{0}$) 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.Comment: 24 pages, 6 figures, 6 tables. Version accepted for publication in Physical Rev. D. Some changes in presentation of figures and text made. Result remains unchange

Can the Aleph Four-Jet Excess be Explained in a Supersymmetric Model with R-Parity Violation?

We investigate the possibility that the excess of four-jet events in $e^+e^-$ collisions at LEP-1.5 which has been reported by the ALEPH Collaboration could be due to the production of charginos or neutralinos, followed by their decay into quark jets through baryon number-violating ($\lambda^{\prime\prime}$) couplings. An estimate at the parton level shows, however, that these events cannot be due to neutralinos because of the low cross-section, and is unlikely to be due to the production of chargino pairs because of the largely different event shapes.Comment: 31 pages, Latex, uses epsf, extensively revised and update

Pre-exposure hydroxychloroquine prophylaxis for COVID-19 in healthcare workers: a retrospective cohort

Background: While several trials are ongoing for treatment of Corona virus 2019 (COVID-19), scientific research on chemoprophylaxis is still lacking even though it has potential to flatten the curve allowing us time to complete research on vaccines.Methods: This retrospective cohort study explores the potential of hydroxychloroquine (HCQ) as a pre- exposure prophylaxis for COVID-19 among 106 health care workers (HCW) exposed to COVID-19 patients, at a tertiary care hospital in India where there was an abrupt cluster outbreak within on duty personnel. HCWs who had voluntarily taken HCQ prior to exposure were considered one cohort while those who had not were considered to be the Control group. All participants with a verifiable high-risk contact history were tested for COVID-19 by RT- PCR.Results: The two cohorts were comparable in terms of age, gender, co-morbidity and exposure. The primary outcome was incidence rates of RT-PCR positive COVID-19 infection among HCQ users and Controls.106 HCW were examined of whom 54 were HCQ users. The comparative analysis of incidence of infection between the two groups demonstrated that voluntary HCQ usage was associated with lesser likelihood of developing severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) infection (4 out of 54 HCW), compared to those who were not on it (20 out of 52 HCW), χ2=14.59, p<0.001. None of the HCQ users noted any serious adverse effects.Conclusions: The study demonstrated that voluntary pre- exposure HCQ prophylaxis by HCWs is associated with a statistically significant reduction in risk of SARS-CoV-2.

Obliterative le fort’s colpocleisis for acute kidney injury caused by pelvic organ prolapse in elderly woman

Pelvic organ prolapse (POP) is the descent of pelvic organs through the vagina, which sometimes causes hydronephrosis. Here authors report a case of an eighty five year old woman with a fourth degree uterine prolapse with obstructive uropathy. She was treated with a conservative surgery Le Fort’s colpocleisis. Following which the patient’s renal functions and symptoms improved. Hence authors conclude that colpocleisis can be considered as the option for elderly women who have completed the family with no desire to preserve the sexual function especially in women with co morbities where pelvic reconstructive surgeries pose a challenge

Observing Doubly Charged Higgs Bosons in Photon-Photon Collisions

We discuss the possibility of observing doubly charged Higgs bosons in $\gamma \gamma$ collisions. We find that one can increase the range of observability close to the kinematic limit by a judicious choice of the polarisations of the initial $e^-/ e^+$ beams as well as the initial laser beam photons which are made to back-scatter from the former. We also note that, in a large region of parameter space, the generally used lepton number violating decay mode is dominated by the decay into a singly charged Higgs and a real or virtual $W$-boson, giving rise to a large number of fermions in the final state. This can qualitatively alter the strategy for discovering doubly-charged scalars.Comment: 10 pages, 2 embedded figure

Unusual Charged Higgs Signals at LEP-2

We have made a detailed study of the signals produced at LEP-2 from charged scalar bosons whose dominant decay channels are into four fermions. The event rates as well as kinematics of the final states are discussed when such scalars are either pair-produced or are generated through a tree-level interaction involving a charged scalar, the W and the Z. The backgrounds in both cases are discussed. We also suggest the possibility of reconstructing the mass of such a scalar at LEP-2.Comment: 12 pages, LateX, 9 Postscript figures, uses eps