Search

Information theory has proven to be a worthwhile tool for investigating the implications of the Higgs sector in the Next-to-minimal supersymmetric Standard Model (NMSSM) using Higgs information at the Large Hadron Collider assessed through the entropy constructed by means of the branching ratios of decay channels of the Higgs boson. The present article focuses on the parameter space of supersymmetric extension with an extra term of gauge singlet in light of various experimental constraints. Our findings show the most preferred values of $m_0$, $m_{1/2}$, $ A_0$, $ tan\beta$, $\lambda$, $\mu_{eff}$, neutralino LSP $ m_{\tilde\chi^{0}_{1}}$, lightest chargino $ m_{\tilde\chi^{\pm}_{1}}$, singlino $ m_{\tilde\chi^{0}_{5}}$, and gluino $ m_{\tilde g}$ to be around 1.93 TeV, 1.78 TeV, $-$3.62 TeV, 27.5, 0.012, 665.7 GeV, 0.74 TeV, 0.79 TeV, 11.24 TeV, and 3.70 TeV, respectively, that is compatible with the relic density of dark matter., Comment: 16 pages, 4 figures

In this work, we study the new physics effects arising due the presence of anomalous $Wtb$ vertex through the semileptonic decay modes of the top-quark at the Large Hadron Collider. An estimate on the sensitivities of the aforementioned interaction at 5$\sigma$ CL in the context of top-quark decay-width measurements and cross-section measurements would also be discussed for the pre-existing 13 TeV LHC data and its projections for the proposed LHC runs at 14 TeV, 27 TeV and 100 TeV. We also incorporate the $\mathcal CP$-violating effects to such interactions by constructing the $\mathcal CP$-violating asymmetries., Comment: 4 pages, 2 figures, 2 tables, To be published in the proceedings of International Conference on High Energy Physics (ICHEP 2022), Bologna (Itly)

In this study, we explore the effects of $\mathcal CP$-violating anomalous interactions of the top-quark through the semileptonic decay modes of the top-quark arising due to pair-production of $t\bar{t}$ at the Large Hardon Collider. Predictions on the LHC sensitivities of the coupling strength to such $\mathcal CP$-violating interactions would be discussed for the 13 TeV LHC data and for the future hadron collider with 14 TeV energy., Comment: 6 pages, 2 figures, Proceedings of the LHCP 2022 conference

Flavour-violating couplings of Higgs boson with stop and scharm quarks could be very important as in addition to lifting the mass of the Higgs boson by a few GeV, it could also play a vital phenomenological role in reducing the Supersymmetry breaking scale significantly. In this work, we investigate effects of such flavour-violating couplings within the Constrained Minimal Supersymmetric Standard Model (CMSSM) framework in the context of LEP data, Higgs data at the LHC, precision observables and the relic density of the dark matter using Bayesian statistics. Our detailed analysis reveals that the most probable values of $m_{0}$, $m_{1/2}$, $A_{0}$, $\tan{\beta}$, $\delta^{LR}_{ct}$ are expected to be around 4.83 TeV, 2.54 TeV, 1.90 TeV, 41.5, and 6.1$\times10^{-2}$, respectively, with flat priors. The corresponding values translate into 3.25 TeV, 2.13 TeV, 1.90 TeV, 44.7, and 5.9$\times10^{-2}$, respectively, if the natural priors are used. Furthermore, a comparison of our model with the CMSSM of flavour-conservation as the base model yields a Bayes factor of about 6 while taking into account all the experimental constraints used in our study. Our analysis also reflects that the lightest neutralino would have a mass of about 1 TeV., Comment: 17 pages, 7 figures

We explore $\mathcal CP$-violation effects of Higgs-top interactions in the associated production of a Higgs boson with top-pair in the dileptonic decay modes of top-quark originating from proton proton collisions $pp \to t\bar{t}H \to (l^+ \nu_l b)(l^{-} \bar{\nu_l} \bar{b})H$ at NLO in QCD matched to parton shower via T-odd observables using momenta of various particles involved in the process. In particular, we predict the constraints on the $\mathcal CP$-violating $t\bar{t}H$ coupling obtained through the production asymmetries associated with the T-odd observables in the dileptonic decay channel of the $t\bar{t}$ pair for the LHC with centre-of-mass energy of 13 TeV and an integrated luminosity of 139 fb$^{-1}$. We also present the corresponding limits for future hadron colliders, namely the High Luminosity LHC (HL-LHC) and the Future Circular Collider (FCC-HH). Our estimates of the $t\bar{t}H$ interaction strength reveal that the upper bound on pseudoscalar coupling $c_p$ corresponding to the largest asymmetry would be of about $1.96 \times 10^{-2}$ at 2.5$\sigma$ C.L. for $c_s$ = 1 at the LHC with $\sqrt{S}$ = 13 TeV for an integrated luminosity of 139 fb$^{-1}$. The respective limits for HL-LHC and FCC-hh with the projected Luminosities of 3 ab$^{-1}$ and 30 ab$^{-1}$ are found to be to $3.4\times 10^{-3}$ and $1.6\times 10^{-4}$ respectively at 2.5$\sigma$ C.L., Comment: 31 pages, 8 figures, 6 Tables

Information theory turns out to be an interesting tool for studying the consequences of Higgs observations to various new physics candidate theories by means of the information measure as the entropy of Higgs-Boson through its various detection modes at the Large Hadron Collider. The present article investigates the parameter space of a supersymmetric scenario where sfermions and one of the Higgs superfields are decoupled, while the gauginos, Higgsinos, and the remaining Higgs doublet are still allowed to be lighter. Our analysis reveals that this is quite a viable choice in the light of LHC discovery of a Higgs which resembles the SM Higgs-Boson and nothing else so far. While the supersymmetry breaking scale $M_S$ could be as high as $10^{11}$ GeV or so, the most preferred values of the $M_{S}$ and $\tan\beta$ are found to be around 3.6$\times10^7$ GeV and $41$ respectively, which is also consistent with the relic abundance of the neutralino dark matter. The corresponding value of neutralino ($ m_{\tilde\chi^{0}_{1}}$) LSP is estimated to be around 1.01 TeV. The preferred values of other parameters, namely, the Higgsino mass ($\mu$) and gaugino mass parameters ($M_1$ and $M_2$) are found to be about 1.05 TeV, 1.74 TeV, and 2.57 TeV, respectively., Comment: 13 pages, 3 figures, 3 tables

Flavour-violating interactions of the stop-quarks are expected to provide an additional few GeV contributions to the Higgs-Boson mass, particularly when mix with scharm-quarks, thereby allowing reduced supersymmetry (SUSY) breaking scale compared to flavour-conserving constrained minimal supersymmetric Standard Model (CMSSM). Inspired by this, we analyse the interactions mentioned above in the context of CMSSM using the information entropy of the Higgs-Boson for a wider region of flavour-violating CMSSM parameter space $(m_0,m_{1/2},A_0,$ $\tan\beta,sgn(\mu),\delta_{ct}^{ij})$, where $\delta_{ct}^{ij}$ represents the flavour-violating coupling of the top-quark with the charm-quark and $i, j$ defining left and right chiralities of squarks. Our information-theoretic analysis of the model mentioned above reveals the most favourable values of $(m_0, m_{1/2},A_0, \tan\beta,\delta_{ct}^{ij})$ as $(4.30 {\rm~TeV}, 2.32 {\rm~TeV}, -4.96{\rm~ TeV},$ $ 22.8,0.037)$ and $(4.16 {\rm ~TeV},$ $3.89~{\rm TeV},-4.10~{\rm TeV}, 19.4, 0.039)$ for $(i, j) = (L, R)$ and $(R, L)$, respectively, corresponding to the maximum entropy which suggest the SUSY breaking scale to be about $5$ TeV, thereby allowing considerable low values of sparticles masses than the flavour-conserving CMSSM., Comment: 17 pages, 8 figures

We perform an exclusive study of the anomalous $Wtb$ interaction in the context of LHC. The limits on $Wtb$ anomalous couplings have been estimated via the measurements of the top-quark decay width and cross-section as well as production asymmetries in case the CP is violated. Our investigations reveal that the upper bounds on $(|C_L|, |C_R|)$ would be of about (1.82, 0.03) $\times 10^{-4}$ at $2.5 \sigma$ C.L., for the already collected data at the LHC with $\sqrt{S} = 13$ TeV for an integrated luminosity of 139 fb$^{-1}$. The corresponding limits for future hadron colliders, namely, High Luminosity LHC (HL-LHC), High Energy LHC (HE-LHC) and Future Circular Collider (FCC-hh) for the projected luminosities of 3 ab$^{-1}$, 12 ab$^{-1}$ and 30 ab$^{-1}$ are found to be to $(0.81, 0.006)\times 10^{-4}$, $(0.44, 0.0017)\times 10^{-4}$ and $(0.21, 0.0004)\times 10^{-4}$ respectively at 2.5$\sigma$ C. L.., Comment: 18 pages, 11 figures

We discuss information theory as a tool to investigate constrained minimal supersymmetric Standard Model (CMSSM) in the light of observation of Higgs boson at the Large Hadron Collider. The entropy of the Higgs boson using its various detection modes has been constructed as a measure of the information and has been utilized to explore a wide range of CMSSM parameter space after including various experimental constraints from the LEP data, B-physics, electroweak precision observables and relic density of dark matter. According to our study while the lightest neutralino is preferred to have a mass around 1.92 TeV, the gluino mass is estimated to be around 7.44 TeV. The values of CMSSM parameters $m_0$, $m_{1/2}$, $A_0$ and $\tan\beta$ correspond to the most preferred scenario are found to be about 6 TeV, 3.6 TeV, $-$6.9 TeV and 36.8 respectively., Comment: 16 pages, 7 figures, 3 tables

We study the effects of T-odd interactions of top-quark via the pair production of top-quark in the semileptonic detection modes at the Large Hadron Collider by means of the T-odd observables constructed through the momenta of the observed decay products of the top (and anti-top)-quark for a wide range of CP-violating scale $\Lambda$. Estimates on the sensitivities of the coupling strength of such interactions for 13 TeV LHC energy with $\int \mathcal L dt$ = 36.1 fb$^{-1}$, 140 fb$^{-1}$ and for HL-LHC with 14 TeV energy with integrated luminosities of 0.3 ab$^{-1}$, 1 ab$^{-1}$, 2 ab$^{-1}$ and 3 ab$^{-1}$ are also presented for $\Lambda$ ranging between $M_W$ and 2 TeV., Comment: 13 Pages and 10 figures

We study the flavor-changing couplings of the Higgs-boson with the top-quark using the processes: (a) pp --> tt, (b) pp --> t_bar j, and, (c) pp --> t_bar j h at the LHC in light of current discovery of a 126 GeV Higgs-Boson. Sensitivities for the flavor-changing couplings are estimated using the LHC data that was collected until spring 2013. It is found that the process (c) is the most capable of yielding the best upper bound on the flavor-changing couplings with 2 sigma level sensitivities of {|xi_{tc}^2 + xi_{tu}^2|}^{1/2} <= 4.2 x 10^{-3} and <= 1.7 x 10^{-3} resulting from t --> b l nu_l, h --> jj with the 7 TeV and 8 TeV centre-of-mass energies respectively using existing data from the LHC. The corresponding bounds from h --> b b_bar are worse by a factor of about 1.8., Comment: 19 Latex Pages, 2 Figures, 6 Tables, More SM backgrounds, corrected some typos and errors, added h->2j detection mode, further improvements and a new subsection on 14 TeV was added. More refs. were incorporated

The ATLAS and CMS collaborations have recently published new limits on CP conserving anomalous couplings from the $W\gamma$ and $Z\gamma$ production processes. We study the corresponding limits that can be placed on the CP violating anomalous couplings $\kappa_tilde_\gamma$ and $h^1_{\gamma, Z}$ at the LHC. We find that the process $pp --> W\gamma$ at 14 TeV can place the 95% CL limit $|\kappa_tilde_\gamma| <~ 0.05$ with 10 fb^{-1} which is comparable to the existing LHC bound on the CP conserving anomalous couplings $\kappa_\gamma$. Similarly, the process $pp --> Z\gamma$ can place the 95% CL limits $|h^1_\gamma| <~ 20$ and $|h^1_Z| <~ 40$ respectively. None of these limits is derived from a truly CP-odd observable so that it is not possible to separate the effects of the CP violating anomalous couplings from the rest., Comment: 16 LaTex pages, 4 figures, 5 tables, accepted version for publication in Physical Review D

We study the connection between the same sign top (SST) and the top quark forward-backward asymmetry $A^t_{FB}$. We find that a large class of new physics models that have been proposed to account for the $A^t_{FB}$ lead to SST quark production rate much larger than the observed rate at the LHC and consequently are severely constrained or ruled out. Our model independent, general, operator analysis shows that none of the tree-level flavor-changing operators are able to explain $A^t_{FB}$ and simultaneously remain consistent with the same-sign top-quark production constraints from the LHC data., Comment: 19 LaTeX pages, 3 Tables and 4 png Figures, accepted version for publication in JHEP

In a Peccei-Quinn extension of supergravity the h --> \gamma\gamma detection rate can be significantly enhanced due to the reduction of the total Higgs decay width. To assess the viability of various Peccei-Quinn extensions of minimal supergravity we perform a Bayesian analysis on three such scenarios. The main constraints on these models come from the currently observed Higgs boson like state by the Large Hadron Collider and from the WMAP observation of dark matter abundance. Our comparative study reveals that under these constraints the PQ violating scenarios with axino dark matter are clearly preferred over the minimal supegravity model with the lightest neutralino as a dark matter candidate., Comment: 9 LaTeX page, 5 Figures, 2 Tables, accepted version for publication in Physical Review D

We consider the phenomenology of the fourth generation heavy quarks which would be pair produced at the LHC. We show that if such a quark with a mass in the phenomenologically interesting range of 400 GeV--600 GeV decays to a light quark and a W-boson, it will produce a signal in a number of channels which can be seen above the background from the three generation Standard Model processes. In particular, such quarks could be seen in channels where multiple jets are present with large missing momentum and either a single hard lepton, an opposite sign hard lepton pair or a same sign lepton pair. In the same sign dilepton channel there is little background and so an excess of such pairs at large invariant mass will indicate the presence of heavy down type quarks. More generally, in our study, the main tool we use to determine the mass of the heavy quark in each of the channels we consider is to use the kinematics of the decay of such quarks to resolve the momenta of the unobserved neutrinos. We show how this can be carried out, even in cases where the kinematics is under-determined by use of the approximation, which holds quite well, that the two heavy quarks are nearly at rest in the center of mass frame. Since it is very likely that at least the lightest heavy quark decays in the mode we consider, this means that it should be observed at the LHC. Indeed, it is expected that the mass splitting between the quarks is less than $m_W$ so that if the Cabbibo-Kobayshi-Maskawa (CKM) matrix element between the fourth and lower generations are not too small, both members of the fourth generation quark doublet will decay in this way. If this is so, the combined signal of these two quarks will make the signal for the fourth generation somewhat more prominent., Comment: 26 pages; 15 Figures; In version 2 we have added some references and corrected some typos; Version 3 we have made minor change to some figure captions

We consider the possibility of studying new physics that singles out the tau-lepton at the LHC. We concentrate on the tau-lepton charge asymmetry in tau+tau- pair production as a tool to probe this physics beyond the Standard Model. We consider two generic scenarios for the new physics. We first study a non-universal Z' boson as an example of a new resonance that can single out tau-leptons. We then consider vector lepto-quarks coupling of the first generation quarks with the third generation leptons as an example of non-resonant new physics. We find that in both cases the charge asymmetry can be sufficiently sensitive to the new physics to provide useful constraints at the LHC., Comment: 16 LaTex Pages, 21 EPS Figures, 6 Tables (Extended to incorporate tau-decay level analysis. A few references have also been added.)

We analyse same sign dilepton signatures in a non-universal flavor changing Z' model. These arise due to tt (or t_bar t_bar) production processes due to the semi-leptonic decays of (anti)tops. We also discuss top reconstruction and spin measurement using the variable MT2 and MT2-Assisted On-Shell (MAOS) Momentum} techniques and will also provide a comparison with the on-shell mass relation method. Sensitivities to the flavor-changing top coupling has also been estimated for different LHC energies and projected LHC luminosities corresponding to them., Comment: 14 LateX pages, 10 EPS Figures, 1 Table

We investigate triphoton signals of the Randall-Sundram model at the Large Hadron Collider. Such a signal can be an important probe to the RS model as these are relatively cleaner from the hadronic activity and bear significant rate. The corresponding standard model background has also been studied in detail. We also show that a clear graviton reconstruction is possible in such signal., Comment: 11 LaTeX Pages, 8 EPS Figures

Models with a non-universal Z' exhibit in general flavor changing neutral currents (FCNC) at tree-level. When the Z' couplings favor the third generation, flavor changing transitions of the form Z'tc and Z'tu could be large enough to be observable at the LHC. In this paper we explore this possibility using the associated production of a single top-quark with the Z' and find that integrated luminosities of a few hundred fb$^{-1}$ are necessary to probe the interesting region of parameter space., Comment: 12 LaTeX Pages, 10 EPS Figures

We discuss T-odd correlations between jet and lepton momenta in tt_bar events at the Tevatron that can be used to search for CP violation. We identify correlations suitable for the lepton plus jets and purely hadronic top-quark pair decay channels. As an example of CP violation we consider the top-quark anomalous couplings, including its chromo-electric dipole moment, and we estimate the limits that can be placed at the Tevatron., Comment: 14 LaTeX Pages, 3 EPS Figures, 1 ref. added, Minor typos corrected

Littlest Higgs model with T-parity and Minimal Supersymmtric standard Model with R-parity both give similar signatures in collider experiment with a huge amount of missing energy depending upon mass of the lightest T-odd/R-odd particle. In this talk, I will discuss possibility of distinguishing the two models at the LHC in hadronically quiet signal where masses of R-odd particles are identical to masses of T-odd particles., Comment: To appear in the proceedings of Supersymmetry and the Unification of Fundamental Interactions (SUSY'09), Boston, USA

In this talk, I review the T-odd correlations induced by CP violating anomalous top-quark couplings at both production and decay level in the process gg --> t t_bar --> (b mu+ nu_mu) (b_bar mu-nu_mu_bar). In addition I will also focus on experimental sensitivities corresponding to the anomalous couplings at the LHC., Comment: To be published in the proceedings of DPF-2009, Detroit, MI, July 2009, eConf C090726

We study the T odd correlations induced by CP violating anomalous top-quark couplings at both production and decay level in the process gg --> t t_bar --> (b mu+ nu_mu) (b_bar mu- nu_mu_bar). We consider several counting asymmetries at the parton level and find the ones with the most sensitivity to each of these anomalous couplings at the LHC., Comment: 14 LaTeX Pages, 1 EPS Figure, minor typos corrected

We study B_s --> mu+ mu- in the context of the R-parity violating minimal supergravity in the high tan beta regime. We find that the lowest value of the branching ratio can go well below the present LHCb sensitivity and hence B_s --> mu+ mu- can even be invisible to the LHC. We also find that the present upper bound on Br(B_s --> mu+ mu-) puts strong constraint on the minimal supergravity parameter space. The constraints become more severe if the upper bound is close to its standard model prediction., Comment: 18 pages, 10 figures; version to be published in European Physical Journal C

We consider the Littlest Higgs Model with T-parity (LHT), in the parameter region where a heavy neutrino is the lightest T-odd particle (LTP). Having emphasized that this corresponds to a sizable region in the parameter space of the theory, we show that both the Cryogenic Dark Matter Search (CDMS) and Xenon10 experiments disallow the entire region where the masses of the new particles in LHT can lie within several TeV. Therefore, any observation of the signals of a heavy neutrino LTP is likely to seriously reopen the issue of cold dark matter in the universe., Comment: 8 pages, 3 figures

We investigate charged tracks signals of a supersymmetric scenario, where the lighter stop is the next-to-lightest supersymmetric particle (NLSP). It is found that such an NLSP is stable on the scale of the detector at the LHC if one has a right-chiral sneutrino as the lightest supersymmetric particle (LSP). After identifying some benchmark points in the parameter space of a supergravity scenario with non-universal scalar masses, we study a few specific classes of signals, namely, stop pair production and gluino pair production followed by each decaying into a stop and a top. It is shown that proper kinematic cuts remove the backgrounds in each case, and, while a few months' worth of data is sufficient to have copious events in the first case, one may require 300 $fb^{-1}$ for the other. One can also aspire to reconstruct the gluino mass, using the `visible' stable NLSP tracks., Comment: 24 pages, 18 eps figures, accepted for publication in Physical Review D (title changed in journal version)

We study a supersymmetric scenario where the lighter tau-sneutrino is the lightest supersymmetric particle, while the lighter stau-state is the next lightest. Such a scenario can be motivated within the framework of minimal supergravity, with just the addition of a right-chiral neutrino superfield. Such a spectrum leads to rather unusual signals of supersymmetry, showing stable tracks of the stau in the muon chambers. We study the event characteristics of the long-lived staus at the LHC and demonstrate that the stau tracks can be distinguished from the muonic ones through proper kinematic cuts which also enable one to remove all standard model backgrounds., Comment: Submitted for the SUSY07 proceedings. 4 pages, Latex, 7 eps figures

We analyse hadronically quiet trilepton signatures in the T-parity conserving Littlest Higgs model and in R-parity conserving supersymmetry at the Large Hadron Collider. We identify the regions of the parameter space where such signals can reveal the presence of these new physics models above the Standard Model background and distinguish them from each other, even in a situation when the mass spectrum of the Littlest Higgs model resembles the supersymmetric pattern., Comment: 14 pages, 4 figures, Latex; v2: a few comments and references added, typos corrected, conclusions unchanged, version to be published in Physics Letters B

We investigate the signals of a supersymmetric scenario where the lighter tau-sneutrino is the lightest supersymmetric particle, while the lighter stau-state is the next lightest. We confirm that such a scenario can be motivated within the framework of minimal supergravity, with just the addition of a right-chiral neutrino superfield. Such a spectrum leads to rather unusual signals of supersymmetry, showing stable tracks of the stau in the muon chambers. We have studied two types of signals, namely, (a) two or more hard jets and two stau tracks, and (b) hard jets with two muons and two stau tracks. We demonstrate that the stau tracks can be distinguished from the muonic ones through proper kinematic cuts which also enable one to remove all standard model backgrounds., Comment: Latex2E, 18 pages, 8 eps figures included (To appear in Phys.Rev. D)

We examine the possibility of detecting signals of split supersymmetry in the loop-induced decay h --> gamma gamma of the Higgs boson at the Large Hadron Collider, where charginos, as surviving light fermions of the supersymmetric spectrum, can contribute in the loop. We perform a detailed study of uncertainties in various parameters involved in the analysis, and thus the net uncertainty in the standard model prediction of the rate. After a thorough scan of the parameter space, taking all constraints into account, we conclude that it will be very difficult to infer about split supersymmetry from Higgs signals alone., Comment: 22 pages, 14eps figures, LateX, Changes in the figures and minor modifications in the text. Final version to appear in Physical Review D

In the recently proposed `split supersymmetry' scenario, the squark and slepton masses are allowed to be at a high scale while the gauginos and Higgsinos are within a TeV. We show that in a theory with broken R-parity, the parameter space of such a scenario allows a situation where the lightest neutralino is still stable on the cosmological scale and can be a dark matter candidate. We also separate the cases where (a) it may be invisible but not a dark matter candidate, or (b) it may decay showing a displaced vertex. It is also emphasized how the constraint on the simultaneous violation of baryon and lepton numbers gets relaxed in this scenario., Comment: LaTex 11 pages, 3 figures, uses axodraw. Final version to appear in Phys.Lett.B. Added references and comments. Title changed in journal