Browsing by Author "Mondal, Tanmoy"

Now showing 1 - 20 of 24

Class of Higgs-portal dark matter models in the light of gamma-ray excess from galactic center
(Elsevier, 2015-05) Mondal, Tanmoy
Recently the study of anomalous gamma-ray emission in the regions surrounding the galactic center has drawn a lot of attention as it points out that the excess of gamma-ray in the low latitude is consistent with the emission expected from annihilating dark matter. The best-fit to the gamma-ray spectrum corresponds to dark matter (DM) candidate having mass in the range annihilating into -pair with cross-section . We have shown that the Higgs-portal dark matter models in presence of scalar resonance (in the annihilation channel) are well-suited for explaining these phenomena. In addition, the parameter space of these models also satisfies constraints from the LHC Higgs searches, relic abundance and direct detection experiments. We also comment on real singlet scalar Higgs-portal DM model which is found to be incompatible with the recent analysis.
Constraining a class of 𝐵��−𝐿�� extended models from vacuum stability and perturbativity
(APS, 2014-03) Mondal, Tanmoy
The precise knowledge of the Standard Model (SM) Higgs boson and top-quark masses and couplings are crucial to understand the physics beyond it. An SM-like Higgs boson having a mass in the range of 123–127 GeV squeezes the parameters for physics beyond the Standard Model. In recent the LHC era many TeV-scale neutrino mass models have earned much attention as they pose many interesting phenomenological aspects. We have contemplated 𝐵−𝐿 extended models which are theoretically well motivated and phenomenologically interesting, and they successfully explain neutrino mass generation. In this article we analyze the detailed structures of the scalar potentials for such models. We compute the criteria which guarantee that the vacuum is bounded from below in all directions. In addition, perturbativity (triviality) bounds are also necessitated. Incorporating all such effects, we constrain the parameters of such models by performing their renormalization-group evolutions.
Constraining minimal 𝑈��⁢(1)𝐵��−𝐿�� model from dark matter observations
(APS, 2014-03) Mondal, Tanmoy
We study the 𝐵−𝐿 gauge extension of the Standard Model which contains a singlet scalar and three right-handed neutrinos. The vacuum expectation value of the singlet scalar breaks the 𝑈⁢(1)𝐵−𝐿 symmetry. Here the third-generation right-handed neutrino is qualified as the dark matter candidate, as an artifact of 𝑍2-charge assignment. Relic abundance of the dark matter is consistent with WMAP9 and PLANCK data, only near scalar resonances where dark matter mass is almost half of the scalar boson masses. Requiring correct relic abundance, we restrict the parameter space of the scalar mixing angle and mass of the heavy scalar boson of this model. Besides this, the maximum value of the spin-independent scattering cross section off nucleon is well below the Xenon100 and recent LUX exclusion limits and can be probed by future Xenon1T experiments. In addition, we compute the annihilation of the dark matter into a two-photon final state in detail and compare with the Fermi-LAT upper bound on ⟨𝜎⁢𝑣⟩𝛾⁢𝛾 for the NFW and Einasto profile.
Constraints on a seesaw model leading to quasidegenerate neutrinos and signatures at the LHC
(APS, 2015-05) Mondal, Tanmoy
We consider a variant of TeV-scale seesaw models in which three additional heavy right-handed neutrinos are added to the standard model to generate the quasidegenerate light neutrinos. This model is theoretically interesting since it can be fully rebuilt from the experimental data of neutrino oscillations except for an unknown factor in the Dirac-Yukawa coupling. We study the constraints on this coupling coming from metastability of electroweak vacuum. An even stronger bound comes from the lepton flavor violating decays on this model, especially in a heavy neutrino mass scenario which is within the collider’s reach. Bestowed with these constrained parameters, we explore the production and discovery potential coming from these heavy neutrinos at the 14 TeV run of the Large Hadron Collider. Signatures with trilepton final state together with backgrounds are considered in a realistic simulation.
Copositive criteria and boundedness of the scalar potential
(APS, 2014-05) Mondal, Tanmoy
To understand physics beyond the standard model it is important to have the precise knowledge of Higgs boson and top quark masses as well as strong coupling. A recently discovered new boson which is likely to be the standard model Higgs with mass 123–127 GeV has a submissive impact on the stability of the new physics beyond standard model. The beyond standard model scenarios that include many scalar fields posses scalar potential with many quartic couplings. Due to the complicated structures of such scalar potentials it is indeed difficult to adjudge the stability of the vacuum. Thus one needs to formulate a proper prescription for computing the vacuum stability criteria. In this paper we have used the idea of copositive matrices to deduce the conditions that guarantee the boundedness of the scalar potential. We have discussed the basic idea behind the copositivity and then used that to determine the vacuum stability criteria for the left-right symmetric models with doublet and triplet scalars and Type-II seesaw. As this idea is based on the strong mathematical arguments, it helps to compute simple and unique stability criteria embracing the maximum allowed parameter space
Demystifying the compressed top squark region with kinematic variables
(APS, 2017-11) Mondal, Tanmoy
The ongoing perplexing scenario with no hints of new physics at the Large Hadron Collider can be elucidated amicably if the exotic particle spectrum in many of the well-motivated theoretical models possesses degenerate mass. We investigate the usefulness of different kinematic variables sensitive to the compressed mass region, and propose a search strategy considering a phenomenological supersymmetric scenario where the top squark undergoes a four-body decay due to its extremely narrow mass difference with the lightest supersymmetric particle. Considering a challenging but relatively clean dileptonic decay channel, we demonstrate that one can effectively restrain the significant background from the top quark, which provides a complementary approach to the present CMS analysis. With the new strategic approach the current limit can be extended to a phase-space region that was not explored before
Electron EDM and muon anomalous magnetic moment in two-Higgs-doublet models
(Springer, 2019-12) Mondal, Tanmoy
The CP violating two-Higgs doublet model of type-X may enhance significantly the electric and magnetic moment of leptons through two-loop Barr-Zee diagrams. We analyze the general parameter space of the type-X 2HDM consistent with the muon g − 2 and the electron EDM measurements to show how strongly the CP violating parameter is constrained in the region explaining the muon g − 2 anomaly.
Electroweak multi-higgs production: a smoking gun for the type-I two-higgs-doublet model
(AIP, 2023-12) Mondal, Tanmoy
Extending the Higgs sector of the standard model (SM) by just one additional Higgs doublet field leads to the two-Higgs-doublet model (2HDM). In the type-I 𝑍2-symmetric limit of the 2HDM, all the five new physical Higgs states can be fairly light, 𝒪⁡(100) GeV or less, without being in conflict with current data from the direct Higgs boson searches and the 𝐵-physics measurements. In this Letter, we establish that the new neutral as well as the charged Higgs bosons in this model can all be simultaneously observable in the multi-𝑏 final state. The statistical significance of the signature for each of these Higgs states, resulting from the electroweak (EW) production of their pairs, can exceed 5⁢𝜎 at the 13 TeV high-luminosity Large Hadron collider (HL-LHC). Since the parameter space configurations where this is achievable are precluded in the other, more extensively pursued, 2HDM types, an experimental validation of our findings would be a clear indication that the true underlying Higgs sector in nature is the type-I 2HDM.
Explaining g − 2 anomalies in two Higgs doublet model with vector-like leptons
(Springer, 2020-11) Mondal, Tanmoy
We consider the two Higgs doublet model (2HDM) along with a generation of vector-like lepton doublet and singlet to explain the observed discrepancies in the electron and muon anomalous magnetic moments. The type-X (lepton-specific) 2HDM can allow a light pseudo-scalar which is known to explain the muon anomalous magnetic moment at two-loop. Such a light particle induces a sizable negative contribution to the electron anomalous magnetic moment at one-loop in the presence of vector-like leptons evading all the experimental constraints.
Gamma-ray signals from multicomponent scalar dark matter decays
(IOP, 2020-01) Mondal, Tanmoy
Within a multicomponent dark matter scenario, novel gamma-ray signals may arise from the decay of the heavier dark matter component into the lighter. For a scalar dark sector of this kind, the decay ϕ2→ϕ1 γ is forbidden by the conservation of angular momentum, but the decay ϕ2 → ϕ1 γγ can have a sizable or even dominant branching ratio. In this paper we present a detailed study of this decay channel. We determine the width and photon energy spectrum generated in the decay, employing an effective theory approach, and in UV complete models where the scalar dark matter components interact with heavy or light fermions. We also calculate limits on the inverse width from current data of the isotropic diffuse photon flux, both for a hierarchical and a degenerate dark matter spectrum. Finally, we briefly comment on the prospects of observing the diphoton signal from sneutrino decay in the minimal supersymmetric standard model extended with right-handed neutrino superfields (tilde nuMSSM) .
Heavy stable charged tracks as signatures of non-thermal dark matter at the LHC: a study in some non-supersymmetric scenarios
(Springer, 2017) Mondal, Tanmoy
We consider two theoretical scenarios, each including a ℤ2-odd sector and leading to an elementary dark matter candidate. The first one is a variant of the Type-III seesaw model where one lepton triplet is ℤ2-odd, together with a heavy sterile neutrino. It leads to a fermionic dark matter, together with the charged component of the triplet being a quasi-stable particle which decays only via a higher-dimensional operator suppressed by a high scale. The second model consists of an inert scalar doublet together with a ℤ2-odd right-handed Majorana neutrino dark matter. A tiny Yukawa coupling delays the decay of the charged component of the inert doublet into the dark matter candidate, making the former long-lived on the scale of collider detectors. The parameter space of each model has been constrained by big-bang nucleosynthesis constraints, and also by estimating the contribution to the relic density through freeze-out of the long-lived charged particle as well the freeze-in production of the dark matter candidate. We consider two kinds of signals at the Large Hadron Collider for each case. For the first kind of models, namely two charged tracks and single track and for the second kind, the characteristic signals are opposite as well as same-sign charged track pairs. We perform a detailed analysis using event selection criteria consistent with the current experimental programmes. It is found that the scenario with a lepton triplet can be probed upto 960 (1190) GeV with an integrated luminosity of 300 (3000) fb−1, while the corresponding numbers for the inert doublet scenario are 630 (800) GeV. Furthermore, the second kind of signal mentioned in each case allows us to differentiate different dark matter scenarios from each other.
Higgs vacuum stability and inflationary dynamics after BICEP2 and PLANCK dust polarisation data
(IOP, 2014-12) Mondal, Tanmoy
If the recent detection of B-mode polarization of the Cosmic Microwave Background by BICEP2 observations, withstand the test of time after the release of recent PLANCK dust polarisation data, then it would surprisingly put the inflationary scale near Grand Unification scale if one considers single-field inflationary models. On the other hand, Large Hadron Collider has observed the elusive Higgs particle whose presently observed mass can lead to electroweak vacuum instability at high scale (∼ Script O(1010) GeV). In this article, we seek for a simple particle physics model which can simultaneously keep the vacuum of the theory stable and yield high-scale inflation successfully. To serve our purpose, we extend the Standard Model of particle physics with a U(1)B-L gauged symmetry which spontaneously breaks down just above the inflationary scale. Such a scenario provides a constrained parameter space where both the issues of vacuum stability and high-scale inflation can be successfully accommodated. The threshold effect on the Higgs quartic coupling due to the presence of the heavy inflaton field plays an important role in keeping the electroweak vacuum stable. Furthermore, this scenario is also capable of reheating the universe at the end of inflation. Though the issues of Dark Matter and Dark Energy, which dominate the late-time evolution of our universe, cannot be addressed within this framework, this model successfully describes the early universe dynamics according to the Big Bang model.
Implications of unitarity and charge breaking minima in a left-right symmetric model
(APS, 2015-11) Mondal, Tanmoy
We examine the usefulness of the unitarity conditions in a left-right symmetric model which can translate into giving a stronger constraint on the model parameters together with the criteria derived from vacuum stability and perturbativity. In this light, we demonstrate the bounds on the masses of the physical scalars present in the model and find the scenario where multiple scalar modes are in the reach of the Large Hadron Collider. We also analyze the additional conditions that can come from charge breaking minima in this context.
Inverse seesaw and (g − 2) anomalies in B − L extended two Higgs doublet model
(Elsevier, 2022-03) Mondal, Tanmoy
We propose a gauged extended two Higgs doublet model to explain both neutrino mass and lepton anomalous magnetic moments (). Neutrino mass is generated via an inverse seesaw mechanism by introducing singlet fermions. Especially, we update the result of muon () in light of the very recent report by E989 experiment at Fermilab, indicating . Combining BNL result, we have the following deviation from the standard model prediction at 4.2 σ. Thanks to an appropriate assignment for symmetry and larger that is favored by type-X model, we realize natural hierarchies among neutral fermions. The lepton anomalous magnetic moments can be induced at the one loop level by introducing an iso-spin singlet singly-charged boson. This charged scalar plays a significant role in evading chiral suppression of these phenomenologies. We show sizable lepton () can be obtained after satisfying all the flavor constraints, such as and flavor conserving leptonic Z boson decays.
Leptophilic bosons and muon g-2 at lepton colliders
(Springer, 2021-07) Mondal, Tanmoy
A light leptophilic boson (scalar or pseudoscalar) has been postulated to explain the muon g-2 anomaly and could be a portal to dark matter. Realizing the leptophilic nature of a singlet boson in the framework of the two-Higgs-doublet-Model of type-X, we identify the parameter space viable for the explanation of the updated muon g-2 discrepancy. It is then shown that such a hypothetical particle will be unambiguously ruled out or discovered via the Yukawa process at a lepton collider designed as a Higgs factory.
Looking for hints of a reconstructible seesaw model at the Large Hadron Collider
(APS, 2015) Mondal, Tanmoy
We study the production of heavy neutrinos at the Large Hadron Collider through the dominant 𝑠-channel production mode as well as the vector boson fusion process. We consider the TeV scale minimal linear seesaw model containing two heavy singlets with the opposite lepton number. This model is fully reconstructible from oscillation data apart from an overall normalization constant which can be constrained from the metastability of the electroweak vacuum and bounds coming from lepton flavor violation searches. The Dirac nature of heavy neutrinos in this model implies suppression of the conventional same-sign-dilepton signal at the Large Hadron Collider. We analyze the collider signatures with the trilepton final state and missing transverse energy as well as vector boson fusion type signals which are characterized by two additional forward tagged jets. Our investigation reveals that due to stringent constraints on light-heavy mixing coming from lepton flavor violation and metastability bounds, the model can be explored only for a light to moderate mass range of heavy neutrinos. We also note that in case of a positive signal, flavor counting of the final trilepton channel can give information about the mass hierarchy of the light neutrinos.
Models of decaying FIMP Dark Matter: potential links with the Neutrino Sector
(2020-08) Mondal, Tanmoy
The absolute stability of a dark matter (DM) particle is not a binding requirement. Here we suggest a few scenarios where the DM particle is liable to decay via extremely feeble interactions. This can happen via inexplicably small Yukawa couplings in the simplest conjectures. After setting down such a model, we go beyond it, thus treading onto scenarios where the spontaneous breakdown of some gauged U(1) symmetry may lead to intermediate scales, and suitably suppressed effective operators which allow the DM particle to decay slowly. The constraints from particle physics as well as cosmology are taken into account in each case. The last and more involved scenario, studied in detail, suggest a link between the model parameters that govern neutrino physics on one side, and the dynamics of a quasi-stable DM particle on the other.
Multiphoton signatures as a probe of violation in extended Higgs sectors
(APS, 2024-02) Mondal, Tanmoy
We propose a novel signature with four-photon final states to probe 𝐶⁢𝑃-violating (CPV) extended Higgs sectors via 𝑓⁡ ¯ 𝑓 →𝑍*→𝐻1⁡𝐻2→4⁢𝛾 processes with 𝐻1,2 being additional neutral Higgs bosons. We focus on the nearly Higgs alignment scenario, in which the discovered Higgs boson almost corresponds to a neutral scalar state belonging to the isospin doublet field with the vacuum expectation value 𝑣≃246 GeV. We show that the branching ratios of 𝐻1,2 →𝛾⁢𝛾 can simultaneously be sizable when CPV phases in the Higgs potential are of order one due to the enhancement of charged-Higgs boson loops. Such branching ratios can be especially significant when the fermiophobic scenario is taken into account. As a simple example, we consider the general two Higgs doublet model, and demonstrate that the cross section for the four-photon process can be 0.1 fb at LHC with the masses of 𝐻1,2 to be a few 100 GeV in the Higgs alignment limit under the constraints from electric dipole moments (EDMs) and LHC Run-II data. We also illustrate that the searches for EDMs and diphoton resonances at high-luminosity LHC play complementary roles to explore CPV extended Higgs sectors.
Nonstandard signatures of vectorlike quarks in a leptophobic 221 model
(APS, 2019-06) Mondal, Tanmoy
We consider vectorlike quarks in a leptophobic 221 model characterized by the gauge group 𝑆⁢𝑈⁢(2)𝐿×𝑆⁢𝑈⁢(2)2×𝑈⁢(1)𝑋, where the 𝑆⁢𝑈⁢(2)2 is leptophobic in nature. We discuss the pattern of mixing between Standard Model quarks and vectorlike quarks and how we prevent tree level flavor-changing interactions in the model. The model also predicts tauphilic scalars decaying mostly to tau leptons. We consider a typical signal of the model in the form of pair production of top-type vectorlike quarks which decays to the tauphilic scalars and a third generation quark. We analyze the resulting final state signal for the 13 TeV LHC, containing ≥3⁢𝑗⁡(1⁢𝑏)+≥2⁢𝜏+≥1⁢𝑙 and discuss the discovery prospects of such vectorlike quarks with nonstandard decay modes.
Reconstructing a light pseudoscalar in the Type-X two Higgs doublet model
(Elsevier, 2017-11) Mondal, Tanmoy
We investigate the detectability as well as reconstructibility of a light pseudoscalar particle A, of mass in the 50–60 GeV range, which is still allowed in a Type-X (lepton-specific) two-Higgs doublet scenario. Such a pseudoscalar can be pair-produced in the decay of the 125 GeV scalar h. The light pseudoscalar in the aforementioned range, helpful in explaining the muon anomalous magnetic moment, has not only substantial branching ratio in the channel but also one of about in the final state. We show how to faithfully reconstruct the A mass using the mode, and establish the existence of a pseudoscalar around 50–60 GeV, using the process . This is the most reliable way of reconstructing the light A mass, with a statistical significance that amounts to discovery, with a few hundred (or less) of integrated luminosity.