arXiv subjects

Pradipta Ghosh

Publications and source records attributed to Pradipta Ghosh.

36 records · Page 2Linked to original sources

arXiv2017

The Waning of the WIMP? A Review of Models, Searches, and Constraints

Weakly Interacting Massive Particles (WIMPs) are among the best-motivated dark matter candidates. In light of no conclusive detection signal yet despite an extensive search program that combines, often in a complementary way, direct, indirect, and collider probes, we find it timely to give a broad overview of the WIMP paradigm. In particular, we review here the theoretical foundations of the WIMP paradigm, discuss status and prospects of various detection strategies, and explore future experimental challenges and opportunities.

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arXiv2016

Scrutinizing a di-photon resonance at the LHC through Moscow zero

The ATLAS and CMS collaborations have recently released their new analyses of the diphoton searches. We look in detail the consequences of their results deriving strong constraints on models where a scalar resonance $s$ decays into two light pseudoscalars which in turn decay into two pairs of collimated photons, mis-identified with two real photons. In our construction, all mass terms are generated dynamically, and only one pair of vector-like fermions generate couplings which will be probed using the upcoming LHC data. Moreover, we show that a stable dark matter candidate, respecting the cosmological constraints, is naturally affordable in the model.

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arXiv2016

Interference Power Bound Analysis of a Network of Wireless Robots

We consider a fundamental problem concerning the deployment of a wireless robotic network: to fulfill various end-to-end performance requirements, a "sufficient" number of robotic relays must be deployed to ensure that links are of acceptable quality. Prior work has not addressed how to find this number. We use the properties of Carrier Sense Multiple Access (CSMA) based wireless communication to derive an upper bound on the spacing between any transmitter-receiver pair, which directly translates to a lower bound on the number of robots to deploy. We focus on SINR-based performance requirements due to their wide applicability. Next, we show that the bound can be improved by exploiting the geometrical structure of a network, such as linearity in the case of flow-based robotic router networks. Furthermore, we also use the bound on robot count to formulate a lower bound on the number of orthogonal codes required for a high probability of interference free communication. We demonstrate and validate our proposed bounds through simulations.

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arXiv2016

Re-opening dark matter windows compatible with a diphoton excess

We investigate a simple setup in which an excess in the di-photon invariant mass distribution around $750$ GeV, as seen by the ATLAS and CMS collaborations, is originated through a pair of collimated photon pairs. In this framework a scalar state $s$ decays into two light pseudo-Goldstone bosons $a$, each of which subsequently decays into a pair of collimated photons which are misidentified as a single photon. In a minimal context of spontaneous symmetry breaking, we show that coupling a complex scalar field $Φ=(s+ia)/\sqrt{2}$ to a fermionic dark matter candidate $χ$, also responsible for generating its mass, allows for the correct relic density in a large region of the parameter space, while not being excluded by the direct or indirect detection experiments. Moreover, the correct relic abundance can naturally co-exist with a relatively large width for the resonant field $s$.

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arXiv2016

Towards Controllability of Wireless Network Quality using Mobile Robotic Routers

We consider a problem of robotic router placement and mobility control with the objective of formation and maintenance of an optimal communication network between a set of transmitter-receiver pairs. In this scenario, the communication path between any transmitter-receiver pair contains a predetermined set of mobile robotic routers nodes. The goal of this work is to design an algorithm to optimize the positions of the robotic nodes to improve the overall performance of the network. We define the optimization metric to be the minimum of the Signal to Interference plus Noise Ratios (SINR) over all the links. In this manuscript, we propose two optimization algorithms to solve this problem in a centralized and a decentralized manner, respectively.We also demonstrate the performances of both algorithms based on a set of simulation experiments.

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arXiv2016

Di-photon resonance around 750 GeV: shedding light on the theory underneath

Both the ATLAS and CMS collaborations have recently observed an excess in the di-photon invariant mass distribution in the vicinity of 750 GeV with a local significance of $\sim3σ$. In this article we try to investigate this excess in the context of a minimal simplified framework assuming effective interactions of the hinted resonance with photons and gluons. We scrutinise the consistency of this observation with possible accompanying yet hitherto unseen signatures of this resonance. Subsequently, we try to probe the nature of new particles, e.g., spin, electric charge and number of colour, etc., that could remain instrumental to explain this excess through loop-mediation.

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arXiv2016

Reconciling $(g-2)_μ$ and charged lepton flavour violating processes through a doubly charged scalar

In this work, we investigate the phenomenological consequences of a doubly charged scalar which may belong to different uncoloured scalar multiplets. This doubly charged scalar couples to the charged leptons as well as gauge bosons, which we parametrize in a model independent way. Restricting ourselves in the regime of conserved charged-parity (CP), we assume only a few non-zero Yukawa couplings ($y_{μ\ell}$, where $\ell=e,μ,τ$) between the doubly charged scalar and the charged leptons. Our choices allow the doubly charged scalar to impinge low-energy processes like anomalous magnetic moment of muon and a few possible charged lepton flavour violating (CLFV) processes. These same Yukawa couplings are also instrumental in producing same-sign dilepton signatures at the LHC. In this article we examine the impact of individual contributions from the diagonal and off-diagonal Yukawa couplings in the light of muon $(g-2)$ excess. Subsequently, we use the derived information to inquire the possible CLFV processes and finally the collider signals from the decay of a doubly charged scalar. Our simplified analyses, depending on the mass of doubly charged scalar, provide a good estimate for the magnitude of the concerned Yukawa couplings. Our findings would appear resourceful to test the phenomenological significance of a doubly charged scalar by using complementary information from muon $(g-2)$, CLFV and the collider experiments.

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arXiv2015

Hunting physics beyond the standard model with unusual $W^\pm$ and $Z$ decays

Nonstandard on-shell decays of $W^\pm$ and $Z$ bosons are possible within the framework of extended supersymmetric models, i.e., with singlet states and/or new couplings compared to the minimal supersymmetric standard model. These modes are typically encountered in regions of the parameter space with light singlet-like scalars, pseudoscalars, and neutralinos. In this letter we emphasize how these states can lead to novel signals at colliders from $Z$- or $W^\pm$-boson decays with prompt or displaced multileptons/tau jets/jets/photons in the final states. These new modes would give distinct evidence of new physics even when direct searches remain unsuccessful. We discuss the possibilities of probing these new signals using the existing LHC run-I data set. We also address the same in the context of the LHC run-II, as well as for the future colliders. We exemplify our observations with the "$μ$ from $ν$" supersymmetric standard model, where three generations of right-handed neutrino superfields are used to solve shortcomings of the minimal supersymmetric standard model. We also extend our discussion for other variants of supersymmetric models that can accommodate similar signatures.

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arXiv2014

Probing the $μν$SSM with light scalars, pseudoscalars and neutralinos from the decay of a SM-like Higgs boson at the LHC

The "$μ$ from $ν$" supersymmetric standard model ($μν$SSM) can accommodate the newly discovered Higgs-like scalar boson with a mass around 125 GeV. This model provides a solution to the $μ$-problem and simultaneously reproduces correct neutrino physics by the simple use of right-handed neutrino superfields. These new superfields together with the introduced $R$-parity violation can produce novel and characteristic signatures of the $μν$SSM at the LHC. We explore the signatures produced through two-body Higgs decays into the new states, provided that these states lie below in the mass spectrum. For example, a pair produced light neutralinos depending on the associated decay length can give rise to displaced multi-leptons/taus/jets/photons with small/moderate missing transverse energy. In the same spirit, a Higgs-like scalar decaying to a pair of scalars/pseudoscalars can produce final states with prompt multi-leptons/taus/jets/photons.

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arXiv2014

Collider signatures of a light NMSSM pseudoscalar in neutralino decays in the light of LHC results

We investigate signatures induced by a very light pseudoscalar Higgs in neutralino decays in the Next-to-Minimal Supersymmetric Standard Model (NMSSM) and determine their observability at the LHC. We concentrate on scenarios which feature two light scalar Higgs bosons (one of them is SM-like with a mass of 125 GeV and a singlet-like lighter one) with a very light (singlet-like) pseudoscalar Higgs in the mass range 2m_tau < m_a1 < 2m_b. We consider neutralino-chargino pair production and the subsequent decay X_{2,3}-> X_1 a1, which leads to topologies involving multi-leptons and missing transverse energy. We determine a set of selection cuts that can effectively isolate the signal from backgrounds of the Standard Model or the Minimal Supersymmetric Standard Model. We also exemplify the procedure with a set of benchmark points, for which we compute the expected number of events and signal strength for LHC with 8 TeV center of mass energy. We show that this signal can already be probed for some points in the NMSSM parameter space.

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arXiv2013

Probing the "$μ$ from $ν$" supersymmetric standard model with displaced multileptons from the decay of a Higgs boson at the LHC

The "$μ$ from $ν$" supersymmetric standard model ($μν$SSM) cures the $μ$-problem and concurrently reproduces measured neutrino data by using a set of usual right-handed neutrino superfields. Recently, the LHC has revealed the first scalar boson which naturally makes it tempting to test $μν$SSM in the light of this new discovery. We show that this new scalar while decaying to a pair of unstable long-lived neutralinos, can lead to a distinct signal with non-prompt multileptons. With concomitant collider analysis we show that this signal provides an unmistakable signature of the model, pronounced with light neutralinos. Evidence of this signal is well envisaged with sophisticated displaced vertex analysis, which deserves experimental attention.

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arXiv2013

Probing the two light Higgs scenario in the NMSSM with a low-mass pseudoscalar

In this article we propose a simultaneous collider search strategy for a pair of scalar bosons in the NMSSM through the decays of a very light pseudoscalar. The massive scalar has a mass around 126 GeV while the lighter one can have a mass in the vicinity of 98 GeV (thus explaining an apparent LEP excess) or be much lighter. The successive decay of this scalar pair into two light pseudoscalars, followed by leptonic pseudoscalar decays, produces clean multi-lepton final states with small or no missing energy. Furthermore, this analysis offers an alternate leptonic probe for the 126 GeV scalar that can be comparable with the ZZ* search channel. We emphasize that a dedicated experimental search for multi-lepton final states can be an useful probe for this scenario and, in general, for the NMSSM Higgs sector. We illustrate our analysis with two representative benchmark points and show how the LHC configuration with 8 TeV center-of-mass energy and 25 inverse femtobarns of integrated luminosity can start testing this scenario, providing a good determination of the light pseudoscalar mass and a relatively good estimation of the lightest scalar mass.

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arXiv2012

Lower Limits on $μ\to e γ$ from new Measurements on $U_{e3}$

New data on the lepton mixing angle $θ_{13}$ imply that the $eμ$ element of the matrix $m_νm_ν^\dagger$, where $m_ν$ is the neutrino Majorana mass matrix, cannot vanish. This implies a lower limit on lepton flavor violating processes in the $eμ$ sector in a variety of frameworks, including Higgs triplet models or the concept of minimal flavor violation in the lepton sector. We illustrate this for the branching ratio of $μ\to e γ$ in the type II seesaw mechanism, in which a Higgs triplet is responsible for neutrino mass and also mediates lepton flavor violation. We also discuss processes like $μ\to e\bar{e}e$ and $μ\to e$ conversion in nuclei. Since these processes have sensitivity on the individual entries of $m_ν$, their rates can still be vanishingly small.

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arXiv2012

Exploring novel correlations in trilepton channels at the LHC for the minimal supersymmetric inverse seesaw model

We investigate signatures of the minimal supersymmetric inverse seesaw model at the large hadron collider (LHC) with three isolated leptons and large missing energy (3\ell + \mET or 2\ell + 1τ+ \mET, with \ell=e,μ) in the final state. This signal has its origin in the decay of chargino-neutralino (\chpm1\ntrl2) pair, produced in pp collisions. The two body decays of the lighter chargino into a charged lepton and a singlet sneutrino has a characteristic decay pattern which is correlated with the observed large atmospheric neutrino mixing angle. This correlation is potentially observable at the LHC by looking at the ratios of cross sections of the trilepton + \mET channels in certain flavour specific modes. We show that even after considering possible leading standard model backgrounds these final states can lead to reasonable discovery significance at the LHC with both 7 TeV and 14 TeV center-of-mass energy.

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arXiv2011

Unusual Higgs boson signal in R-parity violating nonminimal supersymmetric models at the LHC

We predict an unconventional background free signal of the Higgs boson in $R$-parity violating nonminimal supersymmetric models at the Large Hadron Collider (LHC). The signal comprises dilepton plus four hadronic jets and two large displaced vertices. The displaced leptons and jets are coming from the decay of the lightest supersymmetric particle (LSP), which is predominantly a gauge-singlet neutrino. A pair of such LSPs can couple to a Higgs boson, created via gluon fusion. We have analyzed two cases - one corresponding to the tree-level Higgs boson mass and another with the one-loop corrected mass of the Higgs boson. A reliable Higgs mass reconstruction using this signal can lead to discovery at the LHC with center-of-mass energy $\sqrt{s}=14~\rm{TeV}$ and 5 fb$^{-1}$ of integrated luminosity $(\mathcal{L})$. Even at $\sqrt{s}=7~\rm{TeV}$ and $\mathcal{L}$ = 5 fb$^{-1}$, a reasonable number of events are expected. Besides, mass reconstruction of a gauge-singlet LSP can provide an estimate of the seesaw scale.

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arXiv2010

Neutrino masses and mixing in $μν$SSM

$μν$SSM is an $R$-parity violating non-minimal supersymmetric model which uses right chiral neutrino superfields to solve the $μ$-problem. The $R$-parity violation together with a TeV scale seesaw mechanism using right handed neutrinos are instrumental for the light neutrino mass generation in $μν$SSM. We show that it is possible to accommodate three flavour global neutrino data in $μν$SSM with three massive neutrinos at the tree level. Ingression of the one-loop corrections to neutrino masses and mixing shows certain variations over the tree level analysis depending on the specific hierarchy of neutrino masses involved. In $μν$SSM some of the $R$-parity violating decay branching ratios of the lightest neutralino show nice correlation with certain neutrino mixing angle. These correlations along with the presence of displaced vertices in the decay of the lightest neutralino can be further investigated as a test of $μν$SSM in collider experiments.

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arXiv2010

Radiative contribution to neutrino masses and mixing in $μν$SSM

In an extension of the minimal supersymmetric standard model (popularly known as the $μν$SSM), three right handed neutrino superfields are introduced to solve the $μ$-problem and to accommodate the non-vanishing neutrino masses and mixing. Neutrino masses at the tree level are generated through $R-$parity violation and seesaw mechanism. We have analyzed the full effect of one-loop contributions to the neutrino mass matrix. We show that the current three flavour global neutrino data can be accommodated in the $μν$SSM, for both the tree level and one-loop corrected analyses. We find that it is relatively easier to accommodate the normal hierarchical mass pattern compared to the inverted hierarchical or quasi-degenerate case, when one-loop corrections are included.

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arXiv2009

Neutrino masses and mixing, lightest neutralino decays and a solution to the $μ$ problem in supersymmetry

We examine in detail the neutrino masses and mixing patterns in an extension of the minimal supersymmetric standard model with three gauge-singlet neutrinos and R-parity violation. The Majorana masses for the gauge-singlet neutrinos as well as the usual $μ$-term for the Higgs superfields are generated at the electroweak scale through the vacuum expectation values of the singlet sneutrinos. The resulting effective mass matrix for the three light neutrinos have contributions from the seesaw mechanism involving the singlet neutrinos as well as due to the mixing with the heavy neutralinos. This model is popularly known in the literature as the "$μ$ from $ν$ supersymmetric standard model" ($μν$SSM). We show that even with flavour diagonal neutrino Yukawa couplings, the global data on three-flavour neutrinos can be well accounted for in this scenario, at the tree level. We also analyze the mixing in the chargino and the Higgs sector and calculate the decays of the lightest supersymmetric particle in this model. The decay branching ratios show certain correlations with the neutrino mixing angles, which can be tested at the LHC. Some other phenomenological implications of such a model have been discussed.

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