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Kirtiman Ghosh

Publications and source records attributed to Kirtiman Ghosh.

At least 55 records · Page 3Linked to original sources
arXiv2014

Dark Matter, Parallel Universe and Multiple Higgs Signals at the ILC

The existence of dark matter is now well established by several indirect experiments. Several candidates for dark matter has also been proposed. However, the dark matter can just be like our ordinary matter in a parallel Universe with both Universes being described by their own non-abelian gauge symmetries forbidding any kinetic mixing. However, the quartic Higgs interactions involving Higgs fields between the two Universes are allowed by the symmetries of the model. The ensuing mixing between the two lightest Standard Model like Higgses gives rise to interesting signatures at the proposed international electron-positron collider (ILC) specially in the case when mass splitting between the two surviving light Higgs bosons are small ($\sim$ 100 MeV) so that they can not be resolved at the LHC.

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arXiv2014

A predictive model of Dirac Neutrinos

Assuming lepton number conservation, hermiticity of the neutrino mass matrix and $ν_μ - ν_τ$ exchange symmetry, we show that we can determine the neutrino mass matrix completely from the existing data. Comparing with the existing data, our model predicts an inverted mass hierarchy (close to a degenerate pattern) with the three neutrino mass values, $8.91 \times 10^{-2}$ eV, $8.95 \times 10^{-2}$ eV, $7.50 \times 10^ {-2}$ eV, a large value for the CP violating phase, $δ= 110^0$, and of course, the absence of neutrinoless $ββ$ decay. All of these predictions can be tested in the forthcoming or future precision neutrino experiments.

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arXiv2014

Constraining Bosonic Supersymmetry from Higgs results and 8 TeV ATLAS multi-jets plus missing energy data

The collider phenomenology of models with Universal Extra Dimensions (UED) is surprisingly similar to that of supersymmetric (SUSY) scenarios. For each level-1 bosonic (fermionic) Kaluza-Klein (KK) state, there is a fermionic (bosonic) analog in SUSY and thus UED scenarios are often known as bosonic supersymmetry. The minimal version of UED (mUED) gives rise to a quasi-degenerate particle spectrum at each KK-level and thus, can not explain the enhanced Higgs to diphoton decay rate hinted by the ATLAS collaboration of the Large Hadron Collider (LHC) experiment. However, in the non-minimal version of the UED (nmUED) model, the enhanced Higgs to diphoton decay rate can be easily explained via the suitable choice of boundary localized kinetic (BLK) terms for higher dimensional fermions and gauge bosons. BLK terms remove the degeneracy in the KK mass spectrum and thus, pair production of level-1 quarks and gluons at the LHC gives rise to hard jets, leptons and large missing energy in the final state. These final states are studied in details by the ATLAS and CMS collaborations in the context of SUSY scenarios. We find that the absence of any significant deviation of the data from the Standard Model (SM) prediction puts a lower bound of about 2.1 TeV on equal mass excited quarks and gluons.

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arXiv2014

Compressed SUSY at 14 TeV LHC

In this work we study the collider phenomenology of a compressed supersymmetric model with gluino and the lightest neutralino. All other sparticles are assumed to be heavy. We consider gluino pair production at the 14 TeV LHC and present the mass reach of gluino as a function of mass splitting between gluino and the the lightest neutralino. We find that the gluino mass below 1 TeV can be excluded at 95% CL with integrated luminosity of 100 fb$^{-1}$ for extreme degenerate case where mass separation between gluino and the lightest neutralino is about 20 GeV. On the other hand, the lower bound on the mass of gluino increases to 1.2 - 1.3 TeV if the mass splitting between the gluino and neutralino is about 200 GeV. This result shows that for degenerate gluino, the current mass limit may extend approximately 400-500 GeV at 14 TeV LHC.

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arXiv2013

Parallel Universe, Dark Matter and Invisible Higgs Decays

The existence of the dark matter with amount about five times the ordinary matter is now well established experimentally. There are now many candidates for this dark matter. However, dark matter could be just like the ordinary matter in a parallel universe. If both universes are described by a non-abelian gauge symmetries, then there will be no kinetic mixing between the ordinary photon and the dark photon, and the dark proton, dark electron and the corresponding dark nuclei, belonging to the parallel universe, will be stable. If the strong coupling constant, $(α_s)_{dark}$ in the parallel universe is five times that of $α_s$, then the dark proton will be about five time heavier, explaining why the dark matter is five times the ordinary matter. However, the two sectors will still interact via the Higgs boson of the two sectors. This will lead to the existence of a second light Higss boson, just like the Standard Model Higgs boson. This gives rise to the invisible decay modes of the Higgs boson which can be tested at the LHC, and the proposed ILC.

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arXiv2013

Non-universal SUGRA at LHC: Prospects and Discovery Potential

We explore supersymmetry (SUSY) parameter space with non-universal high scale parameters in gravity mediated SUSY breaking (SUGRA) scenario that accommodates a Higgs mass of (125$\pm$2) GeV while satisfying cold dark matter relic density and other low energy constraints. We indicate a few benchmark points consistent with different dark matter annihilation processes where third family squarks are lighter than the first two as a requirement to keep the Higgs mass within the limit. We show that bottom rich and leptonic final states have better reach in such parameter space points and is the most likely scenario to discover SUSY at the upcoming run of LHC with center-of-mass energy 14 TeV.

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arXiv2013

Collider signatures of mirror fermions in the framework of Left Right Mirror Model

The idea of left-right symmetry with mirror fermions is very appealing from the symmetry point of view. In this picture, unlike the Standard Model, the symmetry is not only left-right symmetric, but each left handed fermion multiplet is accompanied by new right handed fermion multiplet of opposite chirality. In this work, we consider a gauge symmetry, $SU(3)_c \otimes SU(2)_L\otimes SU(2)_R \otimes U(1)_{Y^\prime}$ supplemented by a discrete $Z_2$ symmetry. Instead of having right handed multiplets for each left handed multiplets of the same fermions as in the usual left-right model, the mirror model include right handed doublets involving new fermions (called mirrors), and similarly for each right handed singlet, there are corresponding mirror singlets. Thus the gauge anomaly is naturally absent in this model, and the model also provide a solution for the strong CP problem because of parity conservation. The first stage of symmetry breaking is achieved by a doublet mirror Higgs with a vacuum expectation value $\simeq 10^7$ GeV, needed to explain the neutrino mass $\simeq 10^{-11}$ GeV. The mirror fermions can mix with the ordinary fermions via a scalar which is singlet under the gauge symmetry. In this model, only light mirror particles, having masses in the few hundred GeV range are $\hat{e}, \hat{u}, \hat{d}$ with well-defined spectrum. $\hat{u}$ and $\hat{d}$ can be pair produced at the LHC, and can be detected as ($u Z$) and ($d Z$) resonances. We discuss the signals of these mirror fermions at the LHC, and find that the reach at the LHC can be as large as $m_{\hat q}\simeq 800$ GeV.

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arXiv2012

Top anti-top pairs at the LHC heavy ion collision: a new interesting probe of quark gluon plasma

We investigate top anti-top quark pair production in lead-lead collisions at the Large Hadron Collider with nucleon-nucleon center of mass energy of 5.5 TeV. Due to the very high temperature and energy density created in heavy ion collision, a new state of QCD matter known as Quark-Gluon Plasma (QGP) is expected to be produced. Top decay products loose energy inside the QGP medium. Therefore, we also study the medium modifications of different kinematic distributions. We observe significant modification in the dijets and trijets invariant mass distributions.We also found that the peak position and shape of the distributions could be used to characterize the nature of jet energy loss in the QGP.

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arXiv2012

Degenerate SUSY search at the 8 TeV LHC

ATLAS and CMS collaborations have searched for the supersymmetry (SUSY) in different channels with 7 TeV center-of-mass energy and their search strategies are optimized for the SUSY scenarios with fairly large mass splittings among the sparticles. In absence of any significant deviation of the data from the Standard Model (SM) prediction, stringent bounds are imposed on the squarks and gluino masses in the context of different SUSY scenarios. Since the exact SUSY breaking mechanism is not known, some part of the SUSY spectrum may be degenerate. In this paper, we consider two particular cases of degenerate SUSY spectrum and discuss the impact of ATLAS and CMS SUSY searches on these scenarios. We found that present SUSY search strategies of the ATLAS and CMS collaborations are not optimized for the degenerate SUSY scenarios. Even the LHC with 8 TeV center-of-mass energy can not probe large part of the parameter space of degenerate SUSY scenarios with the present search strategies.

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arXiv2012

Constraints on Universal Extra Dimension models with gravity mediated decays from ATLAS diphoton search

We discuss the collider phenomenology of Universal Extra Dimension models with gravity mediated decays. We concentrate on diphoton associated with large missing transverse energy signature. At the collider, level-1 Kaluza-Klein (KK) particles are produced in pairs due to the conservation of KK-parity. Subsequently, KK-particles decay via cascades involving lighter KK-particles until reaching the lightest KK-particle (LKP). Finally, gravity induced decay of the LKP into photons gives rise to the diphoton signature. The search for diphoton events with large missing transverse energy was recently communicated by the ATLAS collaboration for 7 TeV center-of-mass energy and 3.1 inverse femtobarn integrated luminosity of the Large Hadron Collider. Above the Standard Model background prediction, no excess of such events was reported. We translate the absence of any excess of the diphoton events to constrain the model parameters, namely, the radius of compactification (R) and the fundamental Planck mass ($M_D$).

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arXiv2011

Exploring two Universal Extra Dimensions at the CERN LHC

We discuss the signatures, at the LHC, of the (1,0)-th Kaluza-Klein (KK) gluon and quarks in the framework of the two universal extra dimensional (2UED) model. Once produced, these particles typically suffer a cascade of decays terminating in the Dark Matter candidate apart from Standard Model particles. In this article, we are interested in focus on a particular signature of 2UED wherein the final state comprises of at least four jets in association with a hard photon and missing transverse energy. Several kinematic cuts are devised to enhance the signal to background ratio. Finally, as a road map to parameter determination at the LHC, we point out an interesting correlation between the peak position of the M_eff distributions with the compactification radius R and the cut-off scale M_s.

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arXiv2011

Signals of an invisibly decaying Higgs in a scalar dark matter scenario: a study for the Large Hadron Collider

We consider the collider phenomenology of a singlet Majoron model with softly broken lepton number. Lepton number is spontaneously broken when the real part of a new singlet scalar develops vacuum expectation value. With the additional soft terms violating lepton numbers, the imaginary part of this singlet scalar becomes a massive pseudo-Majoron which can account for the dark matter. In presence of the coupling of the pseudo-Majoron with the Standard Model (SM) Higgs, the SM Higgs mostly decays into a pair of pseudo-Majorons, giving rise to missing transverse energy signals at a hadron collider. Since the Higgs visible decay branching fractions get reduced in presence of this invisible decay mode, the bounds on the SM Higgs mass from the LEP and Tevatron experiments get diluted and the invisible decay channel of the Higgs become important for the discovery of low mass Higgs at the Large Hadron Collider.

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arXiv2010

Discrimination of low missing energy look-alikes at the LHC

The problem of discriminating possible scenarios of TeV scale new physics with large missing energy signature at the Large Hadron Collider (LHC) has received some attention in the recent past. We consider the complementary, and yet unexplored, case of theories predicting much softer missing energy spectra. As there is enough scope for such models to fake each other by having similar final states at the LHC, we have outlined a systematic method based on a combination of different kinematic features which can be used to distinguish among different possibilities. These features often trace back to the underlying mass spectrum and the spins of the new particles present in these models. As examples of "low missing energy look-alikes", we consider Supersymmetry with R-parity violation, Universal Extra Dimensions with both KK-parity conserved and KK-parity violated and the Littlest Higgs model with T-parity violated by the Wess-Zumino-Witten anomaly term. Through detailed Monte Carlo analysis of the four and higher lepton final states predicted by these models, we show that the models in their minimal forms may be distinguished at the LHC, while non-minimal variations can always leave scope for further confusion. We find that, for strongly interacting new particle mass-scale ~600 GeV (1 TeV), the simplest versions of the different theories can be discriminated at the LHC running at sqrt{s}=14 TeV within an integrated luminosity of 5 (30) fb^{-1}.

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arXiv2010

Deciphering Universal Extra Dimension from the top quark signals at the CERN LHC

Models based on Universal Extra Dimensions predict Kaluza-Klein (KK) excitations of all Standard Model (SM) particles. We examine the pair production of KK excitations of top- and bottom-quarks at the Large Hadron Collider. Once produced, the KK top/bottom quarks can decay to $b$-quarks, leptons and the lightest KK-particle, $γ_1$, resulting in 2 $b$-jets, two opposite sign leptons and missing transverse momentum, thereby mimicing top-pair production. We show that, with a proper choice of kinematic cuts, an integrated luminosity of 100 fb$^{-1}$ would allow a discovery for an inverse radius upto $R^{-1} = 750$ GeV.

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arXiv2010

Search for the minimal universal extra dimension model at the LHC with $\sqrt{s}$=7 TeV

Universal Extra Dimension (UED) model is one of the popular extension of the Standard Model (SM) which offers interesting phenomenology. In the minimal UED (mUED) model, Kaluza-Klein (KK) parity conservation ensures that $n=1$ KK states can only be pair produced at colliders and the lightest KK particle is stable. In most of the parameter space, first KK excitation of SM hypercharge gauge boson is the lightest one and it can be a viable dark matter candidate. Thus, the decay of $n=1$ KK particles will always involve missing transverse energy as well as leptons and jets. The production cross sections of $n=1$ KK particles are large and such particles may be observed at the Large Hadron Collider (LHC). We explore the mUED discovery potential of the LHC with $\sqrt{s}$ = 7 TeV in the multileptonic final states. Since in the early LHC run, precise determination of missing transverse energy may not be possible, we examine the LHC reach with and without using missing transverse energy information. We observe that missing transverse energy cut will not improve mUED discovery reach significantly. We have found that opposite sign di-lepton channel is the most promising discovery mode and with first $fb^{-1}$ of collected luminosity, LHC will be able to discover the strongly interacting $n=1$ KK particles with masses upto 800 to 900 GeV.

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arXiv2009

Probing two Universal Extra Dimensions at International Linear Collider

We discuss collider signatures of (1,1)-th Kaluza-Klein (KK) mode vector bosons in the framework of two universal extra dimension model, at a future electron-positron collider. Production of the (1,1)-th KK mode of electro-weak vector bosons (B(1,1), W3(1,1)), are considered in association with a hard photon. Without caring about the decay products of those vector bosons, one can measure the masses of these particles just by looking at the photon energy distribution. Once produced these particles dominantly decay to a pair of jets or to a pair of top quarks. Thus we look for a pair of jets or a pair of top quarks in association with a photon. Upto the kinematic limit of the collider, signals from the B(1,1) production and decay in both the above mentioned channels are greater than the $5σ$ fluctuation of the Standard Model background. However, the number of events from W3(1,1) production and decay is smaller and its detection prospect is not very good.

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arXiv2009

Probing two Universal Extra Dimension model with leptons and photons at the LHC and ILC

We discuss the collider signatures of electroweak (1,0)-mode excitations in the framework of two universal extra dimension (2UED) at the LHC and ILC. In general, pair production of electroweak (1,0)-mode particles of 2UED gives rise to multi lepton plus missing transverse momentum signal. Upto 1/R = 400 GeV two lepton plus missing transverse momentum signal and upto 1/R = 600 GeV three lepton plus missing transverse momentum signal stands over the $5σ$ standard deviation of the Standard Model background at the LHC with $100 fb^{-1}$ integrated luminosity. At ILC we study single photon plus missing energy signal from the production of U(1) gauge boson in association with a U(1) spinless adjoint. With proper choice of beam polarization, signal strength is greater than $5σ$ standard deviation of the Standard Model background almost upto the kinematic limit of the collider.

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