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Debajyoti Choudhury

Publications and source records attributed to Debajyoti Choudhury.

At least 73 records · Page 4Linked to original sources
arXiv2011

Late-time acceleration in Higher Dimensional Cosmology

We investigate late time acceleration of the universe in higher dimensional cosmology. The content in the universe is assumed to exert pressure which is different in the normal and extra dimensions. Cosmologically viable solutions are found to exist for simple forms of the equation of state. The parameters of the model are fixed by comparing the predictions with supernovae data. While observations stipulate that the matter exerts almost vanishing pressure in the normal dimensions, we assume that, in the extra dimensions, the equation of state is of the form $P \propto \, ρ^{1 - γ}$. For appropriate choice of parameters, a late time acceleration in the universe occurs with $q_0$ and $z_{tr}$ being approximately -0.46 and 0.76 respectively.

gr-qc↗
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.

hep-ph↗
arXiv2011

Flavour Structure of R-violating Neutralino Decays at the LHC

We study signatures of R-parity violation in the production of supersymmetric particles at the LHC, and the subsequent decay of the lightest neutralino being the end product of a supersymmetric cascade decay. In doing so, we pay particular attention to the possible flavour structure of the operators, and how one may discriminate between different possibilities. A neutralino LSP would couple to all quarks and leptons and a comparative study of its decays provides an optimal channel for the simultaneous study of all 45 R-violating operators. By studying the expected signals from all these operators, we demonstrate the ability to understand whether more than one coupling dominates, and to map the experimental signatures to operator hierarchies that can then be compared against theoretical models of flavour. Detailed comparisons with backgrounds, including those from MSSM cascade decays are made, using the PYTHIA event simulator.

hep-ph↗
arXiv2011

Top polarization, forward-backward asymmetry and new physics

We consider how the measurement of top polarization at the Tevatron can be used to characterise and discriminate among different new physics models that have been suggested to explain the anomalous top forward-backward asymmetry reported at the Tevatron. This has the advantage of catching the essence of the parity violating effect characteristic to the different suggested new physics models. Other observables constructed from these asymmetries are shown to be useful in discriminating between the models, even after taking into account the statistical errors. Finally, we discuss some signals at the 7 TeV LHC.

hep-ph↗
arXiv2011

Search for the lightest scalar top quark in R-parity violating decays at the LHC

The scalar partner of the top quark (the stop) is relatively light in many models of supersymmetry breaking. We study the production of stops at the Large Hadron Collider (LHC) and their subsequent decays through baryon-number violating couplings such that the final state contains no leptons. A detailed analysis performed using detector level observables demonstrate that stop masses upto $\sim 600 \gev$ may be explored at the LHC depending on the branching ratios for such decays and the integrated luminosity available. Extended to other analogous scenarios, the analysis will, generically, probe even larger masses.

hep-ph↗
arXiv2011

Electromagnetic leptogenesis at the TeV scale

We construct an explicit model implementing electromagnetic leptogenesis. In a simple extension of the Standard Model, a discrete symmetry forbids the usual decays of the right-handed neutrinos, while allowing for an effective coupling between the left-handed and right-handed neutrinos through the electromagnetic dipole moment. This generates correct leptogenesis with resonant enhancement and also the required neutrino mass via a TeV scale seesaw mechanism. The model is consistent with low energy phenomenology and would have distinct signals in the next generation colliders, and, perhaps even the LHC.

hep-ph↗
arXiv2010

A fourth generation, anomalous like-sign dimuon charge asymmetry and the LHC

A fourth chiral generation, with $m_{t^\prime}$ in the range $\sim (300 - 500)$ GeV and a moderate value of the CP-violating phase can explain the anomalous like-sign dimuon charge asymmetry observed recently by the D0 collaboration. The required parameters are found to be consistent with constraints from other $B$ and $K$ decays. The presence of such quarks, apart from being detectable in the early stages of the LHC, would also have important consequences in the electroweak symmetry breaking sector.

hep-ph↗
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.

hep-ph↗
arXiv2010

Mutual consistency of the MINOS and MiniBooNE Antineutrino Results and Possible CPT Violation

Discussing the recent MINOS data on muon anti-neutrino disappearance and the MiniBooNE data on muon anti-neutrino to electron anti-neutrino oscillation, we show that the while the respective best fits are inconsistent with each other, significant overlap of allowed regions does exist. Assuming only three neutrino species, the data indicates a discrepancy of mass levels and mixing angles between the neutrino and the antineutrino sectors. We show that the existing data can be reconciled with a model of explicit CPT violation in the neutrino sector and estimate the magnitude of the required violation.

hep-ph↗
arXiv2010

Non-universal scalar mass scenario with Higgs funnel region of SUSY dark matter: a signal-based analysis for the Large Hadron Collider

We perform a multilepton channel analysis in the context of the Large Hadron Collider (LHC) for Wilkinson Microwave Anisotropy Probe (WMAP) compatible points in a model with non-universal scalar masses, which admits a Higgs funnel region of supersymmetry dark matter even for a small $\tanβ$. In addition to two and three-lepton final states, four-lepton events, too, are shown to be useful for this purpose. We also compare the collider signatures in similar channels for WMAP compatible points in the minimal supergravity (mSUGRA) framework with similar gluino masses. Some definite features of such non-universal scenario emerge from the analysis.

hep-ph↗
arXiv2009

Role of polarization in probing anomalous gauge interactions of the Higgs boson

We explore the use of polarized $e^+/e^-$ beams and/or the information on final state decay lepton polarizations in probing the interaction of the Higgs boson with a pair of vector bosons. A model independent analysis of the process $e^+ e^- \to f \bar f H$, where $f$ is any light fermion, is carried out through the construction of observables having identical properties under the discrete symmetry transformations as different individual anomalous interactions. This allows us to probe an individual anomalous term independent of the others. We find that initial state beam polarization can significantly improve the sensitivity to CP-odd couplings of the $Z$ boson with the Higgs boson ($ZZH$). Moreover, an ability to isolate events with a particular $τ$ helicity, with even 40% efficiency, can improve sensitivities to certain $ZZH$ couplings by as much as a factor of 3. In addition, the contamination from the $ZZH$ vertex contributions present in the measurement of the trilinear Higgs-$W$ ($WWH$) couplings can be reduced to a great extent by employing polarised beams. The effects of initial state radiation (ISR) and beamstrahlung, which can be relevant for higher values of the beam energy are also included in the analysis.

hep-ph↗
arXiv2009

Quark Excitations Through the Prism of Direct Photon Plus Jet at the LHC

The quest to know the structure of matter has resulted in various theoretical speculations wherein additional colored fermions are postulated. Arising either as Kaluza-Klein excitations of ordinary quarks, or as excited states in scenarios wherein the quarks themselves are composites, or even in theories with extended gauge symmetry, the presence of such fermions ($q^*$) can potentially be manifested in $γ+ jet$ final states at the LHC. Using unitarized amplitudes and the CMS setup, we demonstrate that in the initial phase of LHC operation (with an integrated luminosity of $200 \pb^{-1}$) one can discover such states for a mass upto 2.0 TeV. The discovery of a $q^*$ with a mass as large as $\sim$5 TeV can be acheived for an integrated luminosity of $\sim 140 \fb^{-1}$. We also comment on the feasibility of mass determination.

hep-ph↗
arXiv2008

Nonstandard, strongly interacting spin one $t \bar t$ resonances

Examining theories with an extended strong interaction sector such as axigluons or flavour universal colorons, we find that the constraints obtained from the current data on $t \bar t$ production at the Tevatron are in the range of $\sim {\cal O}$ TeV and thus competitive with those obtained from the dijet data. We point out that for large axigluon/coloron masses, the limits on the coloron mass may be different than those for the axigluon even for $\cot ξ= 1$. We also compute the expected forward-backward asymmetry for the case of the axigluons which would allow it to be discriminated against the SM as also the colorons. We further find that at the LHC, the signal should be visible in the $t \bar t$ invariant mass spectrum for a wide range of axigluon and coloron masses that are still allowed. We point out how top polarisation may be used to further discriminate the axigluon and coloron case from the SM as well as from each other.

hep-ph↗
arXiv2008

Right sneutrinos and the signals of a stable stop at the Large Hadron Collider

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.

hep-ph↗
arXiv2008

Fermionic un-particles, gauge interactions and the $β$ function

The dynamics of fermionic unparticles is developed from first principles. It is shown that any unparticle, whether fermionic or bosonic, can be recast in terms of a canonically quantized field, but with non-local interaction terms. We further develop a possible gauge theory for fermionic unparticles. Computing the consequent contribution of un-fermions to the $β$ function of the theory, it is shown that this can be viewed as the sum of two contributions, one fermion-like and the other scalar-like. However, if full conformal invariance is imposed, the latter vanishes identically. We discuss the consequences thereof as well as some general phenomenological issues.

hep-ph↗
arXiv2007

Effects of polarisation on study of anomalous VVH interactions at a Linear Collider

We investigate the use of beam polarisation as well as final state $τ$ polarisation effects in probing the interaction of the Higgs boson with a pair of heavy vector bosons in the process $e^+ e^- \to f \bar f H$, where $f$ is any light fermion. The sensitivity of the International Linear Collider (ILC) operating at $\sqrt s=500$ GeV, to such $VVH$($V = W/Z$) couplings is examined in a model independent way. The effects of ISR and beamstrahlung are discussed.

hep-ph↗
arXiv2007

Top production at the Tevatron/LHC and nonstandard, strongly interacting spin one particles

In this note, we consider possible constraints from $t \bar t$ production on the gauge bosons of theories with an extended strong interaction sector such as axigluons or flavour universal colorons. Such constraints are found to be competitive with those obtained from the dijet data. The current $t \bar t$ data from the Tevatron rule out axigluon masses ($m_A$) up to 900 GeV and 850 GeV at 2 $σ$ and 4 $σ$ levels respectively. For the case of flavour universal colorons the data rule out a mass ($m_C$) below 800 GeV (780 GeV) at the $2 (4) σ$ level and also the mass range between 900 GeV to 2.1 TeV at 2 $σ$ level, for $\cot ξ= 1$, where $ξ$ is the mixing angle. For $\cot ξ=2$ on the other hand, the excluded range is $m_C \lsim 950 (920)$ GeV and $m_C \gsim 1.02 (1.15 \lsim m_C \lsim 1.8)$ TeV at $2 σ$ ($4 σ$) level. We point out that for higher axigluon/coloron masses, even for the dijet channel, the limits on the coloron mass, for $\cot ξ= 1$, may be different than those for the axigluon. We also compute the expected forward-backward asymmetry for the case of the axigluons which would allow it to be discriminated against the SM as also the colorons. We further find that at the LHC, the signal should be visible in the $t \bar t$ invariant mass spectrum for a wide range of axigluon and coloron masses that are still allowed. We point out how top polarisation may be used to further discriminate the axigluon and coloron case from the SM as well as from each other.

hep-ph↗