arXiv subjects

Rohini M. Godbole

Publications and source records attributed to Rohini M. Godbole.

At least 73 records · Page 4Linked to original sources

arXiv2010

Soft gluon resummation in the infrared region and the Froissart bound

We describe the taming effect induced by soft gluon $k_t$-resummation on the rapid rise of QCD mini-jet contributions to the total cross-sections.This results from an eikonal model in which the rise of the total cross-section is due to mini-jet contribution. We perform the calculation with current Parton Density Functions (PDFs). The impact parameter distribution we use is obtained as the Fourier transform of the resummed $k_t$-distribution of soft gluons emitted from the initial state during the collision.The emission, which is energy dependent, destroys the initial collinearity of partons.In this model, the strong power-like rise due to the increasing number of low-x gluon collisions is tamed by the acollinearity induced by soft gluon kt-resummation down to zero gluon momenta. It explicitly links a singular soft gluon coupling in the infrared region to the behaviour dictated by the Froissart bound for the total cross-section. The model describes well both proton and photon processes at present accelerator energies and gives predictions in the TeV range. For photons the model predictions agree with fits by Block and Halzen based on Finite Energy Sum Rules (FESR) at low energy and an asymptotic behaviour consistent with the Froissart bound.

hep-ph↗

arXiv2010

The Heart of Matter

In this article I trace the development of the human understanding of the "Heart of Matter" from early concepts of "elements" (or alternatively "Panchmahabhootas") to the current status of "quarks" and "leptons" as the fundamental constituents of matter, interacting together via exchange of the various force carrier particles called "gauge bosons" such as the photon, W/Z-boson etc. I would like to show how our understanding of the fundamental constituents of matter has gone hand in hand with our understanding of the fundamental forces in nature. I will also outline how the knowledge of particle physics at the "micro" scale of less than a Fermi(one millionth of a nanometer), enables us to offer explanations of Cosmological observations at the "macro" scale. Consequently these observations, may in turn, help us address some very fundamental questions of the Physics at the "Heart of the Matter".

physics.pop-ph↗

arXiv2009

Four Generations: SUSY and SUSY Breaking

We revisit four generations within the context of supersymmetry. We compute the perturbativity limits for the fourth generation Yukawa couplings and show that if the masses of the fourth generation lie within reasonable limits of their present experimental lower bounds, it is possible to have perturbativity only up to scales around 1000 TeV. Such low scales are ideally suited to incorporate gauge mediated supersymmetry breaking, where the mediation scale can be as low as 10-20 TeV. The minimal messenger model, however, is highly constrained. While lack of electroweak symmetry breaking rules out a large part of the parameter space, a small region exists, where the fourth generation stau is tachyonic. General gauge mediation with its broader set of boundary conditions is better suited to accommodate the fourth generation.

hep-ph↗

arXiv2009

Supersymmetry and other New Physics at gamma gamma colliders

In this contribution we present a discussion of some aspects of the capabilities of a photon collider to probe physics beyond the standard model. I will take a few examples from Higgs physics, supersymmetry, extra dimensional theories as well as unparticles, pointing out the special rôle that a photon collider can play in each case.

hep-ph↗

arXiv2009

Use of transverse beam polarization to probe anomalous VVH interactions at a Linear Collider

We investigate use of transverse beam polarization in probing anomalous coupling of a Higgs boson to a pair of vector bosons, at the International Linear Collider (ILC). We consider the most general form of VVH (V = W/Z) vertex consistent with Lorentz invariance and investigate its effects on the process e+ e- --> f bar{f} H, f being a light fermion. Constructing observables with definite CP and naive time reversal (tilde T) transformation properties, we find that transverse beam polarization helps us to improve on the sensitivity of one part of the anomalous ZZH coupling that is odd under CP. Even more importantly it provides the possibility of discriminating from each other, two terms in the general ZZH vertex, both of which are even under CP and tilde T. Use of transverse beam polarization when combined with information from unpolarized and linearly polarized beams therefore, allows one to have completely independent probes of all the different parts of a general ZZH vertex.

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↗

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↗

arXiv2007

Aspects of CP violation in the HZZ coupling at the LHC

We examine the CP-conserving (CPC) and CP-violating (CPV) effects of a general HZZ coupling through a study of the process H -> ZZ* -> 4 leptons at the LHC. We construct asymmetries that directly probe these couplings. Further, we present complete analytical formulae for the angular distributions of the decay leptons and for some of the asymmetries. Using these we have been able to identify new observables which can provide enhanced sensitivity to the CPV $H ZZ$ coupling. We also explore probing CP violation through shapes of distributions in different kinematic variables, which can be used for Higgs bosons with mH < 2 mZ.

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↗

arXiv2007

Total cross-section and rapidity gap survival probability at the LHC through an eikonal with soft gluon resummation

New results are presented for total ${\rm pp}/ {\rm \bar p p}$ cross-sections, in the framework of our QCD based model (GGPS). This is an improved eikonal mini-jet model, where soft gluon radiation tames the fast energy rise normally present in mini-jet models. We discuss the variability in our predictions and provide a handy parametrization of our results for the LHC. We find that our model predictions span the range $σ_{tot}^{LHC}=100 ^{+10}_{-13} mb$. While this matches nicely with the range of most other models, it does not agree with recent ones which include a "hard" Pomeron, even though our model does include hard scattering. We compute the survival probability for Large Rapidity Gap (LRG) events at the LHC and at the Tevatron. These events are relevant, for example, for Higgs signal in the $WW$ fusion process. We also explore whether measurements of the total cross-sections at the LHC can help us sharpen the model parameters and hence estimates for these survival probabilities, further.

hep-ph↗

arXiv2007

CP Asymmetries in Higgs decays to ZZ at the LHC

We examine the effect of a general HZZ coupling through a study of the Higgs decay to leptons via Z bosons at the LHC. We discuss various methods for placing limits on additional couplings, including measurement of the partial width, threshold scans, and asymmetries constructed from angular observables. We find that only the asymmetries provide a definitive test of additional couplings. We further estimate the significances they provide.

hep-ph↗

arXiv2007

Fermion Electric Dipole Moments in R-parity violating Supersymmetry

In this talk I discuss some aspects of the study of electric dipole moments (EDMs) of the fermions, in the context of R-parity violating (\rpv) Supersymmetry (SUSY). I will start with a brief general discussion of how dipole moments, in general, serve as a probe of physics beyond the Standard Model (SM) and an even briefer summary of \rpv SUSY. I will follow by discussing a general method of analysis for obtaining the leading fermion mass dependence of the dipole moments and present its application to \rpv SUSY case. Then I will summarise the constraints that the analysis of $e,n$ and $Hg$ EDMs provide for the case of trilinear \rpv SUSY couplings and make a few comments on the case of bilinear \rpv, where the general method of analysis proposed by us does not work.

hep-ph↗

arXiv2007

Signatures of anomalous VVH interactions at a linear collider

We examine, in a model independent way, the sensitivity of a Linear Collider to the couplings of a light Higgs boson to gauge bosons. Including the possibility of CP violation, we construct several observables that probe the different anomalous couplings possible. For an intermediate mass Higgs, a collider operating at a center of mass energy of 500 GeV and with an integrated luminosity of 500 fb$^{-1}$ is shown to be able to constrain the $ZZH$ vertex at the few per cent level, and with even higher sensitivity in certain directions. However, the lack of sufficient number of observables as well as contamination from the $ZZH$ vertex limits the precision with which the $WWH$ coupling can be measured.

hep-ph↗

arXiv2007

Moderately light charged Higgs in \cp MSSM and NMSSM

In this talk I discuss some aspects of the phenomenology of a moderately light charged Higgs ($H^\pm$) with a mass $\gts 130$ GeV, lighter than the top quark, at the LHC. A charged Higgs in this mass range is still allowed in next-to-minimal Supersymmetric Standard Model (NMSSM) at low $\tan β$ as well as in CP-violating (\cp) Minimal Supersymmetric Standard Model (MSSM) for a certain choice of \cp parameters, still respecting all the LEP-II bounds. In both the cases, the $H^\pm$ has a large branching ratio in the $W^\pm ϕ$ channel, where $ϕ$ denotes a generic Higgs which is dominantly pseudoscalar and hence may be substantially lighter than the LEP-II mass bound. This $ϕ$ decays dominantly into a $b \bar b$ pair. Thus production of $H^\pm$ in the top decay gives a striking $t \bar t$ signal at the LHC, where one of the top quarks decays into the $bb \bar b W$ channel, via $t \to b H^\pm, H^\pm \to ϕ$ and $ϕ\to b \bar b$. The characteristic correlation between the $b \bar b$, $b \bar b W$ and $b b \bar b W$ invariant mass peaks helps reduce the Standard Model (SM) background very effectively. For these low values of $\tan β$ the $H^\pm \to τν_τ$ channel does not provide any reach for the $H^\pm$. Thus this is a signal for both a light charged $H^\pm$ and a light $ϕ$, which is mostly pseudoscalar in nature and decays dominantly into a $b \bar b$ pair.

hep-ph↗

arXiv2006

Probing CP-violating Higgs contributions in gamma-gamma -> f anti-f through fermion polarization

We discuss the use of fermion polarization for studying neutral Higgs bosons at a photon collider. To this aim we construct polarization asymmetries which can isolate the contribution of a Higgs boson $ϕ$ in $γγ\to f \bar f$, $f=τ/t$, from that of the QED continuum. This can help in getting information on the $γγϕ$ coupling in case $ϕ$ is a CP eigenstate. We also construct CP-violating asymmetries which can probe CP mixing in case $ϕ$ has indeterminate CP. Furthermore, we take the MSSM with CP violation as an example to demonstrate the potential of these asymmetries in a numerical analysis. We find that these asymmetries are sensitive to the presence of a Higgs boson as well as its CP properties over a wide range of MSSM parameters. In particular, the method suggested can cover the region where a light Higgs boson may have been missed by LEP due to CP violation in the Higgs sector, and may be missed as well at the LHC.

hep-ph↗

arXiv2006

Lepton distribution as a probe of new physics in production and decay of the t quark and its polarization

We investigate the possibilities of studying new physics in various processes of t-quark production using kinematical distributions of the secondary lepton coming from decay of t quarks. We show that the angular distributions of the secondary lepton are insensitive to the anomalous tbW vertex and hence are pure probes of new physics in a generic process of t-quark production. The energy distribution of the lepton is distinctly affected by anomalous tbW couplings and can be used to analyze them independent of the production process of t quarks. The effects of t polarization on the distributions of the decay lepton are demonstrated for top-pair production process at a gamma-gamma collider mediated by a heavy Higgs boson.

hep-ph↗

arXiv2006

Graviton Resonances in E+ E- -> MU+ MU- at Linear Colliders with Beamstrahlung and ISR Effects

Electromagnetic radiation emitted by the colliding beams is expected to play an important role at the next generation of high energy e^+ e^- linear collider(s). Focusing on the simplest process e+e- -> mu+ mu-, we show that radiative effects like initial state radiation (ISR) and beamstrahlung can lead to greatly-enhanced signals for resonant graviton modes of the Randall-Sundrum model.

hep-ph↗