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Prakash Mathews

Publications and source records attributed to Prakash Mathews.

At least 55 records · Page 3Linked to original sources
arXiv2004

Searching for signals of minimal length in extra dimensional models using dilepton production at hadron colliders

Theories of quantum gravity suggest the existence of a minimal length scale. It is interesting to speculate what the consequences of the existence of such a length scale would be for models of large extra dimensions, in particular, the ADD model. When ADD model is conflated with the minimal length scale scenario, processes involving virtual exhange of gravitons cease to be ulraviolent divergent. We study the production of dileptons at hadron colliders as an example of a process mediated by virtual gravitons. We find that the bounds we derive on the effective string scale are significantly different (in fact, less stringent) from those derived in the conventional ADD model, both at the upgraded Tevatron and the Large Hadron Collider.

hep-ph↗
arXiv2004

NLO-QCD corrections to e+ e- --> hadrons in models of TeV-scale gravity

We present results on NLO-QCD corrections to the process e+ e- --> hadrons via photon-, Z- and graviton-exchange in the context of TeV-scale gravity models. The quantitative impact of these QCD corrections for searches of extra dimensions at a Linear Collider is briefly discussed.

hep-ph↗
arXiv2002

Excited Leptons at the CERN Large Hadron Collider

We analyze the potential of the CERN Large Hadron Collider (LHC) to search for excited spin-1/2 electrons and neutrinos. Assuming a SU(2)_L X U(1)_Y invariant model, we study in detail the single production of excited electrons and neutrinos and respective backgrounds through the reactions p p -> e+ e- V and e+- νV with V=photon, W, or Z. We show that the LHC will be able to tighten considerably the direct constraints on these possible new states, probing excited lepton masses up to 1-2 TeV depending on their couplings to fermions and gauge bosons.

hep-ph↗
arXiv2001

Compton scattering in Noncommutative Space-Time at the NLC

We study the Compton scattering in the noncommutative counter part of QED (NC QED). Interactions in NC QED have momentum dependent phase factors and the gauge fields have Yang Mills type couplings, this modifies the cross sections and are different from the commuting Standard Model. Collider signals of noncommutative space-time are studied at the Next Linear Collider (NLC) operating in the $e γ$ mode. Results for different polarised cases are presented and it is shown that the Compton process can probe the noncommutative scale in the range of 1 - 2.5 TeV for typical proposed NLC energies.

hep-ph↗
arXiv2000

Extra Dimensions: A View from the Top

In models with compact extra dimensions, where the Standard Model fields are confined to a 3+1 dimensional hyperplane, the $t \bar t$ production cross-section at a hadron collider can receive significant contributions from multiple exchange of KK modes of the graviton. These are carefully computed in the well-known ADD and RS scenarios, taking the energy dependence of the sum over graviton propagators into account. Using data from Run-I of the Tevatron, 95% C.L. bounds on the parameter space of both models are derived. For Run-II of the Tevatron and LHC, discovery limits are estimated.

hep-ph↗
arXiv1999

Large extra dimensions and dijet production in $γγ$ collisions

We have studied dijet production in $γγ$ collisions with a view to probing the physics of large extra dimensions. The exchange of virtual spin-2 Kaluza-Klein excitations is found to modify the dijet cross-section substantially from its Standard Model value and allows the effective string scale to be probed to values between 2.5 and 6.4 TeV in the unpolarised case. In the case where the photons are polarised, the limits are seen to improve by roughly 20%. Dijet production in $γγ$ collisions is thus shown to be a very effective probe of large extra dimensions.

hep-ph↗
arXiv1999

Probing Large Extra Dimensions Using Top Production in Photon-Photon Collisions

Theories with large extra dimensions predict an infinite tower of Kaluza-Klein states in the 1 TeV range, which can consequently have significant implications for experimental observables. One such observable, which gets affected by the exchange of spin-2 Kaluza-Klein particles, is the t t(bar) production cross-section in photon-photon collisions at NLC energies. We study this process and obtain bounds on the effective quantum gravity scale M_S between 700 and 2400 GeV (depending on the centre-of-mass energy). We show that the use of polarisation will further strengthen these bounds.

hep-ph↗
arXiv1999

J/psi+gamma production at the LHC

The associated production of J/psi + gamma at the LHC is studied within the NRQCD framework. The signal we focus on is the production of a J/psi and an isolated photon produced back-to-back, with their transverse momenta balanced. It is shown that even for very large values of transverse momentum (pT of the order of 50 GeV) the dominant contribution to this process is not fragmentation. This is because of the fact that fragmentation-type contributions to the cross-section come from only a q q(bar) initial state, which is suppressed at the LHC. We identify gg-initiated diagrams higher-order in alpha(s) which do have fragmentation-type vertices. We find, however, that the contribution of these diagrams is negligibly small.

hep-ph↗
arXiv1999

Testing TeV Scale Quantum Gravity using Dijet Production at the Tevatron

Dijet production at the Tevatron including effects of virtual exchanges of spin-2 Kaluza-Klein modes in theories with large extra dimensions is considered. The experimental dijet mass and angular distribution are exploited to obtain stringent limits ($\sim 1.2$ TeV) on the effective string scale $M_S$.

hep-ph↗
arXiv1999

Getting to the top with extra dimensions

The prospect of large extra dimensions and an effective theory of gravity at around a TeV has interesting experimental consequences. In these models, the Kaluza-Klein modes interact with Standard Model particles and these interactions lead to testable predictions at present and planned colliders. We investigate the effect of virtual exchanges of the spin-2 Kaluza-Klein modes in the production cross-section of $t \bar t$ pairs at the Tevatron and the LHC and find that the $t \bar t$ cross-section can be an effective probe of the large extra dimensions. This enables us to put bounds on the effective low-energy scale.

hep-ph↗
arXiv1999

Large extra dimensions and deep-inelastic scattering at HERA

In scenarios motivated by string theories, it is possible to have extra Kaluza-Klein dimensions compactified to rather large magnitudes, leading to large effects of gravity at scales down to a TeV. The effect of the spin-2 Kaluza-Klein modes on the deep-inelastic cross-section at HERA is investigated. We find that the data can be used to obtain bounds on the effective low energy scale, $M_S$.

hep-ph↗
arXiv1998

eta_c Production at the Tevatron: A test of NRQCD

We use NRQCD to predict the cross section for $η_c$ production at the Tevatron. The non-perturbative matrix elements required are obtained, using heavy-quark symmetry, from the matrix elements determined from the CDF $J/ψ$ data. Our numbers are, therefore, predictions of NRQCD and provide a very good test of it. Even after taking into account the small branching ratio of the $η_c$ into two photons, a substantial rate for the production of this resonance at the Tevatron is expected.

hep-ph↗
arXiv1997

Chi_1 and Polarisation Asymmetries for Quarkonia at High Orders in Non-relativistic QCD

We study doubly polarised asymmetries of c-cbar and b-bbar mesons in hadro- and photo-production at low transverse momentum in non-relativistic QCD to high orders in the relative velocity of the pair, v. We give the complete set of expressions required for the asymmetries up to order v^9. The asymmetries in the production of eta_{c,b} states are a stable measure of the polarised gluon densities. The asymmetries for chi_{c,b}, J/psi, psi', and the various Upsilon states are stringent tests of the NRQCD scaling relations.

hep-ph↗
arXiv1997

Higher Orders in the Colour-Octet Model of J/ψProduction

We study the hadro- and photo-production of $\bar cc$ and $\bar bb$ mesons at low transverse momentum to high orders in the relative velocity of the pair, v, in non-relativistic QCD. We evaluate cross sections to order v^7 for $η_c$, sufficient for studies of photo-production in the almost-elastic region. For all other charmonium states we find the cross section to order v^9, sufficient for studies of the ratio of $χ_{c1}$ and $χ_{c2}$ production rates. We find recurrence formulae for generating terms at even higher orders, should they be needed.

hep-ph↗
arXiv1996

J/psi Spin Asymmetries in the Colour-Octet Model

We investigate the pattern of asymmetries in the colour-octet model for inclusive production of charmonium with polarised initial state hadrons and photons. We find that singly polarised asymmetries vanish. The double polarised asymmetry for J/psi involves a new combination of long-distance matrix element. We also investigate the asymmetries for eta_c, chi_c and Upsilon production. The asymmetries distinguish well between different models of charmonium production.

hep-ph↗
arXiv1996

Transverse structure function in the factorisation method

Deep Inelastic scattering experiments using transversely polarised targets yield information on the structure function $g_2$. By means of a free-field analysis, we study the operator structure of $g_2$ and demonstrate the need for retaining the twist three mass terms in order to maintain current-conservation. We show that the structure function $g_T=g_1+g_2$ has a much simpler operator structure as compared to $g_2$, in spite of the fact that, like $g_2$, $g_T$ has a twist-three component. We demonstrate factorisation of the hadronic tensor into hard and soft parts for the case of $g_T$. We show that the first moment of the gluonic contribution to $g_T$ vanishes, and discuss possible physical applications.

hep-ph↗
arXiv1996

Photon Structure Functions: Target Photon Mass Effects and QCD Corrections

We present a systematic analysis of the polarised and unpolarised processes $e^+ ~e^- \rightarrow e^+ ~e^- X$ in the deep inelastic limit and study the effects of target photon mass (virtuality) on the photon structure functions. The effect of target photon virtuality manifests as new singly polarised structure functions and also alters the physical interpretation of the unpolarised structure functions. The physical interpretation of these structure functions in terms of hadronic components is studied using the free field analysis. We also retrieve the real photon results in the limit the virtuality goes to zero. Assuming factorisation of the photon structure tensor, the relevant QCD corrections to the various twist two structure functions are evaluated.

hep-ph↗