Biennial Report 2005-2007 - Saha Institute of Nuclear Physics

Theoretical Physics 9LHC and Tevatron. Inclusion of QCD corrections to NLO stabilises the cross section with respectto scale variations.Prakash Mathews, V Ravindran†Theo1.2.2.10 NLO-QCD corrections to dilepton production in the Randall-SundrummodelThe dilepton production process at hadron colliders in the Randall-Sundrum (RS) model is studiedat next-to-leading order in QCD. The NLO-QCD corrections have been computed for the virtualgraviton exchange process in the RS model, in addition to the usual Z-mediated processes ofstandard Drell-Yan. K-factors for the cross-sections at the LHC and Tevatron for differential inthe invariant mass, Q, and the rapidity, Y, of the lepton pair are presented. We find the K-factorsare large over substantial regions of the phase space.Prakash Mathews, V Ravindran†, K Sridhar†Theo1.2.2.11 Next-to-leading order QCD corrections to the Drell-Yan cross section inmodels of TeV-scale gravityThe first results on next-to-leading order QCD corrections to graviton-induced processes in hadroncollisions in models of TeV-scale gravity are presented focusing on the case of dilepton pair productionand pp collisions. Distributions in the invariant mass Q, the longitudinal fraction x F , therapidity Y and the forward-backward asymmetry of the lepton pair are studied. The quantitativeimpact of the QCD corrections for searches of extra dimensions at hadron colliders is investigated.It turns out that at the LHC the K-factor is rather large (K = 1.6) for large invariant mass Q of thelepton pair, indicating the importance of accounting for these QCD corrections in the experimentalsearch for TeV-scale gravity. At the Tevatron, the K-factor does not substantially deviate from theStandard Model value. However, its inclusion is necessitated to make the cross section stable withrespect to scale variations.Prakash Mathews, V Ravindran†, K Sridhar†, WL van Neerven†Theo1.2.3 Astrophysics & Cosmology1.2.3.1 Hyperon bulk viscosity and its influence on r-modes of neutron starsWe studied the effect of hyperon matter on bulk viscosity. In this connection, we have constructedequations of state within the framework of a relativistic field theoretical model. As large numberof hyperons may be produced in dense matter, hyperon-hyperon interaction becomes importantand have been included in our calculation. We computed the bulk viscosity coefficient due to thenon-leptonic weak process n + p ⇀↽ p + Λ. It was found that the gravitational radiation drivenr-mode instability was suppressed due to large hyperon bulk viscosity coefficient.Debarati Chatterjee, Debades BandyopadhyayTheo