Biennial Report 2005-2007 - Saha Institute of Nuclear Physics

10 Biennial Report 2005-071.2.3.2 Exotica in rotating compact starsWe constructed models of static and uniformly rotating compact stars using equation of state(EoS) including hyperons, first order nuclear to K − condensed matter phase transition and alsoK − condensed matter to quark matter phase transition. Our results are consistent with the massand radius of EXO 0748-676. This, in turn, showed that exotic matter such as hyperon and Bose-Einstein condensed matter might exist in this star. Also, we estimated the moment of inertiafor pulsar A of double pulsar binary PSR J0737-3039. It was found that the values of moment ofinertia and radius obtained with our relativistic EoS were quite different from those of nonrelativisticmodels. Therefore, it would be possible to rule out some EoS with the help of the measured valueof moment of inertia.Debarati Chatterjee, Sarmistha Banik, Debades BandyopadhyayTheo1.2.3.3 Possible Common Origin of the Highest Energy Cosmic Rays and BaryonAsymmetry of the UniverseIt is well-known that the small (sub-eV) neutrino masses inferred from neutrino oscillation experimentscan be explained most naturally through the see-saw mechanism involving a heavy righthandedmajorana neutrino, N R , for every generation. This can be done most simply by extendingthe Standard Model by an extra U(1) B−L gauge symmetry which is spontaneously broken at a sufficientlyhigh energy scale η B−L thereby giving large mass to the N R and consequently small massto the usual left-handed neutrinos through the see-saw mechanism. In this work it is shown that thedecay of the massive gauge bosons, higgs bosons as well as the heavy N R ’s (collectively X particleshereafter) released from rapidly collapsing closed loops of “B − L” cosmic strings arising from theU(1) B−L symmetry-breaking phase transition can provide, for X particle masses ≥ 10 11 GeV, a“top-down” mechanism of production of the observed extremely high energy cosmic ray particleswith energies above 10 11 GeV which are otherwise difficult to produce by means of the standardacceleration mechanisms operating in known astrophysical objects. At the same time the decay ofthe N R ’s released from the B − L cosmic string loops can give a non-thermal contribution to theobserved Baryon Asymmetry of the Universe through the leptogenesis route, ameliorating some ofthe problems of the purely thermal leptogenesis scenario. Thus, the observed baryon asymmetry ofthe Universe, the extremely high energy cosmic rays (EHECR) above 10 11 GeV and small neutrinomasses inferred from neutrino oscillation experiments, all may have a common origin in a U(1) B−Lsymmetry-breaking phase transition in the early Universe.Pijushpani BhattacharjeeTheo1.2.3.4 Baryogenesis via leptogenesis in presence of cosmic stringsThe effect of B −L cosmic strings (in a U(1) B−L extension of the Standard Model) on leptogenesisis studied in detail. The disappearance of closed loops of B − L cosmic strings can produce heavyright handed neutrinos, N R ’s, whose CP-asymmetric decay in out-of-thermal equilibrium conditioncan give rise to a net lepton (L) asymmetry which is then converted, due to sphaleron transitions,to a Baryon (B) asymmetry. This is studied by using the relevant Boltzmann equations andincluding the effects of both thermal and string generated non-thermal N R ’s. The parameter space