arXiv subjects
Publications and source records attributed to G. C. Joshi.
We have investigated the detailed structure of $l$-plane singularities of scattering amplitude saturating the Froissart bound. A self-consistent analysis of these singularities provides us secondary terms in the Froissart bound. These secondary terms lead to ghosts in the $l$-plane, which can only be removed by introducing an odderon singularity. Phenomenological implications of this analysis are also discussed.
In this paper we study the angular distribution of the rare B decay $B \to K^*_2 (\to K π) l^+ l^-$, which is expected to be observed soon. We use the standard effective Hamiltonian approach, and use the form factors that have already been estimated for the corresponding radiative decay $B \to K^*_2 γ$. The additional form factors that come into play for the dileptonic channel are estimated using the large energy effective theory (LEET), which enables one to relate the additional form factors to the form factors for the radiative mode. Our results provide, just like in the case of the $K^*(892)$ resonance, an opportunity for a straightforward comparison of the basic theory with experimental results which may be expected in the near future for this channel.
The role mathematics plays within physics has been of sustained interest for physicists as well as for philosophers and historians of science. We explore this topic by tracing the role the mathematical structure associated with SU(2) has played in three key episodes in 20th century physics - intrinsic spin, isospin, and gauge theory and electro-weak unification. We also briefly consider its role in loop quantum gravity. Each episode has led to new physical notions of a space other than the traditional ones of space and spacetime, and each has had associated with it a complex and in places, contested history. The episodes also reveal ways mathematical structures provide resources for new physical theorizing and we propose our study as a contribution to a need Roger Penrose has identified to develop a "profoundly sensitive aesthetic" sense for locating physically relevant mathematics.
Black holes at the TeV scale are investigated in the extra large dimension scenario. We interpret the lightest black hole excitation as a singlet scalar field, and show how interaction terms can be appended to the standard model at the dimension five non-renormalizable level. Lepton family number violation is natural in this model. Muon magnetic moment, and neutrino masses are investigated. We also present a quantization scheme in n dimensions.
Leptonic decays of $B$-mesons are theoretically very clean probes for testing the Standard Model (SM) and possible physics beyond it. Amongst the various leptonic decays of the $B$-meson, the pure dileptonic decay $B \to \ell^+ \ell^-$ is very important as this mode is helicity suppressed in the SM but can be substantially enhanced in some of the models beyond the SM, such as supersymmetric (SUSY) theories and the two Higgs doublet model (2HDM). Although the purely dileptonic decay mode is helicity suppressed in the SM its associated mode $B \to \ell^+ \ell^- γ$ does not have the same suppression, due to the presence of the $γ$ in the final state. In this paper we will also analyse the effects of enhanced $Z$-penguins on these two decay modes.
We study the neutral current flavour changing rare decay mode $B\to K γγ$ within the framework of Standard Model, including the long distance contributions. It is found that these long distance contributions can larger than the short distance contribution.
Little Higgs models provides us a new solution of the {\it hierarchy problem} of the SM. The problem is associated with the large difference in scales of SM and plank scale. One of the main features of these models is the existence of a vector like top quark. The CP violating $K_L \to π^0 ν\barν$ process n the SM model is dominated by top quark penguin & box graphs. We examine this process in the Little Higgs model where the top quark sector has significant differences from the Standard Model.
Within the framework of Standard Model, the exclusive decay mode $B\to πγγ$ is studied. Although the usual short distance contribution is small compared to the similar $B\to Kγγ$ mode, the process offers the possibility of studying the CP violation, a feature absent in the $B \to K$ counterpart.
Leptonic and semi-leptonic rare decays of B-mesons are very clean (both theoretically and experimentally) signatures of any new physics beyond the Standard Model (SM). More specifically the decay \btokll has been theoretically observed to be very sensitive to new physics as the Forward Backward (FB) asymmetry in this decay mode vanishes in the SM. Supersymmetry, however, predicts a non-vanishing value of this asymmetry. In this work we will study the polarized lepton pair FB asymmetry, i.e. the FB asymmetry of the lepton when one (or both) final state lepton(s) are polarized. We will study these asymmetries both within the SM and for Supersymmetric corrections to the SM.
This paper has being withdrawn by the authors due to an error in the conclusion.
In this work we will study the polarizations of both leptons ($τ$) in the decay channel $B\to K^* τ^- τ^+$. In the case of the dileptonic inclusive decay $B\to K^* \ell^- \ell^+$, where apart from the polarization asymmetries of single lepton $\ell$, one can also observe the polarization asymmetries of both leptons simultaneously. If this sort of measurement is possible then we can have, apart from decay rate, FB asymmetry and the six single lepton polarization asymmetries (three each for $\ell^-$ and $\ell^+$), nine more double polarization asymmetries. This will give us a very useful tool in more strict testing of SM and the physics beyond. We discuss the double polarization asymmetries of $τ$ leptons in the decay mode $B\to K^* τ^- τ^+$ within the SM and the Minimal Supersymmetric extensions of it.
We report the results of the first computation related to the study of the spectator effects in the rare decay mode $B\to K γγ$ within the framework of Standard Model. It is found that the account of these effects results in the enhancement factor for the short-distance reducible contribution to the branching ratio.
In this paper we shall study the phenomenology of a doubly charged and neutral exchange black hole in an $(n+3)$ extra-dimensional scenario, where the black hole shall be treated a normal quantum field.
The nature of the modification to neutrino lensing from galaxies, as caused by possible modifications to Newtonian gravity at large distances, is studied.
We have studied a modified Yang-Mills-Higgs system coupled to Einstein gravity. The modification of the Einstein-Hilbert action involves a direct coupling of the Higgs field to the scalar curvature. In this modified system we are able to write a Bogomol'nyi type condition in curved space and demonstrate that the positive static energy functional is bounded from below. We then investigate non-Abelian sperically symmetric static solutions in a similar fashion to the `t Hooft-Polyakov monopole. After reviewing previously studied monopole solutions of this type, we extend the formalism to included electric charge and we present dyon solutions.
The modifications induced in the standard weak-lensing formula if Newtonian gravity differs from inverse square law at large distances are studied. The possibility of putting bounds on the mass of gravitons from lensing data is explored. A bound on graviton mass, esitmated to be about 100 Mpc$^{-1}$ is obtained from analysis of some recent data on gravitational lensing.
We consider the effect of massive spin-2 gravitons that occur as Kaluza-Klein excitations of the graviton in a Weak scale Quantum Gravity scenario on the process $γγ\to ZZ$, which in the Standard Model can proceed through loop diagrams. For a wide range of parameters, we show that the massive gravitons leave behind signatures that should be verifiable in a TeV scale scattering experiment.
The spin-2 graviton excitations in the Randall-Sundrum gravity model provides a t-channel contribution to electron Compton scattering which competes favourably with the standard QED contributions. The phenomenological implications of these contributions to the unpolarized and polarized cross-sections are evaluated.