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Sandip Pakvasa

Publications and source records attributed to Sandip Pakvasa.

At least 73 records · Page 4Linked to original sources
arXiv1998

Large CP Violation in $B\to K^{(*)} X$ Decays

We consider the possibility of observing CP violation in quasi-inclusive decays of the type $B^-\to K^- X$, $B^-\to K^{*-} X$, $\bar B^0\to K^- X$ and $\bar B^0\to K^{*-} X$, where $X$ does not contain strange quarks. We present estimates of rates and asymmetries for these decays in the Standard Model and comment on the experimental feasibility of observing CP violation in these decays at future $B$ factories. We find the rate asymmetries can be quite sizeable.

hep-ph↗
arXiv1997

Up-Down Asymmetry: A Diagnostic for Neutrino Oscillations

We propose a simple test of underground neutrino data to discriminate amongst neutrino oscillation models. It uses the asymmetry between downward-going events and upward-going events, for electron and muon events separately. Because of the symmetry of typical underground detectors, an asymmetry can be compared with calculations with little need for the intermediary of a simulation program. Furthermore, we show that the various oscillation scenarios give rise to dramatically differing trajectories of asymmetry versus energy for muons and electrons. This permits a clean distinction to be drawn between models.

hep-ph↗
arXiv1997

Pion-Nucleon Phase Shifts in Heavy Baryon Chiral Perturbation Theory

We calculate the phase shifts in the pion-nucleon scattering using the heavy baryon formalism. We consider phase shifts for the pion energy range of 140 to $200 $ MeV. We employ two different methods for calculating the phase shifts - the first using the full third order calculation of the pion-nucleon scattering amplitude and the second by including the resonances $Δ$ and $N^*$ as explicit degrees of freedom in the Lagrangian. We compare the results of the two methods with phase shifts extracted from fits to the pion-nucleon scattering data. We find good to fair agreement between the calculations and the phase shifts from scattering data.

hep-ph↗
arXiv1996

Single Isospin Decay Amplitude and CP Violation

We study partial rate asymmetry in decays with single isospin final state. For K meson or hyperon decays, the partial rate asymmetries are always zero if the final states are single isospin states. In B decays the situation is dramatically different and partial rate asymmetries can be non-zero even if the final states are single isospin states. We calculated partial rate asymmetries for several B decays with single isospin amplitude in the final states using factorization approximation. We find that in some cases the asymmetries can be large.

hep-ph↗
arXiv1996

Sonoluminescence in Neutron Stars

After a brief discussion of a possible relationship between the electroweak phase transition in highly compressed matter and gravitational collapse, we examine the speculative possibility that the electroweak phase transition might be contemporarily occurring in processes in neutron stars. We conjecture that adiabatic compression of neutron star matter due to focusing of the energy from a supernova bounce into a very small volume could result in extreme densities, and Fermi levels or temperature above $\cal{O}$ (100 GeV). We propose a qualitative scenario for sonoluminescence in neutron stars and discuss possible observable consequences.

astro-ph↗
arXiv1995

Radiative Weak Decays of Charm Mesons

We address Standard Model predictions for flavor-changing radiative transitions of the pseudoscalar charm mesons. Short-distance contributions in $D$ radiative transitions are contrasted with those in B decays. A full analysis is presented of the $c\to u+γ$ electromagnetic penguin amplitude with QCD radiative corrections included. Given the importance of long-range effects for the charm sector, special attention is paid to such contributions as the vector dominance and pole amplitudes. A number of two-body final states in exclusive charm radiative decays is considered and the corresponding branching ratio predictions are given.

hep-ph↗
arXiv1994

CP Violation In Hyperon Decays Due To Left-Right Mixing

We consider CP violation due to left-right mixing in a class of Left-Right symmetric models and show that it leads to observable effects in hyperon decays. For S-wave, the contribution to CP violating asymmetry A of the polarization in hyperon and anti-hyperon decays is proportional to $ε'/ε$. While the tree level L-R operators contribution is constrained to be less than $ 10^{-5}$, the gluon penguin operator contribution can be as large as $10^{-4}$. For P-wave, the contribution is not directly related to $ε'/ε$. Its contribution to A can be larger and may reach $6\times 10^{-4}$ in $Λ\rightarrow pπ^-$. This is much larger than the value expected for A in the Standard Model.

hep-ph↗
arXiv1994

S-wave phase shift in Lambda-pi scattering

We calculate the s-wave strong interaction $Λ$$π$ phase shift at the $Ξ$ mass taking into account contributions from the ${{\frac{1}{2}}}^{-}$ and ${{\frac{3}{2}}}^{-}$ $Σ$ resonances. We find the S-wave phase shift to be small, of the order of 0.3 degrees and bounded by 0.5 degrees.

hep-ph↗
arXiv1994

Uncertainties from Long Range Effects in $B \to K^* γ

We reconsider the `long-range' component of the radiative transition $B \to K^* γ$. A careful analysis of the vector dominance amplitude $B \to V_1 V_2 \to V_1 γ$ is carried out, with emphasis on the role of gauge invariance. The procedure for incorporating phenomenological $B\to V_1 V_2$ data is identified and polarization data, only recently available, is employed to estimate the magnitude of the vector dominance effect. We summarize uncertainties in the $B\to K^*γ$ radiative transition produced by long-range effects and provide sugggestions for further experimental work.

hep-ph↗
arXiv1994

Charm as Probe of New Physics

In this talk I would like to discuss two aspects of charm physics. One is to show that many standard model predictions for rare decay modes (along with $D^0 -\bar{D}^0$ mixing and CP violation) are extremely small thus opening a window for new physics effects\cite{1}; and the other is to review the expectations from several plausible and interesting new physics possibilities.

hep-ph↗
arXiv1994

Detecting Nutau Oscillations as PeV Energies

It is suggested that a large deep underocean neutrino detector, given the presence of significant numbers of neutrinos in the PeV range as predicted by various models of Active Galactic Nuclei, can make unique measurements of the properties of neutrinos. It will be possible to observe the existence of the nu_tau, measure its mixing with other flavors, in fact test the mixing pattern for all three flavors based upon the mixing parameters suggested by the atmospheric and solar neutrino data, and measure the nu_tau cross section. The key signature is the charged current nu_tau interaction, which produces a double cascade, one at either end of a minimum ionizing track. At a few PeV these cascades would be separated by roughly 100 m, and thus be easily resolvable in DUMAND and similar detectors. Future applications are precise neutrino astronomy and earth tomography.

hep-ph↗
arXiv1994

Corrections to mass scale predictions in SO(10) GUT with higher dimensional operators

We calculate the two loop contribution to the predictions of the mass scales in an SO(10) grand unified theory. We consider the modified unification scale boundary conditions due to the non-renormalizable higher dimensional terms arising from quantum gravity or spontaneous compactification of extra dimensions in Kaluza-Klein type theory. We find the range of these couplings which allows left-right symmetry to survive till very low energy (as low as $\sim$ TeV) and still be compatible with the latest values of $\sin^2 θ_W$ and $α_s$ derived from LEP. We consider both the situation when the left-right parity is broken and conserved.We consider both supersymmetric and non-supersymmertic versions of the SO(10) theory.Taking the D-conserved non-susy case as an example we calculate the effects of moderate threshold uncertainties at the heavy scale, due to the unknown higgs masses,on the gravity induced couplings.

hep-ph↗
arXiv1993

Solar Neutrino Decay

We re-examine the neutrino decay solution to the solar neutrino problem in light of the new data from Gallex II and Kamiokande III. We compare the experimental data with the solar models of Bahcall and Pinsonneault and Turck-Chieze and find that neutrino decay is ruled out as a solution to the solar neutrino problem at better than the 98\% c.l. even when solar model uncertainties are taken into account.

hep-ph↗