Nilendra G. Deshpande

The

Abstract.On non-commutative spacetime, the standard model (SM) allows new, usually SM forbidden, triple gauge boson interactions to occur. In this letter we propose the SM strictly forbidden

Z \rightarrow \gamma \gamma,\;gg

Z\rightarrow \gamma\gamma

decays in the non-commutative standard model

and

Universal extra dimensions and b→sγ☆

Z\rightarrow gg

ISOSPIN STRUCTURE OF PENGUIN DIAGRAMS AND THEIR CONSEQUENCES IN B MESON PHYSICS

decay modes coming from the gauge sector of the non-commutative standard model (NCSM) as a place where non-commutativity could be experimentally discovered.

Can extra dimensions accessible to the SM explain the recent measurement of anomalous magnetic moment of the muon

We analyze the effect of flat universal extra dimensions (i.e., extra dimensions accessible to all SM fields) on the process b -> s gamma. With one Higgs doublet, the dominant contribution at one-loop is from Kaluza-Klein (KK) states of the charged would-be-Goldstone boson (WGB) and of the top quark. The resulting constraint on the size of the extra dimension is comparable to the constraint from T parameter. In two-Higgs doublet model II, the contribution of zero-mode and KK states of physical charged Higgs can cancel the contribution from WGB KK states. Therefore, in this model, there is no constraint on the size of the extra dimensions from the process b -> s gamma and also the constraint on the mass of the charged Higgs from this process is weakened compared to 4D. In two Higgs doublet model I, the contribution of the zero-mode and KK states of physical charged Higgs and that of the KK states of WGB are of the same sign. Thus, in this model and for small tan beta, the constraint on the size of the extra dimensions is stronger than in one Higgs doublet model and also the constraint on the mass of the charged Higgs is stronger than in 4D.

Hadronic penguin B decays in the standard and the two-Higgs-doublet models

Isospin structure of electroweak penguin diagrams is different from the gluon-mediated or strong penguin. Given the large top mass, these electroweak contributions are significant. This has the consequence that some previous analyses which relied on a simple isospin structure in charmless [ital B] meson decays become inapplicable. We present the general Hamiltonian in next-to-leading order QCD, and illustrate our conclusion quantitatively for [ital B][r arrow][pi][pi] and [ital B][r arrow][ital K][pi] decays in the factorization approximation. Some remarks on [ital CP] asymmetries in [ital B] meson decays are also made.

Flavor-changing electromagnetic vertex in a non-linear Rξ gauge

Abstract We investigate whether models with flat extra dimensions in which SM fields propagate can give a significant contribution to the anomalous magnetic moment of the muon (MMM). In models with only SM gauge and Higgs fields in the bulk, the contribution to the MMM from Kaluza–Klein (KK) excitations of gauge bosons is very small. This is due to the constraint on the size of the extra dimensions from tree-level effects of KK excitations of gauge bosons on precision electroweak observables such as Fermi constant. If the quarks and leptons are also allowed to propagate in the (same) bulk (“universal” extra dimensions), then there are no contributions to precision electroweak observables at tree-level. However, in this case, the constraint from one-loop contribution of KK excitations of (mainly) the top quark to T parameter again implies that the contribution to the MMM is small. We show that in models with leptons, electroweak gauge and Higgs fields propagating in the (same) bulk, but with quarks and gluon propagating in a sub-space of this bulk, both the above constraints can be relaxed. However, with only one Higgs doublet, the constraint from the process b→sγ requires the contribution to the MMM to be smaller than the SM electroweak correction. This constraint can be relaxed in models with more than one Higgs doublet.

Limits on low scale gravity from e+e−→W+W−, ZZ and γγ

Abstract We study in next-to-leading order QCD hadronic penguin B decays in the Standard and two-Higgs-doublet models. Although the gluonic penguin dominates, we find the electroweak contribution non-negligible. In the Standard Model, the branching ratio for B → X s φ is predicted to be in the range (0.6–2) × 10 −4 . The ranges of branching ratios for B → Kφ B → K ∗ φ , and B s → φφ are (0.4−2) × 10 −5 , (0.2−1) × 10 −5 , and (0.15−0.5) × 10 −5 , respectively. The contribution from the charged Higgs boson in two Higgs doublet models depend on cot β, and can be as large as 40%.

Final State Gluon Effects in Charmed Meson Decays

Abstract We calculate the general transition q i → q j + γ for arbitrary quark flavors in a non-linear R ξ gauge. The reduced number of Feynman diagrams as well as simplified Ward identities greatly facilitates this calculation. A general result with intermediate quarks of arbitrary mass is presented and the special cases s → d + γ as well as s → d + gluon are discussed.