arXiv subjects

K. Agashe

Publications and source records attributed to K. Agashe.

23 records · Page 2Linked to original sources

arXiv1999

Determining the Weak Phase $γ$ in the Presence of Rescattering

We suggest a new technique to determine the CKM phase $γ$ {\em without} neglecting the (soft) final state rescattering effects. We use (time integrated) $B$ meson decay rates to $π$'s and $K$'s. A set of 5 $ΔS = 0$ (or 1 $ΔS =0$ and 4 $ΔS= 1$) decay rates is used to compute the strong phases and magnitudes of the tree level and penguin contributions as functions of $γ$. These are used to {\em predict} a $ΔS = 1$ $(ΔS = 0) B_{d/s}$ decay rate as a function of $γ$ (using SU(3) symmetry). The measurement of this decay rate then gives $γ$. We illustrate this technique using different cases. Most of the decay modes we use are expected to be accessible at the B-factories (e^+ e^- or hadron machines).

hep-ph↗

arXiv1998

Supersymmetry Breaking and the Supersymmetric Flavour Problem: An Analysis of Decoupling the First Two Generation Scalars

The supersymmetric contributions to the Flavor Changing Neutral Current processes may be suppressed by decoupling the scalars of the first and second generations. It is known, however, that the heavy scalars drive the stop mass squareds negative through the two-loop Renormalization Group evolution. This tension is studied in detail. Two new items are included in this analysis: the effect of the top quark Yukawa coupling and the QCD corrections to the supersymmetric contributions to $Δm_K$. Even with Cabibbo-like degeneracy between the squarks of the first two generations, these squarks must be heavier than $\sim 40$ TeV to suppress $Δm_K$. This implies, in the case of a high scale of supersymmetry breaking, that the boundary value of the stop mass has to be greater than $\sim 7$ TeV to keep the stop mass squared positive at the weak scale. Low-energy supersymmetry breaking at a scale that is of the same order as the mass of the heavy scalars is also considered. In this case the finite parts of the two-loop diagrams are computed to estimate the contribution of the heavy scalar masses to the stop mass squared. It is found that for Cabibbo-like mixing between the squarks, the stop mass at the boundary needs to be larger than $\sim 2$ TeV. Thus, for both cases, the large boundary value of the stop masses leads to an unnatural amount of fine tuning to obtain the correct $Z$ mass.

hep-ph↗

arXiv1997

Improving the Fine Tuning in Models of Low Energy Gauge Mediated Supersymmetry Breaking

The fine tuning in models of low energy gauge mediated supersymmetry breaking required to obtain the correct $Z$ mass is quantified. To alleviate the fine tuning problem, a model with split $(5+\bar{5})$ messenger fields is presented. This model has additional triplets in the low energy theory which get a mass of $O(500)$ GeV from a coupling to a singlet. The improvement in fine tuning is quantified and the spectrum in this model is discussed. The same model with the above singlet coupled to the Higgs doublets to generate the $μ$ term is also discussed. A Grand Unified version of the model is constructed and a known doublet-triplet splitting mechanism is used to split the messenger $(5+\bar{5})$'s. A complete model is presented and some phenomenological constraints are discussed.

hep-ph↗

arXiv1996

A Consistent model of Electroweak data including $Z\to b\overline{b}$ and $Z\to c \overline{c}$

We have performed an overall fit to the electroweak data with the generation blind $U(1)$ extension of the Standard Model. As input data for fitting we have included the asymmetry parameters, the particle decay widths of $Z$, neutrino scattering, and atomic parity violation. The QCD coupling $α_s$ has been constrained to the world average obtained from all data except the $Z$ width. On the basis of our fit we have constructed a viable gauge model that not only explains $R_b$ and $R_c$ but also provides a much better overall fit to the data than the Standard Model. Despite its phenomenological viability, our model is unfortunately not simple from the theoretical viewpoint. Atomic parity violation experiments strongly disfavor more aesthetically appealing alternatives that can be grand unified.

hep-ph↗

arXiv1995

$R$-Parity Violation in Flavor Changing Neutral Current Processes and Top Quark Decays

We show that supersymmetric $R$-parity breaking ($\not R_p$) interactions always result in Flavor Changing Neutral Current (FCNC) processes. Within a single coupling scheme, these processes can be avoided in either the charge $+2/3$ or the charge $-1/3$ quark sector, but not both. These processes are used to place constraints on \Rp couplings. The constraints on the first and the second generations are better than those existing in the literature. The \Rp interactions may result in new top quark decays. Some of these violate electron-muon universality or produce a surplus of $b$ quark events in $t\bar{t}$ decays. Results from the CDF experiment are used to bound these \Rp couplings.

hep-ph↗