arXiv subjects
Publications and source records attributed to N. G. Deshpande.
We consider the branching ratio of $b \to sγ$ in gauge mediated supersymmetry breaking theories. Useful bounds on the parameter space of these models are derived from the experimental bounds on $b \to sγ$. Constraints on masses of NLSP are presented as a function of $tanβ$ and $M/Λ$ for $μ<0$ and $μ>0$.
We show how an intermediate gauge symmetry breaking scale can be a source of lepton flavor violation and EDM of electron and neutron in SUSY GUTs. The Universal soft supersymmetry breaking operators can be introduced at the GUT scale or above.
We present a model based on the gauge group SU(2)_L\times SU(2)_R \times SU(4)_C with gauge couplings that are found to be unified at a scale near the string unification scale. This model breaks to the MSSM at an intermediate scale which is instrumental in producing a neutrino in a mass range that can serve as hot dark matter and can also solve the strong CP problem via a harmless invisible axion.
We consider the origin of new phases in supersymmetric grand unification model, and show how significant new contributions arise from the gluino mediated diagram. We then present a more general model independent analysis of various modes of B-decays suggested previously for measurement of the CKM phases and point out what they really measure. It is in principle possible to separate out all the phases.
We discuss the production of lepton flavor violation and EDMs and the viability of the $b-τ$ unification hypothesis in SUSY grand unification with an intermediate gauge symmetry breaking scale.
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.
We propose two independent methods to determine the CKM phase $γ$ and the tree and penguin amplitudes using neutral $B$ decays, assuming that the phase $β$ is known. Based on flavor SU(3) symmetry and SU(3) breaking effect, one method uses the decay processes $B^0(t) \rightarrow π^0 K_S$, $B^0 \rightarrow ηK^0 \; (K_S \rightarrow ππ)$ and their charge-conjugate processes, and the other uses the processes $B^0(t) \rightarrow π^0 K_S$, $B^0 \rightarrow π^0 π^0$ and their charge-conjugate processes. From SU(3) breaking consideration, the latter method would be more useful.
We show that an intermediate gauge symmetry breaking scale can be a significant source of electric dipole moments for the electron and neutron in supersymmetric grand unified theories. New phases, similar to that of the CKM matrix, appear which do not arise from the supersymmetry (SUSY) breaking operators. To illustrate, we choose some grand unified SUSY models having an intermediate gauge symmetry breaking scale with some attractive features. We also show how well the $b-τ$ unification hypothesis works in this class of models.
In supersymmetric SO(10) grand unified models, we examine the lepton flavor violation process $μ\rightarrow eγ$ from having the SU(2)$_R\times $U(1)$_{B-L}$ gauge symmetry broken at an intermediate scale $M_I$ below the SO(10) grand unification scale $M_G$. Even in the case that supersymmetry is broken by universal soft terms introduced at the scale $M_G$, we find significant rates for $μ\rightarrow eγ$ with $M_I \sim 10^{12}$ GeV or less. These rates are further enhanced if the universal soft terms appear at a scale greater than $M_G$.
We present a method to measure the CKM phase $α$ and the tree and penguin (strong and electroweak) amplitudes in $B \rightarrow ππ$ decays, based on isospin consideration and the weak assumption that all tree amplitudes have a common strong phase and all penguin amplitudes have a different common phase. The method needs only the time-independent measurements of the relevant decay rates in $B \rightarrow ππ$. We also propose a method to experimentally examine the validity of the assumption that all penguin amplitudes have the same strong phases, and to extract detailed informations about the hadronic matrix elements.
We present a model based on the gauge group SU(2)$_L\times$SU(2)$_R\times$SU(4)$_C$ with gauge couplings that are found to be unified at a scale $M_G$ near the string unification scale. The model breaks to the minimal supersymmetric standard model at a scale $M_I\sim 10^{12}$ GeV, which is instrumental in producing a neutrino in a mass range that can serve as hot dark matter and this scale can also solve the strong CP problem via Peccei-Quinn (PQ) mechanism with an invisible harmless invisible axion. We show how this model can accommodate low and high values of $\tanβ$ and ``exotic" representations that often occur in string derived models. We show that this model has lepton flavor violation which can lead to processes which are one or two orders of magnitude below the current experimental limits.
Contrary to the conventional belief, time integrated asymmetry are measurable in selected final states in the neutral $B$ system at symmetric $e^+e^-$ colliders. They occur due to the interplay of weak and strong phases of two different amplitudes in addition to the $B^0 - \bar B^0$ mixing. Observation of these asymmetries would be evidence for direct CP violation in the decay amplitudes.
We study the influence of penguin (especially, electroweak penguin) effects on some methods of measuring the angles $α$, $β$, and $γ$ in the CKM unitarity triangle. We use next-to-leading order effective Hamiltonian, and present numerical estimates based on the factorization approximation. We find that some techniques suggested in the literature, especially for $α$ determination, are not workable in light of the electroweak penguin effects. Nevertheless, there are methods that would work for each angle determination. For angle $β$ we consider $B \rightarrow D^{+} D^{-}$ mode and estimate the penguin contamination. For angle $γ$ we consider a method based on SU(3) symmetry and carefully consider SU(3) breaking effects. We point out regions in the parameter space where this method could be used reliably.
The importance of dipole penguin operator, $O_{11} = (g_s/8π^2)m_b \bar s σ_{μν}RT^a b G^{μν}_a$, on B decays is demonstrated. It is shown that branching ratios for the inclusive decay $b\to s s\bar s$, the semi-inclusive decay $b\to sϕ$, and the exclusive decay $B\to πK$ are enhanced by 20% to 30%. A useful consequence of this calculation is the inclusive $b\to ss\bar s$ spectrum which will be essential in isolating pure penguin process.
A new way of determining the phases of weak amplitudes in charged $B$ decays based on SU(3) symmetry is proposed. The CP violating phase $γ$ can now be determined without the previous difficulty associated with electroweak penguins.
We study the energy distribution of $ϕ$ in pure penguin induced $B\rightarrow X_s ϕ$ taking into account the fermi motion of b inside $B$ meson for $b\rightarrow sϕ$ and also modification due to gluon bremsstrahlung process $b\rightarrow sϕg$. We find that the contribution to $B\rightarrow X_sϕ$ from $b\rightarrow sϕg$ is less than 3\%. This study provides a criterion for including most of the $ϕ$'s produced in a penguin process.
Electroweak penguin operators become important when $m_t \approx 174$ GeV. We discuss their implications for measuring CP violating phases $α$, $β$ and $γ$.
We prove that CP violating rate difference $Δ(\bar B^0 \rightarrow π^+π^-) = Γ(\bar B^0 \rightarrow π^+π^-) - Γ( B^0 \rightarrow π^-π^+)$ is related to $Δ(\bar B^0 \rightarrow π^+ K^-) = Γ(\bar B^0 \rightarrow π^+K^-) - Γ(B^0 \rightarrow π^-K^+)$ in the three generation Standard Model. Neglecting small annihilation diagrams, and in the SU(3) symmetry limit, we show $Δ(\bar B^0 \rightarrow π^+π^-) = - Δ(\bar B^0 \rightarrow π^+ K^-)$. The SU(3) breaking effects are estimated using factorization approximation, and yield $Δ(\bar B^0\rightarrow π^+π^-) \approx -(f_π/f_K)^2Δ(\bar B^0 \rightarrow π^+K^-)$. Usefulness of this remarkable relation for determining phases in the CKM unitarity triangle is discussed.