arXiv subjects

N. G. Deshpande

Publications and source records attributed to N. G. Deshpande.

At least 55 records · Page 3Linked to original sources

arXiv2003

Higgs pair production in association with a vector boson at e+e- colliders in theories of higher dimensional gravity

The models of large extra compact dimensions, as suggested by Arkani-Hamed, Dimopoulos and Dvali, predict exciting phenomenological consequences with gravitational interactions becoming strong at the TeV scale. Such theories can be tested at the existing and future colliders. In this paper, we study the contribution of virtual Kaluza-Klein excitations (both spin-0 and 2) in the process $e^+e^- \to HHZ$ and $ e^+e^- \to HHγ$ at future linear collider (NLC). We find that the virtual exchange KK gravitons can modify the cross-section $σ(e^+e^- \to HHZ)$ significantly from its Standard Model value and will allow the effective string scale to be probed up to 6.6 TeV. The second process is absent at the tree level in the standard model, and can therefore be used to put limits on the effective string scale of 7.4 TeV.

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arXiv2002

CP Violating Rate Difference Relations for $B\to PP$ and $B \to PV$ in Broken SU(3)

Within the standard model there exist certain relations between CP violating rate differences in B decays in the SU(3) limit. We study SU(3) breaking corrections to these relations in the case of charmless, hadronic, two body $B$ decays using the improved factorization model of Ref.\cite{3}. We consider the cases $B \to PP$ and $B \to PV$ for both $B_d$ and $B_s$ mesons. We present an estimate for $A_{CP}(π^- π^+)$ in terms of $A_{CP}(K^- π^+)$.

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arXiv2002

Weak Phase gamma Using Isospin Analysis and Time Dependent Asymmetry in B_d -> K_s pi^+ pi^-

We present a method for measuring the weak phase gamma using isospin analysis of three body B decays into K pi pi channels. Differential decay widths and time dependent asymmetry in B_d -> K_s pi^+pi^- mode needs to be measured into even isospin pi pi states. The method can be used to extract gamma, as well as, the size of the electroweak penguin contributions. The technique is free from assumptions like SU(3) or neglect of any contributions to the decay amplitudes. By studying different regions of the Dalitz plot, it is possible to reduce the ambiguity in the value of gamma.

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arXiv2001

Triple Neutral Gauge Boson Couplings in Noncommutative Standard Model

It has been shown recently that the triple neutral gauge boson couplings are not uniquely determined in noncommutative extension of the Standard Model (NCSM). Depending on specific schemes used, the couplings are different and may even be zero. To distinguish different realizations of the NCSM, additional information either from theoretical or experimental considerations is needed. In this paper we show that these couplings can be uniquely determined from considerations of unification of electroweak and strong interactions. Using SU(5) as the underlying theory and integrating out the heavy degrees of freedom, we obtain unique non-zero new triple $γγγ$, $γγZ$, $γZZ$, $ZZZ$, $γGG$, $ZGG$ and $GGG$ couplings at the leading order in the NCSM. We also briefly discuss experimental implications.

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arXiv2001

Universal Extra Dimensions and b -> s gamma

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.

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arXiv2001

Muon Anomalous $g -2$ and Gauged $L_μ- L_τ$ Models

In this paper we study $Z'$ contribution to $g -2$ of the muon anomalous magnetic dipole moment in gauged $U(1)_{L_μ- L_τ}$ models. Here $L_i$ are the lepton numbers. We find that there are three classes of models which can produce a large value of $g-2$ to account for possible discrepancy between the experimental data and the Standard Model prediction. The three classes are: a) Models with an exact $U(1)_{L_μ- L_τ}$. In these models, $Z'$ is massless. The new gauge interaction coupling $e a/\cosθ_W$ is constrained to be $ 0.8\times 10^{-3} < |a| < 2.24\times 10^{-3}$. b) Models with broken $U(1)_{L_μ- L_τ}$ and the breaking scale is not related to electroweak symmetry breaking scale. The $Z'$ gauge boson is massive. The allowed range of the coupling and the $Z'$ mass are constrained, but $Z'$ mass can be large; And c) The $U(1)_{L_μ-L_τ}$ is broken and the breaking scale is related to the electroweak scale. In this case the $Z'$ mass is constrained to be $\sim 1.2$ GeV. We find that there are interesting experimental signatures in $μ^+μ^-\to μ^+μ^-, τ^+τ^-$ in these models.

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arXiv2001

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

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 -> s gamma 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.

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arXiv2000

Charged Higgs decays in models with singlet neutrino in large extra dimensions

In models with large extra dimensions and TeV scale quantum gravity, small (Dirac) neutrino masses can be obtained naturally if the right-handed neutrino propagates in the extra dimensions. In this scenario, with 2 Higgs doublets, we show that the decay of charged Higgs into {\em left-handed} charged lepton (say τ) and right-handed neutrino can be significantly enhanced, with O(1) branching ratio, due to the large number of Kaluza-Klein states of the right-handed neutrino. Since τ's from the standard decay of charged Higgs are {\em right-handed}, the above novel charged Higgs decay can provide a distinctive signature of these models at hadron/lepton colliders. Similarly, top quark decays to b μ^+ ν, b τ^+ νthrough virtual charged Higgs can be enhanced.

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arXiv2000

SU(3) Flavor Symmetry and CP Violating Rate Differences for Charmless $B\to P V$ Decays

We derive several relations between CP violating rate differences $Δ(B\to PV) = Γ(B\to PV) - Γ(\bar B \to \bar P \bar V)$ for charmless $B\to P V$ decays in the Standard Model using SU(3) flavor symmetry. It is found that although the relations between branching ratios of $ΔS = 0$ and $ΔS = -1$ processes are complicated, there are simple relations independent of hadronic models between some of the $ΔS =0$ and $ΔS = -1$ rate differences due to the unitarity property of the Kobayashi-Maskawa matrix, such as $ Δ(B\to π^+ ρ^-) = -Δ(B\to π^+ K^{*-})$, $Δ(B\to π^- ρ^+) = - Δ(K^- ρ^+)$. SU(3) breaking effects are also estimated using factorization approximation. These relations can be tested at B factories in the near future.

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arXiv2000

Penguins and Mixing Dependent CP Violation

Constraints on angles of Unitarity triangle are reviewed, and in particular constraint on $γ$ from limit on $Δm_s$ is emphasized. Effects of penguin diagram on measurement of $β$ and $α$ are then reviewed. New measurements on $B \to π^+π^-$ in QCD improved factorization approximation suggest large penguin effects. It is possible to estimate the error in measurement of $α$ as a function of $γ$ for different $|V_{ub} /V_{cb}|$ values.

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arXiv1999

CLEO measurement of $B \to π^+ π^-$ and determination of weak phase $α$

The CLEO collaboration has recently reported a (first) measurement of $BR (B \to π^+ π^-) = (4.7^{+1.8}_{-1.5} \pm 0.6) \times 10^{-6}$. We study, using recent results on QCD improved factorization, the implications of this measurement for the determination of the CKM phase $α$ and also for the rate for $B \to π^0 π^0$. If the $B \to π^-$ form factor is large $(\stackrel{>}{\sim} 0.3)$, then we find that the CLEO measurement favors small $|V_{ub}/V_{cb}|$ so that the expected error (due to neglecting the QCD penguin amplitude) in the measurement of $α$ using {\em only} the time-dependent analysis of the decay $B \to π^+ π^-$ is large $\sim 15^{\circ}$. However, if $|V_{ub}/V_{cb}|$ is known, then it is possible to determine the correct value of $\sin 2 α$.

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arXiv1999

Limits on Low Scale Gravity from $e^+ e^- \to W^+ W^-, ZZ$ and $γγ$

It has been proposed recently that the scale of quantum gravity (``the string scale'') can be $M_S \sim$ few TeV with $n \geq 2$ extra dimensions of size $R \stackrel{<}{\sim}$ mm so that, at distances greater than $R$, Newtonian gravity with $M_{Pl} \sim 10^{18}$ GeV is reproduced if $M_{Pl}^2 \sim R^n M_S^{n+2}$. Exchange of virtual gravitons in this theory generates higher-dimensional operators involving SM fields, suppressed by powers of $M_S$. We discuss constraints on this scenario from the contribution of these operators to the processes $e^+ e^- \to W^+ W^-, ZZ, γγ$. We find that LEP2 can place a limit $M_S \approx 1$ TeV from $e^+ e^- \to W^+ W^-, ZZ, γγ$.

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arXiv1999

Determining the Weak Phase $γ$ using the decays $B_d$, $B^+ \to K η(η')$ and $B_s \to πη(η')$

We suggest two methods (based on flavor SU(3) symmetry) to determine the CKM angle $γ$ using the decays $B_d$, $B^+ \to K η(η')$ and $B_s \to πη(η')$, respectively. Rescattering effects are partly included -- we neglect annihilation amplitudes, but do not assume any other relation between the SU(3) invariant amplitudes. We use the fact that the amplitude (including the Electroweak Penguin contribution) for $B_d$, $B^+ \to πK$ with final state $I (isospin) =3/2$ is known as a function of $γ$ from the decay rate $B^+ \to π^0 π^+$.

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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).

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arXiv1998

A Critical Study of B Decays to Light Pseudoscalar

Motivated by the large branching ratios observed for the process $B\toη^{\prime}K$, we examine critically all the ingredients that go into estimates of B decays into two light pseudoscalars. Within factorization approximation, we examine several assumptions on the input parameters that could have a strong bearing on the predictions. Among these are (i) the QCD scale $μ$ (ii) value of the form factors (iii) value of the light quark masses, and in particular $m_s$ (iv) the value $ξ=1/N_c$, (v) charm content of $η^{\prime}$. It is possible to account for all the data without invoking new physics, though future experiments will provide tighter constraints on the parameter space. We fin that CP violating asymmetries are in the observable range for some modes.

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arXiv1997

Branching Ratios and CP Asymmetries of B Decays to a Vector and a Pseudoscalar Meson

We consider two body decays of B meson into a light vector (V) and a pseudoscalar (P) meson. The constraint obtained from the $B\to P P$ modes on the parameter space of the input parameters is imposed also on $B\to V P$ modes. In particular we constrain $ξ\equiv (1/N_c)$ for those modes from recently measured $B\to ωK, ϕK$ and are able to get a satisfactory pictures for all modes where data exists. Modes that should be seen shortly and those with possibly large CP asymmetries are identified.

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arXiv1997

Leptoquark explanation of HERA anomaly in the context of gauge unification

We examine the consequences of leptoquark explanation of HERA anomaly in the context of R parity conserving supersymmetric gauge unified theory with the gauge unification scale at $\sim 10^{16}$ GeV. We pointed out the difficulty of constructing a grandunified theory. However gauge unification is still possible at $\sim 10^{16}$ GeV when additional multiplets are introduced. We determine the mass spectrum of these additional fields (fermions and scalars) in gauge mediated and supergravity scenarios. Unique signatures and mass bounds are discussed.

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arXiv1997

Contact Interaction Explanation of HERA Events and $SU(3)_C\times SU(2)_L\times U(1)_Y$ Invariance

We reexamine the contact interaction hypothesis for excess high-$Q^2$ events seen at HERA in $e^+ p \to e^+ X$ scattering. We consider the most general structure of contact interactions insisting on $SU(3)_C\times SU(2)_L \times U(1)_Y$ invariance. Apart from constraints for $e^+ e^- \to q\bar q$ , Drell-Yan and atomic parity violation experiments, we find stringent constraints from neutrino deep inelastic data. A possible choice of contact terms that escape present bounds is still possible, althought new data from FERMILAB and LEP should further constrain such a possibility.

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