arXiv subjects

Anirban Kundu

Publications and source records attributed to Anirban Kundu.

At least 91 records · Page 5Linked to original sources

arXiv2005

New Physics in b --> s bar(s) s Decay

We perform a model-independent analysis of the data on branching ratios and CP asymmetries of $B\toϕK$ and $B\toη^{(')} K^{(*)}$ modes. The present data is encouraging to look for indirect evidences of physics beyond the Standard Model. We investigate the parameter spaces for different possible Lorentz structures of the new physics four-Fermi interaction. It is shown that if one takes the data at $1σ$ confidence level, only one particular Lorentz structure is allowed. Possible consequences for the $B_s$ system are also discussed.

hep-ph↗

arXiv2004

R-Parity violation in B --> pi+ pi- decay

We consider the impact of R-parity violating suprsymmetry in the nonleptonic decay B --> pi+ pi-. This is one of the rare instances where new physics contributes to both B-Bbar mixing and B --> pi+ pi- decay. We do a numerical analysis to capture the interplay between these two effects and place constraints on the relevant parameter space.

hep-ph↗

arXiv2004

Constraints on R-parity violating supersymmetry from neutral meson mixing

Upper bounds at the weak scale are put on all $λ'_{ijk}λ'_{imn}$ type products of R-parity violating supersymmetry that may affect K-Kbar and B-Bbar mixing. We constrain all possible products, including some not considered before, using next-to-leading order QCD corrections to the mixing amplitudes. Constraints are obtained for both real and imaginary parts of the couplings. We also discuss briefly some correlated decay channels which should be investigated in future experiments.

hep-ph↗

arXiv2004

Vector Meson Contributions in epsilon'/epsilon

The CP violating parameter epsilon'/epsilon is computed using the low-energy dynamics of a chiral theory supplemented by vector resonances. The divergent contributions coming from strong pi-pi scattering are tamed by vector-meson exchange terms. This amounts to softening the fast growing high-energy behaviour of pi-pi scattering. The final result for epsilon'/epsilon shows a smooth dependence on the cut-off where low energy dynamics is matched with that of QCD.

hep-ph↗

arXiv2004

Large electroweak penguins in B --> pi pi and B --> pi K : implication for new physics

We show that the anomalies in the $B\toππ$ decay channels, {\em viz.}, the large branching ratio of $B\toπ^0π^0$ and large direct CP asymmetry of $B\toπ^+π^-$, can both be explained, even in the framework of existing theoretical models which predict the relative strengths of the tree and the strong penguin amplitudes, if there is an abnormally large electroweak penguin contribution. We also critically examine the expectation of a similarly large electroweak penguin in the $B\toπK$ sector, and show that it can be accomodated, and may even be motivated from an SU(3) flavor symmetry between the $B\toππ$ and the $B\toπK$ amplitudes, but is not necessary to explain the data. We emphasize that if the experimental numbers on these charmless nonleptonic channels survive, they may turn out to be an indirect signal of new physics. Current data is insufficient to discriminate betwen flavor-specific and flavor-blind new physics scenarios.

hep-ph↗

arXiv2003

Reevaluating Bounds on Flavor-Changing Neutral Current Parameters in R-parity Conserving and R-parity Violating Supersymmetry from B0 - bar(B0) Mixing

We perform a systematic reevaluation of the constraints on the flavor-changing neutral current (FCNC) parameters in R-parity conserving and R-parity violating supersymmetric models. As a typical process, we study the constraints coming from the measurements on the B0-\bar{B0} system on the supersymmetric $δ^d_{13}$ parameters, as well as on the products of the lambda' type R-parity violating couplings. Present data allows us to put constraints on both the real and the imaginary parts of the relevant parameters.

hep-ph↗

arXiv2003

Simultaneous solution to B --> phi K CP Asymmetry and B --> eta(prime) K, eta K^* branching ratio anomalies from R-parity violation

The branching ratios for the neutral and charged B decay channels to $η' K$ and $ηK^*$ are well above the Standard Model expectations. Moreover, the mixing-induced CP asymmetry in $B \to ϕK_S$ is incompatible to that found in $B\to J/ψK_S$. We investigate whether a flavour-specific tree-level $b\to s \bar{s} s$ operator coming from R-parity violating supersymmetry can resolve both these discrepancies, without jeopardizing those results which are in agreement with the Standard Model. We found that it is possible to have a parameter space satisfying all these requirements, including that of a low strong phase difference compatible with the color transparency argument. Furthermore, we put a robust bound on the relevant coupling, which is two orders of magnitude better than the existing one.

hep-ph↗

arXiv2003

Effects of Universal Extra Dimensions on $B^0 - {\bar B^0}$ Mixing

We study contributions coming to $Δm_B$ from one or more universal extra dimensions (UED) in which all the Standard Model fields can propagate. In the model with a single UED, the box diagrams for mixing are convergent and therefore insensitive to the cutoff scale of the theory. In the case of two UEDs, the result is not very sensitive to the cut-off scale due to GIM mechanism. Within the present range of the parameters at $1 σ$ level, the lower bound on the compactification scale 1/R has been estimated to be 165 GeV for one UED and 280 GeV for two UEDs. The bound increases drastically if one can have a better determination of the $B$ meson decay constant $f_B$ and the QCD correction parameter $B_B$. For example, it rises to 740 GeV (for one UED) if the error (at $1σ$) in the determination of $f_B\sqrt{B_B}$ from quenched lattice calculation is reduced to one-third from its present value. The UED contributions to the $K$ system are strongly suppressed.

hep-ph↗

arXiv2002

Constraints on R-parity violating supersymmetry from leptonic and semileptonic tau, B_d and B_s decays

We put constraints on several products of R-parity violating lambda lambda' and lambda' lambda' type couplings from leptonic and semileptonic tau, B_d and B_s decays. Most of them are one to two orders of magnitude better than the existing bounds, and almost free from theoretical uncertainties. A significant improvement of these bounds can be made in high luminosity tau-charm or B factories.

hep-ph↗

arXiv2002

B decays and Supersymmetry

I discuss how supersymmetry affects various observables in B decays, and point out the interesting channels in the context of B factories.

hep-ph↗

arXiv2001

New Bounds on Slepton and Wino Masses in Anomaly Mediated Supersymmetry Breaking Models

We show how the spectrum of the minimal anomaly-mediated supersymmetry breaking model can be constrained from the condition that the electroweak symmetry breaking minimum of the scalar potential is the deepest point in the field space. Applying the current experimental bounds and scanning over the whole parameter space, we rule out selectrons below 378 GeV and staus below 269 GeV, the numbers having a modest uncertainty. We also find a new upper bound on the wino-like chargino mass for a given slepton mass. This rules out the possibility of slepton pair production at ongoing or upcoming colliders like the Tevatron or the Next Linear Collider at $\sqrt{s}=500$ GeV, where pair production of charginos may be the only available signal.

hep-ph↗

arXiv2001

Can R-parity violation lower $\sin 2β$?

Recent time-dependent CP asymmetry measurements in the $B_d \to J/ψK_S$ channel by the BaBar and Belle Collaborations yield somewhat lower values of $\sin 2β$ compared to the one obtained from the standard model fit. If the inconsistency between these numbers persists with more statistics, this will signal new physics contaminating the $B_d \to J/ψK_S$ channel, thus disturbing the extraction of $β$. We show that the R-parity-violating interactions in supersymmetric theories can provide extra new phases which play a role in significantly reducing the above CP asymmetry, thus explaining why BaBar and Belle report lower values of $\sin 2β$. The same couplings also affect the $B_d \to ϕK_S$ decay rate and asymmetry, explain the $B \to η' K$ anomaly, and predict nonzero CP asymmetry in dominant $B_s$ decays. The scenario will be tested in the ongoing and upcoming B factories.

hep-ph↗

arXiv2001

Characteristic Wino Signals in a Linear Collider from Anomaly Mediated Supersymmetry Breaking

Though the minimal model of anomaly mediated supersymmetry breaking has been significantly constrained by recent experimental and theoretical work, there are still allowed regions of the parameter space for moderate to large values of $\tanβ$. We show that these regions will be comprehensively probed in a ${\sqrt s} =1$ TeV $e^+e^-$ linear collider. Diagnostic signals to this end are studied by zeroing in on a unique and distinct feature of a large class of models in this genre: a neutral winolike Lightest Supersymmetric Particle closely degenerate in mass with a winolike chargino. The pair production processes $e^+e^- \to {\tilde e}_L^\pm {\tilde e}_L^\mp$, ${\tilde e}_R^\pm {\tilde e}_R^\mp$, ${\tilde e}_L^\pm {\tilde e}_R^\mp$, ${\tilde ν} {\bar {\tilde ν}}$, $\widetilde χ^0_1 \widetilde χ^0_2$, $\widetilde χ^0_2 \widetilde χ^0_2$ are all considered at $\sqrt s = 1$ TeV corresponding to the proposed TESLA linear collider in two natural categories of mass ordering in the sparticle spectra. The signals analysed comprise multiple combinations of fast charged leptons (any of which can act as the trigger) plus displaced vertices $X_D$ (any of which can be identified by a heavy ionizing track terminating in the detector) and/or associated soft pions with characteristic momentum distributions.

hep-ph↗

arXiv2000

Yukawa Unification and Unstable Minima of the Supersymmetric Scalar Potential

Motivated by the possibilities of $b-τ$ or $t-b-τ$ Yukawa unification in the supersymmetric Grand Unified Theories, we consider the dangerous directions of the supersymmetric potential for large values of $\tanβ(\geq 30)$, in two versions of the minimal supergravity model with and without common soft breaking scalar masses at the GUT scale, where the potential may become unbounded from below. We find that for the common trilinear coupling $A_0 \leq 0$ the requirement of $b-τ$ unification in conjunction with the stability condition on the potential yields highly restrictive sparticle spectra with upper, and in many cases, lower bounds stronger than the available experimental lower bounds, on the soft SUSY breaking common scalar mass and the common gaugino mass. Over a significant region of the parameter space, the model becomes even more restrictive if the common sfermion soft mass is different from the soft mass for the Higgs sector. We also find that the bulk of this restricted parameter space can be probed at the LHC. Im models with $t-b-τ$ Yukawa unification, $A_0 \leq 0$ is ruled out from potential constraints.

hep-ph↗

arXiv2000

New Physics Effects From B Meson Decays

In this talk, we point out some of the present and future possible signatures of physics beyond the Standard Model from B-meson decays, taking R-parity conserving and violating supersymmetry as illustrative examples.

hep-ph↗

arXiv1998

A supersymmetric resolution of the anomaly in charmless nonleptonic $B$-decays

We examine the large branching ratio for the process $B\to η^{\prime} K$ from the standpoint of R parity violating supersymmetry. We have given all possible $R_p$ violating contributions to $B\to η^{\prime} K$ amplitudes. We find that only two pairs of $λ^{\prime}$-type $R_p$ violating couplings can solve this problem after satisfying all other experimental bounds. We also analyze those modes where these couplings can appear, {\em e.g.}, $B^\pm \to π^{\pm}K^0$, $B^{\pm,0} \to K^{*\pm,0} η^{(\prime)}$, $B^{\pm} \toϕK^{\pm}$ etc., and predict their branching ratios. Further, one of these two pairs of couplings is found to lower the branching ratio of $B^{\pm}\toϕK^\pm$, thereby allowing larger $ξ\equiv{1\over N_c}$. This allows us to fit $B^{\pm}\to ωK^{\pm}$ and $B^{\pm}\to ωπ^{\pm}$, which could not be done in the SM framework.

hep-ph↗

arXiv1998

Matter effects on $η$ and $η'$ mesons

We show how the nuclear medium affects the masses of the $η$ and $η'$ mesons. The change should be easily detectable for dense matter and/or strong $η(η')N\bar N$ coupling. We also find that the $η-η'$ mixing angle is less in magnitude in the nuclear matter than in vacuum.

nucl-th↗

arXiv1998

Semileptonic charm decay as a test for the spectator model in the $B_c$-meson

The $b$ and the $c$ quark compete with each other in decays of the $B_c$-meson. We emphasize the need of obtaining reliable signals of $c \to s$ in order to assess the merits of the spectator approximation in calculating the relative strengths of the two types of decays. This, we argue, can be done by considering the decay $B_c \to B_s (B_s^*) l \bar{ν_l}$, followed by semileptonic decays of the $B_s$. We suggest looking for like-sign dileptons together with a $D_s$ at the BTeV or LHC-B experiments, and show that such signals can be made background-free by suitable event selection.

hep-ph↗