Search

We consider a scenario of Minimal Supersymmetric Standard Model (MSSM) with $R$-parity violation, where the lightest supersymmetric particle (LSP) is the lighter sbottom $(\tilde b_1)$. We study the production of a sbottom pair at the LHC and their subsequent decays through the baryon number violating $(U D D)$ operators leading to a top pair with two light quarks. Looking for both semi-leptonic and fully hadronic (no leptons) final states, we perform cut-based as well as multivariate analyses (MVA) to estimate the signal significance at the 13 TeV run of the LHC. We find that a cut-based analysis can probe sbottom mass upto $\sim 650 $ GeV which may be extended upto $\sim 750 $ GeV using MVA with $300~{\rm fb}^{-1}$ integrated luminosity. The fully hadronic final state, however, is not as promising., Comment: 19 pages, 9 figures, 8 tables, revised leptonic analysis, new figures added, notable improvement in LHC sensitivity

Taking advantage of the fact that the flavor of the neutrino in semileptonic $B$ decays $B\ensuremath{\rightarrow}{D}^{(*)}\ensuremath{\tau}\ensuremath{\nu}$ is not known, we show how a minimal set of higher-dimensional lepton flavor violating (LFV) operators can explain the $R({D}^{(*)})$ anomalies and, as a spin-off, can give rise to the LFV decay of the Higgs boson, $h\ensuremath{\rightarrow}\ensuremath{\mu}\ensuremath{\tau}$. We also show how none but the minimal set of operators survive the present data.

We reexamine like-sign dilepton signals at the Fermilab Tevatron assuming that the excess high-Q{sup 2} events recently seen at the DESY HERA are due to scalar resonances such as squarks of R-parity-violating supersymmetry. For gluinos in the mass range of 200{endash}350 GeV, the like-sign dilepton signal can help to make the crucial distinction between the most favored squark explanation and other proposed solutions. {copyright} {ital 1997} {ital The American Physical Society}

A light neutral Higgs boson in the framework of the general two Higgs doublet model (2HDM) is not excluded by existing data. We point out that it can be looked for at the proposed low energy {gamma}{gamma} collider. Failure to detect one may lead to important limits on the parameters of the general 2HDM. {copyright} {ital 1997} {ital The American Physical Society}

The initial data on the production and decay of the Higgs boson reported significant deviations from the Standard Model (SM) expectations, prompting much speculation about its couplings to the other particles. Although the latest data has veered towards conformity with the SM, there is yet room for a sizable deviation from the SM values of the coupling of the Higgs boson with $t\bar{t}$, and to a smaller extent, of that with $W^+W^-$ and $ZZ$. Keeping the fluid nature of the data in mind, this opens up an interesting avenue to explore regarding unitarity of gauge boson scattering and the stability of the electroweak vacuum in the presence of anomalous couplings. We show that, for some typical benchmark points, unitarity in gauge boson scattering breaks down between 1 and 10 TeV. We also show that if there are no new light degrees of freedom, the Higgs quartic coupling becomes negative at around the same point, making the electroweak vacuum unstable. Thus, some new ultraviolet completing new physics is demanded at that scale to cancel both these anomalous behaviours if such deviations from the SM couplings are indeed established., 15 pages, 6 figures. Discussion on recent results of ATLAS and CMS. Conclusions unchanged. Author list modified. Version accepted in Physical Review D

We discuss an optimal {ital R}-parity-breaking SUSY solution to the {ital R}{sub {ital b}} excess as well as the ALEPH four-jet anomaly. The latter arises from the pair production of a top squark via chargino decay at CERN LEP 1.5, followed by its {ital R}-violating decay into a light quark pair. The model satisfies top quark and {ital Z}-boson decay constraints along with gaugino mass unification. {copyright} {ital 1996 The American Physical Society.}

We discuss the possibility of measuring ${V}_{\mathrm{ub}}$ via nonleptonic decays of $B$ mesons to exclusive two-meson final states by choosing modes that are theoretically "clean." These clean final states are chosen by requiring that no $q\overline{q}$ of the same flavor should occur in them. The above requirement automatically leads to decays that proceed only via the spectator graphs in the decays of $b$, $c$, and $s$ flavored mesons. These modes may offer a good handle on ${V}_{\mathrm{ub}}$, at a level comparable to that given by the exclusive semileptonic modes.

Phenomenological constraints due to {ital CP} violation in the {ital K}-{ital {bar K}} system and the extent of {ital B}-{ital {bar B}} mixing are used to determine the constraints on the various parameters of the Cabibbo-Kobayashi-Maskawa (CKM) matrix given the {ital Ansatz} is symmetric. An existing parametrization for the CKM matrix is shown to be the most general parametrization for the symmetric {ital Ansatz}. This {ital Ansatz} implies that the mass of the {ital t} quark is at least 180 GeV.

We investigate charged tracks signals of a supersymmetric scenario, where the lighter stop is the next-to-lightest supersymmetric particle. It is found that such a next-to-lightest supersymmetric particle is stable on the scale of the detector at the CERN LHC if one has a right-chiral sneutrino as the lightest supersymmetric particle. After identifying some benchmark points in the parameter space of a supergravity scenario with nonuniversal scalar masses, we study a few specific classes of signals, namely, stop pair production and gluino pair production followed by each decaying into a stop and a top. It is shown that proper kinematic cuts remove the backgrounds in each case, and an integrated luminosity of even 1 fb{sup -1} is likely to yield copious events of the first kind, while a larger luminosity may be required for the other type. One can also aspire to reconstruct the gluino mass, using the ''visible'' stable next-to-lightest supersymmetric particle tracks.

It is argued that neutrinoless double-{beta} decay (({beta}{beta}){sub 0{nu}}) does not depend on the physical Dirac or Majorana mass of the electron neutrino. A new scenario is proposed where the physical neutrino can naturally be a light Majorana particle, without any ({beta}{beta}){sub 0{nu}}. Supersymmetric grand unified theories are constructed incorporating this scenario.

If quarks are composite particles, then excited states are expected to play a role in the Large Hadron Collider phenomena. Concentrating on virtual effects, and using a large part of the compact muon solenoid detection criteria, we present here a realistic examination of their effect in diphoton production at the CERN LHC. For various luminosities, we present the 99% confidence limit (CL) achievable in {lambda}-M{sub q*} parameter space where {lambda} is the compositeness scale and M{sub q*} the mass of the state. For a q* of mass 0.5 TeV, {lambda}{

The Randall-Sundrum warped braneworld model is generalized to six and higher dimensions such that the warping has a nontrivial dependence on more than one dimension. This naturally leads to a brane-boxlike configuration along with scalar fields with possibly interesting cosmological roles. Also obtained naturally are two towers of 3 branes with mass scales clustered around either of the Planck scale and TeV scale. Such a scenario has interesting phenomenological consequences including an explanation for the observed hierarchy in the masses of standard model fermions.

We examine the sensitivity of e{gamma} colliders (based on e{sup +}e{sup -} linear colliders of c.m. energy 500 GeV) to the anomalous couplings of the Higgs to W-boson via the process e{sup -}{gamma}{yields}{nu}WH. This has the advantage over e{sup +}e{sup -} collider in being able to dissociate WWH vertex from ZZH. We are able to construct several dynamical variables which may be used to constrain the various couplings in the WWH vert0008.

The scalar partner of the top quark is relatively light in many models of supersymmetry breaking. We study the production of top squarks (stops) at the Tevatron collider and their subsequent decay through baryon-number violating couplings such that the final state contains no leptons. Performing a detector-level analysis, we demonstrate that, even in the absence of leptons or missing energy, stop masses up to 210 GeV/c{sup 2} can be accessible at the Tevatron.

We examine, in a model independent way, the sensitivity of a Linear Collider to the couplings of a light Higgs boson to gauge bosons. Including the possibility of CP violation, we construct several observables that probe the different anomalous couplings possible. For an intermediate mass Higgs, a collider operating at a center of mass energy of 500 GeV and with an integrated luminosity of 500 fb$^{-1}$ is shown to be able to constrain the $ZZH$ vertex at the few per cent level, and with even higher sensitivity in certain directions. However, the lack of sufficient number of observables as well as contamination from the $ZZH$ vertex limits the precision with which the $WWH$ coupling can be measured., Comment: Typeset in RevTeX4, 16 pages, 12 figures; V2: minor changes in title and Sec. II and III; V3: version appeared in PRD with minor correction

The phases in a generic low-energy supersymmetric model are severely constrained by the experimental upper bounds on the electric dipole moments of the electron and the neutron. Coupled with the requirement of radiative electroweak symmetry breaking, this results in a large degree of fine tuning of the phase parameters at the unification scale. In supergravity type models, this corresponds to very highly tuned values for the phases of the bilinear Higgs coupling parameter $B$ and the universal trilinear coupling $A_0$. We identify a cancellation/enhancement mechanism associated with the renormalization group evolution of $B$, which, in turn, reduces such fine-tuning quite appreciably without taking recourse to very large masses for the supersymmetric partners. We find a significant amount of reduction of this fine-tuning in nonuniversal gaugino mass models that do not introduce any new phases., Comment: Version to appear in Phys.Rev.D. Insignificant changes like a few typos corrected. 26 pages, 7 figures, LaTex

Sneutrino resonances at a high energy linear e+e- collider may be one of the clearest signals of supersymmetry without R-parity, especially when the R-parity-violating coupling is too small to produce observable excesses in four-fermion processes. However, there is no guarantee that the sneutrino pole will lie anywhere near the machine energy. We show that associated photon production induces the necessary energy spread, and that the resonance then leaves a clear imprint in the photon spectrum. It follows that tagging of a hard mono-energetic photon for a variety of possible final states provides a realistic method of separating sneutrino resonance signals from the Standard Model backgrounds., Comment: 25 pages, LaTeX, figures embedded, references added

We investigate the role that baryon number violating interactions may play in B phenomenology. Present in various grand unified theories, supersymmetric theories with R-parity violation and composite models, a fundamental diquark state could be quite light. Using the data on B decays as well as B-B mixing, we find strong constraints on the couplings that such a light diquark state may have with the standard model quarks. Our analysis is most general in nature, and the particular models mentioned above are only specific examples thereof.

We investigate the possible role that baryon number violating Yukawa interactions may take in the inclusive decay B→X s γ. The constraints, derived using the experimental results of the CLEO Collaboration, turn out, in many cases, to be more stringent than the existing bounds.

To explore the discovery possibilities of a high-energy muon-proton collider, we examine signals that could arise from direct-channel formation of supersymmetric-particle resonances through operators that do not respect Rparity.