Search

The Tera-Z phase of future e+e− colliders, FCC-ee and CEPC, is a gold mine for exploring Z portal physics. We focus on axionlike particles (ALPs) that can be produced via Z decays with a monochromatic photon. As a template model, we consider composite Higgs models with a light pseudoscalar that couples through the Wess-Zumino-Witten term to the electroweak gauge bosons. For both photophilic and photophobic cases, we show that the Tera-Z can probe composite scales up to 100s of TeV, well beyond the capability of the LHC and current precision physics. Our results also apply to generic ALPs and, in particular, severely constrain models that explain the muon g−2 anomaly.

The structure of the Higgs sector is a major issue in the quest of a detailed description of the electroweak interactions. Most of the effort is devoted to the study of the standard model\char21{}like Higgs boson at 126 GeV; however, the experimental collaborations at the LHC are also searching for extra scalar particles whose presence may hint at an extended Higgs sector, typical of many extensions of the standard model. We study a model-independent parametrization of a scalar particle lighter than the 126 GeV Higgs boson, which may be easily implemented in the ongoing searches by ATLAS and CMS. Indeed, many effective Lagrangians and parametrizations used at present for the description of the Higgs sector implicitly assume that no light particles other than the standard model ones are present in the spectrum. We therefore introduce a parametrization of a model with two scalars, one corresponding to the 126 GeV Higgs boson and the other to a lighter scalar. After the introduction of this parametrization, we consider two typical examples falling in this category: the two-Higgs-doublet model and the next-to-minimal supersymmetric standard model. We do this for two purposes: to illustrate the use of our parametrization and also show that some well-motivated models giving such a situation can be probed at LHC, advocating for such a search. Our results agree with the specific studies performed for these models. Furthermore, employing such a generic parametrization allows us to translate the bounds to any model beyond the standard model falling into this class.

We model the supermassive Galactic center of the Milky Way Galaxy as a strongly naked singularity lens described by the Janis--Newman--Winicour metric. This metric has an ordinary mass and massless scalar charge parameters. For very accurate results, we use the Virbhadra--Ellis lens equation for computations. The Galactic center serving as a gravitational lens gives rise to four images: two images on the same side as the source and two images on the opposite side of the source from the optic axis. We compute positions and time delays of these images for many values of the angular source position. The time delays of primary images decrease with an increase in angular source position and are always negative. The time delays of the other three images are negative for a small angular source position; however, they increase with an increase in the angular source position. Such observations would support strongly naked singularity interpretation of the Galactic center, and would disprove the cosmic censorship hypothesis proposed by Roger Penrose as well as a weaker version by Virbhadra that allows the existence of weakly, but not marginally, and strongly naked singularities.

The evolution equations of the Yukawa couplings and quark mixings are derived for the one-loop renormalization group equations in six-dimensional models, compactified in different possible ways to yield standard four space-time dimensions. Different possibilities for the matter fields are also discussed, such as the case of bulk propagating or brane localized fields. We discuss in both cases the evolution of the Yukawa couplings, the Jarlskog parameter and the Cabibbo-Kobayashi-Maskawa matrix element, and find that for both scenarios, as we run up to the unification scale, significant renormalization group corrections are present. We also discuss the results of different observables of the five-dimensional universal extra dimension model in comparison with these six-dimensional models and the model dependence of the results.

We discuss possible symmetries of effective theories describing spinless and spin-1 bosons, mainly to concentrate on an intriguing phenomenological possibility: that of a hardly noticeable strong electroweak sector at relatively low energies. Specifically, a model with both vector and axial vector strong interacting bosons may possess a discrete symmetry imposing degeneracy of the two sets of bosons (degenerate BESS model). In such a case its effects at low energies become almost invisible and the model easily passes all low energy precision tests. The reason lies essentially in the fact that the model automatically satisfies decoupling, contrary to models with only vectors. For large mass of the degenerate spin-one bosons the model becomes identical at the classical level to the standard model taken in the limit of infinite Higgs boson mass. For these reasons we have thought it worthwhile to fully develop the model, together with its possible generalizations, and to study the expected phenomenology. For instance, just because of its invisibility at low energy, it is conceivable that degenerate BESS has low mass spin-one states and gives quite visible signals at existing or forthcoming accelerators. \textcopyright{} 1996 The American Physical Society.

Many extensions of the Standard Model (SM) of particle physics predict the existence of charged Higgs bosons with substantial couplings to SM particles, which would render them observable both directly at the LHC and indirectly at B-factories. For example, the charged Higgs boson couplings to fermions in two doublet Higgs models of type II, are proportional to the ratio of the two Higgs doublet vacuum expectation values (tan(beta)) and fermionic mass factors and could thus be substantial at large tan(beta) and/or for heavy fermions. In this work we perform a model-independent study of the charged Higgs boson couplings at the LHC and at B-factories for large values of tan(beta). We have shown that at high luminosity it is possible to measure the couplings of a charged Higgs boson to the third generation of quarks up to an accuracy of 10%. We further argue that by combining the possible measurements of the LHC and the B-factories, it is possible to perform a universality test of charged Higgs boson couplings to quarks., 20 pages, 7 figures, LaTeX (style changed to PRD format, text expanded, references added)

Little Higgs models with $T$ parity can easily satisfy electroweak precision tests and at the same time give a stable particle which is a candidate for cold dark matter. In addition to little Higgs heavy gauge bosons, this type of model predicts a set of new $T$-odd fermions, which may show quite interesting signatures at colliders. We study purely leptonic signatures of $T$-odd leptons at the (LHC.

Little Higgs models with T-parity may provide us with a new source of lepton flavor violation, as such, in this paper we consider the anomalous magnetic moment of the muon (g-2){sub {mu}} and the lepton flavor violating decays {mu}{yields}e{gamma} and {tau}{yields}{mu}{gamma} in the little Higgs model with T-parity [A. Goyal, hep-ph/0609095.]. Our results show that the present experimental constraints of {mu}{yields}e{gamma} are a much more useful tool for constraining the new sources of flavor violation, than from the other processes considered here, which are present in T-parity models.

In this note we discuss a determination for the mass of the Ds(0+,1+) system recently discovered by the BaBar, CLEO II and Belle Collaborations. The value of the mass is derived by making explicit the prediction obtained in a quark-meson model prior to the discovery of these states.

We present an evaluation of the strong couplings ${\mathrm{JD}}^{(*)}{D}^{(*)}$ and ${\mathrm{JD}}^{(*)}{D}^{(*)}\ensuremath{\pi}$ by an effective field theory of quarks and mesons. These couplings are necessary to calculate $\ensuremath{\pi}+J/\stackrel{\ensuremath{\rightarrow}}{\ensuremath{\psi}}{D}^{(*)}+{D}^{(*)}$ cross sections, an important background to the $J/\ensuremath{\psi}$ suppression signal in the quark-gluon plasma. We write down the general effective Lagrangian and compute the relevant couplings in the soft pion limit and beyond.

In the two Higgs doublet model type III and in several other extensions of the standard model, there are no discrete symmetries that suppress flavor changing couplings at the tree level. The experimental observation of the ${\ensuremath{\nu}}_{\ensuremath{\mu}}--{\ensuremath{\nu}}_{\ensuremath{\tau}}$ flavor oscillation may suggest the non-conservation of the lepton number. This would lead to the decay of the type ${A}^{0}{/H}^{0}\ensuremath{\rightarrow}{\ensuremath{\tau}}^{\ifmmode\pm\else\textpm\fi{}}{\ensuremath{\mu}}^{\ensuremath{\mp}}.$ We determine the present low energy limit on lepton flavor violating (LFV) couplings from the muon $g\ensuremath{-}2$ measurement and discuss the prospects for detecting lepton flavor violating decays at the Fermilab Tevatron and at the CERN Large Hadron Collider. The achievable bounds on the LFV coupling parameter ${\ensuremath{\lambda}}_{\ensuremath{\tau}\ensuremath{\mu}}$ are presented.

We study the CERN Large Hadron Collider sensitivity to the charged Higgs boson discovery in the channel ${H}^{\ensuremath{-}}\ensuremath{\rightarrow}{\ensuremath{\tau}}_{L}^{\ensuremath{-}}\ensuremath{\nu}$ in models with a singlet neutrino in large extra dimensions. The observation of such a signal would provide distinctive evidence for these models since in the standard two-Higgs-doublet model type II, ${H}^{\ensuremath{-}}\ensuremath{\rightarrow}{\ensuremath{\tau}}_{L}^{\ensuremath{-}}\ensuremath{\nu}$ is completely suppressed.

We consider the exclusive B_s -> phi mu+ mu- process in the standard model using a constituent quark loop model approach together with a simple parameterization of the quark dynamics. The model allows to compute the decay form factors and therefore can give predictions for the decay rates, the invariant mass spectra and the asymmetries. This process is suppressed in the standard model but can be enhanced if new physics beyond the standard model is present, such as flavor-violating supersymmetric models. It constitutes therefore an interesting precision test of the standard model at forthcoming experiments.

We reconsider two classical proposals for the determination of the angle $\ensuremath{\gamma}$ of the unitarity triangle: ${B}^{\ifmmode\pm\else\textpm\fi{}}\ensuremath{\rightarrow}{\ensuremath{\chi}}_{c0}{\ensuremath{\pi}}^{\ifmmode\pm\else\textpm\fi{}}\ensuremath{\rightarrow}{\ensuremath{\pi}}^{+}{\ensuremath{\pi}}^{\ensuremath{-}}{\ensuremath{\pi}}^{\ifmmode\pm\else\textpm\fi{}}$ and ${B}_{s}\ensuremath{\rightarrow}{\ensuremath{\rho}}^{0}{K}_{S}\ensuremath{\rightarrow}{\ensuremath{\pi}}^{+}{\ensuremath{\pi}}^{\ensuremath{-}}{K}_{S}.$ We point out the relevance, in both cases, of nonresonant amplitudes, where the ${\ensuremath{\pi}}^{+}{\ensuremath{\pi}}^{\ensuremath{-}}$ pair is produced by weak decay of a ${B}^{*}{(J}^{P}{=1}^{\ensuremath{-}})$ or ${B}_{0}{(J}^{P}{=0}^{+})$ off-shell meson. In particular, for the B decay channel, the inclusion of the ${B}_{0}$ pole completes some previous analyses and confirms their conclusions, provided a suitable cut in the Dalitz plot is performed; for the ${B}_{s}$ decay the inclusion of the ${B}^{*},{B}_{0}$ amplitudes enhances the role of the tree diagrams as compared to penguin amplitudes, which makes the theoretical uncertainty related to the ${B}_{s}\ensuremath{\rightarrow}{\ensuremath{\rho}}^{0}{K}_{S}$ decay process less significant. While the first method is affected by theoretical uncertainties, the second one is cleaner, but its usefulness will depend on the available number of events to perform the analysis.

We investigate the potential of the CERN LHC to probe the R parity violating couplings involving the third generation by considering single top quark production. This study is based on particle level event generation for both signal and background, interfaced to a simplified simulation of the ATLAS detector.

We evaluate the form factors describing the exclusive decay B-> pi l nu by using a Constituent Quark-Meson model based on an effective quark-meson Lagrangian (CQM). The model allows for an expansion in the pion momenta and we consider terms up to the first order in the pion field derivatives. We compute the leading terms in the soft pion limit and consider corrections to this limit.

We evaluate the form factors governing the exclusive decays $\stackrel{\ensuremath{\rightarrow}}{B}\ensuremath{\rho}l\ensuremath{\nu}, \stackrel{\ensuremath{\rightarrow}}{B}{a}_{1}l\ensuremath{\nu},$ by using an effective quark-meson Lagrangian. The model is based on meson-quark interactions, and the computation of the mesonic transition amplitudes is performed by considering diagrams with heavy mesons attached to loops containing heavy and light constituent quarks. This approach was successfully employed to compute the Isgur-Wise form factors and other hadronic observables for negative and positive parity heavy mesons and is presently used for exclusive heavy-to-light weak transitions. We also evaluate a few strong coupling constants appearing in chiral effective Lagrangians for heavy and light mesons.