What heavy quanta bounds could be inferred from a Higgs discovery?

The Higgs couplings can receive non-decoupling corrections due to heavy quanta, and deviations from the SM can be used to test its presence. The possible Higgs signal recently reported at LEP, with mh=115 GeV, severely constrains the presence of heavy quanta, such as a heavy fourth family. At Tevatron, the Higgs production by gluon fusion, followed by the decay h -> WW*, can also be used to probe the existence of heavy colored particles, including additional families, chiral sextet and octet quarks. Within the MSSM, we also find that gluon fusion is a sensitive probe for the squark spectrum.Comment: 12 pages, 3 tables, 1 figure. Accepted in Mod. Phys. Lett. A (2001

Mass matrix Ansatz and lepton flavor violation in the THDM-III

Predictive Higgs-fermion couplings can be obtained when a specific texture for the fermion mass matrices is included in the general two-Higgs doublet model. We derive the form of these couplings in the charged lepton sector using a Hermitian mass matrix Ansatz with four-texture zeros. The presence of unconstrained phases in the vertices phi-li-lj modifies the pattern of flavor-violating Higgs interactions. Bounds on the model parameters are obtained from present limits on rare lepton flavor violating processes, which could be extended further by the search for the decay tau -> mu mu mu and mu-e conversion at future experiments. The signal from Higgs boson decays phi -> tau mu could be searched at the large hadron collider (LHC), while e-mu transitions could produce a detectable signal at a future e mu-collider, through the reaction e mu -> h0 -> tau tau.Comment: 17 pages, 9 figure

Bounds for Lepton Flavor Violation and the Pseudoscalar Higgs in the General Two Higgs Doublet Model using g−2g-2 muon factor

Current experimental data from the $g-2$ muon factor, seems to show the necessity of physics beyond the Standard Model (SM), since the difference between SM and experimental predictions is 2.6$\sigma$. In the framework of the General Two Higgs Doublet Model (2HDM), we calculate the muon anomalous magnetic moment to get lower and upper bounds for the Flavour Changing (FC) Yukawa couplings in the leptonic sector. We also obtain lower bounds for the mass of the pseudoscalar Higgs ($m_{A^0}$) as a function of the parameters of the model.Comment: 12 pages, RevTex4, 5 figures. Improved presentation, updated experimental data, amplified analysis, new figures added. Subbmited to Phys. Rev.

Lepton flavor violating Higgs boson decays from massive seesaw neutrinos

Lepton flavor violating Higgs boson decays are studied within the context of seesaw models with Majorana massive neutrinos. Two models are considered: The SM-seesaw, with the Standard Model Particle content plus three right handed neutrinos, and the MSSM-seesaw, with the Minimal Supersymmetric Standard Model particle content plus three right handed neutrinos and their supersymmetric partners. The widths for these decays are derived from a full one-loop diagrammatic computation in both models, and they are analyzed numerically in terms of the seesaw parameters, namely, the Dirac and Majorana mass matrices. Several possible scenarios for these mass matrices that are compatible with neutrino data are considered. In the SM-seesaw case, very small branching ratios are found for all studied scenarios. These ratios are explained as a consequence of the decoupling behaviour of the heavy right handed neutrinos. In contrast, in the MSSM-seesaw case, sizeable branching ratios are found for some of the leptonic flavor violating decays of the MSSM neutral Higgs bosons and for some choices of the seesaw matrices and MSSM parameters. The relevance of the two competing sources of lepton flavor changing interactions in the MSSM-seesaw case is also discussed. The non-decoupling behaviour of the supersymmetric particles contributing in the loop-diagrams is finally shown.Comment: 44pgs. Version to appear in Phys.Rev.

Life after eruption - I. Spectroscopic observations of ten nova candidates

We have started a project to investigate the connection of post-novae with the population of cataclysmic variables. Our first steps in this concern improving the sample of known post-novae and their properties. Here we present the recovery and/or confirmation of the old novae MT Cen, V812 Cen, V655 CrA, IL Nor, V2109 Oph, V909 Sgr, V2572 Sgr, and V728 Sco. Principal photometric and spectroscopic properties of these systems are discussed. We find that V909 Sgr is a probable magnetic CV, and that V728 Sco is a high-inclination system. We furthermore suggest that the two candidate novae V734 Sco and V1310 Sgr have been misclassified and instead are Mira variables.Comment: 11 pages, 7 figures (some of them in lower resolution), to be published in MNRA

Constraints on the parameters of the Left Right Mirror Model

We study some phenomenological constraints on the parameters of a left right model with mirror fermions (LRMM) that solves the strong CP problem. In particular, we evaluate the contribution of mirror neutrinos to the invisible Z decay width (\Gamma_Z^{inv}), and we find that the present experimental value on \Gamma_Z^{inv}, can be used to place an upper bound on the Z-Z' mixing angle that is consistent with limits obtained previously from other low-energy observables. In this model the charged fermions that correspond to the standard model (SM) mix with its mirror counterparts. This mixing, simultaneously with the Z-Z' one, leads to modifications of the \Gamma(Z --> f \bar{f}) decay width. By comparing with LEP data, we obtain bounds on the standard-mirror lepton mixing angles. We also find that the bottom quark mixing parameters can be chosen to fit the experimental values of R_b, and the resulting values for the Z-Z' mixing angle do not agree with previous bounds. However, this disagreement disappears if one takes the more recent ALEPH data.Comment: 7 pages, 2 figures, REVTe

Superconformal Flavor Simplified

A simple explanation of the flavor hierarchies can arise if matter fields interact with a conformal sector and different generations have different anomalous dimensions under the CFT. However, in the original study by Nelson and Strassler many supersymmetric models of this type were considered to be 'incalculable' because the R-charges were not sufficiently constrained by the superpotential. We point out that nearly all such models are calculable with the use of a-maximization. Utilizing this, we construct the simplest vector-like flavor models and discuss their viability. A significant constraint on these models comes from requiring that the visible gauge couplings remain perturbative throughout the conformal window needed to generate the hierarchies. However, we find that there is a small class of simple flavor models that can evade this bound.Comment: 43 pages, 1 figure; V3: small corrections and clarifications, references adde

QCD Corrections to Scalar Production via Heavy Quark Fusion at Hadron Colliders

We recently proposed that, due to the top-quark-mass enhanced Yukawa coupling, the s-channel production of a charged scalar or pseudo-scalar from heavy quark fusion can be an important new mechanism for discovering non-standard spin-0 particles. In this work, we present the complete O(alpha_s) QCD corrections to this s-channel production process at hadron colliders, including the results of QCD resummation over multiple soft-gluon emission. The systematic QCD-improved production and decay rates at the FermiLab Tevatron and the CERN LHC are given for the charged top-pions in the topcolor models and for the charged Higgs bosons in the generic two Higgs doublet model. The direct extension to the production of the neutral (pseudo-)scalars via bb\bar fusion is studied in the minimal supersymmetric standard model (MSSM) with large tan(beta), and in the topcolor model with large bottom Yukawa coupling.Comment: Version to be published in Phys.Rev.D. Discussion on Rb added plus minor improvements. Conclusions not changed. Latex2e, 40 pages, 16 figure

Dissipative Future Universe without Big Rip

The present study deals with dissipative future universe without big rip in context of Eckart formalism. The generalized chaplygin gas, characterized by equation of state $p=-\frac{A}{\rho^\frac{1}{\alpha}}$, has been considered as a model for dark energy due to its dark-energy-like evolution at late time. It is demonstrated that, if the cosmic dark energy behaves like a fluid with equation of state $p=\omega\rho$; $\omega < -1$, as well as chaplygin gas simultaneously then the big rip problem does not arises and the scale factor is found to be regular for all time.Comment: 6 pages, 2 figures, To appear in Int. J. Theor. Phy

Interactions of Heavy Hadrons using Regge Phenomenology and the Quark Gluon String Model

The search for stable heavy exotic hadrons is a promising way to observe new physics processes at collider experiments. The discovery potential for such particles can be enhanced or suppressed by their interactions with detector material. This paper describes a model for the interactions in matter of stable hadrons containing an exotic quark of charges $\pm {1/3}e$ or $\pm {2/3}e$ using Regge phenomenology and the Quark Gluon String Model. The influence of such interactions on searches at the LHC is also discussed