Search

Motivated by the fermion mass hierarchy we study the phenomenology of two flavorful two-Higgs-doublet model (2HDM) scenarios. By virtue of the flavor or singular alignment ansatz it is possible to link the mass of a subset of fermions to the vacuum-expectation-value (VEV) of a unique Higgs doublet and to simultaneously avoid flavor-changing-neutral-currents at tree-level. We explicitly construct two models called Type-A and B. There, either the top quark alone or all third generation fermions couple to the doublet with the larger VEV. The other fermions acquire their masses through the small VEV of the other doublet. Thus, more natural values for the Yukawa couplings can be obtained. The main differences between these models and conventional ones are studied including a discussion of both their structure and phenomenological consequences. In particular, as distinctive deviations for the Yukawa couplings of the light fermions are predicted we discuss possible tests at the LHC based on searches for $h\to J/\Psi + \gamma$, $h\to\mu\mu$, and heavy scalar resonances decaying to muon pairs. We find that for a wide region of parameter space this specific set of signatures can be used to distinguish among the new proposed types and the conventional ones., Comment: 13 pages, 5 tables, 9 figures; new references added and major improvements; version accepted by Phys. Rev. D

In this work we study the annihilation of fermionic dark matter, considering it as a neutral particle with non-vanishing magnetic ($M$) and electric ($D$) dipole moments. Effective cross section of the process $\chi \overline{\chi} \rightarrow \gamma \gamma$ is computed starting from a general form of the coupling $\chi \overline{\chi} \gamma$ in the framework of an extension of the Standard Model. By taking into account the annihilation of dark matter pairs into mono-energetic photons, we found that for masses of $O(10^2)$ GeV, an electric dipole moment $\sim 10^{-16}\, \textrm{e cm}$ is required to satisfy the current relic density inferences. Additionally, in order to pin down models viable to describe the physics of dark matter in the early Universe, we also constrain our model according to recent measurements of the temperature anisotropies of the cosmic microwave background radiation, and report constraints to the electric and magnetic dipole moments for a range of masses within our model., Comment: 20 pages, 6 figures

The search for Flavons with a mass of $\mathcal{O}$(1) TeV at current and future colliders might probe low-scale flavor models. We are interested in the simplest model that invokes the Froggatt-Nielsen (FN) mechanism with an Abelian flavor symmetry, which includes a Higgs doublet and a FN complex singlet. Assuming a CP conserving scalar potential, there are a $CP$-even $H_F$ and a $CP$-odd $A_F$ Flavons with lepton flavor violating (LFV) couplings. The former can mix with the standard-model-like Higgs boson, thereby inducing tree-level LFV Higgs interactions that may be at the reach of the LHC. We study the constraints on the parameter space of the model from low-energy LFV processes, which are then used to evaluate the Flavon decay widths and the $gg\to \phi \to \tau\mu$ ($\phi=H_F,\,A_F$) production cross section at hadron colliders. After imposing several kinematic cuts to reduce the SM main background, we find that for $m_{H_F}$ about 200-350 GeV, the decay $H_F \to \tau \mu$ might be at the reach of the LHC for a luminosity in the range 1-3 ab$^{-1}$, however, a luminosity of the order of 10 ab$^{-1}$ would be required to detect the $A_F \to \tau \mu$ decay. On the other hand a future 100 TeV $pp$ collider could probe masses as high as $\mathcal{O}$(10) TeV if it reaches an integrated luminosity of at least 20 ab$^{-1}$. Therefore, the 100 TeV Collider could work as a Flavon factory., Comment: 22 pages, 17 Figures,4 Tables. Version to be published in PRD

The strong CP problem is one of many puzzles in the theoretical description of elementary particle physics that still lacks an explanation. While top-down solutions to that problem usually comprise new symmetries or fields or both, we want to present a rather bottom-up perspective. The main problem seems to be how to achieve small CP violation in the strong interactions despite large CP violation in weak interactions. Observation of CP violation is exclusively through the Higgs--Yukawa interactions. In this paper, we show that with minimal assumptions on the structure of mass (Yukawa) matrices they do not contribute to the strong CP problem and thus we can provide a pathway to a solution of the strong CP problem within the structures of the Standard Model and no extension at the electroweak scale is needed. However, to address the flavor puzzle, models based on minimal SU(3) flavor groups leading to the proposed flavor matrices are favored. Though we refrain from an explicit a UV completion of the Standard Model, we provide a simple requirement those models should have to intrinsically not show a strong CP problem., Comment: 12 pages; v2: extended discussion, title changed to be more general

Higgs-flavon fields appear as a part of the Froggatt-Nielsen (FN) mechanism, which attempts to explain the hierarchy of Yukawa couplings. We explore the possibility that the 750 GeV diphoton resonance recently reported at the LHC13, could be identified with a low-scale Higgs-flavon field $H_F$ and find the region of the parameter space consistent with CMS and ATLAS data. It is found that the extra vector-like fermions of the ultraviolet completion of the FN mechanism are necessary in order to reproduce the observed signal. We consider a standard model (SM) extension that contains two Higgs doublets (a standard one and an inert one) and one complex FN singlet. The inert doublet includes a stable neutral boson, which provides a viable dark matter candidate, while the mixing of the standard doublet and the FN singlet induces flavor violation in the Higgs sector at the tree-level. Constraints on the parameters of the model are derived from the LHC Higgs data, which include the search for the lepton flavor violating decay of the SM Higgs boson $h\to \bar{\mu}\tau $. It is also found that in some region of the parameter space the model may give rise to a large branching ratio for the $H_F \to hh$ decay, of the order of 0.1, which could be searched for at the LHC., Comment: 18 pages, 7 Figures, includes updated files to match published version

The general two-higgs doublet model (2HDM) contains a rich spectrum of neutral and charged Higgs bosons, whose detection would be a clear signal of new physics. When the Higgs potential is CP-conserving, the spectrum includes a pseudoscalar mass eigenstate $A^{0}$, which does not couple to vector bosons at tree-level. However, fermionic loops (top and bottom mainly) induce the coupling $AVV'$ (with $V,V'=\gamma, Z$) at higher orders. We evaluate the amplitude for the decays ${A^0} \to ZZ, Z\gamma, \gamma\gamma$, including a generic fermionic loop contribution, and present results on the branching ratios for 2HDM-I,II and III. Current LHC searches on heavy Higgs bosons are used as an estimate to constrain the allowed mass range for $A^0$., Comment: 19 pages, 8 figures, This article has been accepted for publication in Physical Review D

The rare top decay t-> c l+l-, which involves flavor violation, is studied as a possible probe of new physics. This decay is analyzed with the simplest Standard Model extensions with additional gauge symmetry formalism. The considered extension is the Left-Right Symmetric Model, including a new neutral gauge boson Z' that allows to obtain the decay at tree level through Flavor Changing Neutral Currents (FCNC) couplings. The neutral gauge boson couplings are considered diagonal but family non-universal in order to induce these FCNC. We find the $BR(t-> c l+l-)~10^{-13} for a range 1 TeV < M_{Z'} < 3 TeV., Comment: 9 pages, 6 figures

We discuss the most general formulation of the Two-Higgs doublet model, which incorporates flavor changing neutral scalar interactions (FCNSI) and CP violation (CPV) from several sources. CP violation can arise either from Yukawa terms or from the Higgs potential, be it explicit or spontaneous. We show how the model, which is denoted as 2HDM-X, reduces to some versions known in the literature (2HDM-I,II,III), as well as some of their variants (top, lepton, dark) denoted here as 2HDM-IV. We also discuss another limit that includes CPV and Yukawa four textures to control FCNSI, which we denote as 2HDM-V. We evaluate the CPV asymmetry for the decay $h\to bcW$, which may allow to test the patterns of FCNSI and CPV, that arises in these models., Comment: 21 pages, 10 figures

Supersymmetric Grand Unified Theories (SGUTs) have achieved some degree of success, already present in the minimal models (with SU(5) or SO(10)). However, there are open problems that suggest the need to incorporate more elaborate constructions, specifically the use of higher-dimensional representations in the Higgs sector. For example, a $45$ representation of SU(5) is often included to obtain correct mass relations for the first and second families of d-type quarks and leptons. When one adds these higher-dimensional Higgs representations one must verify the cancellation of anomalies associated to their fermionic partners. One possible choice, free of anomalies, include both $45,\overline{45}$ representations to cancel anomalies. We review the necessary conditions for the cancellation of anomalies and discuss the different possibilities for supersymmetric SU(5) models. Alternative anomaly-free combinations of Higgs representations, beyond the usual vectorlike choice, are identified, and it is shown that their corresponding $\beta$ functions are not equivalent. Although the unification of gauge couplings is not affected, the introduction of multidimensional representations leads to different scenarios for the perturbative validity of the theory up to the Planck scale. We study the effect on the evolution of the gauge coupling up to the Planck scale due to the different sets of fields and representations that can render an anomaly-free model., Comment: 6 pages, 3 figures. Presented by ADR at the Dark Side of the Universe Conference, Leon, Gto. Mexico 2010

We explore in detail the Higgs phenomenology that results in a model where right-handed neutrinos have a mass scale of the order of the electroweak scale. In this model all scales arise from spontaneous symmetry breaking, and this is achieved with a Higgs sector that includes an extra Higgs singlet in addition to the standard model Higgs doublet. The scalar spectrum includes two neutral CP-even states ($h$ and $H$ with $m_{h} < m_{H}$)and a neutral CP-odd state ($\sigma$) that can be identified as a pseudo-Majoron. The parameter of the Higgs potential are constrained using a perturbativity criteria. Higgs BR and cross-sections are discussed, with special emphasis on the detection at the LHC., Comment: 22 pages, 10 figures

We discuss the implications of assuming a four-zero Yukawa texture for the properties of the charged Higgs boson within the context of the general 2-Higgs Doublet Model of Type III. We begin by presenting a detailed analysis of the charged Higgs boson couplings with heavy quarks and the resulting pattern for its decays. The production of charged Higgs bosons is also sensitive to the modifications of its couplings, so that we also evaluate the resulting effects on the top decay $t \to b H^{+}$ as well as on `direct' $c\bar{b}\to H^++c. c.$ and `indirect' $q\bar q,gg\to \bar t b H^++c. c.$ production. Significant scope exists at the Large Hadron Collider for several $H^\pm$ production and decay channels combined to enable one to distinguish between such a model and alternative 2-Higgs doublet scenarios., Comment: 30 pages, 18 figures

Within the $\nu$MSSM, a Minimal Supersymmetric neutrino See-saw Model, Lepton Flavour Violating Higgs couplings are strongly enhanced at large $\tan\beta$ ($\gsim30$), which can lead to BR$(H^0/A^0 \to \tau\mu) \simeq O(10^{-4})$, for $M_{H^0/A^0}\gsim 160$ GeV. Enhancements on the production of Higgs bosons, through the gluon fusion mechanism, $gg\to H^0/A^0$, and the associated production channel $gg,q\bar q\to b\bar bH^0/A^0$, whose rates grow with $\tan\beta$, as well as the mass degeneracy that occurs between the $H^0$ and $A^0$ states in this regime, also contribute to further the possibilities to detect a heavy Higgs signal into $\tau\mu$ pairs. We show that the separation of $\tau\mu$ Higgs events from the background at the upcoming CERN Large Hadron Collider could be done for Higgs masses up to about 600 GeV for 300 fb$^{-1}$ of luminosity, for large $\tan\beta$ values. However, even with as little as 10 fb$^{-1}$ one can probe $H^0/A^0$ masses up to 400 GeV or so, if $\tan\beta=60$. Altogether, these processes then provide a new Higgs discovery mode as well as an independent test of flavour physics., Comment: 13 pages, 5 figures

Top quark decays are of particular interest as a mean to test the standard model (SM) predictions, both for dominant (t -> b + W) and rare decays (t -> q + W, cV, cVV, c phi^{0}, bWZ). As the latter are highly suppressed, they become an excellent window to probe the predictions of thories beyond the SM. In particular, we evaluate the corrections from new physics to the CKM-suppressed SM top quark decay t -> q + W (q = d, s), both within the an effective model with right-handed currents and the MSSM. We also discuss the perspectives to probe those predictions at the ILC., Comment: 11 pages

We present a detailed study of the Higgs sector within an extension of the Minimal Supersymmetric Standard Model that includes one Complex Higgs Triplet (MSSM+1CHT). The model spectrum includes three singly charged Higgs bosons as well as three CP-even (or scalar) and two CP-odd (or pseudoscalar) neutral Higgs bosons. We present an approximated calculation of the one-loop radiative corrections to the neutral CP-even Higgs masses ($m_{H_i^0}$) and the couplings $H_i^0 Z^0 Z^0$ ($i=1$, 2, 3), which determine the magnitude of the Higgs-strahlung processes $e^+ e^-\to Z^0 H^0_i$. Limits from LEP2 are then considered, in order to obtain bounds on the neutral Higgs sector. Further, we also include the experimental limits from LEP2 on $e^+e^-\to H^+H^-$ and those on BR($t \to b H^+$) from Tevatron, to derive bounds on the mass of the two lightest charged Higgs bosons ($H_1^{\pm}$ and $H_2^{\pm}$). Concerning the latter, we find some cases, where $m_{H_1^{\pm}} \simeq 90$ GeV, that are not excluded by any experimental bound, even for large values of $\tan\beta$, so that they should be looked for at the Large Hadron Collider (LHC)., Comment: 49 pages, 43 figures

We discuss a scenario consisting of an effective 4D theory containing fundamental and composite fields. The strong dynamics sector responsible for the compositeness is assumed to be of extra dimensional origin. In the 4D effective theory the SM fermion and gauge fields are taken as fundamental fields. The scalar sector of the theory resembles a bosonic topcolor in the sense there are two scalar Higgs fields, a composite scalar field and a fundamental gauge-Higgs unification scalar. A detailed analysis of the scalar spectrum is presented in order to explore the parameter space consistent with experiment. It is found that, under the model assumptions, the acceptable parameter space is quite constrained. As a part of our phenomenological study of the model, we evaluate the branching ratio of the lightest Higgs boson and find that our model predicts a large FCNC mode h -> tc, which can be as large as O(10^{-3}). Similarly, a large BR for the top FCNC decay is obtained, namely B.R.(t -> c + H) \simeq 10^{-4}, Comment: 14 pages, 7 figures

We analyze the possibility that the lighter stop {\tilde t_1} could be the next-to-lightest supersymmetric particle (NLSP) in models where the gravitino is the lightest supersymmetric particle (LSP). We do not find any possibility for a stop NLSP in the constrained MSSM with universal input soft supersymmetry-breaking masses at the GUT scale (CMSSM), but do find small allowed regions in models with non-universal Higgs masses (NUHM). We discuss the cosmological evolution of stop hadrons. Most {\tilde t_1}qq `sbaryons' and the corresponding `antisbaryons' annihilate with conventional antibaryons and baryons into {\tilde t_1}{\bar q} `mesinos' and the corresponding `antimesinos', respectively, shortly after the quark-hadron transition in the early Universe, and most mesinos and antimesinos subsequently annihilate. As a result, insufficient metastable charged stop hadrons survive to alter Big Bang nucleosynthesis., Comment: 31 pages, 14 figures

Top quark decays are of particular interest as a mean to test the standard model (SM) predictions, both for the dominant ($t\to b+W$) and rare decays ($t\to q+W, cV, cVV,c\phi^0,bWZ$). As the latter are highly suppressed, they become an excellent window to probe the predictions of theories beyond the SM. In particular, in this paper, we evaluate the corrections from new physics to the CKM-suppressed SM top quark decay $t\to q+W$ ($q=d,s$), both within the effective lagrangian approach and the MSSM and we discuss the perspectives to probe those predictions at the ILC., Comment: 5 pages, 1 table. Published in the Proceedings of the International Conference: New Trends in High-Energy Physics, Crimea, September 2006

We obtain the mass spectrum and the Higgs self-coupling of the two Higgs doublet model (THDM) in an alternative unification scenario where the parameters of the Higgs potential $\lambda_i$ ($i=1,2,3,4,5$) are determined by imposing their unification with the electroweak gauge couplings. An attractive feature of this scenario is the possibility to determine the Higgs boson masses by evolving the $\lambda_i$,s from the electroweak-Higgs unification scale $M_{GH}$ down to the electroweak scale. The unification condition for the gauge ($g_1,g_2$) and Higgs couplings is written as $g_1=g_2=f(\lambda_i)$, where $g_1=k_Y^{1/2} g_Y$, and $k_Y$ being the normalization constant. Two variants for the unification condition are discussed; Scenario I is defined through the linear relation: $g_1=g_2=k_H(i)\lambda_i(M_{GH})$, while Scenario II assumes a quadratic relation: $g^2_1=g^2_2=k_H(i)\lambda_i(M_{GH})$. Working in Scenario I, fixing {\it ad hoc} $-k_H(5)={1/2} k_H(4)={3/2} k_H(3)=k_H(2)=k_H(1) =1$, taking $\tan\beta=1$ and using the standard normalization ($k_Y=5/3$), we obtain the following spectrum for the Higgs boson masses $m_{h^0} = 109.1$ GeV, $m_{H^0} = 123.2$ GeV, $m_{A^0} = 115.5$ GeV, and $m_{H^{\pm}} = 80.3$ GeV, with similar results for other normalizations such as $k_Y=3/2$ and $k_Y=7/4$., Comment: 27 pages, 17 figures, 6 Tables

There are many possibilities for new physics beyond the Standard Model that feature non-standard Higgs sectors. These may introduce new sources of CP violation, and there may be mixing between multiple Higgs bosons or other new scalar bosons. Alternatively, the Higgs may be a composite state, or there may even be no Higgs at all. These non-standard Higgs scenarios have important implications for collider physics as well as for cosmology, and understanding their phenomenology is essential for a full comprehension of electroweak symmetry breaking. This report discusses the most relevant theories which go beyond the Standard Model and its minimal, CP-conserving supersymmetric extension: two-Higgs-doublet models and minimal supersymmetric models with CP violation, supersymmetric models with an extra singlet, models with extra gauge groups or Higgs triplets, Little Higgs models, models in extra dimensions, and models with technicolour or other new strong dynamics. For each of these scenarios, this report presents an introduction to the phenomenology, followed by contributions on more detailed theoretical aspects and studies of possible experimental signatures at the LHC and other colliders., Comment: Report of the CPNSH workshop, May 2004 - Dec 2005, 542 pages. The complete report as well as its individual chapters are also available from http://kraml.home.cern.ch/kraml/cpnsh/report.html

We study the SUSY flavor problem in the MSSM, we are namely interested in estimating the size of the SUSY flavor problem and its dependence on the MSSM parameters. For that, we made a numerical analysis randomly generating the entries of the sfermion mass matrices and then determinated which percentage of the points are consistent with current bounds on the flavor violating transitions on lepton flavor violating (LFV) decays $l_i \to l_j \gamma$. We applied two methods, mass-insertion approximation method (MIAM) and full diagonalization method (FDM). Furthermore, we determined which fermion masses could be radiatively generated (through gaugino-sfermion loops) in a natural way, using those random sfermion matrices. In general, the electron mass generation can be done with 30% of points for large $\tan\beta$, in both schemes the muon mass can be generated by 40% of points only when the most precise sfermion splitting (from the FDM) is taken into account., Comment: 23 pages, 10 figures

We propose an alternative unification scenario where the Higgs self-coupling (lambda) is unified with the electroweak SU(2)L x U(1)Y interactions at an intermediate scale MGH, lower than the GUT scale. In this model the SM remains valid up to this scale MGH, where the gauge and Higgs couplings satisfy the unification condition g1 = g2 = f(lambda). Two variants for this unification condition are discussed; scenario I is defined through the linear relation: g1 = g2 = k lambda(MGH), while scenario II assumes a quadratic relation: g1**2 = g2**2 = k lambda(MGH). An attractive feature of this class of models is the possibility to determine the SM Higgs boson mass by evolving lambda back from MGH down to the electroweak scale; fixing k = O(1) we obtain a Higgs mass value mH approx. 200 GeV. Above MGH, the single coupling gH that describes the electroweak-Higgs interactions, keeps evolving until it unifies with the strong coupling constant. We discuss a realization o this unification scenario within the context of a six-dimensional SU(3)c x SU(3)w Gauge-Higgs unified model., Comment: 28 pages, 19 figures

New family dependent fermionic interactions have been conjectured in several extensions of the Standard Model that range from Supersymmetry to composite theory up to flavor interactions. Strong constraints on these theoretical scenarios can be derived from light fermion phenomenology and from B-mesons studies. Corresponding constrains on the top quark sector are, on the other hand, rather week. Tevatron data, on top quark pair production and decay in dilepton channel, may suggest some deviation from the Standard Model expectations. Such a deviation can be successfully re-interpreted in terms of an exotic top decay that can arise in several theories beyond the Standard Model. Further investigations at present and future colliders will provide crucial tests on the models under discussion., Comment: 5 pages, 2 tables, submitted to Phys. Rev. Lett

We study the fermionic couplings of the neutral Higgs bosons in the THDM, assuming a four-texture structure for the Yukawa matrices. We then derive the low-energy constraints on the model, focusing in b-quark and lepton physics, and apply them to study Higgs boson detection at future colliders., Comment: 29 pages, 35 figures

The work contained herein constitutes a report of the ``Beyond the Standard Model'' working group for the Workshop "Physics at TeV Colliders", Les Houches, France, 26 May--6 June, 2003. The research presented is original, and was performed specifically for the workshop. Tools for calculations in the minimal supersymmetric standard model are presented, including a comparison of the dark matter relic density predicted by public codes. Reconstruction of supersymmetric particle masses at the LHC and a future linear collider facility is examined. Less orthodox supersymmetric signals such as non-pointing photons and R-parity violating signals are studied. Features of extra dimensional models are examined next, including measurement strategies for radions and Higgs', as well as the virtual effects of Kaluza Klein modes of gluons. An LHC search strategy for a heavy top found in many little Higgs model is presented and finally, there is an update on LHC $Z'$ studies., Comment: 113 pages, ed B.C. Allanach, v5 has changes to part XVI

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 figures

The vertex H^+_\alpha W^-h^0_\beta, involving the gauge boson W^+- and the charged (H^+-_\alpha) and neutral Higgs bosons (h^0_\beta), arises within the context of many extensions of the SM, and it can be used to probe the quantum numbers of the Higgs multiplet. After presenting a general discusion for the expected form of this vertex with arbitrary Higgs representations, we discuss its strength for several specific models, which include: i) the Two-Higgs Doublet Model (THDM), both the generic and the SUSY case, and ii) models with additional Higgs triplets, including both SUSY and non-SUSY cases. We find that in these models, there are regions of parameters where the decay H^+_\alpha -> W^+ h^0_\beta, is kinematically allowed, and reaches Branching Ratios (BR) that may be detectable, thus allowing to test the properties of the Higgs sector., Comment: 20 pages, 9 figures

A definition of the rho parameter based on the Higgs couplings with the gauge bosons, rho_h= g_{hWW}}/c^2_W g_{hZZ}, is proposed as a new probe into the origin of the mechanism of electroweak symmetry breaking. While $\rho_h=1$ holds in the SM, deviations from one are predicted in models with extended Higgs sector. We derive a general expresion of rho_h for a model with arbitrary Higgs multiplets, and discuss its size within the context of specific models with Higgs triplets, including the ``Little Higgs'' models recently proposed. We find the even for Higgs models that incorporate the custodial symmetry to make rho=1, one could have rho_h\neq 1, which could be tested at the level of a few percent, with the precision Higgs meassurements expected at the NLC., Comment: 12 pages, 2 figures

We show how the well studied $\gamma\gamma$ inclusive Higgs signal can be used at the Large Hadron Collider to test Gauge Mediated Supersymmetry Breaking scenarios in which a rather heavy Higgs boson decays into two light neutralinos, the latter yielding two photons and missing (transverse) energy, Comment: 17 pages, latex, 4 figures (preprint number and reference added)

We review some of the results of our recent work dealing with the novel type of Higgs signals that arise when one considers extensions of the standard model. We discuss first possible deviations on the Higgs couplings due to heavy particles, in the context of the MSSM and with large extra-dimensions. Then, we present several models where it is possible to induce flavor violating Higgs couplings, and probe them at future hadron colliders through the LFV Higgs decay h-> tau mu or with rare top decays., Comment: Talk given at the X Mexican School of Particles and Fields, Playa del Carmen, Mexico, 2002

Electroweak precision measurements indicate that the standard model Higgs boson is light and that it could have already been discovered at LEP 2, or might be found at the Tevatron Run 2. In the context of a TeV^-1 size extra dimensional model, we argue that the Higgs boson production rates at LEP and the Tevatron are suppressed, while they might be enhanced at the LHC or at CLIC. This is due to the possible mixing between brane and bulk components of the Higgs boson, that is, the non-trivial brane-bulk `location' of the lightest Higgs. To parametrize this mixing, we consider two Higgs doublets, one confined to the usual space dimensions and the other propagating in the bulk. Calculating the production and decay rates for the lightest Higgs boson, we find that compared to the standard model (SM), the cross section receives a suppression well below but an enhancement close to and above the compactification scale M_c. This impacts the discovery of the lightest (SM like) Higgs boson at colliders. To find a Higgs signal in this model at the Tevatron Run 2 or at the LC with sqrt(s)=1.5 TeV, a higher luminosity would be required than in the SM case. Meanwhile, at the LHC or at CLIC with sqrt(s) ~ 3-5 TeV one might find highly enhanced production rates. This will enable the latter experiments to distinguish between the extra dimensional and the SM for M_c up to about 6 TeV., Comment: 15 pages, 3 figures. Discussion of KK width and cutoff, new LHC figure and references added

We study the conditions under which flavor violation arises in scalar-fermion interactions, as a result of the mixing phenomena between the standard model and exotic fermions. Phenomenological consequences are discussed within the specific context of a left-right model where these additional fermions have mirror properties under the new SU(2)_R gauge group. Bounds on the parameters of the model are obtained from LFV processes; these results are then used to study the LFV Higgs decays (H --> tau l_j, l_j = e, mu), which reach branching ratios that could be detected at future colliders., Comment: 12 pages, 2 figures, ReVTex4, graphicx, to be published in Phys. Rev. D

We discuss the experimental and theoretical uncertainties on precision electroweak observables and their relationship to the indirect constraints on the Higgs-boson mass, $\MH$, in the Standard Model (SM). The critical experimental measurements ($\MW$, $\sweff$, $\mt$, ...) are evaluated in terms of their present uncertainties and their prospects for improved precision at future colliders, and their contribution to the constraints on $\MH$. In addition, the current uncertainties of the theoretical predictions for $\MW$ and $\sweff$ due to missing higher order corrections are estimated and expectations and necessary theoretical improvements for future colliders are explored. The constraints from rare B decays are also discussed. Analysis of the present experimental and theoretical precisions yield a current upper bound on $\MH$ of $\sim 200$ GeV. Including anticipated improvements corresponding to the prospective situation at future colliders (Tevatron Run II, LHC, LC/GigaZ), we find a relative precision of about 25% to 8% (or better) is achievable in the indirect determination of $\MH$., Comment: Summary report of the Precision Measurement working group at Snowmass 2001

Charged Higgs decays are discussed within an effective lagrangian extension of the two-higgs doublet model, assuming new physics appearing in the Higgs sector of this model. Low energy constrains are used to imposse bounds on certain dimension -six operators that describe the modified charged Higgs interactions. These bounds are used then to study the decays H^+ -> Wg, WZ and Wh, which can have branching ratios of order 10^-5, 10^-1 and O(1), respectively; thse modes are thus sensitive probes of the symmetries of the Higgs sector that could be tested at future colliders., Comment: 15 pages, 3 figures

The squark mass-matrix from the soft supersymmetry (SUSY) breaking sector contains a rich flavor-mixing structure that allows O(1) mixings among top- and charm-squarks while being consistent with all the existing theoretical and experimental bounds. We formulate a {\it minimal} flavor-changing-neutral current scheme in which the squark mixings arise from the non-diagonal scalar trilinear interactions. This feature can be realized in a class of new models with horizontal U(1)_H symmetry which generates realistic quark-mass matrices and provides a solution to the SUSY \mu-problem. Finally, without using the mass-insertion approximation, we analyze SUSY radiative corrections to the bcH^+ and tch^0 couplings, and show that these couplings can reveal exciting new discovery channels for the Higgs boson signals at the Tevatron and the LHC., Comment: To match the version in Phys. Lett. B (two references added, result/conclusion un-changed)

A complete study for the production of neutral (h^0, H^0, A^0 (= \phi^0_i)) and charged Higgs (H^\pm) bosons at electron-photon colliders is presented in the context of the minimal supersymmetric standard model. A particular choice of the non-linear R_\xi gauge is used to evaluate the amplitudes of the reaction e-gamma --> e \phi^0_i. The resulting cross section indicates that it will be possible to detect a signal from the neutral Higgs bosons for most regions of parameter space at the future linear colliders with \sqrt{s}=500 GeV through the reaction e gamma --> e \phi^0_i. This reaction also offers the interesting possibility to measure the Higgs mass through the detection of the outgoing electron. The production of the charged Higgs boson through the reaction e gamma --> \nu_e H^\pm$ has in general smaller values for the cross section, which seems more difficult to observe., Comment: submitted to Phys. Rev. D

We study the contribution of charged Higgs boson to the rare decay of the top quark t->q+WZ (q=d,s,b) in models with Higgs sector that includes doublets and triplets. Higgs doublets are needed to couple charged Higgs with quarks, whereas the Higgs triplets are required to generate the non-standard vertex HWZ at tree-level. It is found that within a model that respect the custodial SU(2) symmetry and avoids flavour changing neutral currents by imposing discrete symmetries, the decay mode t->b+WZ, can reach a branching ratio of order 0.0178, whereas the decay modes t->(d,s)+WZ, can reach a similar branching ratio in models where flavour changing neutral currents are suppressed by flavour symmetries., Comment: Typeset using REVTEX and EPSF, 5 pag, 2 figures

We study the inter-relations that exist between the present experimental bounds on the Higgs mass, as obtained from radiative corrections to $m_W$, and the effective parameters, $\alpha_i$ and $\Lambda$. We find that the SM bounds on $m_H$, arising from a precise determination of the $m_W$ mass, can be substantially modified by the presence of dimension-6 operators which appear in the linear realization of the effective Lagrangian approach. A Higgs mass as heavy as 700 GeV can be allowed for scales of new physics of the order of 1 TeV., Comment: 8 pages, 3 ps figures, uses elsevier style

We discuss the Flavor-Changing Neutral Current (FCNC) decays of the top quark t -> c Vi Vj (Vi=gamma, Z, g) in the framework of the Standard Model (SM) and in a two-higgs doublet model (2HDM) with tree-level FCNC couplings. While in the SM the expected branching ratios are extremelly small, in the 2HDM they may be sizable, of order 10^(-5) - 10^(-5), and thus accesible at the CERN LHC. We conclude with the interesting observation that the FCNC decay modes may not be equally suppressed as their corresponding decays t ->c Vi in this 2HDM., Comment: RevTeX, 2 epsi figures, 10 pgs. Comments and references added. Submitted to Physical Review D

The small mass of the bottom quark, relative to its weak isospin partner, the top quark, makes the bottom an effective probe of new physics in Higgs and top sectors. We study the Higgs boson production associated with bottom quarks, ppbar/pp to phi+b+bbar to 4b, at the Fermilab Tevatron and the CERN LHC. We find that strong and model-independent constraints on the size of the phi-b-bbar coupling can be obtained for a wide range of Higgs boson masses. Their implications for the composite Higgs models with strong dynamics associated with the third family quarks (such as the top-condensate/topcolor models with naturally large bottom Yukawa couplings), and for the supersymmetric models with large tan(beta), are analyzed. We conclude that the Tevatron and the LHC can put stringent bounds on these models, if the phi+b+bbar signal is not found., Comment: Version to be published in Phys. Rev. D, RevTex, 52 pages, including 16 EPS figures, typos corrected plus minor refinements for discussions

We study the discovery reach of the Tevatron and the LHC for detecting a Higgs boson (h), predicted in composite models of the electroweak symmetry breaking or in supersymmetric theories, with an enhanced b-quark Yukawa coupling via p \bar{p} / p p \to b \bbar h (\to b \bbar) + X. Our analysis shows that studying this process at the Tevatron Run II or the LHC can provide strong constraints on these models., Comment: Revtex, 4 pages, Corrected 1 reference and a few typographical errors

We study the production of the SM Higgs boson (H^0) at future e gamma colliders, through the reaction e gamma --> e H^0. The amplitude is evaluated using the non-linear R_\xi gauge, which greatly simplifies the calculation. Complete analytical expressions for the amplitudes are presented, which include the contributions from 1-loop triangles "gamma gamma^* H^0" and "gamma Z^* H^0" as well as the W- and Z-boxes with their related $eeH^0$ triangle graphs. The resulting cross section for this mechanism indicates that it could be used to detect the Higgs signal and to test its properties., Comment: 6 pages, 2 figures, RevTeX

We study the possibility to detect heavy physics effects in the interactions of Higgs bosons and the top quark at future colliders using the effective Lagrangian approach. The modification of the interactions may enhance the production of Higgs bosons at hadron colliders through the mechanisms of gluon fusion and associated production with a W boson or $t\bar{t}$ pairs. The most promising signature is through the decay of the Higgs boson into two photons, whose branching ratio is also enhanced in this approach. As a consequence of our analysis we get a bound on the chromomagnetic dipole moment of the top quark., Comment: 14 pages, Latex, two figures available by fax under request. To be published in Phys. Lett B

We compute isospin corrections to the charmless semileptonic $B \rightarrow V$ transitions arising from $\rho-\omega$ mixing and discuss its relevance in the determination of $V_{ub}$., Comment: Latex, 8 pages, no figures

We study a model with two Higgs doublets where FCNC are allowed at tree-level. In this model, the interactions of charged Higgs with fermions ($H^\pm f \bar{f'}$), include a term that is not proportional to the fermion masses, which we constraint using the following low-energy processes: i) tau decays ($\tau \to \nu_{\tau} e\nu_e, \nu_{\tau}\mu\nu_{\mu}, \nu_{\tau}\pi$), ii) leptonic decays of pseudoscalar mesons ($\pi, K \to \ell\nu_{\ell}$) and iii) semileptonic b-decays. With these constraints it is possible to make predictions; we illustrate this by presenting the rates for the (FCNC) decay $c\to u+\gamma$, the (second class-current) decay $\tau\to \nu_{\tau}+ \eta\pi$, and also the theoretical value of the neutron life-time., Comment: 22 pages, phyzz, 1 figure upon request, corrected version of paper published in Phys. Rev. D51, 5263 (1995)

The top group studied discovery issues as well as measurements to be made at the Tevatron, the LHC and the SSC., Comment: 11 pages, LaTeX

The Higgs sector in spontaneously broken R Parity supersymmetry (RPSUSY) shows interesting features that require new search techniques. Both the mass spectrum and production rates may differ from the standard model and minimal supersymmetric model (MSSM) expectations. For some parameter choices, the dominant Higgs boson decay mode can even be invisible, leading to events with large missing transverse momentum carried by superweakly interacting majorons. We study the reaction $pp \ra Z + H + X$, and find that it canlead to detectable events at LHC/SSC for a large region of parameter space., Comment: Latex (Matex included), 13 pag.(figures not included), FTUV/92-30 IFIF/92-38