The forward-backward asymmetry of top quark production at the Tevatron in warped extra dimensional models

The CDF and D0 experiments have reported on the measurement of the forward-backward asymmetry of top quark pair production at the Tevatron and the result is that it is more than 2 standard deviations above the predicted value in the Standard Model. This has to be added to the longstanding anomaly in the forward-backward asymmetry for bottom quark production at LEP which is 3 standard deviations different from the Standard Model value. The discrepancy in the bottom asymmetry can be accounted for by the contributions of Kaluza-Klein excitations of electroweak gauge bosons at LEP in warped extra dimensional models in which the fermions are localized differently along the extra dimension so that the gauge interactions of heavy third generation fermions are naturally different from that of light fermions. In this paper, we show that it is more difficult to elaborate a model generating a significant top asymmetry in a similar way -- through exchanges of Kaluza-Klein gluons at the Tevatron -- due to the indirect constraints originating from precision electroweak data.Comment: 4 pages, 1 figure, published versio

Search for a Higgs Boson Decaying into Two Photons with the L3 Detector at LEP

A search is performed for a Higgs boson, decaying into two photons, using the L3 data collected at centre of mass energies between $\sqrt s$ = 189 and 202 GeV, corresponding to an integrated luminosity of 400 pb$^{-1}$. The processes $e^{+}e^{-}\to {Zh} \to {q} \bar{q} \gamma \gamma$, $e^{+}e^{-}\to {Zh} \to \nu \bar{\nu} \gamma \gamma$, $e^{+}e^{-}\to {Zh} \to {l}^{+} {l}^{-} \gamma \gamma$ are considered. The observed data are found to be consistent with the expected background from standard physics processes. Limits on the branching fraction of the Higgs boson decay into two photons as a function of the Higgs mass are shown and a lower mass limit on a fermiophobic Higgs is derived.Comment: 3 pages, 2 postscript figures, Presented at the DPF2000 Conference, August 9-12, 2000, The Ohio State University, Columbus, Ohi

e+ e- -> t anti-t H including decays: on the size of background contributions

We present results for the lowest order cross sections, calculated with the complete set of the standard model Feynman diagrams, of all possible detection channels of the associated production of the top quark pair and the light Higgs boson, which may be used for determination of the top-Higgs Yukawa coupling at the future e+e- linear collider. We show that, for typical particle identification cuts, the background contributions are large. In particular, the QCD background contributions are much bigger than could be expected when taking into account a possibly low virtuality of exchanged gluons. Moreover, we include the initial state radiation effects and discuss the dependence of the cross sections on the Higgs boson and top quark masses.Comment: 13 pages, 1 figure; substantially revised version, accepted for publication in Eur.Phys.J.

Probing the spin-parity of the Higgs boson via jet kinematics in vector boson fusion

Determining the spin and the parity quantum numbers of the recently discovered Higgs-like boson at the LHC is a matter of great importance. In this paper, we consider the possibility of using the kinematics of the tagging jets in Higgs production via the vector boson fusion (VBF) process to test the tensor structure of the Higgs-vector boson ($HVV$) interaction and to determine the spin and CP properties of the observed resonance. We show that an anomalous $HVV$ vertex, in particular its explicit momentum dependence, drastically affects the rapidity between the two scattered quarks and their transverse momenta and, hence, the acceptance of the kinematical cuts that allow to select the VBF topology. The sensitivity of these observables to different spin-parity assignments, including the dependence on the LHC center of mass energy, are evaluated. In addition, we show that in associated Higgs production with a vector boson some kinematical variables, such as the invariant mass of the system and the transverse momenta of the two bosons and their separation in rapidity, are also sensitive to the spin--parity assignments of the Higgs--like boson.Comment: 15 pages, 5 figure

The Search for Higgs particles at high-energy colliders: Past, Present and Future

I briefly review the Higgs sector in the Standard Model and its minimal Supersymmetric extension, the MSSM. After summarizing the properties of the Higgs bosons and the present experimental constraints, I will discuss the prospects for discovering these particle at the upgraded Tevatron, the LHC and a high-energy $e^+e^-$ linear collider. The possibility of studying the properties of the Higgs particles will be then summarized.Comment: 28 pages, latex, 15 figures, talk at WHEPP VII, Allahabad, Indi

The Higgs sector of the phenomenological MSSM in the light of the Higgs boson discovery

The long awaited discovery of a new light scalar at the LHC opens up a new era of studies of the Higgs sector in the SM and its extensions. In this paper we discuss the consequences of the observation of a light Higgs boson with the mass and rates reported by the ATLAS and CMS collaborations on the parameter space of the phenomenological MSSM, including also the so far unsuccessful LHC searches for the heavier Higgs bosons and supersymmetric particle partners in missing transverse momentum as well as the constraints from B physics and dark matter. We explore the various regimes of the MSSM Higgs sector depending on the parameters MA and tan beta and show that only two of them are still allowed by all present experimental constraints: the decoupling regime where there is only one light and standard--like Higgs boson and the supersymmetric regime in which there are light supersymmetric particle partners affecting the decay properties of the Higgs boson, in particular its di-photon and invisible decays.Comment: 21 pages, 9 figures v2 - Discussion of the impact of LHC data extended, scan statistics increased, a few figures added and typos correcte

Higgs Physics at Future Colliders: recent theoretical developments

I review the physics of the Higgs sector in the Standard Model and its minimal supersymmetric extension, the MSSM. I will discuss the prospects for discovering the Higgs particles at the upgraded Tevatron, at the Large Hadron Collider, and at a future high--energy $e^+e^-$ linear collider with centre--of--mass energy in the 350--800 GeV range, as well as the possibilities for studying their fundamental properties. Some emphasis will be put on the theoretical developments which occurred in the last two years.Comment: 20 pages, latex, 12 figures. Talk given at PASCOS 2003 (Bombay, India

Three-Body Decays of Top and Bottom Squarks

We investigate the decays of third generation scalar quarks in the Minimal Supersymmetric extension of the Standard Model, focusing on the three-body modes. We calculate the partial widths of the decays of heavier top and bottom squarks into the lighter ones and a fermion pair [through virtual vector boson, Higgs boson or gaugino exchanges] and the partial widths of the three-body decays of both top squarks into bottom quarks and a pair of fermion and scalar fermion [we consider the case of lighter $\tilde{\tau}$ or $\tilde{b}$ states] and into a bottom quark, the lightest neutralino and a $W$ or a charged Higgs boson $H^\pm$. Some of these decay modes are shown to have substantial branching ratios in some areas of the parameter space.Comment: 24 pages with 4 psfigures, late

Higgs Physics: Theory

I review the theoretical aspects of the physics of Higgs bosons, focusing on the elements that are relevant for the production and detection at present hadron colliders. After briefly summarizing the basics of electroweak symmetry breaking in the Standard Model, I discuss Higgs production at the LHC and at the Tevatron, with some focus on the main production mechanism, the gluon-gluon fusion process, and summarize the main Higgs decay modes and the experimental detection channels. I then briefly survey the case of the minimal supersymmetric extension of the Standard Model. In a last section, I review the prospects for determining the fundamental properties of the Higgs particles once they have been experimentally observed.Comment: 21 pages, 15 figures. Talk given at the XXV International Symposium on Lepton Photon Interactions at High Energies (Lepton Photon 11), 22-27 August 2011, Mumbai, Indi