Testing the Higgs boson gluonic couplings at LHC

We study Higgs + jet production at hadron colliders in order to look for new physics residual effects possibly described by the $dim=6$ operators {\O}_{GG} and {\widetilde\O}_{GG} which induce anomalous $Hgg$ and $Hggg$ couplings. Two ways for constraining these operators at LHC may be ~useful. The first is based on the total Higgs boson production rate induced by gluon-gluon fusion, in which the main cause of limitations are due to theoretical uncertainties leading to sensitivities of $|d_G|\simeq 3.\times 10^{-4}$ and $|\widetilde{d}_G|\simeq 1.4\times 10^{-3}$ for the corresponding anomalous couplings, in the mass range 100 GeV \lsim \mh \lsim 2~00 GeV. These results imply sensitivity to new physics scales of 51 and 24 TeV respectively. The second way investigated here concerns the shape of the Higgs transverse momentum; for which the theoretical uncertainties are less severe and the limitations are mainly induced by statistics. A simple analysis, based on the ratio of the number of events at large and low $p_T$ at LHC, leads to similar sensitivities, if only the $H\to \gamma \gamma$ decay mode is used. But the sensitivities can now be improved by a factor 2 to 10, depending on the Higgs mass, if the Higgs decay modes to $WW^*$, $ZZ^*$, $WW$, $ZZ$ are also used.Comment: 23 pages and 7 figures, version to appear in Phys.ReV.D. e-mail: [email protected]

Application of Current Algebra in Three Pseudoscalar Meson Decays of τ\tau Lepton

The decays of $\tau \to 3\pi \nu$ and $\tau \to \pi K^{*} \nu, K\rho \nu$ are calculated using the hard pion and kaon current algebra and assuming the Axial-Vector meson dominance of the hadronic axial currents. Using the experimental data on their masses and widths, the $\tau$ decay branching ratios into these channels are calculated and found to be in a reasonable agreement with the experimental data. In particular, using the available Aleph data on the $3\pi$ spectrum, we determine the $A_1$ parameters, $m_A=1.24\pm 0.02 GeV$, $\Gamma _A=0.43\pm 0.02$ GeV; the hard current algebra calculation yields a $3\pi$ branching ratio of $19 \pm 3 \%$.Comment: 14 pages, Tex, 6 included figure

Dimension-six CP-conserving operators of the third-family quarks and their effects on collider observables

We list all possible dimension-six CP-conserving $SU_c(3)\times SU_L(2) \times U_Y(1)$ invariant operators involving the third-family quarks which could be generated by new physics at a higher scale. Expressions for these operators after electroweak gauge symmetry breaking and the induced effective couplings $Wt\bar b$, $Xb\bar b$ and $Xt\bar t$ $( X=Z,\gamma,g,H)$ are presented. Analytic expressions for the tree level contributions of all these operators to the observables $R_b$ and $A^b_{FB}$ at LEP I, $\sigma(e^+e^-\rightarrow b\bar b)$ and $A^b_{FB}$ at LEP II, $\sigma(e^+e^-\rightarrow t\bar t)$ and $A_{FB}^t$ at the NLC, as well as $\sigma(p\bar p\rightarrow t\bar b+X)$ at the Tevatron upgrade, are provided. The effects of these operators on different electroweak observables are discussed and numerical examples presented. Numerical analyses show that in the coupling region allowed by $R_b$ and $A^b_{FB}$ at LEP I, some of the new physics operators can still have significant contributions at LEP II, the Tevatron and the NLC.Comment: 25 page

Diagonalization of the neutralino mass matrix and boson-neutralino interaction

We analyze a connection between neutralino mass sign, parity and structure of the neutralino-boson interaction. Correct calculation of spin-dependent and spin-independent contributions to neutralino-nuclear scattering should consider this connection. A convenient diagonalization procedure, based on the exponetial parametrization of unitary matrix, is suggested.Comment: 21 pages, RevTex

The relevance of polarized bZ production at LHC

We consider the Z polarization asymmetry A_Z=(sigma(Z_R)-sigma(Z_L))/(sigma(Z_R)+sigma(Z_L)) in the process of associated bZ production at the LHC. We show that in the Standard Model (SM) this quantity is essentially given by its Born approximation, remaining almost unaffected by QCD scales and parton distribution functions variations as well as by electroweak corrections. The theoretical quantity that appears in A_Z is the same that provides the LEP1 Z -> b bbar forward-backward asymmetry, the only measured observable still in some contradiction with the SM prediction. In this sense, A_Z would provide the possibility of an independent verification of the possible SM discrepancy, which could reach, if consistency with LEP1 measurements is imposed, values of the relative ten percent size.Comment: 10 pages, 5 eps figure

Towards Collinear Evolution Equations in Electroweak Theory

We consider electroweak radiative corrections to hard inclusive processes at the TeV scale, and we investigate how collinear logarithms factorize in a spontaneously broken gauge theory, similarly to the DGLAP analysis in QCD. Due to the uncancelled double logs noticed previously, we find a factorization pattern which is qualitatively different from the analogous one in QCD. New types of splitting functions emerge which are needed to describe the initial beam charges and are infrared-sensitive, that is dependent on an infrared cutoff provided, ultimately, by the symmetry breaking scale. We derive such splitting functions at one-loop level in the example of SU(2) gauge theory, and we also discuss the structure functions' evolution equations, under the assumption that isospin breaking terms present in the Ward identities of the theory are sufficiently subleading at higher orders.Comment: 5 pages, 3 figure

Single Neutralino production at CERN LHC

The common belief that the lightest supersymmetric particle (LSP) might be a neutralino, providing also the main Dark Matter (DM) component, calls for maximal detail in the study of the neutralino properties. Motivated by this, we consider the direct production of a single neutralino \tchi^0_i at a high/energy hadron collider, focusing on the \tchi^0_1 and \tchi^0_2 cases. At Born level, the relevant subprocesses are q\bar q\to \tchi^0_i \tilde g, g q\to \tchi^0_i \tilde q_{L,R} and q\bar q'\to \tchi^0_i\tchi^\pm_j; while at 1-loop, apart from radiative corrections to these processes, we consider also gg\to \tchi^0_i\tilde{g}, for which a numerical code named PLATONgluino is released. The relative importance of these channels turns out to be extremely model dependent. Combining these results with an analogous study of the direct \tchi^0_i\tchi^0_j pair production, should help in testing the SUSY models and the Dark Matter assignment.Comment: 22 pages and 12 figures; version to appear in Phys.Rev.

High-Energy Vector-Boson Scattering with Non-Standard Interactions and the Role of a Scalar Sector

The high-energy behavior of vector-boson scattering amplitudes is examined within an effective theory for non-standard self-interactions of electroweak vector-bosons. Irrespectively of whether this theory is brought into a gauge invariant form by including non-standard interactions of a Higgs particle I find that terms that grow particularly strongly with increasing scattering energy are absent. Different theories are compared concerning their high-energy behavior and the appearance of divergences at the one-loop level.Comment: 21 pages LaTeX, condensed version of BI-TP 93/5