Electroweak phase transition: recent results

Recent results of four-dimensional (4d) lattice simulations on the finite temperature electroweak phase transition (EWPT) are discussed. The phase transition is of first order in the SU(2)-Higgs model below the end point Higgs mass 66.5$\pm$1.4 GeV. For larger masses a rapid cross-over appears. This result completely agrees with the results of the dimensional reduction approach. Including the full Standard Model (SM) perturbatively the end point is at 72.1$\pm$1.4 GeV. Combined with recent LEP Higgs mass lower bounds, this excludes any EWPT in the SM. A one-loop calculation of the static potential makes possible a precise comparison of the lattice and perturbative results. Recent 4d lattice studies of the Minimal Supersymmetric SM (MSSM) are also mentioned.Comment: Latex, 3 pages, 4 figures. Talk presented at the International Europhysics Conference on High Energy Physics (EPS-HEP99), Tampere, Finland, Jul y 15-21, 199

The Pentaquarks in the Linear Molecular Heptaquark Model

In this talk, multiquarks are studied microscopically in a standard quark model. In pure ground-state pentaquarks the short-range interaction is computed and it is shown to be repulsive. An additional quark-antiquark pair is then considered, and this is suggested to produce linear molecular system, with a narrow decay width. The quarks assemble in three hadronic clusters, and the central hadron provides stability. The possible crypto-heptaquark hadrons with exotic pentaquark flavours, with strange, charmed and bottomed quarks, are predicted.Comment: 6 pages, 3 tables, talk presented as the Eighth Workshop on Non-Perturbative Quantum Chromodynamics 7-11 June 2004, Paris, proceedings edited by B. Muller, Chung-I Tan and Y. Gabellin

Constraints on Mirror Fermion Mixing Angles from Anomalous Magnetic Moment Data

The new contributions to the electron (muon) anomalous magnetic moment arising in mirror fermion theories have been calculated. Imposing the experimental constraint lowers the current upper bound on the ordinary - mirror lepton mixing angles by a factor of 50 making predictions for mirror lepton production at HERA undetectably small. A way out is to allow for different mixing angles of the L and R field components. Choosing very small right mixing angles compatibility with the anomalous magnetic moment measurement may be easily maintained, while choosing left mixing angles close to the upper limits yields still reasonable HERA cross-sections.Comment: 10 pages, 2 figures (not included), Latex file; ITP-BUDAPEST REPORT NO. 48

Lattice study of the Coleman--Weinberg mass in the SU(2)-Higgs model

Radiative symmetry breaking is a well known phenomenon in perturbation theory. We study the problem in a non-perturbative framework, i.e. lattice simulations. The example of the bosonic sector of the SU(2)-Higgs model is considered. We determine the minimal scalar mass which turns out to be higher than the mass value given by 1-loop continuum perturbation theory.Comment: Contribution to ICHEP-02, Amsterdam, 24-31 July 2002, 2 pages, 1 figur

Perturbative and non-perturbative studies of the SU(2)-Higgs model on lattices with asymmetric lattice spacings

We present a calculation of the O(g^2,\lambda) perturbative corrections to the coupling anisotropies of the SU(2)-Higgs model on lattices with asymmetric lattice spacings. These corrections are obtained by a one-loop calculation requiring the rotational invariance of the gauge and Higgs boson propagators in the continuum limit. The coupling anisotropies are also determined from numerical simulations of the model on appropriate lattices. The one-loop perturbation theory and the simulation results agree with high accuracy. It is demonstrated that rotational invariance is also restored for the static potential determined from space-space and space-time Wilson loops.Comment: 27pages, Latex, 7 figures (7 eps, 3 ps files), correction of misprint

Electroweak phase transition by four dimensional simulations

The finite temperature phase transition in the SU(2)-Higgs model at a Higgs boson mass $M_H \simeq 35$ GeV is studied in numerical simulations on four dimensional lattices with time-like extensions up to $L_t=5$. $T_c/M_H$ is extrapolated to the continuum limit and a comparison with the perturbative prediction is made. A one-loop calculation to the coupling anisotropies of the SU(2)-Higgs model on lattices with asymmetric lattice spacings is presented. Our numerical simulations show that the above perturbative result is applicable in the phenomenologically interesting parameter region.Comment: 3 pages, Latex, 3 figures, Talk presented at LATTICE96(electroweak) by Z. Fodo

The end point of the first-order phase transition of the SU(2) gauge-Higgs model on a four-dimensional isotropic lattice

We report results of a study of the end point of the electroweak phase transition of the SU(2) gauge-Higgs model defined on a four-dimensional isotropic lattice with N_t=2. Finite-size scaling study of Lee-Yang zeros yields lambda_c=0.00116(16) for the end point. Combined with a zero-temperature measurement of Higgs and W boson masses, this leads to M_{H,c}=68.2+-6.6 GeV for the critical Higgs boson mass. An independent analysis of Binder cumulant gives a consistent value lambda_c=0.00102(3) for the end point.Comment: LATTICE98(electroweak), 3 pages of LaTeX, 4 figure

Where does the hot electroweak phase transition end?

We give the nonperturbative phase diagram of the four-dimensional hot electroweak phase transition. A systematic extrapolation $a \to 0$ is done. Our results show that the finite temperature SU(2)-Higgs phase transition is of first order for Higgs-boson masses $m_H<66.5 \pm 1.4$ GeV. The full four-dimensional result agrees completely with that of the dimensional reduction approximation. This fact is of particular importance, because it indicates that the fermionic sector of the Standard Model (SM) can be included perturbatively. We obtain that the Higgs-boson endpoint mass in the SM is $72.4 \pm 1.7$ GeV. Taking into account the LEP Higgs-boson mass lower bound excludes any electroweak phase transition in the SM.Comment: LATTICE98(electroweak), presented by Z. Fodor. Latex, 3 pages, 3 figu res. Comment line change

Determining the β\beta-function of the strong interaction and closing the light gluino window

We discuss the perturbative running of alpha_s in a model independent way. Our analysis contains the data on the hadronic tau decay and all the total hadronic cross sections in e+e- annihilation between 5 GeV and M_Z. We determine the color coefficients and the perturbative beta-function of the strong interaction. The perturbative approach shows a nice convergence of the confidence level (CL) regions. The results are in agreement with QCD and rule out the QCD+light gluino scenario on the 90% CL. We combine our method with that of the multi-jet analysis at LEP. The combined result rules out light gluinos on the 99% CL