236 research outputs found

### 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

### 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

### 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

### 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

### 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

### 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

### 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

### 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

### A Review of Pentaquark Calculations on the Lattice

We review lattice calculations of pentaquarks and discuss issues pertaining
to interpolation fields, distinguishing the signal of pentaquarks from those of
the KN scattering states, chiral symmetry, and ghost state contaminations.Comment: Talk at International Conference on QCD and Hadronic Physics, 8
pages, 3 figure

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