arXiv subjects

Z. Fodor

Publications and source records attributed to Z. Fodor.

215 records · Page 12Linked to original sources

arXiv1998

Endpoint of the hot electroweak phase transition

We give the nonperturbative phase diagram of the four-dimensional hot electroweak phase transition. The Monte-Carlo analysis is done on lattices with different lattice spacings ($a$). 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. At this endpoint the phase transition is of second order, whereas above it only a rapid cross-over can be seen. 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 can be included perturbatively. We obtain that the Higgs-boson endpoint mass in the Standard Model is $72.4 \pm 1.7$ GeV. Taking into account the LEP Higgs-boson mass lower bound excludes any electroweak phase transition in the Standard Model.

hep-ph↗

arXiv1997

Abundance of Delta Resonances in 58Ni+58Ni Collisions between 1 and 2 AGeV

Charged pion spectra measured in 58Ni-58Ni collisions at 1.06, 1.45 and 1.93 AGeV are interpreted in terms of a thermal model including the decay of Delta resonances. The transverse momentum spectra of pions are well reproduced by adding the pions originating from the Delta-resonance decay to the component of thermal pions, deduced from the high transverse momentum part of the pion spectra. About 10 and 18% of the nucleons are excited to Delta states at freeze-out for beam energies of 1 and 2 AGeV, respectively.

nucl-ex↗

arXiv1997

Determining the 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 data on the hadronic tau decay and 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 results are in agreement with QCD and rule out the QCD+light gluino scenarios on the 70.8 - 93.0% CL. We combine our method with that of the multi-jet analysis at LEP. The combined result rules out light gluinos at least on the 99.76% CL, provided that nonperturbative effects are not large.

hep-ph↗

arXiv1996

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.

hep-lat↗

arXiv1996

Numerical tests of the electroweak phase transition and thermodynamics of the electroweak plasma

The finite temperature phase transition in the SU(2) Higgs model at a Higgs boson mass $M_H \simeq 34$ GeV is studied in numerical simulations on four-dimensional lattices with time-like extensions up to $L_t=5$. The effects of the finite volume and finite lattice spacing on masses and couplings are studied in detail. The errors due to uncertainties in the critical hopping parameter are estimated. The thermodynamics of the electroweak plasma near the phase transition is investigated by determining the relation between energy density and pressure.

hep-lat↗

arXiv1996

The SU(2)-Higgs model on asymmetric lattices

We calculate the ${\cal O}(g^2,λ)$ 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.

hep-lat↗

arXiv1995

Interface Tension of the Electroweak Phase Transition

In our nonperturbative lattice investigation we study the interface tension of the finite-temperature electroweak phase transition. In this analysis the Higgs mass has been chosen to be about $35$ GeV. At the transition point of a finite volume system, tunnelling between the symmetric and the Higgs phase takes place. This phenomenon leads to a splitting of the ground state, which can be used to determine the interface tension. The result obtained this way agrees with the result of the two-coupling method and with the prediction of the perturbative approach.

hep-lat↗

arXiv1995

THERMODYNAMICS OF THE ELECTROWEAK PHASE TRANSITION

We discuss several general aspects of the free energy of the standard model at high temperatures. In particular the Clausius-Clapeyron equation is shown to yield a relation between the latent heat and the jump in the order parameter. The free energy is calculated as function of temperature in resummed perturbation theory to two-loop order. A new resummation procedure is proposed in which the symmetric phase and the Higgs phase are treated differently. A quantitative description of the phase transition is achieved for Higgs masses below $\sim 70$ GeV. The results are found to be in agreement with recent numerical simulations on large lattices. The phase transition provides no evidence for strong non-perturbative effects in the symmetric phase.

hep-ph↗

arXiv1994

The electroweak phase transition: a non-perturbative lattice investigation

We present results obtained from a numerical investigation of the electroweak phase transition in the SU(2)-Higgs model. The simulations are performed at two values of the Higgs boson mass, $M_H\approx 20$ GeV and $M_H\approx 50$ GeV. While the phase transition is of strongly first order at the smaller value of the Higgs mass it weakens rapidly when the Higgs mass is increased. This is in qualitative agreement with perturbation theory as the comparison of various physical quantities shows.

hep-lat↗

arXiv1994

Simulating the Electroweak Phase Transition in the SU(2) Higgs Model

Numerical simulations are performed to study the finite temperature phase transition in the SU(2) Higgs model on the lattice. In the presently investigated range of the Higgs boson mass, below 50 GeV, the phase transition turns out to be of first order and its strength is rapidly decreasing with increasing Higgs boson mass. In order to control the systematic errors, we also perform studies of scaling violations and of finite volume effects.

hep-lat↗

arXiv1994

Numerical Simulations and the Strength of the Electroweak Phase Transition

Numerical simulations are performed to study the finite temperature phase transition in the SU(2) Higgs model on the lattice. The strength of the first order phase transition is investigated by determining the latent heat and the interface tension on $L_t=2$ lattices. The values of the Higgs boson mass presently chosen are below 50 GeV. Our results are in qualitative agreement with two-loop resummed perturbation theory.

hep-lat↗

arXiv1994

Gauge Invariant Treatment of the Electroweak Phase Transition

We evaluate the gauge invariant effective potential for the composite field $σ=2Φ^{\dagger}Φ$ in the SU(2)-Higgs model at finite temperature. Symmetric and broken phases correspond to the domains $σ\leq T^2/3$ and $σ> T^2/3$, respectively. The effective potential increases very steeply at small values of $σ$. Predictions for several observables, derived from the ordinary and the gauge invariant effective potential, are compared. Good agreement is found for the critical temperature and the jump in the order parameter. The results for the latent heat differ significantly for large Higgs masses.

hep-ph↗

arXiv1994

Confinement in Three Dimensions and the Electroweak Phase Transition

The infrared behaviour of the standard model at finite temperature is determined by the confining phase of the SU(2)-Higgs model in three dimensions. Due to the Landau singularity of the three-dimensional gauge theory the perturbative treatment of the electroweak phase transition breaks down for Higgs masses above a critical mass $m_H^c$. Based on a renormalization group improved effective potential we find $m_H^c\sim$ 70 GeV. The scalar self-coupling has a Landau-type singularity also in the abelian U(1)-Higgs model, which leads to a breakdown of perturbation theory in the symmetric phase.

hep-ph↗

arXiv1994

Finite Temperature Effective Potential to Order $g^4,\la^2$ and the Electroweak Phase Transition

The standard model effective potential is calculated at finite temperature to order $g^4,\la^2$ and a complete zero temperature renormalization is performed. In comparison with lower order calculations the strength of the first order phase transition has increased dramatically. This effect can be traced back to infrared contributions from typical non-Abelian diagrams and to the infrared behaviour of the scalar sector close to the critical temperature. Several quantities, e.g. surface tension, latent heat and field expectation value are analyzed for an SU(2)-Higgs model and for the full standard model in detail. An explicit formula enabling further analytic or numerical study is presented. (DESY-94-025)

hep-ph↗

arXiv1993

Aspects of the Cosmological Electroweak Phase Transition

We study the decay of the metastable symmetric phase in the standard model at finite temperature. For the SU(2)-Higgs model the two wave function correction terms $Z_{\vp}(\vp^2,T)$ and $Z_χ(\vp^2,T)$ of Higgs and Goldstone boson fields are calculated to one-loop order. We find that the derivative expansion of the effective action is reliable for Higgs masses smaller than the W-boson mass. We propose a new procedure to evaluate the decay rate by first integrating out the vector field and the components of the scalar fields with non-zero Matsubara frequencies. The static part of the scalar field is treated in the saddle point approximation. As a by-product we obtain a formula for the decay rate of a homogeneous unstable state. The course of the cosmological electroweak phase transition is evaluated numerically for different Higgs boson masses and non-vanishing magnetic mass of the gauge boson. For Higgs masses above $\sim 60$ GeV the latent heat can reheat the system to the critical temperature which qualitatively changes the nature of the transition.

hep-ph↗

arXiv1993

Searching for Supersymmetry in High-Energy Photon-Proton Scattering

We investigate the possibility to search for supersymmetry in the scattering of protons and Compton back-scattered laser light. We evaluate the cross sections for inelastic and elastic production of wino pairs for different electron-proton c.m.s. energies. For $\sqrt{s}=1\ TeV$ the cross section exceeds $1\ fb$ for $m_w<190\ GeV$.

hep-ph↗

arXiv1992

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.

hep-ph↗