arXiv subjects

M. Laine

Publications and source records attributed to M. Laine.

At least 199 records · Page 11Linked to original sources

arXiv1998

A Strong Electroweak Phase Transition up to m_H ~ 105 GeV

Non-perturbative lattice simulations have shown that there is no electroweak phase transition in the Standard Model for the allowed Higgs masses, m_H \gsim 75 GeV. In the Minimal Supersymmetric Standard Model, in contrast, it has been proposed that the transition should exist and even be strong enough for baryogenesis up to m_H ~ 105 GeV, provided that the lightest stop mass is in the range 100...160 GeV. However, this prediction is based on perturbation theory, and suffers from a noticeable gauge parameter and renormalization scale dependence. We have performed large-scale lattice Monte Carlo simulations of the MSSM electroweak phase transition. Extrapolating the results to the infinite volume and continuum limits, we find that the transition is in fact stronger than indicated by 2-loop perturbation theory. This guarantees that the perturbative Higgs mass bound m_H ~ 105 GeV is a conservative one, allows slightly larger stop masses (up to ~ 165 GeV), and provides a strong motivation for further studies of MSSM electroweak baryogenesis.

hep-ph↗

arXiv1998

Thermodynamics of Non-Topological Solitons

In theories with low energy supersymmetry breaking, the effective potential for squarks and sleptons has generically nearly flat directions, V(phi) ~ M^4 (log(phi/M))^n. This guarantees the existence of stable non-topological solitons, Q-balls, that carry large baryon number, B >> (M/m_p)^4, where m_p is the proton mass. We study the behaviour of these objects in a high temperature plasma. We show that in an infinitely extended system with a finite density of the baryon charge, the equilibrium state is not homogeneous and contains Q-balls at any temperature. In a system with a finite volume, Q-balls evaporate at a volume dependent temperature. In the cosmological context, we formulate the conditions under which Q-balls, produced in the Early Universe, survive till the present time. Finally, we estimate the baryon to cold dark matter ratio in a cosmological scenario in which Q-balls are responsible for both the net baryon number of the Universe and its dark matter. We find out naturally the correct orders of magnitude for M ~ 1...10 TeV: η~ 10^{-10} (M/TeV)^{-2} (B/10^{26})^{-1/2}.

hep-ph↗

arXiv1997

High Temperature Dimensional Reduction and Parity Violation

The effective super-renormalizable 3-dimensional Lagrangian, describing the high temperature limit of chiral gauge theories, has more symmetry than the original 4d Lagrangian: parity violation is absent. Parity violation appears in the 3d theory only through higher-dimensional operators. We compute the coefficients of dominant P-odd operators in the Standard Electroweak theory and discuss their implications. We also clarify the parametric accuracy obtained with dimensional reduction.

hep-ph↗

arXiv1997

Three-dimensional U(1) gauge+Higgs theory as an effective theory for finite temperature phase transitions

We study the three-dimensional U(1)+Higgs theory (Ginzburg-Landau model) as an effective theory for finite temperature phase transitions from the 1 K scale of superconductivity to the relativistic scales of scalar electrodynamics. The relations between the parameters of the physical theory and the parameters of the 3d effective theory are given. The 3d theory as such is studied with lattice Monte Carlo techniques. The phase diagram, the characteristics of the transition in the first order regime, and scalar and vector correlation lengths are determined. We find that even rather deep in the first order regime, the transition is weaker than indicated by 2-loop perturbation theory. Topological effects caused by the compact formulation are studied, and it is demonstrated that they vanish in the continuum limit. In particular, the photon mass (inverse correlation length) is observed to be zero within statistical errors in the symmetric phase, thus constituting an effective order parameter.

hep-lat↗

arXiv1997

Gauge-invariant scalar and field strength correlators in 3d

Gauge-invariant non-local scalar and field strength operators have been argued to have significance, e.g., as a way to determine the behaviour of the screened static potential at large distances, as order parameters for confinement, as input parameters in models of confinement, and as gauge-invariant definitions of light constituent masses in bound state systems. We measure such "correlators" in the 3d pure SU(2) and SU(2)+Higgs models on the lattice. We extract the corresponding mass parameters and discuss their scaling and physical interpretation. We find that the finite part of the MS-bar scheme mass measured from the field strength correlator is large, more than half the glueball mass. We also determine the non-perturbative contribution to the Debye mass in the 4d finite T SU(2) gauge theory with a method due to Arnold and Yaffe, finding $δm_D\approx 1.06(4)g^2T$.

hep-lat↗

arXiv1997

Plasmon properties in classical lattice gauge theory

In order to investigate the features of the classical approximation at high temperatures for real time correlation functions, the plasmon frequencies and damping rates were recently computed numerically in the SU(2)+Higgs model and in the pure SU(2) theory. We compare the lattice results with leading order hard thermal loop resummed perturbation theory. In the broken phase of the SU(2)+Higgs model, we show that the lattice results can be reproduced and that the lattices used are too coarse to observe some important plasmon effects. In the symmetric phase, the main qualitative features of the lattice results can also be understood. In the pure SU(2) theory, on the other hand, there are discrepancies which might point to larger Landau and plasmon damping effects than indicated by perturbation theory.

hep-ph↗

arXiv1997

High-T QCD and dimensional reduction: measuring the Debye mass

We study the high-temperature phase of SU(2) and SU(3) QCD using lattice simulations of an effective 3-dimensional SU(N) + adjoint Higgs -theory, obtained through dimensional reduction. We investigate the phase diagram of the 3D theory, and find that the high-T QCD phase corresponds to the metastable symmetric phase of the 3D theory. We measure the Debye screening mass m_D with gauge invariant operators; in particular we determine the O(g^2) and O(g^3) corrections to m_D. The corrections are seen to be large, modifying the standard power-counting hierarchy in high temperature QCD.

hep-lat↗

arXiv1997

Masses and Phase Structure in the Ginzburg-Landau Model

We study numerically the phase structure of the Ginzburg-Landau model, with particular emphasis on mass measurements. There is no local gauge invariant order parameter, but we find that there is a phase transition characterized by a vanishing photon mass. For type I superconductors the transition is of 1st order. For type II 1st order is excluded by susceptibility analysis, but the photon correlation length suggests 2nd order critical behaviour with ν~ 1/2. The scalar mass, in contrast, does not show clear critical behaviour in the type II regime for V \to \infty, contrary to the conventional picture.

cond-mat.supr-con↗

arXiv1997

Non-perturbative Debye mass in finite T QCD

Employing a non-perturbative gauge invariant definition of the Debye screening mass m_D in the effective field theory approach to finite T QCD, we use 3d lattice simulations to determine the leading O(g^2) and to estimate the next-to-leading O(g^3) corrections to m_D in the high temperature region. The O(g^2) correction is large and modifies qualitatively the standard power-counting hierarchy picture of correlation lengths in high temperature QCD.

hep-ph↗

arXiv1997

3d effective theories for the Standard Model and extensions

The construction and analysis of 3d effective theories for the description of the thermodynamics of the cosmological electroweak phase transition are reviewed. For the Standard Model and for the MSSM with stops somewhat heavier than the top, the effective theory is 3d SU(2)+Higgs, and the transition is strong enough for baryogenesis at no Higgs mass for the Standard Model, and up to m_H ~ 80 GeV for the MSSM. For lighter stops, the effective theory is SU(3)xSU(2) + two scalars and the transition could be strong enough up to m_H ~ 100 GeV. However, a lattice study in 3d is needed to confirm the last bound.

hep-ph↗

arXiv1997

The finite temperature real time \hbar^2 corrections in quantum mechanics

We study non-perturbative real time correlation functions at finite temperature. In order to see whether the classical term gives a good approximation in the high temperature limit T >> \hbarω, we consider the first \hbar^2 quantum corrections. We find that for the simplest non-trivial case, the quantum mechanical anharmonic oscillator, the classical result is reliable only for moderately large times: after some time t_* the classical approximation breaks down even at high temperatures. Moreover, the result for the first quantum corrections cannot, in general, be reproduced by modifying the parameters of the classical theory.

hep-ph↗

arXiv1997

Lattice-continuum relations for 3d SU(N)+Higgs theories

3d lattice studies have recently attracted a lot of attention, especially in connection with finite temperature field theories. One ingredient in these studies is a perturbative computation of the 2-loop lattice counterterms, which are exact in the continuum limit. We extend previous such results to SU(N) gauge theories with Higgs fields in the fundamental and adjoint representations. The fundamental SU(3)xSU(2) case might be relevant for the electroweak phase transition in the MSSM, and the adjoint case for the GUT phase transition and for QCD in the high temperature phase. We also revisit the standard SU(2)xU(1) and U(1) theories.

hep-lat↗

arXiv1997

3d SU(N) + adjoint Higgs theory and finite temperature QCD

We study to what extent the three-dimensional SU(N)+adjoint Higgs theory can be used as an effective theory for finite temperature SU(N) gauge theory, with N=2,3. The parameters of the 3d theory are computed in 2-loop perturbation theory in terms of T/Lambda_MSbar,N,N_f. The perturbative effective potential of the 3d theory is computed to two loops for N=2. While the Z(N) symmetry probably driving the 4d confinement-deconfinement phase transition (for N_f=0) is not explicit in the effective Lagrangian, it is partly reinstated by radiative effects in the 3d theory. Lattice simulations in the 3d theory are carried out for N=2, and the static screening masses relevant for the high-temperature phase of the 4d theory are measured. In particular, we measure non-perturbatively the O(g^2 T) correction to the Debye screening mass. We find that non-perturbative effects are much larger in the SU(2) + adjoint Higgs theory than in the SU(2) + fundamental Higgs theory.

hep-ph↗

arXiv1996

The 2-loop MSSM finite temperature effective potential with stop condensation

We calculate the finite temperature 2-loop effective potential in the MSSM with stop condensation, using a 3-dimensional effective theory. We find that in a part of the parameter space, a two-stage electroweak phase transition appears possible. The first stage would be the formation of a stop condensate, and the second stage is the transition to the standard electroweak minimum. The two-stage transition could significantly relax the baryon erasure bounds, but the parameter space allowing it (m_H \lsim 100 GeV, m_tR \sim 155-160 GeV) is not very large. We estimate the reliability of our results using renormalization scale and gauge dependence. Finally we discuss some real-time aspects relevant for the viability of the two-stage scenario.

hep-ph↗

arXiv1996

A Non-Perturbative Analysis of the Finite T Phase Transition in SU(2)xU(1) Electroweak Theory

The continuum 3d SU(2)$\times$U(1)+Higgs theory is an effective theory for a large class of 4d high-temperature gauge theories, including the minimal standard model and some of its supersymmetric extensions. We study the effects of the U(1) subgroup using lattice Monte Carlo techniques. When $g'^2/g^2$ is increased from the zero corresponding to pure SU(2)+Higgs theory, the phase transition gets stronger. However, the increase in the strength is close to what is expected perturbatively, and the qualitative features of the phase diagram remain the same as for $g'^2=0$. In particular, the first order transition still disappears for $m_H>m_{H,c}$. We measure the photon mass and mixing angle, and find that the mass vanishes in both phases within the statistical errors.

hep-lat↗

arXiv1996

The order of the phase transition in 3d U(1)+Higgs theory

We study the order of the phase transition in the 3d U(1)+Higgs theory, which is the Ginzburg-Landau theory of superconductivity. We confirm that for small scalar self-coupling the transition is of first order. For large scalar self-coupling the transition ceases to be of first order, and a non-vanishing scalar mass suggests that the transition may even be of higher than second order.

hep-lat↗

arXiv1996

Real-Time History of the Cosmological Electroweak Phase Transition

We study numerically the real-time history of the cosmological electroweak phase transition, as it may take place in the Standard Model or in MSSM for m_H < m_W according to recent lattice results. We follow the nucleated bubbles from the initial stages of acceleration and rapid growth, through collisions with compression waves resulting in slowing down and reheating to T_c, until the final stages of slow growth and evaporation. We find that collisions with compression waves may make the bubble walls oscillate in the radial direction, and that reheating to T_c takes generically place.

hep-ph↗

arXiv1996

Is There a Hot Electroweak Phase Transition at $m_H\gsim m_W$?

We provide non-perturbative evidence for the fact that there is no hot electroweak phase transition at large Higgs masses, $m_H = 95$, 120 and 180 GeV. This means that the line of first order phase transitions separating the symmetric and broken phases at small $m_H$ has an end point $m_{H,c}$. In the minimal standard electroweak theory 70 GeV $<m_{H,c}<$ 95 GeV and most likely $m_{H,c} \approx 80$ GeV. If the electroweak theory is weakly coupled and the Higgs boson is found to be heavier than the critical value (which depends on the theory in question), cosmological remnants from the electroweak epoch are improbable.

hep-ph↗