arXiv subjects

K. Kajantie

Publications and source records attributed to K. Kajantie.

At least 73 records · Page 4Linked to original sources

arXiv1998

The universality class of the electroweak theory

We study the universality class and critical properties of the electroweak theory at finite temperature. Such critical behaviour is found near the endpoint m_H=m_{H,c} of the line of first order electroweak phase transitions in a wide class of theories, including the Standard Model (SM) and a part of the parameter space of the Minimal Sypersymmetric Standard Model (MSSM). We find that the location of the endpoint corresponds to the Higgs mass m_{H,c} = 72(2) GeV in the SM with sin^2 theta_W = 0, and m_{H,c} < 80 GeV with sin^2 theta_W = 0.23. As experimentally m_H > 88 GeV, there is no electroweak phase transition in the SM. We compute the corresponding critical indices and provide strong evidence that the phase transitions near the endpoint fall into the three dimensional Ising universality class.

hep-lat↗

arXiv1998

Thermodynamics of Gauge-Invariant U(1) Vortices from Lattice Monte Carlo Simulations

We study non-perturbatively and from first principles the thermodynamics of vortices in 3d U(1) gauge+Higgs theory, or the Ginzburg-Landau model, which has frequently been used as a model for cosmological topological defect formation. We discretize the system and introduce a gauge-invariant definition of a vortex passing through a loop on the lattice. We then study with Monte Carlo simulations the total vortex density, extract the physically meaningful part thereof, and demonstrate that it has a well-defined continuum limit. The total vortex density behaves as a pseudo order parameter, having a discontinuity in the regime of first order transitions and behaving continuously in the regime of second order transitions. Finally, we discuss further gauge-invariant observables to be measured.

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

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

Hydrodynamics of nuclear collisions with initial conditions from perturbative QCD

We compute the longitudinal hydrodynamic flow in ultrarelativistic heavy ion collisions at $\sqrt{s}$ = 5500 GeV by using boost non-invariant initial conditions following from perturbative QCD. The transfer of entropy and energy from the central region to larger rapidities caused by boost non-invariance is determined and the associated decrease in the lifetime of the system is estimated.

nucl-th↗

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

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

Baryon-to-entropy ratio in very high energy nuclear collisions

We compute as a function of rapidity $y$ the baryon number carried by quarks and antiquarks with $p_T > p_0 \approx$ 2 GeV produced in Pb+Pb collisions at TeV energies. The computation is carried out in lowest order QCD perturbation theory using structure functions compatible with HERA results. At $p_0=2$ GeV the initial gluon density is both transversally saturated and thermalised in the sense that the energy/gluon equals to that of an ideal gas with the same energy density. Even at these high energies the initial net baryon number density at $y=0$ at $τ=0.1$ fm will be more than the normal nuclear matter density but the baryon-to-entropy ratio is only $(B-\bar B)/S\sim 1/5000$. Further evolution of the system is discussed and the final baryon-to-entropy ratio is estimated.

nucl-th↗

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↗

arXiv1995

The Electroweak Phase Transition: A Non-Perturbative Analysis

We study on the lattice the 3d SU(2)+Higgs model, which is an effective theory of a large class of 4d high temperature gauge theories. Using the exact constant physics curve, continuum ($V\to\infty, a\to 0$) results for the properties of the phase transition (critical temperature, latent heat, interface tension) are given. The 3-loop correction to the effective potential of the scalar field is determined. The masses of scalar and vector excitations are determined and found to be larger in the symmetric than in the broken phase. The vector mass is considerably larger than the scalar one, which suggests a further simplification to a scalar effective theory at large Higgs masses. The use of consistent 1-loop relations between 3d parameters and 4d physics permits one to convert the 3d simulation results to quantitatively accurate numbers for different physical theories, such as the Standard Model -- excluding possible nonperturbative effects of the U(1) subgroup -- for Higgs masses up to about 70 GeV. The applications of our results to cosmology are discussed.

hep-lat↗

arXiv1995

Results from 3D Electroweak Phase Transition Simulations

We study the phase transition in SU(2)-Higgs model on the lattice using the 3D dimensionally reduced formalism. The 3D formalism enables us to obtain highly accurate Monte Carlo results, which we extrapolate both to the infinite volume and to the continuum limit. Our formalism also provides for a well-determined and unique way to relate the results to the perturbation theory. We measure the critical temperature, latent heat and interface tension for Higgs masses up to 70 GeV.

hep-lat↗

arXiv1995

Generic Rules for High Temperature Dimensional Reduction and Their Application to the Standard Model

We formulate the rules for dimensional reduction of a generic finite temperature gauge theory to a simpler three-dimensional effective bosonic theory in terms of a matching of Green's functions in the full and the effective theory, and present a computation of a generic set of 1- and 2-loop graphs needed for the application of these rules. As a concrete application we determine the explicit mapping of the physical parameters of the standard electroweak theory to a three-dimensional SU(2)xU(1) gauge-Higgs theory. We argue that this three-dimensional theory has a universal character and appears as an effective theory for many extensions of the Standard Model.

hep-ph↗

arXiv1994

3d physics and the electroweak phase transition: a framework for lattice Monte Carlo analysis

We discuss a framework relying on both perturbative and non-perturbative lattice computations which will be able to reliably determine the parameters of the EW phase transition. A motivation for the use of 3d effective theory in the lattice simulations, rather than the complete 4d one, is provided. We introduce and compute on the 2-loop level a number of gauge-invariant order parameters -- condensates, which can be measured with high accuracy in MC simulations. The relation between MSbar and lattice condensates is found, together with the relation between lattice couplings and continuum parameters (the constant physics curves). These relations are exact in the continuum limit.

hep-lat↗

arXiv1994

Hot electroweak matter

This talk summarises recent results on lattice Monte Carlo studies of finite T electroweak phase transition. Particular attention is given to the 3d effective theory approach, replacing the full 4d theory by a three dimensional effective theory of the modes constant in imaginary time.

hep-lat↗

arXiv1994

Large Scale Inhomogeneities from the QCD Phase Transition

We examine the first-order cosmological QCD phase transition for a large class of parameter values, previously considered unlikely. We find that the hadron bubbles can nucleate at very large distance scales, they can grow as detonations as well as deflagrations, and that the phase transition may be completed without reheating to the critical temperature. For a subset of the parameter values studied, the inhomogeneities generated at the QCD phase transition might have a noticeable effect on nucleosynthesis.

hep-ph↗