We provide nonperturbative evidence for the fact that there is no hot first or second order 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 , m H,c , 95 GeV and most likely m H,c ഠ 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.[S0031-9007(96)01335-X]PACS numbers: 11.30. Qc, 11.10.Wx, 11.15.Ha, 98.80.Cq The transition between the high temperature symmetric (or confinement) phase and the low T broken (or Higgs) phase in the standard electroweak theory (MSM) or its extensions is known to be of first order for small values of the Higgs mass m H . This follows from perturbative studies of the effective potential [1] and nonperturbative lattice Monte Carlo simulations [2][3][4]. In the region of applicability of the perturbative expansion the strength of the electroweak phase transition decreases when m H increases. However, the nature of the electroweak phase transition at "large" Higgs masses m H * m W remains unclear, since the perturbative expansion for the description of the phase transition is useless there. This Letter contains the results of the first nonperturbative lattice analysis of the problem for "large" Higgs masses, m H 95, 120, 180 GeV. We shall show that the system behaves very regularly there, much like water above the critical point. As there is no distinction between liquid water and vapor, there is no distinction between the symmetric and broken phases; there is no long-range order.In Ref.[3] it has been shown that in a weakly coupled electroweak theory and in many of its extensions (supersymmetric or not) the hot electroweak (EW) phase transition can be described by an SU͑2͒ 3 U͑1͒ 1 Higgs model in three Euclidean dimensions. Dimensional reduction has its own limitations, described in detail in [3]. For example, for the MSM the 3D approximation is accurate to within a few percent for 30 & m H & 250 GeV. At the lower end of this inequality the high temperature expansion breaks down because the phase transition is very strongly first order and particle masses in the broken phase are ϳT [5]. The upper end is the usual condition for the applicability of perturbation theory in the scalar sector of the MSM. In the minimal sypersymmetric standard model (MSSM) the latter condition is satisfied automatically. Hence, the 3D description is valid for a wide range of the phenomenologically interesting part of the parameter space of the MSM and MSSM.Since the effects of the U(1) subgroup are perturbative deep in the Higgs phase and high in the symmetric phase, the presence of the U(1) factor cannot change the qualitative features of the phase diagram. Thus we shall take sin u W 0. The effective Lagrangian iswhere G a i...

Many l o w energy hadrons, such as the rho, can observed as resonances in scattering experiments. A proposal by L uscher enables one to determine innite volume elastic scattering phases from the two-particle energy spectrum measured from nite periodic lattices. In this work, we generalize the formalism to the case where the total momentum of the particles is non-zero; i.e.,the lattice frame is not the center-of-mass frame of the scattering particles. There are several advantages to this procedure including making a wider variety of center of mass energies accessible with a xed lattice volume, and making the avoided level crossing in a P-wave decay occur with a smaller volume.The formalism is tested with a simple lattice model of two elds with dierent masses and a 3-point coupling in 3 + 1 dimensions. We nd remarkable agreement b e t w een the rest-frame and non-rest-frame scattering.

We investigate the potential for observing gravitational waves from cosmological phase transitions with LISA in light of recent theoretical and experimental developments. Our analysis is based on current state-of-the-art simulations of sound waves in the cosmic fluid after the phase transition completes. We discuss the various sources of gravitational radiation, the underlying parameters describing the phase transition and a variety of viable particle physics models in this context, clarifying common misconceptions that appear in the literature and identifying open questions requiring future study. We also present a web-based tool, PTPlot, that allows users to obtain up-to-date detection prospects for a given set of phase transition parameters at LISA.

The free energy density, or pressure, of QCD has at high temperatures an expansion in the coupling constant g, known so far up to order g 5 . We compute here the last contribution which can be determined perturbatively, g 6 ln(1/g), by summing together results for the 4-loop vacuum energy densities of two different three-dimensional effective field theories. We also demonstrate that the inclusion of the new perturbative g 6 ln(1/g) terms, once they are summed together with the so far unknown perturbative and non-perturbative g 6 terms, could potentially extend the applicability of the coupling constant series down to surprisingly low temperatures.