The Quantum Effective Action, Wave Functions and Yang-Mills (2+1)

We explore the relationship between the quantum effective action and the ground state (and excited state) wave functions of a field theory. Applied to the Yang-Mills theory in 2+1 dimensions, we find the leading terms of the effective action from the ground state wave function previously obtained in the Hamiltonian formalism by solving the Schrodinger equation.Comment: 16 pages, expanded discussion section, added references, version accepted for Phys. Rev.

The spectrum of the three-dimensional adjoint Higgs model and hot SU(2) gauge theory

We compute the mass spectrum of the SU(2) adjoint Higgs model in 2+1 dimensions at several points located in the (metastable) confinement region of its phase diagram. We find a dense spectrum consisting of an almost unaltered repetition of the glueball spectrum of the pure gauge theory, and additional bound states of adjoint scalars. For the parameters chosen, the model represents the effective finite temperature theory for pure SU(2) gauge theory in four dimensions, obtained after perturbative dimensional reduction. Comparing with the spectrum of screening masses obtained in recent simulations of four-dimensional pure gauge theory at finite temperature, for the low lying states we find quantitative agreement between the full and the effective theory for temperatures as low as T = 2 Tc. This establishes the model under study as the correct effective theory, and dimensional reduction as a viable tool for the description of thermodynamic properties. We furthermore compare the perturbative contribution O(g.T) with the non-perturbative contributions O(g^2.T) and O(g^3.T) to the Debye mass. The latter turns out to be dominated by the scale g^2.T, whereas higher order contributions are small corrections.Comment: LaTeX. Typos corrected and references adde

On the Phase Diagram of the SU(2) Adjoint Higgs Model in 2+1 Dimensions

The phase diagram is investigated for SU(2) lattice gauge theory in d=3, coupled to adjoint scalars. For small values of the quartic scalar coupling, lambda, the transition separating Higgs and confinement phases is found to be first-order, in agreement with earlier work by Nadkarni. The surface of second-order transitions conjectured by Nadkarni, however, is shown instead to correspond to crossover behaviour. This conclusion is based on a finite size analysis of the scalar mass and susceptibility. The nature of the phase transition at the termination of first-order behaviour is investigated and we find evidence for a critical point at which the scalar mass vanishes. The photon mass and confining string tension are measured and are found to be negligibly small in the Higgs phase. This is correlated with the very small density of magnetic monopoles in the Higgs phase. The string tension and photon mass rise rapidly as the crossover is traversed towards the symmetric phase.Comment: LaTeX. Replaced with version to be published in Physics Letters B. Minor changes onl

The Friedberg-Lee model at finite temperature and density

The Friedberg-Lee model is studied at finite temperature and density. By using the finite temperature field theory, the effective potential of the Friedberg-Lee model and the bag constant $B(T)$ and $B(T,\mu)$ have been calculated at different temperatures and densities. It is shown that there is a critical temperature $T_{C}\simeq 106.6 \mathrm{MeV}$ when $\mu=0 \mathrm{MeV}$ and a critical chemical potential $\mu \simeq 223.1 \mathrm{MeV}$ for fixing the temperature at $T=50 \mathrm{MeV}$. We also calculate the soliton solutions of the Friedberg-Lee model at finite temperature and density. It turns out that when $T\leq T_{C}$ (or $\mu \leq \mu_C$), there is a bag constant $B(T)$ (or $B(T,\mu)$) and the soliton solutions are stable. However, when $T>T_{C}$ (or $\mu>\mu_C$) the bag constant $B(T)=0 \mathrm{MeV}$ (or $B(T,\mu)=0 \mathrm{MeV}$) and there is no soliton solution anymore, therefore, the confinement of quarks disappears quickly.Comment: 12 pages, 11 figures; version accepted for publication in Phys. Rev.

Use of recurrence quantification analysis to examine associations between changes in text structure across an expressive writing intervention and reductions in distress symptoms in women wth breast cancer

The current study presents an exploratory analysis of using Recurrence Quantification Analysis (RQA) to analyze text data from an Expressive Writing Intervention (EWI) for Danish women treated for Breast Cancer. The analyses are based on the analysis of essays from a subsample with the average age 54.6 years (SD = 9.0), who completed questionnaires for cancer-related distress (IES) and depression symptoms (BDI-SF). The results show a significant association between an increase in recurrent patterns of text structure from first to last writing session and a decrease in cancer-related distress at 3 months post-intervention. Furthermore, the change in structure from first to last essay displayed a moderate, but significant correlation with change in cancer-related distress from baseline to 9 months post-intervention. The results suggest that changes in recurrence patterns of text structure might be an indicator of cognitive restructuring that leads to amelioration of cancer-specific distress

String Breaking in Non-Abelian Gauge Theories with Fundamental Matter Fields

We present clear numerical evidence for string breaking in three-dimensional SU(2) gauge theory with fundamental bosonic matter through a mixing analysis between Wilson loops and meson operators representing bound states of a static source and a dynamical scalar. The breaking scale is calculated in the continuum limit. In units of the lightest glueball we find $r_{\rm b} m_G\approx13.6$. The implications of our results for QCD are discussed.Comment: 4 pages, 2 figures; equations (4)-(6) corrected, numerical results and conclusions unchange

Overlap of the Wilson loop with the broken-string state

Numerical experiments on most gauge theories coupled with matter failed to observe string-breaking effects while measuring Wilson loops only. We show that, under rather mild assumptions, the overlap of the Wilson loop operator with the broken-string state obeys a natural upper bound implying that the signal of string-breaking is in general too weak to be detected by the conventional updating algorithms. In order to reduce the variance of the Wilson loops in 3-D Z_2 gauge Higgs model we use a new algorithm based on the L\"uscher-Weisz method combined with a non-local cluster algorithm which allows to follow the decay of rectangular Wilson loops up to values of the order of 10^{-24}. In this way a sharp signal of string breaking is found.Comment: 12 pages, 3 figure

Hot electroweak matter near to the endpoint of the phase transition

The electroweak phase transition is investigated near to its endpoint in the framework of an effective three-dimensional model. We measure the very weak interface tension with the tunneling correlation length method. First results for the mass spectrum and the corresponding wave functions in the symmetric phase are presented.Comment: 3 pages, 5 figures, uses espcrc2.sty, contribution to LATTICE9

The Polyakov Loop and its Relation to Static Quark Potentials and Free Energies

It appears well accepted in the literature that the correlator of Polyakov loops in a finite temperature system decays with the "average" free energy of the static quark-antiquark system, and can be decomposed into singlet and adjoint (or octet for QCD) contributions. By fixing a gauge respecting the transfer matrix, attempts have been made to extract those contributions separately. In this paper we point out that the "average" and "adjoint" channels of Polyakov loop correlators are misconceptions. We show analytically that all channels receive contributions from singlet states only, and give a corrected definition of the singlet free energy. We verify this finding by simulations of the 3d SU(2) pure gauge theory in the zero temperature limit, which allows to cleanly extract the ground state exponents and the non-trivial matrix elements. The latter account for the difference between the channels observed in previous simulations.Comment: 14 pages, 3 figures, 1 table; note and reference adde