Spectral function of the Bloch-Nordsieck model at finite temperature

In this paper we determine the exact fermionic spectral function of the Bloch-Nordsieck model at finite temperature. Analytic results are presented for some special parameters, for other values we have numerical results. The spectral function is finite and normalizable for any nonzero temperature values. The real time dependence of the retarded Green's function is power-like for small times and exhibits exponential damping for large times. Treating the temperature as an infrared regulator, we can also give a safe interpretation of the zero temperature result.Comment: 16 pages, 9 figures, revtex4-

Validating the 2PI resummation: the Bloch-Nordsieck example

In this work we provide a numerical method to obtain the Bloch-Nordsieck spectral function at finite temperature in the framework of the 2PI approximation. We find that the 2PI results nicely agree with the exact one, provided we perform a coupling constant matching. In the paper we present the resulting finite temperature running of the 2PI coupling constant. This result may apply for the finite temperature behavior of the coupling constant in QED, too.Comment: 14 pages, 14 figures, uses revtex4-

Non-Gaussian fixed points in fermionic field theories without auxiliary Bose-fields

The functional equation governing the renormalization flow of fermionic field theories is investigated in $d$ dimensions without introducing auxiliary Bose-fields on the example of the Gross-Neveu and the Nambu--Jona-Lasinio model. The UV safe fixed points and the eigenvectors of the renormalization group equations linearized around them are found in the local potential approximation. The results are compared carefully with those obtained with partial bosonisation. The results do not receive any correction in the next-to-leading order approximation of the gradient expansion of the effective action.Comment: extended version to appear in EPJC, 15 pages, 4 figures, uses svjour

Harmonic expansion of the effective potential in Functional Renormalization Group at finite chemical potential

In this paper we propose a method to study the Functional Renormalization Group at finite chemical potential. The method consists of mapping the FRG equations within the Fermi surface into a differential equation defined on a rectangle with zero boundary conditions. To solve this equation we use an expansion of the potential in a harmonic basis. With this method we determined the phase diagram of a simple Yukawa-type model; as expected, the bosonic fluctuations decrease the strength of the transition.Comment: 15 pages, 10 figure

Analytic determination of the T-\mu phase diagram of the chiral quark model

Using a gap equation for the pion mass a nonperturbative method is given for solving the chiral quark-meson model in the chiral limit at the lowest order in the fermion contributions encountered in a large N_f approximation. The location of the tricritical point is analytically determined. A mean field potential is constructed from which critical exponents can be obtained.Comment: 8 pages, 2 figures. To be published in Proc.of Budapest'04 Workshop on Hot and Dense Matter in Relativistic Heavy Ion Physics, Budapest, Hungary, March 24-27, 200

Nothingness/ in words enclose : supplementarity and the veil of language in Samuel Beckett\u27s Murphy and Watt

Samuel Beckett has asserted that language is a veil in which he must bore one hole after another..., until what lurks behind it - be it something or nothing - begins to seep through. This thesis employs Derrida\u27s assertion that language involves the play of differance and the supplementarity of the sign. Since the supplement, in Derrida\u27s words, fills and marks a determined lack, language calls attention to the gap of nothingness already present in the play of differance. Murphy and Watt present both the desire for semantic succour of the veil and the awareness - more fully developed in Beckett\u27s later work - that, despite a continued wish to enclose nothingness, the veil must continually rent. This dynamic is thematically and linguistically apparent in these two works. Thus Beckett\u27s characters may not enclose nothingness, but continuing to go on with words they may find value in continuing the process

Electroweak Phase Transition in the MSSM: 4-Dimensional Lattice Simulations

Recent lattice results have shown that there is no Standard Model (SM) electroweak phase transition (EWPT) for Higgs boson masses above \approx 72 GeV, which is below the present experimental limit. According to perturbation theory and 3-dimensional (3d) lattice simulations there could be an EWPT in the Minimal Supersymmetric Standard Model (MSSM) that is strong enough for baryogenesis up to m_h \approx 105 GeV. In this letter we present the results of our large scale 4-dimensional (4d) lattice simulations for the MSSM EWPT. We carried out infinite volume and continuum limits and found a transition whose strength agrees well with perturbation theory, allowing MSSM electroweak baryogenesis at least up to m_h = 103 \pm 4 GeV. We determined the properties of the bubble wall that are important for a successful baryogenesis.Comment: 4 pages, 4 figures included; lightest Higgs mass bound relaxed (abstract, fig. 3 changed), version to appear in Phys. Rev. Letter

Four-dimensional lattice results on the MSSM electroweak phase transition

We present the results of our large scale 4-dimensional (4d) lattice simulations for the MSSM electroweak phase transition (EWPT). We carried out infinite volume and continuum limit extrapolations and found a transition whose strength agrees well with perturbation theory. We determined the properties of the bubble wall that are important for a successful baryogenesis.Comment: 5 pages, 3figures. Talk presented at Johns Hopkins Workshop on Nonperturbative Quantum Field Theory Methods and their Applications (19-21 August 2000.