Renormalisation of out-of-equilibrium quantum fields

We consider the initial value problem and its renormalisation in the framework of the two-particle-irreducible (2PI) effective action. We argue that in the case of appropriately chosen self-consistent initial conditions, the counterterms needed to renormalise the system in equilibrium are also sufficient to renormalise its time evolution. In this way we improve on Gaussian initial conditions which have the disadvantage of generically not showing a continuum limit. For a more detailed discussion see arXiv:0809.0496.Comment: To appear in the proceedings of SEWM08, Amsterdam, The Netherlands, 26-29 August 200

Low-cost fermions in classical field simulations

We discuss the possible extension of the bosonic classical field theory simulations to include fermions. This problem has been addressed in terms of the inhomogeneous mean field approximation by Aarts and Smit. By performing a stochastic integration of an equivalent set of equations we can extend the original 1+1 dimensional calculations so that they become feasible in higher dimensions. We test the scheme in 2 + 1 dimensions and discuss some classical applications with fermions for the first time, such as the decay of oscillons.Comment: 13 pages, revtex

Ising-like dynamical signatures and the end-point of the QCD transition line

An increase in the size of coherent domains in the one component $\Phi^4$ field theory under the influence of a uniformly changing external magnetic field near the critical end-point $T_{\Phi}=T_c, h_{\Phi}=0$ was proposed recently as an estimate also for the variation of the chiral correlation length of QCD near its respective hypothetical end point in the $T_{QCD}-\mu_{QCD}$ plane. The present detailed numerical investigation of the effective model suggests that passing by the critical QCD end point with realistic rate of temperature change will trigger large amplitude oscillations in the temporal variation of the chiral correlation length. A simple mechanism for producing this phenomenon is suggested.Comment: 10 pages, RevTeX, 5 figures. Version accepted for publication in PR

Out of Equilibrium Non-perturbative Quantum Field Dynamics in Homogeneous External Fields

The quantum dynamics of the symmetry broken lambda (Phi^2)^2 scalar field theory in the presence of an homogeneous external field is investigated in the large N limit. We choose as initial state the ground state for a constant external field J .The sign of the external field is suddenly flipped from J to - J at a given time and the subsequent quantum dynamics calculated. Spinodal instabilities and parametric resonances produce large quantum fluctuations in the field components transverse to the external field. This allows the order parameter to turn around the maximum of the potential for intermediate times. Subsequently, the order parameter starts to oscillate near the global minimum for external field - J, entering a novel quasi-periodic regime.Comment: LaTex, 30 pages, 12 .ps figures, improved version to appear in Phys Rev

Dynamical Manifestation of the Goldstone Phenomenon at 1-loop

We have calculated the damping rate $\Gamma (|{\bf k}|)$ for classical on-shell Goldstone modes of the O(2) symmetric scalar fields propagating in a thermal medium of the broken symmetry phase taking into account the effect of the explicit symmetry breaking. The result of the one-loop analysis can be expanded around $\Gamma (0)$, which depends non-analytically on the parameter of the explicit symmetry breaking, h. $\Gamma (0)$ vanishes when $h\to 0$, demonstrating in this way the absence of the restoring force, when the equilibrium direction of the symmetry breaking is modulated homogeneously.Comment: 8 pages, Late

Renormalised nonequilibrium quantum field theory: scalar fields

We discuss the renormalisation of the initial value problem in quantum field theory using the two-particle irreducible (2PI) effective action formalism. The nonequilibrium dynamics is renormalised by counterterms determined in equilibrium. We emphasize the importance of the appropriate choice of initial conditions and go beyond the Gaussian initial density operator by defining self-consistent initial conditions. We study the corresponding time evolution and present a numerical example which supports the existence of a continuum limit for this type of initial conditions.Comment: 18 pages in revtex4, 5 figure

Static QˉQ\bar{Q}Q pair free energy and screening masses from correlators of Polyakov loops: continuum extrapolated lattice results at the QCD physical point

We study the correlators of Polyakov loops, and the corresponding gauge invariant free energy of a static quark-antiquark pair in 2+1 flavor QCD at finite temperature. Our simulations were carried out on $N_t$ = 6, 8, 10, 12, 16 lattices using Symanzik improved gauge action and a stout improved staggered action with physical quark masses. The free energies calculated from the Polyakov loop correlators are extrapolated to the continuum limit. For the free energies we use a two step renormalization procedure that only uses data at finite temperature. We also measure correlators with definite Euclidean time reversal and charge conjugation symmetry to extract two different screening masses, one in the magnetic, and one in the electric sector, to distinguish two different correlation lengths in the full Polyakov loop correlator

Non-perturbative construction of counterterms for 2PI-approximation

A concise method is presented for the non-perturbative computation of the counterterms renormalising 2PI-actions. The procedure is presented for a real scalar field up to lambda^2 order in the skeleton truncation of Gamma_2PI with respect to the self-coupling, and in a constant symmetry breaking background. The method is easily generalizable to field theories with arbitrary global symmetry.Comment: 4 pages, poster presented at Strong and Electroweak Matter (SEWM2008), Amsterdam,August 25-29 200

Class D audio power amplifier with integrated DSP

Táto bakalárska práca sa zaoberá návrhom a vytvorením rozmerovo malého, energeticky efektívneho nízkofrekvenčného zosilňovača, s rozšírenou tónovou korekciou a užívateľsky prijateľným nastavovaním. Tieto očakávania spĺňa zosilňovač v triede D s prídavným DSP – digitálnym signálovým procesorom. Práca zahŕňa celkový dizajn, návrh a simulácie stavebných blokov ako A/D prevodník (PCM1850A), koncový stupeň spolu s DSP (TAS5706A), riadiaca jednotka (ATmega128) a napájací zdroj. V práci je možné nájsť aj teoretický popis princípu triedy D, tipov modulácii, možností prevodu analógového signálu na číslicový, stručný úvod do digitálneho spracovania signálu. Témou sú aj možnosti a limitácie takto spracovaného signálu, ako aj opis konkrétnych obvodov použitých v práci a obrazcov dosiek plošných spojov, ďalej popis riadiaceho programu a postupu riešenia softwaru pre každý blok systému a v neposlednej rade meranie funkčného prototypu.This project deals with design and creation of a physically small, energetically effective audio amplifier, with extended tone corrections and user friendly settings. These expectations meets audio amplifier in class D with additional DSP, digital signal processor. Project includes overall design of all blocks, like A/D converter (PCM1850A), power stage together with DSP (TAS5706A), control unit (ATmega128) and power supply. In this work you’ll find theoretical description of class D, types of modulation, ways to convert analog signals to digital, short introduction to digital signal processing, options and limitations of these principles, description of specific circuits and layouts of printed circuit boards. The project further discusses the control program, its ways of solving the software for each block of the system, and finally includes the measurement of the prototype.