Charm mass effects in bulk channel correlations

The bulk viscosity of thermalized QCD matter at temperatures above a few hundred MeV could be significantly influenced by charm quarks because their contribution arises four perturbative orders before purely gluonic effects. In an attempt to clarify the challenges of a lattice study, we determine the relevant imaginary-time correlator (of massive scalar densities) up to NLO in perturbation theory, and compare with existing data. We find discrepancies much larger than in the vector channel; this may hint, apart from the importance of taking a continuum limit, to larger non-perturbative effects in the scalar channel. We also recall how a transport peak related to the scalar density spectral function encodes non-perturbative information concerning the charm quark chemical equilibration rate close to equilibrium.Comment: 24 pages. v2: clarifications added, published versio

Massive vector current correlator in thermal QCD

We present an NLO analysis of the massive vector current correlator at temperatures above a few hundred MeV. The physics of this correlator originates from a transport peak, related to heavy quark diffusion, and from the quark-antiquark threshold, related to quarkonium physics. In the bottom case both can be studied with separate effective theories, but for charm these may not be accurate, so a study within the full theory is needed. Working in imaginary time, the NLO correlator can be computed in unresummed perturbation theory; comparing with lattice data, we find good agreement. Subsequently we inspect how non-perturbative modifications of the transport peak would affect the imaginary-time correlator. The massive NLO quark-number susceptibility is also contrasted with numerical measurement.Comment: 28 pages. v2: references and clarifications added, published versio

Lattice calculation of the heavy quark potential at non-zero temperature

We calculated the real and imaginary parts of the static quark anti-quark potential at T>0 in 2+1 flavor QCD using correlators of Wilson lines in Coulomb gauge and lattices with temporal extent N_tau=12. We find that the real part of the potential is larger than the singlet free energy but smaller than the zero temperature potential. The imaginary part of the potential is similar in size to the perturbative HTL result.Comment: LaTeX, 4 pages, 3 figures, uses elsarticle.cls , proceedings of Hard Probes 2013, 3-8 November 2013 Stellenbosch, South Afric

Effective action of a five-dimensional domain wall

We calculate the four-dimensional low-energy effective action for the perturbations of a two-scalar domain wall model in five dimensions. Comparison of the effective action to the Nambu-Goto action reveals the presence of an additional coupling between the light scalar field and the massless translation mode (branon excitation), which can be written in terms of the curvature scalar of the induced metric. We comment on the impact of this interaction to branon physics.Comment: 24 page

Comments on branon dressing and the Standard Model

This technical note shows how Electrodynamics and a Yukawa model are dressed after integrating out perturbative brane fluctuations, and it is found that first order corrections in the inverse of the brane tension occur for the fermion and scalar wave functions, the couplings and the masses. Nevertheless, field redefinitions actually lead to effective actions where only masses are dressed to this first order. We compare our results with the literature and find discrepancies at the next order, which, however, might not be measurable in the valid regime of low-energy brane fluctuations.Comment: 12 page

Compact extra-dimensions as solution to the strong CP problem

We show that the strong CP problem can, in principle, be solved dynamically by adding extra-dimensions with compact topology. To this aim we consider a toy model for QCD, which contains a vacuum angle and a strong CP like problem. We further consider a higher dimensional theory, which has a trivial vacuum structure and which reproduces the perturbative properties of the toy model in the low-energy limit. In the weak coupling regime, where our computations are valid, we show that the vacuum structure of the low-energy action is still trivial and the strong CP problem is solved. No axion-like particle occur in this setup and therefore it is not ruled out by astrophysical bounds.Comment: Discussion adde

From the chiral magnetic wave to the charge dependence of elliptic flow

The quark-gluon plasma formed in heavy ion collisions contains charged chiral fermions evolving in an external magnetic field. At finite density of electric charge or baryon number (resulting either from nuclear stopping or from fluctuations), the triangle anomaly induces in the plasma the Chiral Magnetic Wave (CMW). The CMW first induces a separation of the right and left chiral charges along the magnetic field; the resulting dipolar axial charge density in turn induces the oppositely directed vector charge currents leading to an electric quadrupole moment of the quark-gluon plasma. Boosted by the strong collective flow, the electric quadrupole moment translates into the charge dependence of the elliptic flow coefficients, so that $v_2(\pi^+) < v_2(\pi^-)$ (at positive net charge). Using the latest quantitative simulations of the produced magnetic field and solving the CMW equation, we make further quantitative estimates of the produced $v_2$ splitting and its centrality dependence. We compare the results with the available experimental data.Comment: Contains 12 pages, 6 figures, written as a proceeding for the talk of Y. Burnier at the conference "P and CP-odd Effects in Hot and Dense Matter 2012" held in BN

Heavy Quark Interactions and Quarkonium Binding

We consider heavy quark interactions in quenched and unquenched lattice QCD. In a region just above the deconfinement point, non-Abelian gluon polarization leads to a strong increase in the binding. Comparing quark-antiquark and quark-quark interaction, the dependence of the binding on the separation distance $r$ is found to be the same for the colorless singlet $Q\bar Q$ and the colored anti-triplet $QQ$ state. In a potential model description of in-medium $J/\Psi$ behavior, this enhancement of the binding leads to a survival up to temperatures of 1.5 $T_c$ or higher; it could also result in $J/\Psi$ flow.Comment: 8 pages, 8 Figures; invited talk at "Strangeness in Quark Matter 2008", Beijing/China, to appear in the Proceeding

One-loop fermionic corrections to the instanton transition in two dimensional chiral Higgs model

The one-loop fermionic contribution to the probability of an instanton transition with fermion number violation is calculated in the chiral Abelian Higgs model in 1+1 dimensions, where the fermions have a Yukawa coupling to the scalar field. The dependence of the determinant on fermionic, scalar and vector mass is determined. We show in detail how to renormalize the fermionic determinant in partial wave analysis, which is convenient for computations.Comment: 36 pages, 5 figure