arXiv subjects

Harmen J. Warringa

Publications and source records attributed to Harmen J. Warringa.

At least 19 recordsLinked to original sources

arXiv2012

Dynamics of the Chiral Magnetic Effect in a weak magnetic field

We investigate the real-time dynamics of the chiral magnetic effect in quantum electrodynamics (QED) and quantum chromodynamics (QCD). We consider a field configuration of parallel (chromo)electric and (chromo)magnetic fields with a weak perpendicular electromagnetic magnetic field. The chiral magnetic effect induces an electromagnetic current along this perpendicular magnetic field, which we will compute using linear response theory. We discuss specific results for a homogeneous sudden switch-on and a pulsed (chromo)electric field in a static and homogeneous (chromo)magnetic field. Our methodology can be easily extended to more general situations. The results are useful for investigating the chiral magnetic effect with heavy ion collisions and with lasers that create strong electromagnetic fields. As a side result we obtain the rate of chirality production for massive fermions in parallel electric and magnetic fields that are static and homogeneous.

hep-th↗

arXiv2012

Phase diagram of the rotating two-component Fermi gas including vortices

We determine the conditions under which superfluidity with and without quantized vortices appears in a weakly interacting two-component atomic Fermi gas that is trapped in a rotating cylindrical symmetric harmonic potential. We compute the phase diagram as a function of rotation frequency, scattering length, temperature, total number of trapped atoms, and population imbalance.

cond-mat.quant-gas↗

arXiv2011

Vortex formation in a rotating two-component Fermi gas

A two-component Fermi gas with attractive s-wave interactions forms a superfluid at low temperatures. When this gas is confined in a rotating trap, fermions can unpair at the edges of the gas and vortices can arise beyond certain critical rotation frequencies. We compute these critical rotation frequencies and construct the phase diagram in the plane of scattering length and rotation frequency for different total number of particles. We work at zero temperature and consider a cylindrically symmetric harmonic trapping potential. The calculations are performed in the Hartree-Fock-Bogoliubov approximation which implies that our results are quantitatively reliable for weak interactions.

cond-mat.quant-gas↗

arXiv2010

Real-time dynamics of the Chiral Magnetic Effect

In quantum chromodynamics, a gauge field configuration with nonzero topological charge generates a difference between the number of left- and right-handed quarks. When a (electromagnetic) magnetic field is added to this configuration, an electromagnetic current is induced along the magnetic field; this is called the chiral magnetic effect. We compute this current in the presence of a color flux tube possessing topological charge, with a magnetic field applied perpendicular to it. We argue that this situation is realized at the early stage of relativistic heavy-ion collisions.

hep-ph↗

arXiv2009

Electric-current Susceptibility and the Chiral Magnetic Effect

We compute the electric-current susceptibility χof hot quark-gluon matter in an external magnetic field B. The difference between the susceptibilities measured in the directions parallel and perpendicular to the magnetic field is ultraviolet finite and given by χ^\parallel-χ^\perp = VTN_c\sum_f q_f^2 |q_f B|/(2π^2), where V denotes the volume, T the temperature, N_c the number of colors, and q_f the charge of a quark of flavor f. This non-zero susceptibility difference acts as a background to the Chiral Magnetic Effect, i.e. the generation of electric current along the direction of magnetic field in the presence of topological charge. We propose a description of the Chiral Magnetic Effect that takes into account the fluctuations of electric current quantified by the susceptibility. We find that our results are in agreement with recent lattice QCD calculations. Our approach can be used to model the azimuthal dependence of charge correlations observed in heavy ion collisions.

hep-ph↗

arXiv2009

Pion condensation in a dense neutrino gas

We argue that using an equilibrated gas of neutrinos it is possible to probe the phase diagram of QCD for finite isospin and small baryon chemical potentials. We discuss this region of the phase diagram in detail and demonstrate that for large enough neutrino densities a Bose-Einstein condensate of positively charged pions arises. Moreover, we show that for nonzero neutrino density the degeneracy in the lifetimes and masses of the charged pions is lifted.

hep-ph↗

arXiv2009

Chiral Magnetic conductivity

Gluon field configurations with nonzero topological charge generate chirality, inducing P- and CP-odd effects. When a magnetic field is applied to a system with nonzero chirality, an electromagnetic current is generated along the direction of the magnetic field. The induced current is equal to the Chiral Magnetic conductivity times the magnetic field. In this article we will compute the Chiral Magnetic conductivity of a high-temperature plasma for nonzero frequencies. This allows us to discuss the effects of time-dependent magnetic fields, such as produced in heavy ion collisions, on chirally asymmetric systems.

hep-ph↗

arXiv2009

The Chiral Magnetic Effect: Measuring event-by-event P- and CP-violation with heavy ion-collisions

Gluon field configurations with nonzero topological charge induce P- and CP-odd effects. Such configurations are likely to be produced during heavy ion collisions. In this article, I will argue that in the intense (electromagnetic) magnetic field produced in non-central heavy ion collisions, topological charge creates an electromagnetic current in the direction of the magnetic field. This is the Chiral Magnetic Effect. It leads to separation of positive from negative charge along the direction of the magnetic field. I will point out that this effect can be investigated experimentally with a charge correlation study and will refer to interesting data from the STAR collaboration.

hep-ph↗

arXiv2008

The Chiral Magnetic Effect

Topological charge changing transitions can induce chirality in the quark-gluon plasma by the axial anomaly. We study the equilibrium response of the quark-gluon plasma in such a situation to an external magnetic field. To mimic the effect of the topological charge changing transitions we will introduce a chiral chemical potential. We will show that an electromagnetic current is generated along the magnetic field. This is the Chiral Magnetic Effect. We compute the magnitude of this current as a function of magnetic field, chirality, temperature, and baryon chemical potential.

hep-ph↗

arXiv2008

Implications of CP-violating transitions in hot quark matter on heavy ion collisions

Quantum Chromodynamics (QCD) predicts that topological charge changing transitions will take place in hot quark matter. Such transitions induce P- and CP-violating effects. We will show that in the presence of a magnetic field these transitions can separate quarks according to their electric charge along the direction of the magnetic field. This is the so-called Chiral Magnetic Effect. We will argue that it might be possible to observe the Chiral Magnetic Effect in heavy ion collisions.

hep-ph↗

arXiv2007

The effects of topological charge change in heavy ion collisions: "Event by event P and CP violation"

Quantum chromodynamics (QCD) contains field configurations which can be characterized by a topological invariant, the winding number Q_w. Configurations with nonzero Q_w break the charge-parity CP symmetry of QCD. We consider a novel mechanism by which these configurations can separate charge in the presence of a background magnetic field - the "Chiral Magnetic Effect". We argue that sufficiently large magnetic fields are created in heavy ion collisions so that the Chiral Magnetic Effect causes preferential emission of charged particles along the direction of angular momentum. Since separation of charge is CP-odd, any observation of the Chiral Magnetic Effect could provide a clear demonstration of the topological nature of the QCD vacuum. We give an estimate of the effect and conclude that it might be observed experimentally.

hep-ph↗

arXiv2007

Color superconducting matter in a magnetic field

We investigate the effect of a magnetic field on cold dense three-flavor quark matter using an effective model with four-Fermi interactions with electric and color neutrality taken into account. The gap parameters Delta_1, Delta_2, and Delta_3 representing respectively the predominant pairing between down and strange (d-s) quarks, strange and up (s-u) quarks, and up and down (u-d) quarks, show the de Haas-van Alphen effect, i.e. oscillatory behavior as a function of the modified magnetic field B that can penetrate the color superconducting medium. Without applying electric and color neutrality we find Delta_2 \approx Delta_3 >> Delta_1 for 2 e B / mu_q^2, where e is the modified electromagnetic coupling constant and mu_q is one third of the baryon chemical potential. Because the average Fermi surface for each pairing is affected by taking into account neutrality, the gap structure changes drastically in this case; we find Delta_1 >> Delta_2 \approx Delta_3 for 2 e B > mu_q^2. We point out that the magnetic fields as strong as presumably existing inside magnetars might induce significant deviations from the gap structure Delta_1 \approx Delta_2 \approx Delta_3 at zero magnetic field.

hep-ph↗

arXiv2006

The effects of quantum instantons on the thermodynamics of the CP^(N-1) model

Using the 1/N expansion, we study the influence of quantum instantons on the thermodynamics of the CP^(N-1) model in 1+1 dimensions. We do this by calculating the pressure to next-to-leading order in 1/N, without quantum instanton contributions. The fact that the CP^1 model is equivalent to the O(3) nonlinear sigma model, allows for a comparison to the full pressure up to 1/N^2 corrections for N=3. Assuming validity of the 1/N expansion for the CP^1 model makes it possible to argue that the pressure for intermediate temperatures is dominated by the effects of quantum instantons. A similar conclusion can be drawn for general N values by using the fact that the entropy should always be positive.

hep-th↗

arXiv2006

The phase diagram of neutral quark matter with pseudoscalar condensates in the color-flavor locked phase

We calculate the phase diagram of color and electrically neutral quark matter in weak equilibrium using the NJL model at high baryon densities. We extend previous analyses by taking into account the possibility of formation of pseudoscalar meson condensates in the color-flavor locked (CFL) phase. We find that the kaon condensed phase (CFL-K0) is preferred over the CFL phase at low temperatures. It is found that the CFL-K0 phase contains no gapless modes. The results we have obtained should be of relevance for the modeling of compact stars.

hep-ph↗

arXiv2006

Thermodynamics of QCD-inspired theories

In this thesis I investigate the thermodynamics of the O(N) nonlinear sigma model and the CP^(N-1) model in 1 + 1 dimensions, which are toy models for QCD. In particular I put emphasis on the calculation of the effective potential and the pressure to next-to-leading order in 1/N. One interesting result is that the effective potential contains temperature-dependent ultraviolet divergences that vanish in the minimum. Furthermore I discuss two low-energy effective theories, the O(N) linear sigma model in 3 + 1 dimensions and the NJL model. In the O(N) model I calculate the effective potential and the pressure up to next-to-leading order in 1/N. I also discuss a rather low bound on the mass of the sigma meson in that model. The NJL model is used to calculate phase diagrams with pseudoscalar condensation and color superconductivity as a function of different quark chemical potentials. I find that phases with pseudoscalar condensation are separated from the color superconducting phases by a first order transtion.

hep-ph↗

arXiv2005

Phase diagrams of the three-flavor NJL model with color superconductivity and pseudoscalar condensation

We present results of the calculation of phase diagrams of the three-flavor NJL model as a function of temperature and different quark chemical potentials. These phase diagrams are an extension of earlier calculations in the literature in which either only the possibility of color superconductivity or the possibility of pseudoscalar condensation was investigated. This study takes into account both options and hence allows one to investigate their competition. It turns out that the color superconducting phase and the phase in which the pseudoscalar mesons condense are separated by a first order transition.

hep-ph↗

arXiv2005

Color superconductivity vs. pseudoscalar condensation in a three-flavor NJL model

We calculate numerically the phase diagram of the three-flavor Nambu-Jona-Lasinio model at zero and finite temperature as a function of the up, down, and strange quark chemical potentials. We focus on the competition between pseudoscalar condensation and color superconductivity. We find that the two types of phases are separated by first-order transitions.

hep-ph↗

arXiv2004

Thermodynamics of the 1+1-dimensional nonlinear sigma model through next-to-leading order in 1/N

We discuss the thermodynamics of the O(N) nonlinear sigma model in 1+1 dimensions. In particular we investigate the NLO 1/N correction to the 1PI finite temperature effective potential expressed in terms of an auxiliary field. The effective potential contains temperature-dependent divergences which cannot be renormalized properly. We argue that this problem vanishes at the minimum of the effective potential. Therefore physical quantities like the pressure are well defined and can be renormalized in a temperature-independent way. We give a general argument for the occurrence of temperature-dependent divergences outside the minimum. We present calculations of the pressure and show that 1/N is a good expansion. It turns out that the pressure normalized to that at infinite temperature is N-independent like the flavor independence of the same quantity in QCD.

hep-ph↗