Photon radiation in hot nuclear matter by means of chiral anomalies

A new mechanism of photon emission in the quark-gluon plasma is proposed. Photon dispersion relation in the presence of the $CP$-odd topological regions generated by the chiral anomaly acquires an imaginary mass. It allows photon radiation through the decay $q\to q\gamma$ and annihilation $q\bar q\to \gamma$ processes closely related to the chiral Cherenkov radiation. Unlike previous proposals this mechanism does not require an external magnetic field. The differential photon emission rate per unit volume is computed and shown to be comparable to the rate of photon emission in conventional processes.Comment: 12 pages, 1 figur

Violation of geometric scaling in DIS due to Coulomb corrections

I compute the Coulomb correction to the total and diffractive cross sections for virtual photon scattering off a heavy nucleus at low $x$. I show that it violates the geometric scaling in a wide range of photon virtualities and is weakly $x$-independent. In heavy nuclei at low $Q^2$ the Coulomb correction to the total and diffractive cross sections is about 20% and 40% correspondingly.Comment: 4 pages, 4 figure

The impact of domain walls on the chiral magnetic effect in hot QCD matter

The Chiral Magnetic Effect (CME) -- the separation of positive and negative electric charges along the direction of the external magnetic field in quark-gluon plasma and other topologically non-trivial media -- is a consequence of the coupling of electrodynamics to the topological gluon field fluctuations that form metastable $CP$-odd domains. In phenomenological models it is usually assumed that the domains are uniform and the influence of the domain walls on the electric current flow is not essential. This paper challenges the latter assumption. A simple model consisting of a uniform spherical domain in a uniform time-dependent magnetic field is introduced and analytically solved. It is shown that (i) no electric current flows into or out of the domain, (ii) the charge separation current, viz. the total electric current flowing inside the domain in the external field direction, is a dissipative Ohm current, (iii) the CME effect can be produced either by the anomalous current or by the boundary conditions on the domain wall and (iv) the charge separation current oscillates in plasma long after the external field decays. These properties are qualitatively different from the CME in an infinite medium.Comment: 16 pages, 6 figure

Coulomb corrections to DIS off heavy nuclei

An essential part of experimental program at the future Electron Ion Collider is the study of the nuclear structure and dynamics at low $x$. DIS at low $x$ is characterized by large longitudinal coherence length that by far exceeds radii of heavy nuclei. The coherent behavior is essential feature of the nuclear matter at low $x$. This pertains not only to the strong interactions, but also to electromagnetic ones. Coherent interactions of a projectile with nucleons in a heavy nucleus are characterized by parameters $\alpha_s^2 A^{1/3}\sim 1$ and $\alpha Z\sim 1$ in strong and electromagnetic interactions respectively. Contributions exhibiting non-trivial dependence on $\alpha Z$ are called the Coulomb corrections. We compute the Coulomb corrections to the cross sections of the semi-inclusive and diffractive DIS. We show that they violate the geometric scaling in a wide range of photon virtualities and is weakly $x$-independent. In heavy nuclei at low $Q^2$ the Coulomb correction to the total and diffractive cross sections is about 20% and 40% correspondingly.Comment: Contribution to the proceedings of DIS201

Chiral Cherenkov and chiral transition radiation in anisotropic matter

A significant contribution to the electromagnetic radiation by a fast electric charge moving in anisotropic chiral matter arises from spontaneous photon radiation due to the chiral anomaly. While such a process, also known as the "vacuum Cherenkov radiation", is forbidden in the QED vacuum, it can occur in chiral matter, where it is more appropriate to call it the "chiral Cherenkov radiation". Its contribution to the radiation spectrum is of order $\alpha^2$ compared to $\alpha^3$ of the bremsstrahlung. I derive the frequency spectrum and the angular distribution of this radiation in the high energy limit. The quantum effects due to the hard photon emission and the fermion mass are taken into account. The obtained spectra are analyzed in the case the quark-gluon plasma and a Weyl semimetal.Comment: 13 pages, 6 figure

Coherent and incoherent diffractive hadron production in pA collisions and gluon saturation

We study coherent and incoherent diffractive hadron production in high energy quarkonium--heavy nucleus collisions as a probe of the gluon saturation regime of QCD. Taking this process as a model for pA collisions, we argue that the coherent diffractive gluon production, in which the target nucleus states intact, exhibits a remarkable sensitivity to the energy, rapidity and atomic number dependence. The incoherent diffractive gluon production is less sensitive to the details of the low-x dynamics but can serve as a probe of fluctuations in the color glass condensate. As a quantitative measure of the nuclear effects on diffractive hadron production we introduce a new observable -- the diffractive nuclear modification factor. We discuss possible signatures of gluon saturation in diffractive gluon production at RHIC, LHC and EIC.Comment: 22 pages, 6 figures; v2: a few typos correcte

Synchrotron radiation of vector bosons at relativistic colliders

Magnetic fields produced in collisions of electrically charged particles at relativistic energies are strong enough to affect the dynamics of the strong interactions. In particular, it induces radiation of vector bosons by relativistic fermions. To develop deeper insight into this problem, I calculate the corresponding spectrum in constant magnetic field and analyze its angular distribution and mass dependence. As an application, I consider synchrotron radiation of virtual photon by the quark-gluon plasma.Comment: 13 pages, 6 figure

Time and space dependence of electromagnetic field in relativistic heavy-ion collisions

Exact analytical solution for the space-time evolution of electromagnetic field in electrically conducting nuclear matter produced in heavy-ion collisions is discussed. It is argued that the parameter that controls the strength of the matter effect on the field evolution is $\sigma\gamma b$, where $\sigma$ is electrical conductivity, $\gamma$ is the Lorentz boost-factor and $b$ is the characteristic transverse size of the matter. When this parameter is of the order one or larger, which is the case at RHIC and LHC, space-time dependence of electromagnetic field is completely different form that in vacuum.Comment: 7 page

Bulk viscosity of QCD matter near the critical temperature

Kubo's formula relates bulk viscosity to the retarded Green's function of the trace of the energy-momentum tensor. Using low energy theorems of QCD for the latter we derive the formula which relates the bulk viscosity to the energy density and pressure of hot matter. We then employ the available lattice QCD data to extract the bulk viscosity as a function of temperature. We find that close to the deconfinement temperature bulk viscosity becomes large, with viscosity-to-entropy ratio zeta/s about 1.Comment: 8 pages, 1 figur

Electrodynamics of dual superconducting chiral medium

We study the electrodynamics of a chiral medium with electric and magnetic charges using the effective Maxwell-Chern-Simons theory extended to include the magnetic current. The exchange of helicity between the chiral medium and the magnetic field, known as the inverse cascade, is controlled by the chiral anomaly equation. In the presence of the magnetic current, the magnetic helicity is dissipated, so that the inverse cascade stops when the magnetic helicity vanishes while the chiral conductivity reaches a non-vanishing stationary value satisfying $\sigma_\chi^2< 4\sigma_e\sigma_m$, where $\sigma_e$, $\sigma_m$ and $\sigma_\chi$ are the electric, magnetic and chiral conductivities respectively. We argue that this state is superconducting and exhibits the Meissner effect for both electric and magnetic fields. Moreover, this state is stable with respect to small magnetic helicity fluctuations; the magnetic helicity becomes unstable only when the inequality mentioned above is violated.Comment: 13 pages, 11 figures. To appear in Phys. Lett.