arXiv subjects

V. Skalozub

Publications and source records attributed to V. Skalozub.

At least 19 recordsLinked to original sources

arXiv2026

Effective vertexes in magnetized quark-gluon plasma

In quark-gluon plasma (QGP), at high temperatures $T$ the spontaneous generation of color magnetic fields, $b^3(T), b^8(T) \not = 0$ (3, 8 are color indexes), and usual magnetic field $b(T) \not = 0$ happens. Also, the Polyakov loop and related to it the $A_0(T)$ condensate, which is solution to Yang-Mills imaginary time equations, create. Recently, with the new type two-loop effective potential, which generalizes the known integral representation for the Bernoulli polynomials and takes into consideration the magnetic background, these effects were derived. The corresponding effective potential $W(T, b^3, b^8, b, A_0 )$ was calculated either in SU(2) gluodynamics or full quantum chromodynamics (QCD). The values of magnetic field strengths at different temperatures were calculated and the mechanism for stabilizing the background due to $A_0(T)$ was also discovered. In present paper, we concentrate on the one-loop quark contributions. In particular, we derive the effective vertexes, which couple magnetic fields and $A_0$. The vertexes result in new specific effects signalling the creation of QGP in heavy ion collision experiments. Key words: spontaneous magnetization, high temperature, asymptotic freedom, effective potential, $A_0$ condensate, effective vertexes.

hep-ph↗

arXiv2023

Induced color charges in QGP at Polyakov's loop and chromomagnetic fields

In quark-gluon plasma (QGP), at high temperature the spontaneous generation of color magnetic fields, H^3(T), H^8(T) and usual magnetic field $H(T) is realized. Also, classical field - A_0(T) condensate directly related to the Polyakov loop - is spontaneously created. The common generation of both of them within the two loop effective potential was investigated recently for SU(2) gluodynamics. The values of the field strengths and the mechanism of the magnetic fields stabilization due to A_0(T) have been discovered. In the present paper, we develop further these investigations in order to find new effects of QGP. First of all, we generalize the SU(2) consideration to the full QCD case. Then we calculate the induced color charge Q_(ind)^3 at the background magnetic field H(T) and the condensates A_0^3(T). The field $ A_0^8(T) is zero in used two-loop approximation. So, Q_{ind}^8 is zero also. We conclude that magnetic field essentially influences the induced charge compared to the zero field case investigated in \cite{skal21-cond-156}. The extension to other type magnetic fields is given. Key words: spontaneous magnetization, high temperature, asymptotic freedom, effective potential, $A_0$ condensate, effective charge, effective vertexes.

hep-ph↗

arXiv2023

Spontaneous magnetization of a vacuum in high temperature gluodynamics (two-loop approximation

In SU(N) gluodynamics, at high temperature the spontaneous magnetization, b(T) not equal to 0, of a vacuum happens in the approximation to the effective potential - the tree plus the one-loop, plus daisy diagrams, W(b)= b^2/2 g^2 + W^(1)(b) + W^(daisy)(b). At the same time, in two-loop approximation, W(A_0)= W^(1)(A_0) + W^(2)(A_0), other classical field - A_0 condensate directly related to the Polyakov loop - is also spontaneously generated. To investigate the creation of the condensates together, the two loop effective potential of both fields should be calculated. This program was realized recently for SU(2) in [1]. However, the generation of magnetic field in two-loop order was not studied in detail. In the present paper, we compute the value of chromomagnetic field b(T) for latter case. Then, considering the spectrum of color charged gluons at the background of both condensates, we conclude that the A_0 stabilizes the magnetized vacuum at high temperature. This is in agreement with the lattice simulations carried out already and clarifies the mechanism of the magnetic field stabilization. Key words: condetsation, high temperature, gluodynamics, A0 condensate, spontaneous magnetization, vacuum

hep-ph↗

arXiv2022

Effective color charge in high temperaure gluon plasma at A_0 background

In high temperature SU(2) gluodynamics, in a relativistic background R^{ext.}_xi gauge, the effective color charge (g^2(A_0))_eff. is calculated in the presence of the A_0 condensate which is related to Polyakov's loop and also serves as the order parameter of the deconfinement phase transition at high temperature. The gauge-invariant value of the condensate ((A_0)^cl)_0 is obtained from the two-loop effective potential of order parameter W_L(A_0^cl) which is independent of the gauge-fixing parameter xi and has a nontrivial minimum position. Due to smallness of the expansion parameter ~ g^2/(8 pi^2), this potential is applicable at high temperatures beginning from the deconfinement temperature T_d. The effective charge accounts for a correlation between the one- and the two-loop terms of the W_L(A_0^cl). It results in decreasing of the effective gluon interactions in the plasma, compared to the zero condensate case. Temperature dependence of (g^2(A_0))_eff. is investigated. The importance of the found dependence for different applications is noted.

hep-ph↗

arXiv2021

Effective potential of gluodynamics in background of Polyakov loop and colormagnetic field

In SU(N) gluodynamics, above the de-confinement temperature, the effective potential has minima at non-zero $A_0$-background fields in the two-loop approximation. Also, it has a minimum at non-zero chromomagnetic background field, known as 'Savvidy'-vacuum, which shows up on the one-loop level. In this paper, we join these two approaches. We formulate, at finite temperature, the effective action, or the free energy, in SU(2) gluodynamics on the two-loop level, with both, $A_0$ background and magnetic background present at the same time, which was not done so far. We provide the necessary representations for both, effective numerical calculation and high-temperature expansions. The results are represented as a 3D plot of the real part of the effective potential. Also, we reproduce for zero either, the $A_0$-background or the magnetic background, the known minima and compare them. The imaginary part is, on the two-loop level, still present. We mention that, as is known from literature for the case without $A_0$-background, the imaginary part is compensated by the ring ('daisy') diagrams. However, our results reveal an unnatural, singular behavior of the effective potential in the region, where the imaginary part sets in. Our conclusion is that one has to go beyond the two-loop approximation and its ring improved version, in order to investigate the minimum of the effective action as a function of $A_0$ and chromomagnetic field, and its stability, at least in the approximation of superdaisy diagrams, i.e., the Hartree approximation in the CJT formalism.

hep-th↗

arXiv2021

On direct search for dark matter in scattering processes within Yukawa model

\begin{abstract} Nowadays, no dark matter candidates have been discovered. We consider two possible reasons for that, both related to the approach of on-peak resonance searching for. As is believed usually, a new particle suits the conditions that the ratio of the width to the mass is less than $1-3 \%$ and a narrow width approximation (NWA) is applicable to identify the such type resonant peak in the invariant mass spectrum of collision products. In the present paper, in the framework of generalized Yukawa model, we find out the properties of the searched particle when its width is larger than a maximal one expected during experiments and so this state could be missed as a noise. We also ascertain the values of particle's parameters when the NWA is not applicable and estimate the width value when it happens. These estimations are relevant to interactions between the Standard model and dark matter particles. Such approach is focused on the role of couplings and mass values introduced in the model describing interaction of visible and dark matter. Key words: dark matter; resonance; narrow width approximation; mixing of fields.

hep-ph↗

arXiv2021

A0--condensation in quark-gluon plasma with finite baryon density

In the present paper, we return to the problem on a spontaneous generation of the $A_0$-background field in QCD at finite temperature and include in addition a quark chemical potential, $μ$. We reproduce the known expressions in terms of Bernoulli's polynomials for the gluons and quarks using the same formalism. Then we calculate the $μ$-dependence, both for small $μ$ as expansion, and numerically for finite $μ$. One result is that the chemical potential only weakly changes the values of the condensed field, but quite strongly deepens the minima of the effective potential. The gauge dependence of the condensation is discussed in terms of Nielsen's identity. It also is expressed in terms of Polyakov's loop. Both these representations guarantee gauge invariance of the condensation phenomenon. Also, we discuss the dependence of the Polyakov loop in the minimum of the effective potential on the chemical potential.

hep-th↗

arXiv2020

Induced color charges, effective gamma-gamma-gluon vertex in QGP. Applications to heavy-ion collisions

We calculate the induced color charges Q_{ind.}^3, Q_{ind.}^8 and the effective vertex gamma - gamma - gluon generated in quark-gluon plasma with the A_0 condensate because of the color parity violation at this background. To imitate the case of heavy-ion collisions, we consider the model of the plasma confined in the narrow infinite plate and derive the classical gluon potentials Phi^3, Phi^8 produced by these charges. Two applications - scattering of photons on the plasma and conversion of gluon fields in two photons radiated from the plasma - are discussed.

hep-ph↗

arXiv2018

Photon dispersion relations in $A_0$-background

We calculate the photon dispersion relations generated by the quark loop in a quark-gluon plasma with the color $A_0$ background condensate $A_0^c = A_0^{c3} + A_0^{c8}$ = const. It is found that both transversal and longitudinal modes are exited. They have a gap at low momenta and are stable in high temperature approximation. The background fields act as imaginary chemical potentials and decrease the photon frequencies compared to the case of zero background. The comparison with QED plasma with chemical potential is discussed.

hep-ph↗

arXiv2018

Model-independent constraints on the Abelian $Z'$ couplings within the ATLAS data on the dilepton production processes at $\sqrt{s} =$ 13 TeV

The study of lepton pair production is a powerful test of the Standard Model (SM) and can be used to search for phenomena beyond the SM. New heavy neutral bosons $Z'$ decaying to charged lepton pairs $l^+l^-$ ($l=e, μ$) are predicted by many scenarios of new physics, including models with extended gauge sector. We estimate the LHC $Z'$ discovery potential with Run 2 data comprised of 36.1 fb$^{-1}$ of $pp$ collisions at $\sqrt{s}=13$ TeV and recorded by ATLAS detector at the CERN LHC. The model-independent constraints on the $Z'$ fermion couplings were obtained for the first time for a selected set of $Z'$ signal mass points of $M_{Z'}=2$, 3, and 4 TeV by using the ATLAS data collected at the LHC. The analysis is based on the derived earlier special relations between the $Z'$ couplings proper to the renormalizable theories. Taking into account the dependence of $Z-Z'$ mixing angle $θ_0$ on the $Z'$ axial-vector coupling $a$, the limits on $θ_0$ are established as $θ_0 < 10^{-4} - 10^{-3}$ in the investigated $Z'$ mass range.

hep-ph↗

arXiv2017

Magnetized quark-gluon plasma at the LHC

In QCD, the strengths of the large scale temperature dependent chromomagnetic, $B_3, B_8$, and usual magnetic, $H$, fields spontaneously generated in quark-gluon plasma after the deconfinement phase transition (DPT), are estimated. The consistent at high temperature effective potential accounting for the one-loop plus daisy diagrams is used. The heavy ion collisions at the LHC and temperatures T not much higher than the phase transition temperature $T_d$ are considered. The critical temperature for the magnetized plasma is found to be $T_d(H)$ ~ $110 - 120$ MeV. This is essentially lower compared to the zero field value $T_d(H=0)$~ $160-180$ MeV usually discussed in the literature. Due to contribution of quarks, the color magnetic fields act as the sources generating H. The strengths of the fields are $B_3(T), B_8(T) \sim 10^{18} - 10^{19}G, H(T) \sim 10^{16} - 10^{17}G$ for temperatures T ~ 160 - 220 MeV. At temperatures $T < 110 - 120$ MeV the effective potential minimum value being negative approaches to zero. This is signaling the absence of the background fields and color confinement.

hep-ph↗

arXiv2016

On magnetization of quark-gluon plasma at the LHC experiment energies

Large scale chromomagnetic, B_3, B_8, and usual magnetic,H, fields have to be generated in QCD after the deconfinement phase transition (DPT) at temperatures T larger than deconfinement temperature T_d. The two former fields are created spontaneously due to asymptotic freedom of gluon intaractions. Whereas H is produced due to either the feature of quarks to possess both electric and color charges or a vacuum polarization in this case. At the polarization, the vacuum quark loops mix the external fields. As a result, B_3, B_8 become the sources generating H. The latter field appears at $T$ much lower than the electroweak phase transition temperature T_ew. This mechanism should exhibit itself at the LHC experiments on heavy ion collisions. It operates at the one-loop diagram level for an effective potential. The created fields are temperature dependent and occupying the macroscopic volume of quark-gluon plasma. The magnetization influences different processes and may serve as a signal for the DPT.

hep-ph↗

arXiv2016

Estimates of Z'couplings within data on the A_{FB} for Drell-Yan process at the LHC at s^(1/2) = 7 TeV and 8 TeV

Model-independent search for the Abelian Z' gauge boson in the Drell-Yan process at the LHC at s^{1/2}= 7 TeV and 8 TeV is fulfilled. Estimations of the Z' axial-vector coupling a_f^2 to the standard model fermions, the couplings of the axial-vector to lepton vector currents a_f v_l and the couplings of the axial-vector to quark vector currents a_f v_q are derived within data on the forward-backward asymmetry presented by the CMS Collaboration. The analysis takes into consideration the behaviour of the differential cross-section which exhibits itself if the derived already special relations between the couplings proper to the renormalizable theories are accounted for. In particular, they hold in all the models of Abelian Z' usually considered in the model-dependent analysis of the LHC data. The coupling values are estimated at ~ 92 % CL by means of the maximum likelihood function. They weakly depend on the Z' mass in the investigated interval 1.2 TeV < m_Z' < 5 TeV. Taking into account the dependence of Z-Z' mixing angle theta_0 on m_Z' and the LEP constraints |theta_0|~ 10^{-3}-10^{-4}, the optimistic limits on m_{Z'} are established as 3 < m_Z' < 7-8 TeV. Comparison with the results of other authors is given.

hep-ph↗

arXiv2014

Observables for model-independent detections of Z' boson at the ILC

The integral observables for model-independent detections of Abelian Z' gauge boson in e^+ e^- -> mu^+ mu^- (tau^+ τ^-) process with unpolarized beams at the ILC energies are proposed. They are based on the differential cross-section of deviations from the standard model predictions calculated with a low energy effective Lagrangian and taking into consideration the relations between the Z' couplings to the fermions derived already. Due to these relations, the cross-section exhibits angular distribution giving a possibility for introducing one- or two parameter observables which effectively fit the mass m_Z', the axial-vector (a_Z)'^2 and the product of vector couplings v_e v_mu (v_e v_tau). Comparison with other results and approaches is given.

hep-ph↗

arXiv2014

On the type of the temperature phase transition in O(N) models within a perturbative analysis

We investigate the type of the temperature phase transition in the $N$ component $\la ϕ^4$ ($O(N)$) model of scalar fields. Actual calculations are carried out in the beyond-super-daisy approximation (BSDA). The cases $N = 1$ and larger $N$ are considered separately. Using the solutions of gap equations we show that the character of the phase transition depends on the account for graphs BSDA. The role of different kinds of diagrams (especially the "sunset" one) is clarified. It is shown in a perturbation theory in the effective expansion parameter $N^{- 1/3}$ that the kind of the phase transition depends on the value of coupling $\la$. It turns from a weak first-order to the second-order one for increasing $\la$. This is in agreement with the observation found recently for the $O(1)$ model in Monte Carlo simulations on a lattice. Comparison with results of other authors is given.

hep-th↗

arXiv2012

The type of the phase transition and coupling values in λϕ^4 model

The temperature induced phase transition is investigated in the one-component scalar field ϕ^4 model on the lattice. Using the GPU cluster a huge amount of Monte Carlo simulation data is collected for a wide interval of coupling values. This gives a possibility to determine the low bound on the coupling constant λ_0 when the transition happens and investigate its type. We found that for the values of λclose to this bound a weak-first-order phase transition takes place. It converts into a second order one with the increase of λ. A comparison with the results obtained in analytic and numeric calculations by other authors is given.

hep-lat↗

arXiv2012

Spontaneous magnetization of the vacuum and the strength of the magnetic field in the hot Universe

Intergalactic magnetic fields are assumed to have been spontaneously generated at the reheating stage of the early Universe, due to vacuum polarization of non-Abelian gauge fields at high temperature. The fact that the screening mass of this type of fields has zero value was discovered recently. A procedure to estimate their field strengths, $B(T)$, at different temperatures is here developed, and the value $B(T_{ew}) \sim 10^{14} G$ at the electroweak phase transition temperature, is derived by taking into consideration the present value of the intergalactic magnetic field strength, $B_0 \sim 10^{- 15} G$, coherent on the $\sim 1$ Mpc scale. As a particular case, the standard model is considered and the field scale at high temperature is estimated in this case. Model dependent properties of the phenomena under investigation are briefly discussed, too.

hep-ph↗

arXiv2012

Groundstate projection of the charged SU(2) polarization tensor in a chromomagnetic background field

We consider the polarization tensor of a color charged gluon field in SU(2) in the background of a homogeneous color magnetic field and calculate its projection onto the lower (tachyonic) state. We obtain a quite simple representation of the polarization tensor in terms of double parametric integral. We provide examples for the numerical evaluation of the polarization tensor in this case. Also, we consider the corresponding expressions at high temperature and calculate the charged gluon magnetic mass in this limit. We conclude that radiation corrections stabilize the ground state. Applications of the results obtained are discussed.

hep-th↗