arXiv subjects

P. M. Zhang

Publications and source records attributed to P. M. Zhang.

At least 19 recordsLinked to original sources

arXiv2025

Conformally related vacuum gravitational waves, and their symmetries

A special conformal transformation which carries a vacuum gravitational wave into another vacuum one is built by using Möbius-redefined time. It can either transform a globally defined vacuum wave into a vacuum sandwich wave, or carry the gravitational wave into itself. The first type, illustrated by linearly and circularly polarized vacuum plane gravitational waves, permutes the symmetries and the geodesics. Our pp waves with conformal O(2,1) symmetry of the second type, which seem to ahve escaped attention so far, are anisotropic generalizations of the familiar inverse-square profile. An example inspired by molecular physics, for which the particle can escape, or perform periodic motion, or fall into the singularity is studied in detail.

gr-qc↗

arXiv2025

Lukash plane waves, revisited

The Lukash metric is a homogeneous gravitational wave which at late times approximates the behaviour of a generic class of spatially homogenous cosmological models with monotonically decreasing energy density. The transcription from Brinkmann to Baldwin-Jeffery-Rosen (BJR) to Bianchi coordinates is presented and the relation to a Sturm-Liouville equation is explained. The 6-parameter isometry group is derived. In the Bianchi VII range of parameters we have two BJR transciptions. However using either of them induces a mere relabeling of the geodesics and isometries. Following pioneering work of Siklos, we provide a self-contained account of the geometry and global structure of the spacetime. The latter contains a Killing horizon to the future of which the spacetime resembles an anisotropic version of the Milne cosmology and to the past of which it resemble the Rindler wedge.

gr-qc↗

arXiv2024

Forward $J/ψ+ J/ψ$ and $J/ψ+ ψ^\prime$ production with High Energy Factorization

We calculate the cross sections of associated $J/ψ+ ψ^\prime$ and $J/ψ+ J/ψ$ production in $pp$ collisions at $\sqrt s = 13$ TeV in the forward kinematic region. The High Energy Factorization ($k_T$-factorization) framework supplemented with the Catani-Ciafaloni-Fiorani-Marchesini evolution of gluon densities in a proton is applied. We demonstrate that latest data on $J/ψ+ J/ψ$ production and first experimental data on $J/ψ+ ψ^\prime$ events taken very recently by the LHCb Collaboration can be described well by the color singlet terms and contributions from the double parton scattering (DPS) with the standard choice for $σ_{\rm eff}$ parameter. The relative production rate $σ(J/ψ+ ψ^\prime)/σ(J/ψ+ J/ψ)$ is found to be sensitive to the DPS terms as well as to feeddown contributions.

hep-ph↗

arXiv2024

Shadowing and antishadowing in the rescaling model

Nuclear deep inelastic structure functions F_2^A(x,Q^2) as well as parton distribution functions in a nuclei are investigated in the framework of rescaling model. Our analysis is based on analytical expressions for quark and gluon densities in a proton derived at the leading order of QCD coupling. By fitting the rescaling parameters from the experimental data on F_2^A(x,Q^2)/F_2^D(x,Q^2) ratio for several nuclear targets, we derive predictions for corresponding nuclear parton distributions and, thus, for shadowing and antishadowing effects.

hep-ph↗

arXiv2020

Stiff self-interacting string near QCD deconfinement point

We compare the predictions of Nambu-Goto effective string model at two loop-order for the Casimir energy and the width of the quantum delocalization of the string to the corresponding quark-antiquark potential and width profile of the color tube in pure SU (3) Yang-Mills LGT at 4-dimensions near the deconfinement point. Minor effects are returned, when considering NLO terms for both the $Q\bar{Q}$ potential and broadening of the color tube, at the temperature $T/T_c= 0.8$. At a closer temperature to the critical point $T/T_c$= 0.9, we found that the NLO contributions, from the expansion of the Nambu-Goto string, to have a significant effect in improving the match to lattice data in the intermediate distances scales. The string's self-interactions contribute towards the suppressed broadening of the string's width and the squeezed profile along the string at the intermediate color source separation distance.

hep-lat↗

arXiv2019

Gauge covariant approach to the electroweak interactions of mesons in the Nambu-Jona-Lasinio model with spin-1 states

An extended Nambu-Jona-Lasinio (NJL) model with chiral group $U(2)\times U(2)$ and spin-0 and spin-1 four quark interactions is used to develop the gauge covariant approach to the diagonalization of the $π-a_1$ mixing in the presence of electroweak forces. This allows for manifestly gauge covariant description of both the non-anomalous and anomalous parts of the effective Lagrangian. It is shown that in the non-anomalous sector the theory is equivalent to the standard non-covariant approach.

hep-ph↗

arXiv2018

Hadronic electroweak current and $π- a_1$ mixing

It is found that in presence of electroweak interactions the gauge covariant diagonalization of the axial-vector -- pseudoscalar mixing in the effective meson Lagrangian leads to a deviation from the vector meson and the axial-vector meson dominance of the entire hadronic electroweak current. The essential features of such a modification of the theory are investigated in the framework of the extended Nambu-Jona-Lasinio model with explicit breaking of chiral $U(2) \times U(2)$ symmetry. The Schwinger-DeWitt method is used as a major tool in our study of the real part of the relevant effective action. Some straightforward applications are considered.

hep-ph↗

arXiv2018

Microscopic vacuum structure in a pure QCD

We propose a class of stationary color magnetic solutions in a pure quantum chromodynamics (QCD) which are stable under gluon quantum fluctuations. This resolves a long-standing problem of microscopic description of a stable non-trivial vacuum in a pure QCD. The solutions represent fixed points in a full space of gauge fields under Weyl group transformations. An important feature of the solutions is the phenomenon of Weyl invariant Abelian projection and Abelian dominance in the vacuum structure. As an application of our approach we consider an effective Lagrangian of pure Abelian glueballs in the presence of vacuum gluon condensate.

hep-th↗

arXiv2018

Axially-symmetric stationary solutions in a pure SU(3) QCD

We propose an ansatz for a class of regular axially-symmetric solutions in SU(3) QCD. After averaging over time period the solution can be treated as a non-topological monopole-antimonopole pair. We demonstrate that QCD Lagrangian on the space of such solutions is explicitly Weyl symmetric and reduces to a generalized phi^4 model with four independent fields. All solutions possess quantum stability under vacuum gluon fluctuations.

hep-th↗

arXiv2017

On microscopic structure of the QCD vacuum

We propose a new class of regular stationary axially symmetric solutions in a pure QCD which correspond to monopole-antimonopole pairs at macroscopic scale. The solutions represent vacuum field configurations which are locally stable against quantum gluon fluctuations in any small space-time vicinity. This implies that the monopole-antimonopole pair can serve as a structural element in microscopic description of QCD vacuum formation through the monopole pair condensation.

hep-th↗

arXiv2017

Mesonic String of Diquark-Quark Configuration at Finite Temperature

We investigate the distance and temperatures scale for which the string in baryonic quark configuration approaches the limiting behavior of mesonic strings in pure Yang-Mills SU(3) lattice gauge theory. We calculate and compare the numerical values of the Polyakov loop correlators and the width profile of both diquark-quark $(QQ)Q$ and mesonic $Q\bar{Q}$ strings. We find the diquark-quark configuration to exhibit an identical behavior to the mesonic string for the potential and energy-density width profile for temperature near the end of QCD plateau. In the vicinity of the deconfinement point; however, the symmetry in the energy-width profile with the meson does not manifest at both short and intermediate distance scales. Moreover, we observe significantly different numerical values for Polyakov loop correlators corresponding to each system. The splitting of the two identical system suggest that, in the high temperature region of the confined phase of QCD, the subsisted baryonic decouplet states overlap with the excited mesonic spectrum yielding the diquark-quark symmetry with the meson inexact in a small enough neighborhood of the critical point $T_{c}$.

hep-lat↗

arXiv2017

The Memory Effect for Plane Gravitational Waves

We give an account of the gravitational memory effect in the presence of the exact plane wave solution of Einstein's vacuum equations. This allows an elementary but exact description of the soft gravitons and how their presence may be detected by observing the motion of freely falling particles. The theorem of Bondi and Pirani on caustics (for which we present a new proof) implies that the asymptotic relative velocity is constant but not zero, in contradiction with the permanent displacement claimed by Zel'dovich and Polnarev. A non-vanishing asymptotic relative velocity might be used to detect gravitational waves through the "velocity memory effect", considered by Braginsky, Thorne, Grishchuk, and Polnarev.

gr-qc↗

arXiv2017

Gauge invariant gluon spin operator for spinless non-linear wave solutions

We consider non-linear wave type solutions with mass scale parameter and vahished canonical spin density operator in a pure SU(2) quantum chtomodynamics (QCD). A new stationary solution which can be treated as a system of static Wu-Yang monopole dressed in off-diagonal gluon field is proposed. A remarkable feature of such a solution is that it possesses a finite energy density everywhere. All considered non-linear wave type solutions have common features: presence of a mass scale parameter, non-vanishing projection of the color magnetic field along the propagation direction and zero spin density. The last property requires revision of the gauge invariant definition of the spin density operator which supposed to be massless vector field in the classical theory. We construct a gauge invariant definition of the classical gluon spin density which is unique and Lorentz frame independent.

hep-th↗

arXiv2015

Non-monopole magnetic solutions in the Weinberg-Salam model

The structure of finite energy non-monopole solutions with azimuthal magnetic flux of topological origin is studied in the pure bosonic sector of the Weinberg-Salam model. Applying a variational method we have found simple magnetic field configurations which minimize the energy functional and possess energies of order 1 TeV. Such configurations correspond to composite bound states of W, Z and Higgs bosons with essentially less energy in comparison to monopole like particles supposed to be found at LHC.

hep-ph↗

arXiv2015

On finite energy monopole solutions in Weinberg-Salam model

We study the problem of existence of finite energy monopole solutions in the Weinberg-Salam model starting with a most general ansatz for static axially-symmetric electroweak magnetic fields. The ansatz includes an explicit construction of field configurations with various topologies described by the monopole and Hopf charges. We introduce a unique SU(2) gauge invariant definition for the electromagnetic field. It has been proved that the magnetic charge of any finite energy monopole solution must be screened at far distance. This implies non-existence of finite energy monopole solutions with a non-zero total magnetic charge. In a case of a special axially-symmetric Dashen-Hasslacher-Neveu ansatz we revise the structure of the sphaleron solution and show that sphaleron represents a non-trivial system of monopole and antimonopole with their centers located in one point. This is different from the known interpretation of the sphaleron as a monopole-antimonopole pair like Nambu's "dumb-bell". In general, the axially-symmetric magnetic field may admit a helical structure. We conjecture that such a solution exists and estimate an upper bound for its energy, E_{bound}=4.65 TeV.

hep-th↗

arXiv2014

Gauge invariance, Lorentz covariance and canonical quantization in nucleon structure studies

There are different operators of quark and gluon momenta, orbital angular momenta, and gluon spin in the nucleon structure study. The precise meaning of these operators are studied based on gauge invariance, Lorentz covariance and canonical quantization rule. The advantage and disadvantage of different definitions are analyzed. A gauge invariant canonical decomposition of the total momentum and angular momentum into quark and gluon parts is suggested based on the decomposition of the gauge potential into gauge invariant (covariant) physical part and gauge dependent pure gauge part. Challenges to this proposal are answered. \keywords{Physical and pure gauge potentials; Gauge invariant canonical quark and gluon momenta, orbital angular momenta and spins; Homogeneous and non-homogeneous Lorentz transformations; Gauge invariant decomposition and gauge invariant extension; Classical and quantum measurements.

hep-ph↗

arXiv2014

Carroll versus Newton and Galilei: two dual non-Einsteinian concepts of time

The Carroll group was originally introduced by Levy-Leblond [1] by considering the limit of the Poincaré group as $c\to0$. In this paper an alternative definition, based on the geometric properties of a non-Minkowskian, non-Galilean but nevertheless boost-invariant, space-time structure is proposed. A "duality" with the Galilean limit $c\to\infty$ is established. Our theory is illustrated by Carrollian electromagnetism.

gr-qc↗

arXiv2013

Monopoles without magnetic charges: Finite energy monopole-antimonopole configurations in CP1 model and restricted QCD

We propose a new type of regular monopole-like field configuration in quantum chromodynamics (QCD) and CP^1 model. The monopole configuration can be treated as a monopole-antimonopole pair without localized magnetic charges. An exact numeric solution for a simple monopole-antimonopole solution has been obtained in CP^1 model with an appropriate potential term. We suppose that similar monopole solutions may exist in effective theories of QCD and in the electroweak standard model.

hep-th↗