Polarization operator in the 2+1 dimensional quantum electrodynamics with a nonzero fermion density in a constant uniform magnetic field

The polarization operator (tensor) for planar charged fermions in a constant uniform magnetic field is calculated in the one-loop approximation of 2+1 -dimensional quantum electrodynamics (QED 2+1 ) with a nonzero fermion density. We construct the Green function of the Dirac equation with a constant uniform external magnetic field in QED 2+1 at a finite chemical potential, find the imaginary part of this Green function, and then obtain the polarization tensor related to the combined contribution from real particles occupying the finite number of energy levels and magnetic field. We expect that some physical effects under consideration seem likely to be revealed in a monolayer graphene sample in the presence of an external constant uniform magnetic field B perpendicular to it

Effect of vacuum polarization of charged massive fermions in an Aharonov–Bohm field

The effect of vacuum polarization of charged massive fermions in an Aharonov–Bohm (AB) potential in 2 + 1 dimensions is investigated. The causal Green function of the Dirac equation with the AB potential is represented via the regular and irregular solutions of the two-dimensional radial Dirac equation. It is shown that the vacuum current density contains the contribution from free filled states of the negative energy continuum as well as that from a bound unfilled state, which can emerge in the above background due to the interaction of the fermion’s spin magnetic moment with the AB magnetic field, while the induced charge density contains only the contribution from the bound state. The expressions for the vacuum charge and induced current densities are obtained (recovered for massless fermions) for the graphene in the field of infinitesimally thin solenoid perpendicular to the plane of a sample. We also find the bound state energy as a function of magnetic flux, fermion spin, and the radius of solenoid, and we discuss the role of the so-called self-adjoint extension parameter and determine it in terms of the physics of the problem

Associated W±D(⁎) production at the LHC and prospects to observe double parton interactions

Associated production of charged gauge bosons and charged charmed mesons at the LHC is considered in the framework of kt -factorization approach. Theoretical predictions are compared with ATLAS data, and reasonably good agreement is found. Predictions on the same-sign W±D± configurations are presented including single parton scattering and double parton scattering contributions. The latter are shown to dominate over the former, thus giving evidence that the proposed process can serve as another indicator of double parton interactions

On the possibility to detect the Higgs decay H→bb¯ in the associated Z+bb¯ production at the LHC

We investigate the possibility to detect the scalar Higgs boson decay H→bb¯ in the associated Z and bb¯ production at the LHC using the kT -factorization QCD approach. Our consideration is based on the off-shell (i.e. depending on the transverse momenta of initial quarks and gluons) production amplitudes of q∗q¯∗→ZH→Zq′q¯′ , q∗q¯∗→Zq′q¯′ , and g∗g∗→Zq′q¯′ partonic subprocesses supplemented with the Catani–Ciafoloni–Fiorani–Marchesini (CCFM) dynamics of parton densities in a proton. We argue that the H→bb¯ signal could be observed at large transverse momenta near the Higgs boson peak despite the overwhelming QCD background, and we point out the important role of angular correlations between the produced Z boson and b -quarks

Higher harmonics of azimuthal anisotropy in relativistic heavy-ion collisions in HYDJET++ model

The LHC data on azimuthal anisotropy harmonics from PbPb collisions at center-of-mass energy 2.76 TeV per nucleon pair are analyzed and interpreted in the framework of the HYDJET++ model. The cross-talk of elliptic <math><msub><mi>v</mi><mn>2</mn></msub></math> and triangular <math><msub><mi>v</mi><mn>3</mn></msub></math> flow in the model generates both even and odd harmonics of higher order. Comparison with the experimental data shows that this mechanism is able to reproduce the <math><msub><mi>p</mi><mi mathvariant="normal">T</mi></msub></math> and centrality dependencies of quadrangular flow <math><msub><mi>v</mi><mn>4</mn></msub></math> , and also the basic trends for pentagonal <math><msub><mi>v</mi><mn>5</mn></msub></math> and hexagonal <math><msub><mi>v</mi><mn>6</mn></msub></math> flows

Millicharged neutrino with anomalous magnetic moment in rotating magnetized matter

New exact solutions of the modified Dirac equation describing a neutrino with nontrivial electromagnetic properties in extreme background conditions are obtained. Within the quasi-classical treatment the effective Lorentz force that describes the neutrino propagation in the magnetized rotating matter is introduced. We predict the effect of the spatial separation of different types of relativistic neutrinos and antineutrinos (different in flavors and energies) by the magnetized rotating matter of a star. Low energy neutrinos can be even trapped inside the star. We also predict two new phenomena: a new type of the neutrino electromagnetic radiation (termed “Light of (milli)Charged Neutrino”, LCν ) and a new mechanism of the star angular velocity shift due to neutrinos escaping the star (termed “Neutrino Star Turning” mechanism, νST ). The possible impact of the νST mechanism on a supernova explosion yields a new astrophysical limit on the neutrino millicharge <math altimg="si1.gif" xmlns="http://www.w3.org/1998/Math/MathML"><msub><mrow><mi>q</mi></mrow><mrow><mi>ν</mi></mrow></msub><mo>&lt;</mo><mn>1.3</mn><mo>×</mo><msup><mrow><mn>10</mn></mrow><mrow><mo>−</mo><mn>19</mn></mrow></msup><msub><mrow><mi>e</mi></mrow><mrow><mn>0</mn></mrow></msub></math> . In addition, the νST mechanism can be also used to explain the origin of pulsar “anti-glitches” and ordinary glitches as well

Theory of Neutrino-Atom Collisions: The History, Present Status, and BSM Physics

An overview of the current theoretical studies on neutrino-atom scattering processes is presented. The ionization channel of these processes, which is studied in experiments searching for neutrino magnetic moments, is brought into focus. Recent developments in the theory of atomic ionization by impact of reactor antineutrinos are discussed. It is shown that the stepping approximation is well applicable for the data analysis practically down to the ionization threshold

Nonlocal Quantum Effects in Cosmology

Since it is commonly believed that the observed large-scale structure of the universe is an imprint of quantum fluctuations existing at the very early stage of its evolution, it is reasonable to pose the question: do the effects of quantum nonlocality, which are well established now by the laboratory studies, manifest themselves also in the early universe? We try to answer this question by utilizing the results of a few experiments, namely, with the superconducting multi-Josephson-junction loops and the ultracold gases in periodic potentials. Employing a close analogy between the above-mentioned setups and the simplest one-dimensional Friedmann-Robertson-Walker cosmological model, we show that the specific nonlocal correlations revealed in the laboratory studies might be of considerable importance also in treating the strongly nonequilibrium phase transitions of Higgs fields in the early universe. Particularly, they should substantially reduce the number of topological defects (e.g., domain walls) expected due to independent establishment of the new phases in the remote spatial regions. This gives us a hint on resolving a long-standing problem of the excessive concentration of topological defects, inconsistent with observational constraints. The same effect may be also relevant to the recent problem of the anomalous behavior of cosmic microwave background fluctuations at large angular scales

Fragmentation fractions of c and b quarks into charmed hadrons at LEP

The fragmentation fractions of c and b quarks into the weakly decaying charmed hadrons D0 , D+ , Ds+ and Λc+ , and into the charmed vector meson D∗+ have been derived from the LEP measurements and averaged. The c quark fragmentation fractions represent probabilities to hadronise as a given charmed hadron, while the b quark fragmentation fractions are defined as sums of probabilities to produce a particular charmed hadron or its antiparticle

Observational constraints on the types of cosmic strings

This paper is aimed at setting observational limits to the number of cosmic strings (Nambu–Goto, Abelian-Higgs, semilocal) and other topological defects (textures). Radio maps of CMB anisotropy, provided by the space mission Planck for various frequencies, were filtered and then processed by the method of convolution with modified Haar functions (MHF) to search for cosmic string candidates. This method was designed to search for solitary strings, without additional assumptions as regards the presence of networks of such objects. The sensitivity of the MHF method is δT≈10μK in a background of δT≈100μK . The comparison of these with previously known results on search string network shows that strings can only be semilocal in the range of 1÷5 , with the upper restriction on individual string tension (linear density) of Gμ/c2≤7.36×10-7 . The texture model is also legal. There are no strings with Gμ/c2>7.36×10-7 . However, a comparison with the data for the search of non-Gaussian signals shows that the presence of several (up to three) Nambu–Goto strings is also possible. For Gμ/c2≤4.83×10-7 the MHF method is ineffective because of unverifiable spurious string candidates. Thus the existence of strings with tensions Gμ/c2≤4.83×10-7 is not prohibited but it is beyond the Planck data possibilities. The same string candidates have been found in the WMAP 9-year data. Independence of Planck and WMAP data sets serves as an additional argument to consider those string candidates as very promising. However, the final proof should be given by optical deep surveys