arXiv subjects

David Vasak

Publications and source records attributed to David Vasak.

25 records · Page 2Linked to original sources

arXiv2020

Vanishing torsion coupling of the Maxwell field in canonical gauge theory of gravity

The Maxwell field can be viewed as a $U(1)$-gauge theory, therefore, generalizing it to form-invariance in dynamical spacetime backgrounds should take this symmetry into account. This is of essential importance when generalizations of general relativity to theories with non-vanishing torsion are considered. Despite the many statements in literature that a $U(1)$-gauge field cannot couple to torsion, this issue was recently revived. In this letter we contribute to the discussion by demonstrating via a canonical transformation within the framework of the DeDonder-Weyl Hamiltonian formalism that a $U(1)$-gauge field does not couple to torsion.

gr-qc↗

arXiv2019

Inflation from fermions with curvature-dependent mass

A model of inflation realization driven by fermions with curvature-dependent mass is studied. Such a term is derived from the Covariant Canonical Gauge Theory of gravity (CCGG) incorporating Dirac fermions. We obtain an initial de Sitter phase followed by a successful exit, and moreover, we acquire the subsequent thermal history, with an effective matter era, followed finally by a dark-energy epoch. This behavior is a result of the effective `weakening' of gravity at early times, due to the decreased curvature-dependent fermion mass. Through the perturbation level, we obtain the scalar spectral index and the tensor-to-scalar ratio, which are in agreement with the Planck observations. The efficiency of inflation from fermions with curvature-dependent mass, at both the background and perturbation level, reveals the capabilities of the scenario and makes it a good candidate for the description of nature.

gr-qc↗

arXiv2019

Energy transfer from space-time into matter and a bouncing inflation from Covariant Canonical Gauge theory of Gravity

Cosmological solutions for covariant canonical gauge theories of gravity are presented. The underlying covariant canonical transformation framework invokes a dynamical space-time Hamiltonian consisting of the Einstein-Hilbert term plus a quadratic Riemann tensor invariant with a fundamental dimensionless coupling constant $g_1$. A typical time scale related to this constant, $τ= \sqrt{8 πG g_1}$, is characteristic for the type of cosmological solutions: for $t \ll τ$ the quadratic term is dominant, the energy-momentum tensor of the matter is not covariantly conserved, and we observe modified dynamics of matter and space-time. On the other hand, for $t \gg τ$, the Einstein term dominates and the solution converges to classical cosmology. This is analyzed for different types of matter and dark energy with a constant equation of state. While for a radiation dominated universe solution the cosmology does not change, we find for a dark energy universe the well known de-Sitter space. However, we also identify a special bouncing solution (for $k=0$) which for large times approaches the de-Sitter space again. For a dust dominated universe (with no pressure) deviations are seen only in the early epoch. In the late epoch, the solution asymptotically behaves like the standard dust solution.

gr-qc↗

arXiv2018

Quadratic curvature theories formulated as Covariant Canonical Gauge theories of Gravity

The Covariant Canonical Gauge theory of Gravity is generalized by including at the Lagrangian level all possible quadratic curvature invariants. In this approach, the covariant Hamiltonian principle and the canonical transformation framework are applied to derive a Palatini type gauge theory of gravity. The metric $g_{μν}$, the affine connection $γ\indices{^λ_{μν}}$ and their respective conjugate momenta, $k^{μνσ}$ and $q\indices{_η^{αξβ}}$ tensors, are the independent field components describing the gravity. The metric is the basic dynamical field, and the connection is the gauge field. The torsion-free and metricity-compatible version of the space-time Hamiltonian is built from all possible invariants of the $q\indices{_η^{αξβ}}$ tensor components up to second order. These correspond in the Lagrangian picture to Riemann tensor invariants of the same order. We show that the quadratic tensor invariant is necessary for constructing the canonical momentum field from the gauge field derivatives, and hence for transforming between Hamiltonian and Lagrangian pictures. Moreover, the theory is extended by dropping metric compatibility and enforcing conformal invariance. This approach could be used for the quantization of the quadratic curvature theories, as for example in the case of conformal gravity.

gr-qc↗

arXiv2017

Wigner functions of massive fermions in strong magnetic fields

We compute the covariant Wigner function for spin-1/2 fermions in an arbitrarily strong magnetic field by exactly solving the Dirac equation at non-zero fermion-number and chiral-charge densities. The Landau energy levels as well as a set of orthonormal eigenfunctions are found as solutions of the Dirac equation. With these orthonormal eigenfunctions we construct the fermion field operators and the corresponding Wigner-function operator. The Wigner function is obtained by taking the ensemble average of the Wigner-function operator in global thermodynamical equilibrium, i.e., at constant temperature $T$ and non-zero fermion-number and chiral-charge chemical potentials $μ$ and $μ_5$, respectively. Extracting the vector and axial-vector components of the Wigner function, we reproduce the currents of the chiral magnetic and separation effect in an arbitrarily strong magnetic field.

hep-ph↗

arXiv2016

Gauge Theory by canonical Transformations

Electromagnetism, the strong and the weak interaction are commonly formulated as gauge theories in a Lagrangian description. In this paper we present an alternative formal derivation of U(1)-gauge theory in a manifestly covariant Hamilton formalism. We make use of canonical transformations as our guiding tool to formalize the gauging procedure. The introduction of the gauge field, its transformation behaviour and a dynamical gauge field Lagrangian/Hamiltonian are unavoidable consequences of this formalism, whereas the form of the free gauge Lagrangian/Hamiltonian depends on the selection of the gauge dependence of the canonically conjugate gauge fields.

hep-th↗

arXiv2015

Glueballs amass at RHIC and LHC Colliders! - The early quarkless 1st order phase transition at $T=270$ MeV - from pure Yang-Mills glue plasma to GlueBall-Hagedorn states

The early stage of high multiplicity pp, pA and AA collider is represented by a nearly quarkless, hot, deconfined pure gluon plasma. According to pure Yang-Mills Lattice Gauge Theory, this hot pure glue matter undergoes, at a high temperature, $T_c = 270$ MeV, a first order phase transition into a confined Hagedorn-GlueBall fluid. These new scenario should be characterized by a suppression of high $p_T$ photons and dileptons, baryon suppression and enhanced strange meson production. We propose to observe this newly predicted class of events at LHC and RHIC.

hep-ph↗