Anomalous Gravitomagnetic Moment Research Articles

Anomalous gravitomagnetic moment and nonuniversality of the axial vortical effect at finite temperature

The coupling between the spin of a massive Dirac fermion and the angular momentum of the medium, i.e. the gravitomagnetic moment, is shown here to be renormalized by QED interactions at finite temperature. This means that the anomalous gravitomagnetic moment (AGM) does not vanish, and implies that thermal effects can break the Einstein equivalence principle in quantum field theory, as argued previously. We also show that the AGM causes radiative corrections to the axial current of massive fermions induced by vorticity in quantum relativistic fluids, similarly to the previous findings for massless fermions. The radiative QCD effects on the AGM should significantly affect the production of polarized hadrons in heavy-ion collisions.

Rigorous constraints on the matrix elements of the energy–momentum tensor

The structure of the matrix elements of the energy–momentum tensor play an important role in determining the properties of the form factors A(q2), B(q2) and C(q2) which appear in the Lorentz covariant decomposition of the matrix elements. In this paper we apply a rigorous frame-independent distributional-matching approach to the matrix elements of the Poincaré generators in order to derive constraints on these form factors as q→0. In contrast to the literature, we explicitly demonstrate that the vanishing of the anomalous gravitomagnetic moment B(0) and the condition A(0)=1 are independent of one another, and that these constraints are not related to the specific properties or conservation of the individual Poincaré generators themselves, but are in fact a consequence of the physical on-shell requirement of the states in the matrix elements and the manner in which these states transform under Poincaré transformations.

Gravitational form factors and nucleon spin structure

Nucleon scattering by the classical gravitational field is described by the gravitational (energy-momentum tensor) form factors (GFFs), which also control the partition of nucleon spin between the total angular momenta of quarks and gluons. The equivalence principle (EP) for spin dynamics results in the identically zero anomalous gravitomagnetic moment, which is the straightforward analog of its electromagnetic counterpart. The extended EP (ExEP) describes its (approximate) validity separately for quarks and gluons and, in turn, results in equal partition of the momentum and total angular momentum. It is violated in quantum electrodynamics and perturbative quantum chromodynamics (QCD), but may be restored in nonperturbative QCD because of confinement and spontaneous chiral symmetry breaking, which is supported by models and lattice QCD calculations. It may, in principle, be checked by extracting the generalized parton distributions from hard exclusive processes. The EP for spin-1 hadrons is also manifested in inclusive processes (deep inelastic scattering and the Drell–Yan process) in sum rules for tensor structure functions and parton distributions. The ExEP may originate in either gravity-proof confinement or in the closeness of the GFF to its asymptotic values in relation to the mediocrity principle. The GFFs in time-like regions reveal some similarity between inflation and annihilation.

Quark Angular Momentum and Gravitational Form Factors

We investigate the quark angular momentum in a light-cone spectator model. The canonical angular momentum sum rule is satisfied in both the scalar and the axial-vector cases. Then we perform a calculation of the gravitational form factors which are expected to be related to the angular momentum of each constituent in this no gauge field model. We find this relation is satisfied for the total angular momentum as a direct conclusion of the momentum fraction sum rule and the anomalous gravitomagnetic moment sum rule, but for each constituent it is violated.

Electromagnetic and gravitational form factors in simulated QED and Yukawa model

The light-cone Fock state representation of composite systems has a number of remarkable properties and for systems such as hadrons they have exact representation for angular momentum, energy–momentum tensor. We investigate the electromagnetic and gravitational form factors with zero momentum transfer in Quantum Electrodynamics (QED) and Yukawa theory. To improve the convergence near the end points of x qualitatively as well as to check the consistency of the model, we differentiate the wave function w.r.t. bound state mass. We test the behavior of the anomalous gravitomagnetic moment, which follows directly from the Lorentz boost properties of the light-cone Fock representation, for the simulated model as well as the Yukawa model. We also discuss the Pauli form factor obtained from the spin-flip matrix element.

Dirac particle spin in strong gravitational fields

Dynamics of the Dirac particle spin in general strong gravitational fields is discussed. The Hermitian Dirac Hamiltonian is derived and transformed to the Foldy-Wouthuysen (FW) representation for an arbitrary metric. The quantum mechanical equations of spin motion are found. These equations agree with corresponding classical ones. The new restriction on the anomalous gravitomagnetic moment (AGM) by the reinterpretation of Lorentz invariance tests is obtained.

Deeply virtual Compton scattering at small [formula omitted] and the access to the GPD H

We give a partonic interpretation for the deeply virtual Compton scattering (DVCS) measurements of the H1 and ZEUS Collaborations in the small- x B region in terms of generalized parton distributions. Thereby we have a closer look at the skewness effect, parameterization of the t-dependence, revealing the chromomagnetic pomeron, and at a model-dependent access to the anomalous gravitomagnetic moment of nucleon. We also quantify the reparameterization of generalized parton distributions resulting from the inclusion of radiative corrections up to next-to-next-to-leading order. Beyond the leading order approximation, our findings are compatible with a ‘holographic’ principle that would arise from a (broken) SO ( 2 , 1 ) symmetry. Utilizing our leading-order findings, we also perform a first model-dependent “dispersion relation” fit of HERMES and JLAB DVCS measurements. From that we extract the generalized parton distribution H on its cross-over line and predict the beam charge-spin asymmetry, measurable at COMPASS.

Equivalence principle and experimental tests of gravitational spin effects

We study the possibility of experimentally testing the manifestations of the equivalence principle in spin-gravity interactions. We reconsider the earlier experimental data and get the first experimental bound on the anomalous gravitomagnetic moment. The spin coupling to the Earth's rotation may also be explored at the extensions of neutron electric-dipole-moment and $g\ensuremath{-}2$ experiments. The spin coupling to terrestrial gravity produces a considerable effect which may be discovered at the planned deuteron electric-dipole-moment experiment. The Earth's rotation should also be taken into account in optical experiments in search of axionlike particles.

Light-cone representation of the spin and orbital angular momentum of relativistic composite systems

The matrix elements of local operators such as the electromagnetic current, the energy momentum tensor, angular momentum, and the moments of structure functions have exact representations in terms of light-cone Fock state wavefunctions of bound states such as hadrons. We illustrate all of these properties by giving explicit light-cone wavefunctions for the two-particle Fock state of the electron in QED, thus connecting the Schwinger anomalous magnetic moment to the spin and orbital momentum carried by its Fock state constituents. We also compute the QED one-loop radiative corrections for the form factors for the graviton coupling to the electron and photon. Although the underlying model is derived from elementary QED perturbative couplings, it in fact can be used to simulate much more general bound state systems by applying spectral integration over the constituent masses while preserving all of the Lorentz properties, giving explicit realization of the spin sum rules and other local matrix elements. The role of orbital angular momentum in understanding the "spin crisis" problem for relativistic systems is clarified. We also prove that the anomalous gravitomagnetic moment B(0) vanishes for any composite system. This property is shown to follow directly from the Lorentz boost properties of the light-cone Fock representation and holds separately for each Fock state component. We show how the QED perturbative structure can be used to model bound state systems while preserving all Lorentz properties. We thus obtain a theoretical laboratory to test the consistency of formulae which have been proposed to probe the spin structure of hadrons.