Electromagnetic Sector Research Articles

New rotating black holes in nonlinear Maxwell f(R) gravity

We investigate static and rotating charged spherically symmetric solutions in the framework of $f(\mathcal{R})$ gravity, allowing additionally the electromagnetic sector to depart from linearity. Applying a convenient, dual description for the electromagnetic Lagrangian, and using as an example the square-root $f(\mathcal{R})$ correction, we solve analytically the involved field equations. The obtained solutions belong to two branches, one that contains the Kerr-Newman solution of general relativity as a particular limit, and one that arises purely from the gravitational modification with no general relativity limit. The novel black hole solution has a true central singularity which is hidden behind a horizon; however, for particular parameter regions the horizon disappears and the singularity becomes a naked one. Furthermore, we investigate the thermodynamical properties of the solutions, such as the temperature, energy, entropy, heat capacity, and Gibbs free energy. We extract the entropy and quasilocal energy positivity conditions, we show that negative-temperature, ultracold, black holes are possible, and we show that the obtained solutions are thermodynamically stable for suitable model parameter regions.

Testing the violation of the equivalence principle in the electromagnetic sector and its consequences in f(T) gravity

A violation of the distance-duality relation is directly linked with a temporal variation of the electromagnetic fine-structure constant. We consider a number of well-studied f(T) gravity models and we revise the theoretical prediction of their corresponding induced violation of the distance-duality relationship. We further extract constraints on the involved model parameters through fine-structure constant variation data, alongside with supernovae data, and Hubble parameter measurements. Moreover, we constrain the evolution of the effective f(T) gravitational constant. Finally, we compare with revised constraints on the phenomenological parametrisations of the violation of the equivalence principle in the electromagnetic sector.

Screening away the H0 tension

This Essay explores consequences of a dark nonlinear electromagnetic sector in a universe with a net dark charge for matter. The cosmological dynamics can be described by a Lemaître model and can be understood, thanks to a screening mechanism driven by the electromagnetic nonlinearities that suppress the dark force on small scales. Only at low redshift, when the screening scale enters the Hubble horizon, do cosmological structures commence to feel the dark repulsion. This repulsive force enhances the local value of the Hubble constant, thus providing a promising scenario for solving the Hubble tension. Remarkably, the dark electromagnetic interaction can have a crucial impact on peculiar velocities, i.e. introducing a bias in their reconstruction methods, and having the potential to explain the presence of a dark flow.

Dynamics of quantum entanglement in matter field models

A review of the linear canonical transformations and its unitary representation is presented and its importance in the mathematical generation of a special two photon coherent state of light is demonstrated. The dynamical behaviour of the entanglement of the matter and field sectors of an initial composite system under the action of two effective model Hamiltonians is shown. The quantumness and delocalization properties of the corresponding electromagnetic field sectors are established. Finally for the two-photon process interacting with a two-level system, the violation of the Cauchy-Schwarz inequality is exhibited.

Distinguishing freezing and thawing dark energy models through measurements of the fine-structure constant

Mapping the behaviour of dark energy is a pressing task for observational cosmology. Phenomenological classification divides dynamical dark energy models into freezing and thawing, depending on whether the dark energy equation of state is approaching or moving away from w = p/ρ = −1. Moreover, in realistic dynamical dark energy models the dynamical degree of freedom is expected to couple to the electromagnetic sector, leading to variations of the fine-structure constant α. We discuss the feasibility of distinguishing between the freezing and thawing classes of models with current and forthcoming observational facilities and using a parametrisation of the dark energy equation of state, which can have either behaviour, introduced by Mukhanov as fiducial paradigm. We illustrate how freezing and thawing models lead to different redshift dependencies of α, and use a combination of current astrophysical observations and local experiments to constrain this class of models, improving the constraints on the key coupling parameter by more than a factor of two, despite considering a more extended parameter space than the one used in previous studies. We also briefly discuss the improvements expected from future facilities and comment on the practical limitations of this class of parametrisations. In particular, we show that sufficiently sensitive data can distinguish between freezing and thawing models, at least if one assumes that the relevant parameter space does not include phantom dark energy models.

Recent results from VERITAS

VERITAS has been observing the northern sky at TeV energies with full sensitivity since 2007. Consisting of a ground based array of four 12 m imaging atmospheric Cherenkov telescopes, sited in southern Arizona, it is one of the world’s most sensitive detectors of gamma-rays between 85 GeV to 30 TeV. VERITAS maintains a broad scientific programme in many areas of astroparticle physics, including, but not limited to: studies of the acceleration, propagation and indirect measurements of cosmic rays and their spectra; searching for indirect detection signatures of dark matter candidates; and tests of fundamental physics, such as setting constraints on Lorentz invariance violation. There is also an active multi-messenger programme with partners in the electromagnetic, neutrino, and gravitational wave sectors. We review here the current status and some recent results from VERITAS and examine the prospects for future studies.

Design optimization of a giant magnetostrictive driving system for large stroke application considering vibration suppression in working process

Light weight and low energy consumption of giant magnetostrictive driving system (GMDS) signify two main challenges facing in aerospace engineering, which conflict with the capability of the GMDS to some extent. For aim of addressing this dilemma, meanwhile realizing a large stroke and passive vibration suppression in space environment, this article proposes a GMDS scheme consisted of giant magnetostrictive actuator and compliant amplification mechanism, and moreover introduces a new design optimization strategy. First, a novel GMDS is proposed for realizing those functions. Then, three sectors, namely the electromagnetic conversion sector, the magnetic energy transfer sector and the magneto-mechanical conversion sector, are divided according to energy flow structure theory, to accurately evaluate the energy consumption. Therefore, the key energy consumption model of each sector could be formulated clearly by the aid of equivalent circuit diagram, equivalent magnetic circuit diagram and work-energy theory. Afterward, the equivalent vibration suppression natural frequency model of the compliant amplification mechanism is formulated through pseudo-rigid-body model method (PRBM), for evaluating the vibration suppression capability. Next, the equivalent mass of the whole system could be constructed on basis of the key components parameters. Finally, the design optimization strategy is proposed and implemented to capture the global optimal solution. Additionally, the performance of the optimized GMDS is validated by finite element analysis and experimental tests.

Dimensional reduction of the electromagnetic sector of the nonminimal standard model extension

In the current paper, we construct a Lorentz-violating electrodynamics in (1+2) spacetime dimensions from the electromagnetic sector of the nonminimal Standard-Model Extension (SME) in (1+3) dimensions. Subsequently, we study some of the basic properties of this framework. We obtain the field equations, the Green's functions, and the perturbative Feynman rules. Furthermore, the modified dispersion relations are computed at leading order in Lorentz violation. We then remove the unphysical degrees of freedom from the electromagnetic Green's function that are present due to gauge invariance. The resulting object is used to construct the general solutions of the uncoupled field equations with external inhomogeneities present. This modified planar electrodynamics may be valuable to describe electromagnetic phenomena in two-dimensional condensed-matter systems. Furthermore, it supports a better understanding of the electromagnetic sector of the nonminimal SME.

Optimal basis for the generalized Dicke model

A methodology is devised for building optimal bases for the generalized Dicke model based on the symmetry adapted variational solution to the problem. At order zero, the matter sector is constructed by distributing $N_a$ particles in all the possible two-level subsystems connected with electromagnetic radiation; the next order is obtained when the states of $N_a-1$ particles are added and distributed again into the two-level subsystems; and so on. In the electromagnetic sector, the order zero for each mode is the direct sum of the Fock spaces, truncated to a value of the corresponding constants of motion of each two-level subsystem; by including contributions of the other modes, the next orders are obtained. As an example of the procedure we consider $4$ atoms in the $\Xi$ configuration interacting dipolarly with two modes of electromagnetic radiation. The results may be applied to situations in quantum optics, quantum information, and quantum computing.

Flux Quantization in Dilatonic Taub–Nut Dyons

Spacetimes that include a boundary at infinity have a non-trivial topology. The homology of the background influences gauge fields living on them and lead to topological charges. We investigate the charges and fluxes of fields over a Taub--NUT background in Einstein--Maxwell dilaton--axion gravity, by using the relative homology and de Rham cohomology. It turns out that the electromagnetic sector is devoid of restrictions from a topological viewpoint. There are, however, flux quanta for the axion and dilaton fields. These results are obtained from the absolute homology of the spacetime boundary. The solutions we probe originate in the four dimensional low energy limit of heterotic string theory. So our results are complemented by the stringy coupling present in the fields. The quantization has a bundle theoretic interpretation as the axion's flux corresponds to the topological index of an underlying 2-bundle.

Maxwell electrodynamics modified by a CPT -odd dimension-five higher-derivative term

In this paper, we consider an electrodynamics of higher derivatives coupled to a Lorentz-violating background tensor. Specifically, we are interested in a dimension-five term of the CPT-odd sector of the nonminimal Standard-Model Extension. By a particular choice of the operator $\hat{k}_{AF}$, we obtain a higher-derivative version of the Carroll-Field-Jackiw (CFJ) term, $\frac{1}{2}\epsilon^{\kappa\lambda\mu\nu}A_{\lambda}D_{\kappa}\square F_{\mu\nu}$, with a Lorentz-violating background vector $D_{\kappa}$. This modification is subject to being investigated. We calculate the propagator of the theory and from its poles, we analyze the dispersion relations of the isotropic and anisotropic sectors. We verify that classical causality is valid for all parameter choices, but that unitarity of the theory is generally not assured. The latter is found to break down for certain configurations of the background field and momentum. In an analog way, we also study a dimension-five anisotropic higher-derivative CFJ term, which is written as $\epsilon^{\kappa\lambda\mu\nu}A_{\lambda}T_{\kappa}(T\cdot\partial)^{2}F_{\mu\nu}$ and is directly linked to the photon sector of Myers-Pospelov theory. Within the second model, purely timelike and spacelike $T_{\kappa}$ are considered. For the timelike choice, one mode is causal, whereas the other is noncausal. Unitarity is conserved, in general, as long as the energy stays real - even for the noncausal mode. For the spacelike scenario, causality is violated when the propagation direction lies within certain regimes. However, there are particular configurations preserving unitarity and strong numerical indications exist that unitarity is guaranteed for all purely spacelike configurations. The results improve our understanding of nonminimal CPT-odd extensions of the electromagnetic sector.

Nonlinear perturbations of Reissner-Nordström black holes

We develop a nonlinear perturbation theory of Reissner-Nordstr\"om black holes. We show that, at each perturbation level, Einstein-Maxwell equations can be reduced to four inhomogeneous wave equations, two for polar and two for axial sector. Gravitational part of these equations is similar to Regge-Wheeler and Zerilli equations with source and additional coupling to the electromagnetic sector. We construct solutions to the inhomogeneous part of wave equations in terms of sources for Einstein-Maxwell equations. We discuss $\ell=0$ and $ \ell=1$ cases separately.

Early cosmological evolution of primordial electromagnetic fields

It is usually assumed that when Weyl invariance is unbroken in the electromagnetic sector, the energy density of primordial magnetic fields will redshift as radiation. Here we show that primordial magnetic fields do not exhibit radiation-like redshifting in the presence of stronger electric fields, as a consequence of Faraday's law of induction. In particular for the standard Maxwell theory, magnetic fields on super-horizon scales can redshift as $B^2 \propto a^{-6} H^{-2}$, instead of the usually assumed $a^{-4}$. Taking into account this effect for inflationary magnetogenesis can correct previous estimates of the magnetic field strength by up to 37 orders of magnitude. This opens new possibilities for inflationary magnetogenesis, and as an example we propose a scenario where femto-Gauss intergalactic magnetic fields are created on Mpc scales, with high-scale inflation producing observable primordial gravitational waves, and reheating happening at low temperatures.

Regular multihorizon black holes in f(G) gravity with nonlinear electrodynamics

In this work, we study the existence of regular black holes solutions with multihorizons in general relativity and in some alternative theories of gravity. We consider the coupling between the gravitational theory and nonlinear electrodynamics. The coupling generates modifications in the electromagnetic sector. This paper has as main objective generalize solutions already known from general relativity to the $f(G)$ theory. To do that, we first correct some misprints of the Odintsov and Nojiri's work in order to introduce the formalism that will be used in the $f(G)$ gravity. In order to satisfy all field equations, the method to find solutions in alternative theories generates different $f(R)$ and $f(G)$ functions for each solution, where only the nonlinear term of $f(G)$ contributes to the field equations. We also analyze the energy conditions, since it is expected that some must be violated to find regular black holes, and using an auxiliary field, we analyze the nonlinearity of the electromagnetic theory.

Unification Principle and a Cosmological Model

We present a cosmological model constructed using a pure geometric field theory. The unification principle implies defining any physical object in the model using the building blocks of the geometry used, the Absolute Parallelism (AP) geometry. The type of AP geometry used has simultaneously nonvanishing curvature and torsion. The AP geometric structure, used for this application, satisfies the cosmological principle and switches off the electromagnetic sector of the theory automatically. The model obtained is found to be free from particle horizons and flatness problems. This model can be considered as representing a transition phase between a decelerated and accelerated Universe. Conservation in the model is guaranteed by the theory used.

Neutrino decoupling beyond the Standard Model: CMB constraints on the Dark Matter mass with a fast and precise Neff evaluation

The number of effective relativistic neutrino species represents a fundamental probe of the thermal history of the early Universe, and as such of the Standard Model of Particle Physics. Traditional approaches to the neutrino decoupling are either very technical and computationally expensive, or assume that neutrinos decouple instantaneously. In this work, we aim to fill the gap between these two approaches by modeling the neutrino decoupling in terms of two simple coupled differential equations for the electromagnetic and neutrino sector temperatures, in which all the relevant interactions are taken into account and which allows for a straightforward implementation of BSM species. Upon including finite temperature QED corrections we reach an accuracy on Neff in the SM of 0.01. We illustrate the usefulness of this approach to the neutrino decoupling by considering, in a model independent manner, the impact of MeV thermal dark matter on Neff. We show that Planck rules out electrophilic and neutrinophilic thermal dark matter particles of m< 3.8 MeV at 95% CL regardless of their spin, and of their annihilation being s-wave or p-wave. We point out that thermal dark matter particles with non-negligible interactions with both electrons and neutrinos are more elusive to CMB observations than purely electrophilic or neutrinophilic ones. In addition, assisted by the accuracy of our approach, we show that CMB Stage-IV experiments will generically test thermal dark matter particles with m ≲ 20 MeV. We make publicly available the codes developed for this study at this https://github.com/MiguelEA/nudec_BSM.

Magnetogenesis in cyclical Universe

We propose a simple solution to the magnetogenesis problem based on cyclic cosmology. It is demonstrated that magnetic fields, of sufficient strengths to account for the present observational bounds, can be created in the contracting phase preceding the beginning of the current cosmological cycle. The basic assumption of this model is that the Universe enters a contraction phase essentially empty, characterized by small seed electric fields. We discuss how such small seed electric fields can be naturally created due to charge separation of astrophysical currents during the expansion of the Universe or, alternatively, due to ionization as a consequence of the growth of the effective dark energy contribution reaching the hydrogen atom ionization potential. In this framework, there is no need for any new theoretical additions to explain magnetogenesis, such as new scalar fields or the non-minimal coupling between curvature, scalar fields and the electromagnetic sector. Moreover, the proposed model is general in the sense that it does not assume any specific modified gravity theory to enable the cosmological bounce. When compared to the inflationary magnetogenesis paradigm, the proposed model also has the advantage of not leading to the backreaction and strong coupling problems.

Chiral anomalous dispersion

The linearized Einstein equation describing graviton propagation through a chiral medium appears to be helicity dependent. We analyze features of the corresponding spectrum in a collision-less regime above a flat background. In the long wave-length limit, circularly polarized metric perturbations travel with a helicity dependent group velocity that can turn negative giving rise to a new type of an anomalous dispersion. We further show that this chiral anomalous dispersion is a general feature of polarized modes propagating through chiral plasmas extending our result to the electromagnetic sector.

Sgoldstino searches at CERN Electron Beam Dump

In the present paper we discussed light scalar sgoldstino in context of low scale SUSY breaking. We analyzed electromagnetic sector of interaction of sgoldstino with SM. We also took into account the impact on this interaction of the admixture of lightest MSSM Higgs scalar in the sgoldstino state. The signal rate of rare sgoldstino decays into SM particles at CERN electron beam dump experiment NA64 for the scalar sgoldstino has been estimated. We used expected signal rate to obtain some regions of sgoldstino parameter space (sgoldstino mass and SUSY breaking scale √F).

Constraints on direction-dependent cosmic birefringence from Planck polarization data

Cosmic birefringence is the process that rotates the plane of polarization by an amount, α, as photons propagate through free space. Such an effect arises in parity-violating extensions to the electromagnetic sector, such as the Chern-Simons term common in axion models, quintessence models, or Lorentz-violating extensions to the standard model. Most studies consider the monopole of this rotation, but it is also possible for the effect to have spatial anisotropies. Paying particular attention to large scales, we implement a novel pixel-based method to extract the spherical harmonics for L ≤ 30 and a pseudo-CL method for L > 30. Our results are consistent with no detection and we set 95 % upper limits on the amplitude of a scale-invariant power spectrum of L(L+1)CL/2π<[2.2 (stat.)±0.7 (syst.)]×10-5=[0.07 (stat.)±0.02 (syst.)] deg2, on par with previous constraints. This implies specific limits on the dipole and quadrupole amplitudes to be √C1/4π ≲ 0.̂2 and √C2/4π ≲ 0.̂1, at 95 % CL, respectively, improving previous constraints by an order of magnitude. We further constrain a model independent M=0 quadrupole in an arbitrary direction to be α20 = 0.̂02 ± 0.̂21, with an unconstrained direction. However, we find an excess of dipolar power with an amplitude √3C1/4π = 0.̂32±0.̂10 (stat.)±0.̂08 (syst.)], in the direction (l,b)=(295̂,17̂)±(22̂,17̂) (stat.)±(5̂,16̂) (syst.), larger than 1.4 % of simulations with no birefringence. We attribute part of this signal to the contamination of residual foregrounds not accounted for in our simulations, although this should be further investigated.