Examples of test electromagnetic waves on a Friedmann-Lemaitre-Robertson-Walker(FLRW) background are constructed from explicit perturbations of the FLRW space-times describing gravitational waves propagating in the isotropic universes. A possible physical mechanism for the production of the test electromagnetic waves is shown to be the coupling of the gravitational waves with a test magnetic field, confirming the observation of Marklund, Dunsby and Brodin [Phys.Rev. D62,101501(R) (2000)].
Exact solutions construction in scalar fields cosmology is of growing interest. In this work we review the results which obtained with the help of one of the most effective method. Namely, the method of generating functions for exact solutions construction in the scalar field cosmology. We also included into debate the superpotential method which may be considered as the bridge to slow roll approximation equations. Basing on the review, we suggested classification for the generating functions and found connection for all of them with the superpotential.
The plane-symmetric inhomogeneous cosmological models of perfect fluid distribution with electro-magnetic field is obtained in the framework of Lyra's geometry. To get the deterministic solution, I have considered $ A=f(x)ν(t) $, $ B=g(x)μ(t) $ and $ C=h(x)μ(t) $, where A, B and C are metric coefficients. It has been found that the solutions generalize the solution obtained by Pradhan, Yadav and Singh (2007) and are consistent with the recent observations of type Ia supernovae. A detailed study of physical and kinematical properties of the models have been carried out.
We investigate the quantum cosmology of a closed spatially homogeneous and isotropic Friedmann-Lemaître-Robertson-Walker (FLRW) minisuperspace model with electromagnetic radiation as matter content. We solve the corresponding Wheeler-DeWitt equation by utilizing Riemann's zeta function regularization method. We demonstrate that the regularized vacuum energy of the electromagnetic field can overcome factor ordering, boundary conditions, and singularity problems.
A Friedmann-Robertson-Walker cosmology with dark energy can be modelled using a quintessence field. That system is equivalent to a relativistic particle moving on a two-dimensional conformal spacetime. When the quintessence behaves as a free massless scalar field in a Universe with cosmological constant, the quantized version of that theory can lead to a Supersymmetric Majorana quantum cosmology. The purpose of this work is to show that such quantum cosmological model correspond to the Maxwell equations for electromagnetic waves propagating in a medium with specific values for its relative per…
If a homogeneous plane light-like shell collides head-on with a homogeneous plane electromagnetic shock wave having a step-function profile then no backscattered gravitational waves are produced. We demonstrate, by explicit calculation, that if the matter is accompanied by a homogeneous plane electromagnetic shock wave with a step-function profile then backscattered gravitational waves appear after the collision.
The standard siren approach of gravitational wave cosmology appeals to the direct luminosity distance estimation through the waveform signals from inspiralling double compact binaries, especially those with electromagnetic counterparts providing redshifts. It is limited by the calibration uncertainties in strain amplitude and relies on the fine details of the waveform. The Einstein Telescope is expected to produce $10^4-10^5$ gravitational wave detections per year, $50-100$ of which will be lensed. Here we report a waveform-independent strategy to achieve precise cosmography by combining the a…
Starting from an exact (in the Regge slope alpha') functional method for a bosonic stringy sigma-model, we investigate four-dimensional cosmological string solutions in graviton, dilaton and antisymmetric tensor backgrounds, compatible with world-sheet conformal invariance, and valid beyond perturbative expansions in powers of alpha'. The antisymmetric tensor field, playing the role of an axion in the four-dimensional target space time, leads to spatial anisotropies of the emergent Robertson-Walker expanding Universe, and, upon coupling the system to the electromagnetic field, it results in no…
In the context of metric f(R) gravity, we consider a FLRW space-time, filled with a perfect fluid described by a barotropic equation of state (p = γρ). We give the equivalent mini-superspace description and use the reparametrization invariance of the resulting Lagrangian to work in the equivalent constant potential description. At that point, we restrict our analysis to those models for which the ensuing scaled mini-superspace is maximally symmetric. Those models exhibit the maximum number of autonomous integrals of motion linear in the momenta, which are constructed by the Killing vectors of …
The cosmological model consisting of an electromagnetic Born-Infeld (BI) field coupled to a Robertson-Walker geometry is tested with the standard probes of SNIa, GRBs and direct Hubble parameter. The analysis shows that the inclusion of the nonlinear electromagnetic component does not contribute in a significative way to the observed expansion. The BI electromagnetic matter is considered with an abundance of $Ω_{BI}$, that our best fit leads to $Ω_{BI}=0.037$ when tested with SNIa and the Hubble parameter data (0.1<z<1.75); while when tested with GRBs the result is of $Ω_{BI}=0.304$, which may…
Loop quantum cosmology leads to a difference equation for the wave function of a universe, which in general has solutions changing rapidly even when the volume changes only slightly. For a semiclassical regime such small-scale oscillations must be suppressed, by choosing the parameters of the solution appropriately. For anisotropic models this is not possible to do numerically by trial and error; instead, it is shown here for the Bianchi I LRS model how this can be done analytically, using generating function techniques. Those techniques can also be applied to more complicated models, and the …
In the inflationary scenarios suggested by string theory, the vacuum fluctuations of the electromagnetic field can be amplified by the time-evolution of the dilaton background, and can grow large enough to explain both the origin of the cosmic magnetic fields and of the observed CMB anisotropy. The normalization of the perturbation spectrum is fixed, and implies a relation between the perturbation amplitude at the COBE scale and the spectral index $n$. Working within a generic two-parameter family of backgrounds, a large scale anisotropy $ΔT/T\simeq 10^{-5}$ is found to correspond to a spectra…
The direct detection of gravitational waves by the LIGO-Virgo collaboration has opened a new window with which to measure cosmological parameters such as the Hubble constant $H_0$, and also probe general relativity on large scales. In this paper we present a new phenomenological approach, together with its inferencial implementation, for measuring deviations from general relativity (GR) on cosmological scales concurrently with a determination of $H_0$. We consider gravitational waves (GWs) propagating in an expanding homogeneous and isotropic background, but with a modified friction term and d…
We study the generation of electromagnetic fields in a string-inspired scenario associated with a rolling massive scalar field $ϕ$ on the anti-D3 branes of KKLT de Sitter vacua. The 4-dimensional DBI type effective action naturally gives rise to the coupling between the gauge fields and the inflaton $ϕ$, which leads to the production of cosmological magnetic fields during inflation due to the breaking of conformal invariance. We find that the amplitude of magnetic fields at decoupling epoch can be larger than the limiting seed value required for the galactic dynamo. We also discuss the mechani…
We consider a Bianchi type III axisymmetric geometry in the presence of an electromagnetic field. A first result at the classical level is that the symmetry of the geometry need not be applied on the electromagnetic tensor $F_{μν}$; the algebraic restrictions, implied by the Einstein field equations to the stress energy tensor $T_{μν}$, suffice to reduce the general $F_{μν}$ to the appropriate form. The classical solution thus found contains a time dependent electric and a constant magnetic charge. The solution is also reachable from the corresponding mini-superspace action, which is strikingl…
Examples are presented of applications of the Lemaître - Tolman model to problems of astrophysics and gravitation theory. They are: 1. Inferring the spatial distribution of matter by interpretation of observations; 2. Interaction of inhomogeneities in matter distribution with the CMB radiation; 3. Evolution of voids; 4. Singularities; 5. Influence of electromagnetic field on gravitational collapse. This review is meant to demonstrate that the theory is already well-prepared to meet the challenges posed by an inhomogeneous Universe.
We consider a class of cosmological models in which the universe is filled with a (non-electric) charge density that repels itself by means of a force carried by a vector boson with a tiny mass. When the vector's mass depends upon other fields, the repulsive interaction gives rise to an electromagnetic barrier which prevents these fields from driving the mass to zero. This can modify the cosmology dramatically. We present a very simple realization of this idea in which the vector's mass arises from a scalar field. The electromagnetic barrier prevents this field from rolling down its potential …
We explore a correspondence between Melvin magnetic fluxtubes and anisotropic cosmological solutions, which we call `Melvin cosmologies'. The correspondence via analytic continuation provides useful information in both directions. Solution generating techniques known on the fluxtube side can also be used for generating cosmological backgrounds. Melvin cosmologies interpolate between different limiting Kasner behaviors at early and late times. This has an analogue on the fluxtube side between limiting Levi-Civita behavior at small and large radii. We construct generalized Melvin fluxtubes and c…
The interaction between gravitational and electromagnetic radiation has a rather long research history. It is well known, in particular, that gravity-wave distortions can drive propagating electromagnetic signals. Since forced oscillations provide the natural stage for resonances to occur, gravito-electromagnetic resonances have been investigated as a means of more efficient gravity-wave detection methods. In this report, we consider the coupling between the Weyl and the Maxwell fields on a Minkowski background, which also applies to astrophysical environments where gravity is weak, at the sec…
Asymptotic properties of electromagnetic waves are studied within the context of Friedmann-Robertson-Walker (FRW) cosmology. Electromagnetic fields are considered as small perturbations on the background spacetime and Maxwell's equations are solved for all three cases of flat, closed and open FRW universes. The asymptotic character of these solutions are investigated and their relevance to the problem of cosmological tails of electromagnetic waves is discussed.
Information about the mass spectrum of compact stars can be used to infer cosmological parameters from gravitational waves (GW) in the absence of redshift measurements obtained from electromagnetic (EM) observations. This method will be fundamental in measuring and testing cosmology with GWs for current and future ground-based GW detectors where the majority part of sources are detected without an associated EM counterpart. In this proceeding, we will discuss the prospects and limitations of this approach for studying cosmology. We will show that, even when assuming GW detectors with current s…
We investigate the quantum cosmologies of the Bianchi IX and VIII models when a cosmological constant, aligned electromagnetic field and free scalar field are present. The conserved quantity $p_ϕ$ associated with our free scalar field results in $ϕ$ classically being a quantity which monotonically increases with respect to time, thus allowing it to fulfill the role of an 'emergent' internal clock for our constrained quantum systems. We embark on this investigation to better understand how matter sources can affect general anisotropic quantum cosmologies. To aid us we use the Euclidean-signatur…
We study Weyssenhoff spin fluids in Bianchi type-I cosmological models, within the framework of torsional f(R)-gravity; the resulting field equations are derived and discussed in both Jordan and Einstein frames, clarifying the role played by the spin and the non-linearity of the gravitational Lagrangian f(R) in generating the torsional dynamical contributions. The general conservation laws holding for f(R)-gravity with torsion are employed to provide the conditions needed to ensure the preservation of the Hamiltonian constraint and the consequent correct formulation of the associated initial v…
We present exact non-singular bounce solutions of general relativity in the presence of a positive cosmological constant and an electromagnetic field, without any exotic matter. The solutions are distinguished by being spatially inhomogeneous in one direction, while they can also contain non-trivial electromagnetic field lines. The inhomogeneity may be substantial, for instance, there can be one bounce in one region of the universe and two bounces elsewhere. Since the bounces are followed by a phase of accelerated expansion, the metrics described here also permit the study of (geodesically com…
The generation of large-scale magnetic fields in inflationary cosmology is explored, in particular, in a kind of moduli inflation motivated by racetrack inflation in the context of the Type IIB string theory. In this model, the conformal invariance of the hypercharge electromagnetic fields is broken thanks to the coupling of both the scalar and pseudoscalar fields to the hypercharge electromagnetic fields. The following three cosmological observable quantities are first evaluated: The current magnetic field strength on the Hubble horizon scale, which is much smaller than the upper limit from t…
Sufficiently large seeds for generating the observed (inter)galactic magnetic fields emerge naturally in string cosmology from the amplification of electromagnetic vacuum fluctuations due to a dynamical dilaton background. The success of the mechanism depends crucially on two features of the so-called pre-big-bang scenario, an early epoch of dilaton-driven inflation at very small coupling, and a sufficiently long intermediate stringy era preceding the standard radiation-dominated evolution.
We investigate a novel approach to measuring the Hubble constant using gravitational-wave (GW) signals from compact binaries by exploiting the narrowness of the distribution of masses of the underlying neutron-star population. Gravitational-wave observations with a network of detectors will permit a direct, independent measurement of the distance to the source systems. If the redshift of the source is known, these inspiraling double-neutron-star binary systems can be used as standard sirens to extract cosmological information. Unfortunately, the redshift and the system chirp mass are degenerat…
We consider the dynamics of electromagnetic fields in an almost-Friedmann-Robertson-Walker universe using the covariant and gauge-invariant approach of Ellis and Bruni. Focusing on the situation where deviations from the background model are generated by tensor perturbations only, we demonstrate that the coupling between gravitational waves and a weak magnetic test field can generate electromagnetic waves. We show that this coupling leads to an initial pulse of electromagnetic waves whose width and amplitude is determined by the wavelengths of the magnetic field and gravitational waves. A numb…
The spatial gradient expansion of the generating functional was recently developed by Parry, Salopek, and Stewart to solve the Hamiltonian constraint in Einstein-Hamilton-Jacobi theory for gravitationally interacting dust and scalar fields. This expansion is used here to derive an order-by-order solution of the Hamiltonian constraint for gravitationally interacting electromagnetic and scalar fields. A conformal transformation and functional integral are used to derive the generating functional up to the terms fourth order in spatial gradients. The perturbations of a flat Friedmann-Robertson-Wa…
If inflationary paradigm is correct, then it must create conditions for the hot big bang model with all observed matter, baryons and the seed perturbations for the structure formation. In this paper we propose a scenario where the inflaton energy density is dumped into the bulk in a brane world setup, and all the required physical conditions are created by the right handed neutrino sector within supersymmetry. The scalar component of the right handed Majorana neutrino is responsible for generating the scale invariant fluctuations in the cosmic microwave background radiation, reheating the Univ…
Gravitational-wave cosmology began in 2017 with the observation of the gravitational waves emitted in the merger of two neutron stars, and the coincident observation of the electromagnetic emission that followed. Although only a $30\%$ measurement of the Hubble constant was achieved, future observations may yield more precise measurements either through other coincident events or through cross correlation of gravitational-wave events with galaxy catalogs. Here, we implement a new way to measure the Hubble constant without an electromagnetic counterpart and through the use of the binary Love re…
Gravitational-wave standard sirens and application in cosmology
University of Science and Technology of China（中国科学技术大学）；School of Astronomy and Space Sciences, University of Science and Technology of China（中国科学技术大学天文与空间科学学院）；Department of Astronomy, University of Science and Technology of China（中国科学技术大学天文学系）；University of Chinese Academy of Sciences（中国科学院大学）；National Astronomical Observatories, Chinese Academy of Sciences（中国科学院国家天文台）
We study the amplification of the electromagnetic fluctuations, and the production of "seeds" for the cosmic magnetic fields, in a class of string cosmology models whose scalar and tensor perturbations reproduce current observations and satisfy known phenomenological constraints. We find that the condition of efficient seeds production can be satisfied and compatible with all constraints only in a restricted region of parameter space, but we show that such a region has significant intersections with the portions of parameter space where the produced background of relic gravitational waves is s…
In this paper we contrasted two cosmological perturbation theory formalisms, the 1+3 covariant gauge invariant and the gauge invariant by comparing their gauge invariant variables associated with magnetic field defined in each approach. In the first part we give an introduction to each formalism assuming the presence of a magnetic field. We found that gauge invariant quantities defined by 1+3 covariant approach are related with spatial variations of the magnetic field (defined in the gauge invariant formalism) between two closed fundamental observers. This relation was computed by choosing the…
Knowledge of the shape of the mass spectrum of compact objects can be used to help break the degeneracy between the mass and redshift of the gravitational wave (GW) sources, and thus can be used to infer cosmological parameters in the absence of redshift measurements obtained from electromagnetic observations. In this paper, we study extensively different aspects of this approach, including its computational limits and achievable accuracy. We focus on ground-based detectors with current and future sensitivities, we first perform the analysis of an extensive set of simulated data with a hierarc…
In addition to producing loud gravitational waves (GW), the dynamics of a binary black hole system could induce emission of electromagnetic (EM) radiation by affecting the behavior of plasmas and electromagnetic fields in their vicinity. We here study how the electromagnetic fields are affected by a pair of orbiting black holes through the merger. In particular, we show how the binary's dynamics induce a variability in possible electromagnetically induced emissions as well as an enhancement of electromagnetic fields during the late-merge and merger epochs. These time dependent features will li…
The advanced gravitational wave (GW) detector network has started {routine detection of } signals from merging compact binaries. Data indicate that in a fair fraction of these sources, at least one component was a neutron star, bringing with it the possibility of electromagnetic (EM) radiation. So far, a confirmed link between EM and GW radiation has been established for only one source, GW170817. Joint analysis of broadband multiwavelength data and the GW signal have yielded rich information spanning fields as varied as jet physics, cosmology, and nucleosynthesis. Here, we discuss the importa…
Binary neutron star mergers offer a new and independent means of measuring the Hubble constant $H_0$ by combining the gravitational-wave inferred source luminosity distance with its redshift obtained from electromagnetic follow-up. This method is limited by intrinsic degeneracy between the system distance and orbital inclination in the gravitational-wave signal. Observing the afterglow counterpart to a merger can further constrain the inclination angle, allowing this degeneracy to be partially lifted and improving the measurement of $H_0$. In the case of the binary neutron star merger GW170817…
We analyze the functional integral for quantum Conformal Gravity and show that with the help of a Hubbard-Stratonovich transformation, the action can be broken into a local quadratic-curvature theory coupled to a scalar field. A one-loop effective action calculation reveals that strong fluctuations of the metric field are capable of spontaneously generating a dimensionally transmuted parameter which in the weak-field sector of the broken phase induces a Starobinsky-type f(R)-model with a gravi-cosmological constant. A resulting non-trivial relation between Starobinsky'sparameter and the cosmol…
Atom interferometers (AIs) as gravitational-wave (GW) detectors have been proposed a decade ago. Both ground and space-based projects will be in construction and preparation in the near future. In this paper, for the first time, we investigate the potential of the space-borne AIs on detecting GW standard sirens and hence the applications on cosmology. We consider AEDGE as our fiducial AI GW detector and estimate the number of bright sirens that would be obtained within a 5-years data-taking period of GW and with the follow-up observation of electromagnetic (EM) counterparts. We then construct …
A variable speed of light (VSL) cosmology is described in which the causal mechanism of generating primordial perturbations is achieved by varying the speed of light in a primordial epoch. This yields an alternative to inflation for explaining the formation of the cosmic microwave background (CMB) and the large scale structure (LSS) of the universe. The initial value horizon and flatness problems in cosmology are solved. The model predicts primordial scalar and tensor fluctuation spectral indices $n_s=0.96$ and $n_t=- 0.04$, respectively. We make use of the $δ{\cal N}$ formalism to identify si…
Well-tempering is a promising classical method of dynamically screening an arbitrarily large vacuum energy and generating a late-time, low energy de Sitter vacuum state. In this paper, we study for the first time self-tuning in teleparallel gravity and obtain well-tempered cosmological models in the teleparallel gravity analogue of Horndeski theory. This broadens the scope of well-tempered cosmology and teases the potentially far richer cosmological dynamics that could be anchored on teleperallel gravity. We expand the well-tempered recipe to its most general form so far and use it to search f…
Proposed space-based gravitational-wave (GW) detectors such as DECIGO and BBO will detect ~10^6 neutron-star (NS) binaries and determine the luminosity distances to the binaries with high precision. Combining the luminosity distances with cosmologically-induced phase corrections on the GWs, cosmological expansion out to high redshift can be measured without the redshift determinations of host galaxies by electromagnetic observation and be a unique probe for dark energy. On the other hand, such a NS-binary foreground should be subtracted to detect primordial GWs produced during inflation. Thus,…
On the one hand, inflation is an extremely convincing scenario: it solves most cosmological paradoxes and generates fluctuations that became the seeds for the growth of structures. It, however, suffers from a "naturalness" problem: generating initial conditions for inflation is far from easy. On the other hand, loop quantum cosmology is very successful: it solves the Big Bang singularity through a non-perturbative and background-independent quantization of general relativity. It, however, suffers from a key drawback: it is extremely difficult to test. Recent results can let us hope that inflat…
In this Letter we constrain for the first time both cosmology and modified gravity theories conjointly, by combining the GW and electromagnetic observations of GW170817. We provide joint posterior distributions for the Hubble constant $H_0$, and two physical effects typical of modified gravity: the gravitational wave (GW) friction, encoded by the parameter $α_M$, and several GW dispersion relations. Among the results of this analysis, we can improve by 15\% the bound of the graviton mass with respect to measurement using the same event, but fixing $H_0$. We obtain a value of $m^2_g=2.08_{-4.25…
One possibility for explaining the apparent accelerating expansion of the universe is that we live in the center of a spherically inhomogeneous universe. Although current observations cannot fully distinguish $Λ$CDM and these inhomogeneous models, direct measurement of the acceleration of the universe can be a powerful tool in probing them. We have shown that, if $Λ$CDM is the correct model, DECIGO/BBO would be able to detect the positive redshift drift (which is the time evolution of the source redshift $z$) in 3--5 year gravitational wave (GW) observations from neutron-star binaries, which e…
Gravitational waves (GWs) originated from mergers of stellar-mass binary black holes (SBBHs) are considered as dark sirens in cosmology since they usually do not have electromagnetic counterparts. In order to study cosmos with these events, we not only need the luminosity distances extracted from GW signals, but also require the redshift information of sources via, say, matching GW sky localization with galaxy catalogs. Based on such a methodology, we explore how well decihertz GW detectors, DO-Optimal and DECIGO, can constrain cosmological parameters. Using Monte-Carlo simulated dark sirens, …
We investigate the impact on cosmological observables of $f(Q)$-gravity, a specific class of modified gravity models in which gravity is described by the non-metricity scalar, $Q$. In particular we focus on a specific model which is indistinguishable from the $Λ$-cold-dark-matter ($Λ$CDM) model at the background level, while showing peculiar and measurable signatures at linear perturbation level. These are attributed to a time-dependent Planck mass and are regulated by a single dimensionless parameter, $α$. In comparison to the $Λ$CDM model, we find for positive values of $α$ a suppressed matt…
