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The detection of gravitational waves in 2015 ushered in a new era of gravitational wave (GW) astronomy capable of probing the strong field dynamics of black holes and neutron stars. It has opened up an exciting new window for laboratory and space tests of Einstein's theory of classical general relativity (GR). In recent years, two interesting proposals have aimed to reveal the quantum nature of perturbative gravity: (1) theoretical predictions on how graviton noise from the early universe, after the vacuum of the gravitational field was strongly squeezed by inflationary expansion; (2) experimental proposals using the quantum entanglement between two masses, each in a superposition (gravitational cat, or gravcat) state. The first proposal focuses on the stochastic properties of quantum fields (QFs), and the second invokes a key concept of quantum information (QI). An equally basic and interesting idea is to ask whether (and how) gravity might be responsible for a quantum system becoming classical in appearance, known as gravitational decoherence. Decoherence due to gravity is of special interest because gravity is universal, meaning, gravitational interaction is present for all massive objects. This is an important issue in macroscopic quantum phenomena (MQP), underlining many proposals in alternative quantum theories (AQTs). To fully appreciate or conduct research in these exciting developments requires a working knowledge of classical GR, QF theory, and QI, plus some familiarity with stochastic processes (SPs), namely, noise in quantum fields and decohering environments. Traditionally a new researcher may be conversant in one or two of these four subjects: GR, QFT, QI, and SP, depending on his/her background. This tutorial attempts to provide the necessary connective tissues between them, helping an engaged reader from any one of these four subjects to leapfrog to the frontier of these interdisciplinary research topics. In the present version, we shall address the three topics listed in the title, excluding gravitational entanglement, because, despite the high attention some recent experimental proposals have received, its nature and implications in relation to quantum gravity still contain many controversial elements. [ABSTRACT FROM AUTHOR]

In light of the gravitational waves observation and the discrete structure of spacetime at high scales , we describe the behavior of the spacetime deformation patterns in terms of gravitons and investigate the effective results with respect to photons. In particular, using the GW150914 data and related known results, we derive an upper bound of the time delay s as well as the velocity difference of the emitted photons with respect to gravitons. [ABSTRACT FROM AUTHOR]

The detection of gravitational waves in 2015 ushered in a new era of gravitational wave (GW) astronomy capable of probing the strong field dynamics of black holes and neutron stars. It has opened up an exciting new window for laboratory and space tests of Einstein’s theory of classical general relativity (GR). In recent years, two interesting proposals have aimed to reveal the quantum nature of perturbative gravity: (1) theoretical predictions on how graviton noise from the early universe, after the vacuum of the gravitational field was strongly squeezed by inflationary expansion; (2) experimental proposals using the quantum entanglement between two masses, each in a superposition (gravitational cat, or gravcat) state. The first proposal focuses on the stochastic properties of quantum fields (QFs), and the second invokes a key concept of quantum information (QI). An equally basic and interesting idea is to ask whether (and how) gravity might be responsible for a quantum system becoming classical in appearance, known as gravitational decoherence. Decoherence due to gravity is of special interest because gravity is universal, meaning, gravitational interaction is present for all massive objects. This is an important issue in macroscopic quantum phenomena (MQP), underlining many proposals in alternative quantum theories (AQTs). To fully appreciate or conduct research in these exciting developments requires a working knowledge of classical GR, QF theory, and QI, plus some familiarity with stochastic processes (SPs), namely, noise in quantum fields and decohering environments. Traditionally a new researcher may be conversant in one or two of these four subjects: GR, QFT, QI, and SP, depending on his/her background. This tutorial attempts to provide the necessary connective tissues between them, helping an engaged reader from any one of these four subjects to leapfrog to the frontier of these interdisciplinary research topics. In the present version, we shall address the three topics listed in the title, excluding gravitational entanglement, because, despite the high attention some recent experimental proposals have received, its nature and implications in relation to quantum gravity still contain many controversial elements.

In Newton's theory, all mass gravitates in an isotropic (spherical) manner. In this paper, we will consider aspherical-anisotropic-gravitating processes, which lead to a unique view of dark matter: dark matter is a graviton condensate. We also discuss dark energy and the possibility of a final, fifth interaction. [ABSTRACT FROM AUTHOR]

A statistical combination of searches for heavy resonances decaying to pairs of bosons or leptons is presented. The data correspond to an integrated luminosity of 35.9 fb−1 collected during 2016 by the CMS experiment at the LHC in proton-proton collisions at a center-of-mass energy of 13 TeV. The data are found to be consistent with expectations from the standard model background. Exclusion limits are set in the context of models of spin-1 heavy vector triplets and of spin-2 bulk gravitons. For mass-degenerate W′ and Z′ resonances that predominantly couple to the standard model gauge bosons, the mass exclusion at 95% confidence level of heavy vector bosons is extended to 4.5 TeV as compared to 3.8 TeV determined from the best individual channel. This excluded mass increases to 5.0 TeV if the resonances couple predominantly to fermions.

Although it has been approximately 80 years since the graviton was theoretically predicted, it has not yet been discovered. To resolve this puzzle, this study developed a model wherein the gravitational force is incorporated into the fundamental structure of the universal space. A physical object diminishes the energy density of space exactly by the amount of energy it contains. The resulting area of space with a diminished energy density is pushed in the direction of the closest area with the lowest energy density. A physical object situated in the corresponding space with a lower energy density follows the motion of this area towards the closest area with the lowest energy density. Therefore, there is no direct gravitational force between the physical objects and gravity is incorporated into the variable energy density of the space. This model of gravity has advanced Newton’s ether model with the extension of the mass-energy equivalence principle to space and works without the hypothetical graviton.

Probing the polarization of gravitational waves (GWs) would provide evidence of graviton, indicating the quantization of gravity. Motivated by the next generation of gravitational wave detectors, we make an attempt to study the possible helicity coupling of structured lights to GWs. With the analog between gravitational fields and the generic electromagnetic media, we present a 4-vector optical Dirac equation based on the Maxwell theory under the paraxial approximation. It is found that twisted lights propagating in a gravitational field can be viewed as a non-Hermitian system with PT symmetry. We further demonstrate that the coupling effect between angular momentums of the GWs and twisted lights may make photons undergo both dipole and quadrupole transitions between different orbital-angular-momentum (OAM) eigenstates and lead to some measurable optical features, including the central intensity brightening and macroscopic rotation of the intensity pattern for twisted lights. The former is spin-independent, while the latter is a spin-dependent phenomenon, both of which can be viewed alternatively as the spin-orbital-Hall effect of structured lights in the GWs and can serve as an indicator of the particle nature of GWs. [ABSTRACT FROM AUTHOR]

Particle production during cosmic expansion can be interpreted as a two-mode squeezing process of quantum states. The two-mode squeezed states consist of an infinite number of entangled particles and then enhance the nonclassicality of particles. There are two methods for estimating the degree of squeezing. One is to employ instantaneous vacuum states, and the other is to adopt adiabatic vacuum states. We analytically study the squeezing process of gravitons and axions by using the two methods. We first consider a cosmological model of inflation followed by instantaneous reheating leading to a radiation dominated era. In the case of gravitons, we find no qualitatively difference in the squeezing between the two methods. However, for the axions, it turns out that the squeezing in the instantaneous vacuum increases as the mass increases while the squeezing decreases in the adiabatic vacuum as the mass increases. We then study the effect of noninstantaneous reheating on the the squeezing and show that the squeezing is enhanced compared with the instantaneous reheating. We also illustrate how the squeezed states enhance the violation of Bell inequality and quantum noise of gravitons and axions. [ABSTRACT FROM AUTHOR]

We reason that it is the gravitation of all ordinary matter, extending from the dense distant past to the sparse present, rather than dark matter, that shows up in galaxy rotation and velocity dispersion. Likewise, we argue that it is this gradient in the gravitational energy due to the expansion, rather than dark energy, that explains Type 1a supernovae brightness vs. redshift data. Our conclusions follow from statistical mechanics, the thermodynamic theory based on the atomistic axiom that everything comprises quanta. In line with the Einstein field equations, the vacuum quanta embodying gravitation, geometrized as spacetime, equate in dynamic balance to the quanta embodying the substance of the stress–energy tensor. In accordance with quantum field theory, the proposed ground-state field of paired light quanta complies with Bose–Einstein statistics and assumes an excited state around a particle.

There is a well known result from the Fierzâ€"Pauli (FP) theory in de Sitter background, it is the existence of a lower bound for the mass m of the spin 2 particle, the Higuchi bound. It establishes that m 2 â©ľ 2 H 2, where H is the Hubble parameter, in order to the theory presents no ghost-like instabilities. In this sense, m should be unacceptable high in order to fulfill this condition at the time of the inflationary epoch of the Universe, posing a difficulty to conciliate the FP theory with cosmology. In this article we show that the Higuchi bound can be circumvented in an alternative description of massive spin-2 particles known as L ( a 1 ) models. In maximally symmetric spaces the theory has two free parameters which can be consistently chosen in order to make the model absent of a lower bound for m. Then, m can be arbitrarily smaller than the energy scale of inflation avoiding instabilities at that time. [ABSTRACT FROM AUTHOR]

We give a pedagogical introduction to black holes (BHs) greybody factors (GFs) and quasinormal modes (QNMs) and share the recent developments on those subjects. To this end, we present some particular analytical and approximation techniques for the computations of the GFs and QNMs. We first review the gravitational GFs and show how they are analytically calculated for static and spherically symmetric higher dimensional BHs, consisting the charged BHs and existence of cosmological constant (i.e. de Sitter (dS)/anti-de Sitter (AdS)AdS BHs). The computations performed involve both the low-energy (having real and small frequencies) and the asymptotic (having extremely high frequency of the scattered wave throughout the imaginary axis) cases. A generic method is discussed at low frequencies. This method can be used for all three types of spacetime asymptotics and it is unaffected by the BH's features. For asymptotically dS BHs, GF varies depending on whether the spacetime dimension is even or odd, and is proportional to the ratio of the event and cosmic horizon areas. At asymptotic frequencies, the GFs can be computed by using a matching technique inspired by the monodromy method. In the meantime, we also make a general literature review on the matching technique in a separate section. While the GFs for charged or asymptotically dS BHs are generated by nontrivial functions, the GF for asymptotically AdS BHs is precisely one: pure black-body emission. QNMs, which are solutions to the relevant perturbation equations that satisfy the boundary conditions for purely outgoing (gravitational) waves at spatial infinity and purely ingoing (gravitational) waves at the event horizon, are considered using some particular analytical (like the matching technique) and approximation methods. In this study, our primary focus will be on the bosonic and fermionic GFs and QNMs of various BH and brane geometries and reveal the fingerprints of the invisibles with the radiation spectra to be obtained by the WKB approximation and bounding the Bogoliubov coefficients (together with the Miller-Good transformation) methods. [ABSTRACT FROM AUTHOR]

The controlled motion of a body in a central gravitational field without mass flow is considered. The possibility of moving the body in the radial direction from the center of attraction due to changes in the kinetic moment relative to the center of mass of the body is shown. A scheme for moving the body using a system of flywheels located in the same plane in near-circular orbits with different heights is proposed. The use of the spin of elementary particles is considered as flywheels. It is proved that using the spin of elementary particles with a Compton wavelength exceeding the distance to the attracting center is energetically more profitable than using the momentum of these particles to move the body. The calculation of motion using hypothetical particles (gravitons) is presented. A hypothesis has been put forward about the radiation of bodies during accelerated motion, which finds indirect confirmation in stellar dynamics and in an experiment with the fall of two bodies in a vacuum. The results can be used in experiments to search for elementary particles with low energy, explain cosmic phenomena and to develop transport objects on new physical principles.

Each type of Coulomb (Newton) charge corresponds to a kind of Coulomb (Newton) mass. Such a mass-charge duality principle explains the availability of the united rest mass and charge in a neutrino equal to all its mass and charge consisting of the electric, weak, and strong components and the range of other innate components. A neutrino itself, similarly to all other quantum matter with Coulomb (Newton) mass and charge, testifies hereby in favor of a kind of mononeutrino with magnetocoulomb (magnetonewton) rest mass and charge equal to all its mass and charge including the magnetoelectric, magnetoweak, and magnetostrong parts and the range of other innate parts. We discuss a theory in which symmetry between electricity and magnetism comes forward at the level of a grand unification mathematical logic as the defined symmetry between gravity and magnetogravity within the same allgravity responsible for all that in a curved space-time. This allgravity relates a graviton and a monograviton as a consequence of force unification forming a single allgraviton. Thereby, it establishes a set of forces and the role of mass and charge in their formation and thus directly reveals the most diverse properties of a curved space that have remained hitherto latent. [ABSTRACT FROM AUTHOR]

Probing the polarization of gravitational waves (GWs) would provide evidence of graviton, indicating the quantization of gravity. Motivated by the next generation of gravitational wave detectors, we make an attempt to study the possible helicity coupling of structured lights to GWs. With the analog between gravitational fields and the generic electromagnetic media, we present a 4-vector optical Dirac equation based on the Maxwell theory under the paraxial approximation. It is found that twisted lights propagating in a gravitational field can be viewed as a non-Hermitian system with PT symmetry. We further demonstrate that the coupling effect between angular momentums of the GWs and twisted lights may make photons undergo both dipole and quadrupole transitions between different orbital-angular-momentum (OAM) eigenstates and lead to some measurable optical features, including the central intensity brightening and macroscopic rotation of the intensity pattern for twisted lights. The former is spin-independent, while the latter is a spin-dependent phenomenon, both of which can be viewed alternatively as the spin-orbital-Hall effect of structured lights in the GWs and can serve as an indicator of the particle nature of GWs.

A toy model of a graviton is explored by considering the minimum amount of information gravitons could carry. The total entropy of the universe is calculated and compared to estimates from super massive black holes and massive models of the graviton. The running cosmological constant is calculated using the entropy relation previously computed and compared to its experimentally accepted value. Both results are quantified considering radiation and matter-dominated universes. [ABSTRACT FROM AUTHOR]

This study attempts to answer the question of what space is made of and explores in this objective the analogy between the Einstein’s gravitational geometrical theory in one- and two-dimensional linear deformations and a possible space material based on strain measures done on the Ligo or Virgo interferometers. It draws an analogy between the Einstein’s gravitational constant κ and the Young’s modulus and Poisson’s ratio of an elastic material that can constitute the space fabric, in the context of propagation of weak gravitational waves. In this paper, the space is proposed to have an elastic microstructure of 1.566 × 10 - 35 m grain size as proposed in string theory, with an associated characteristic frequency f. The gravitational constant G is the macroscopic manifestation of the said frequency via the formula G = π f 2 / ρ , where ρ is the density of the space material. [ABSTRACT FROM AUTHOR]

The presence of massive gravitons in the field of massive gravity is considered an important factor in investigating the structure of compact objects. Hence, we are encouraged to study the dark energy star structure in the Vegh's massive gravity. We consider that the equation of state governing the inner spacetime of the star is the extended Chaplygin gas, and then using this equation of state, we numerically solve the Tolman–Oppenheimer–Volkoff (TOV) equation in massive gravity. In the following, assuming different values of free parameters defined in massive gravity, we calculate the properties of dark energy stars such as radial pressure, transverse pressure, anisotropy parameter, and other characteristics. Then, after obtaining the maximum mass and its corresponding radius, we compute redshift and compactness. The obtained results show that for this model of dark energy star, the maximum mass and its corresponding radius depend on the massive gravity's free parameters and anisotropy parameter. These results are consistent with the observational data and cover the lower mass gap. We also demonstrate that all energy conditions are satisfied for this model, and in the presence of anisotropy, the dark energy star is potentially unstable. [ABSTRACT FROM AUTHOR]

As shown by Gertsenshtein in 1961, an external magnetic field can couple electromagnetic to gravitational waves, giving rise to oscillations between them. Viewed as a quantum process, the magnetic field has catalyzed the mixing of photon and graviton states. We show that the self-interaction terms of the Yang–Mills SU(2) field can take the place of the external magnetic field and autocatalyze the mixing of Yang–Mills bosons and gravitons. In the process, rotational symmetry is broken and the Yang–Mills boson acquires a mass. [ABSTRACT FROM AUTHOR]

The experiments of Kopeikin and Fomalont (2002) had confirmed, measure the velocity of gravity wave of Quasar J0842+1835 is 1.06xc. Neil Cornish, Diego Blas, Germano Nardini (2017) confirmed, the velocity of gravity wave cgw has interval 0.55xc < cgw < 1.42xc. That had shown the gravity waves are one among parts of Seven Energy States (SES). Where the parts of SES are combinations of de Broglie's wavelength with The Frequency of Universe. It gives us a new understanding of what gravity is. Later we know, the electromagnetic effect is combinations of the SES's components. By this approximation, we can construct how the physics sub-particle is looked like. [ABSTRACT FROM AUTHOR]

The process of gravitation confirms that the coherence of any relation in physical space comes from a universal function located in the internal space of the universe. This function requires time to handle a coherent change of state in physical space [S. Battisti, Phys. Essays 29, 117 (2016)]. During this time, the state's change cannot be transferred or observed in physical space. This limitation of the observation of the variations in the physical space justifies the principle of uncertainty. The complex potential energy, integrated in the internal space of the object, is an essential means to regulate the coherent process. The photon, being able to integrate the potential energy, is able to produce the gravitational relationship. The function of universe justifies both the probability law of quantum mechanics in an atom and the deterministic law of gravitation in cosmology: the two laws maximize the number of accessible states of the partners of relationship. Although gravitational movement is only pseudo inertial, general relativity agrees with quantum physics because gravitational quanta are transferred within the internal space of universe: graviton does not exist in the physical space. Therefore, the same universal function, by using the same laws and processes, explains in detail the observed relationships in a cosmological system as well as in a quantum system, without resorting to general relativity. [ABSTRACT FROM AUTHOR]

Results are presented of a search for heavy particles decaying into two photons. The analysis is based on a 19.7fb−1 sample of proton–proton collisions at s=8TeV collected with the CMS detector at the CERN LHC. The diphoton mass spectrum from 150 to 850GeV is used to search for an excess of events over the background. The search is extended to new resonances with natural widths of up to 10% of the mass value. No evidence for new particle production is observed and limits at 95% confidence level on the production cross section times branching fraction to diphotons are determined. These limits are interpreted in terms of two-Higgs-doublet model parameters.

Abstract The principles of quantum field theory in flat spacetime suggest that gravity is mediated by a massless particle with helicity ± 2 , the so-called graviton. It is regarded as textbook knowledge that, when the self-coupling of a particle with these properties is considered, the long-wavelength structure of such a nonlinear theory is fixed to be that of general relativity. However, here we indicate that these arguments conceal an implicit assumption which is surreptitiously motivated by the very knowledge of general relativity. This is shown by providing a counterexample: we revisit a nonlinear theory of gravity which is not structurally equivalent to general relativity and that, in the non-interacting limit, describes a free helicity ± 2 graviton. We explicitly prove that this theory, known as Weyl-transverse gravity (unimodular gravity with explicit Weyl invariance), can be understood as the result of self-coupling in complete parallelism to the well-known case of general relativity. We discuss the absence of cosmological constant problem in this theory, highlighting that it provides a particular realization of previous arguments formulated in studies of the emergence of the gravitational interaction from condensed-matter-like models. Overall, we conclude that the consideration that gravity is mediated by a massless particle with helicity ± 2 does not inextricably lead to the cosmological constant problem. [ABSTRACT FROM AUTHOR]

A search for a massive resonance decaying into a pair of standard model Higgs bosons, in a final state consisting of two b quark–antiquark pairs, is performed. A data sample of proton–proton collisions at a centre-of-mass energy of 13 TeV is used, collected by the CMS experiment at the CERN LHC in 2016, and corresponding to an integrated luminosity of 35.9 fb −1 . The Higgs bosons are highly Lorentz-boosted and are each reconstructed as a single large-area jet. The signal is characterized by a peak in the dijet invariant mass distribution, above a background from the standard model multijet production. The observations are consistent with the background expectations, and are interpreted as upper limits on the products of the s -channel production cross sections and branching fractions of narrow bulk gravitons and radions in warped extra-dimensional models. The limits range from 126 to 1.4 fb at 95% confidence level for resonances with masses between 750 and 3000 GeV, and are the most stringent to date, over the explored mass range. [ABSTRACT FROM AUTHOR]

We discuss the existence of graviton in a Friedmann–Lemaitre–Robertson–Walker (FLRW) metric of isotropic and homogeneous universe based on de Rham–Gabadadze–Tolley (dRGT) nonlinear massive gravity theory. We consider a similar FLRW fiducial metric in the formulation that lead to a Friedmann–Lemaitre equation similar to the case of cosmological constant based dark energy model. We show that these equations can be constructed by considering a constraint equation found from varying the corresponding action with respect to the fiducial metric. Under a specific choice of fiducial metric lapse function, we determine the range of present cosmological time bare graviton mass in a parameter space by considering the observed cosmological constant density parameter and the related Higuchi bound for the lower dressed graviton mass value. The existence of an indefinite condition in the corresponding parameter space is also discussed and analyzed, as well as the characteristics of the related bare graviton mass and the strong-coupling scale quantity. [ABSTRACT FROM AUTHOR]