Massive graviton as a testable cold-dark-matter candidate

We construct a consistent model of gravity where the tensor graviton mode is massive, while linearized equations for scalar and vector metric perturbations are not modified. The Friedmann equation acquires an extra dark-energy component leading to accelerated expansion. The mass of the graviton can be as large as approximately (10(15) cm)(-1), being constrained by the pulsar timing measurements. We argue that nonrelativistic gravitational waves can comprise the cold dark matter and may be detected by the future gravitational wave searches.     

Dual models for non-hadrons

The possibility of describing particles other than hadrons (leptons, photons, gauge bosons, gravitons, etc.) by a dual model is explored. The Virasoro-Shapiro model is studied first, interpreting the massless spin-two state of the model as a graviton. We prove that in the limit of zero slope (with g_vs²α′ held fixed) one obtains the Einstein theory of gravitation accompanied by a massless scalar field. Next, the Veneziano model is studied for small slope as an expansion in powers of α′. It is known from previous work that the zeroth order term is precisely the Yang-Mills theory of a multiplet of massless vector bosons. We show that there are order α′ terms arising both from the dual tree and loop graphs. The former constitutes a relatively unimportant modification of the Yang-Mills theory, whereas the latter involves the coupling of the massless scalar and graviton states of the Virasoro-Shapiro model. Thus one may take the point of view that gravity arises as a unitarization effect in a dual unified theory of electromagnetism and weak interactions. In order to obtain the correct values for the electric charge and Newton's constant it is necessary that α′ ? 10^?34 GeV^?2 The coupling of massless scalar states is also studied.     

General covariance violation and the gravitational dark matter: Scalar graviton

The violation of the general covariance is proposed as a resource of the gravitational dark matter. The minimal violation of the covariance to the unimodular one is associated with the massive scalar graviton as the simplest representative of such matter. The Lagrangian formalism for a continuous medium, a perfect fluid in particular, in the scalar graviton environment is developed. The implications for cosmology are briefly indicated. The text was submitted by the author in English.     

Covariant Lagrange multiplier constrained higher derivative gravity with scalar projectors

We formulate higher derivative gravity with Lagrange multiplier constraint and scalar projectors. Its gauge-fixed formulation as well as vector fields formulation is developed and corresponding spontaneous Lorentz symmetry breaking is investigated. We show that the only propagating mode is higher derivative graviton while scalar and vector modes do not propagate. Despite to higher derivatives structure of the action, its first FRW equation is the first order differential equation which admits the inflationary universe solution.     

Spin identification of graviton resonances in the process pp → e+e? + X at the Large Hadron Collider (LHC)

Prospects for discovering heavy graviton resonances in decays to an electron-positron pair and for identifying the nature of these resonances in the ATLAS experiment at the Large Hadron Collider (LHC) are investigated. Gravitons in the Randall-Sundrum model, which features extra spatial dimensions, are considered by way of example. A comparative analysis of effects of new different-spin heavy resonances, scalar [supersymmetric neutrino (sneutrino)], vector (new gauge Z′ boson), and tensor (graviton) ones, is performed in order to identify the graviton spin. An identification of gravitons is performed by using the integrated center-edge asymmetry. For LHC, the graviton discovery (identification) reach is found to be 2.1 TeV (1.2 TeV) and 3.9 TeV (2.9 TeV) at a confidence level of 5δ (95%) for the graviton coupling constants of k/$ \bar M $ \bar M _Pl = 0.01 and 0.1, respectively. This analysis is the most general, since, for the first time, it takes into account the possible existence of scalar resonances, which affects substantially quantitative estimates of the identification reach.     

Massive graviton propagation of the deformed Hořava–Lifshitz gravity without projectability condition

We study graviton propagations of scalar, vector, and tensor modes in the deformed Ho?ava–Lifshitz gravity (λR  -model) without projectability condition. The quadratic Lagrangian is invariant under diffeomorphism only for λ=1$\lambda =1$ case, which contradicts to the fact that λ is irrelevant to a consistent Hamiltonian approach to the λR-model. In this case, as far as scalar propagations are concerned, there is no essential difference between deformed Ho?ava–Lifshitz gravity (λR  -model) and general relativity. This implies that there are two degrees of freedom for a massless graviton without Ho?ava scalar, and five degrees of freedom appear for a massive graviton when introducing Lorentz-violating and Fierz–Pauli mass terms. Finally, it is shown that for λ=1$\lambda =1$, the vDVZ discontinuity is absent in the massless limit of Lorentz-violating mass terms by considering external source terms.     

Linear perturbations on the cosmological background in the relativistic theory of gravitation: I. Theory

We have derived a system of second-order ordinary differential equations to describe the evolution of small perturbations in the gravitational field and matter characteristics in RTG, with the cosmological solution being a background. These equations are shown to admit the effective gauge invariance, since the graviton mass can be neglected in most cases of interest. The standard expansion in scalar, vector, and tensor components is performed. The equations have been derived for each component.     

Scalar graviton and the modified black holes

Under the explicit violation of the general covariance to the unimodular one, the effect of the emerging scalar graviton on the static spherically symmetric metrics is studied. The main results are threefold. First, there appears the two-parametric family of such metrics, instead of the one-parametric black-hole family in General Relativity (GR). Second, there may exist the one-parametric subfamily describing a peculiar object, the “graviball,” missing in GR. Third, in a simplifying assumption, all the metrics possess the correct Newtonian limit as in GR. The text was submitted by the authors in English.     

Hamiltonian analysis of linearized extension of Hořava–Lifshitz gravity

We investigate the Hamiltonian structure of linearized extended Ho?ava–Lifshitz gravity in a flat cosmological background following the Faddeev–Jackiw's Hamiltonian reduction formalism. The Hamiltonian structure of extended Ho?ava–Lifshitz gravity is similar to that of the projectable version of original Ho?ava–Lifshitz gravity, in which there is one primary constraint and so there are two physical degrees of freedom. In the infrared (IR) limit, however, there is one propagating degree of freedom in the general cosmological background, and that is coupled to the scalar graviton mode. We find that extra scalar graviton mode in an inflationary background can be decoupled from the matter field in the IR limit. But it is necessary to go beyond linear order in order to draw any conclusion of the strong coupling problem.     

On the glueball spectrum in the Klebanov-Strassler model

The spectrum of the linearized equations of IIB supergravity above the Klebanov-Strassler background solution is investigated. It is shown that the spectrum of a scalar particle minimally interacting with the background is degenerate with the spectrum of the graviton (traceless spin-2 mode), and this spectrum is studied in detail. The results are generalized to the more general case of the solution that is known in the literature as a baryonic branch.     

Nonlinear properties of vielbein massive gravity

We propose a nonlinear extension of the Fierz–Pauli mass for the graviton through a functional of the vielbein and an external Minkowski background. The functional generalizes the notion of the measure, since it reduces to a cosmological constant if the external background is formally sent to zero. Such a term and the explicit external background emerge dynamically from a bi-gravity theory, having both a massless and a massive graviton in its spectrum, in a specific limit in which the massless mode decouples, while the massive one couples universally to matter. We investigate the massive theory using the Stückelberg method and providing a ’t Hooft–Feynman gauge fixing, in which the tensor, vector and scalar Stückelberg fields decouple. We show that this model has the softest possible ultraviolet behavior that can be expected from any generic (Lorentz-invariant) theory of massive gravity, namely that it becomes strong only at the scale Λ₃=(m_g ²M_P)^1/3.     

Massive supergravity from spontaneously breaking orthosymplectic gauge symmetry

We construct a Lagrangian density which is manifestly invariant under the orthosymplectic gauge group OSP(1; 4) and under general coordinate transformations. This is done by the use of two multiplets, the symmetric and antisymmetric representations of OSP(1; 4). We present the general features of OSP(m; 2n) and, in particular, its irreducible representations. The absence of OSP(1; 4) symmetry from the ground state indicates that one of the scalar fields, which is an element of the symmetric multiplet, has a nonvanishing vacuum expectation value. A shift in the fields reveals the physical spectrum of our Lagrangian. Two Goldstone fields are present, a vector and a spinor, corresponding to the breakdown of OSP(1; 4) to the Lorentzian group. The full Lagrangian contains a graviton, a massive $\text{spin}\text{-}\text{3}\text{2}$ field, and two massive scalar fields. The generalization to OSP(2; 4) is immediate.     

Hard thermal loops in a gravitational field

We calculate the high-temperature (T ⁴) limit of the 3-graviton vertex function, with a single loop of internal scalar particles in thermal equilibrium. We use the analytically continued imaginary-time formalism. We verify a particular case of the Ward identity connecting the 3- and 2-graviton functions. This confirms that there is covariance under general coordinate transformations (which reduce to the identity at infinity). We remark that the ghost-ghost-graviton vertex (with ghost and graviton internal lines) has noT ⁴ term. This implies that the 3-graviton function with internal graviton (and ghost) lines must satisfy the Ward identity too, so it is possible for it to be proportional to the scalar contribution. We have verified this for that part of the vertex function which is manifestly symmetric and traceless in the six Lorentz indices.     

General relativity with an auxiliary dimension

I consider an extension of General Relativity by an auxiliary nondynamical dimension that enables our space–time to acquire an extrinsic curvature. Obtained gravitational equations, without or with a cosmological constant, have a selfaccelerated solution that is independent of the value of the cosmological constant, and can describe the cosmic speedup of the Universe as a geometric effect. Background evolution of the selfaccelerated solution is identical to that of ordinary de Sitter space. I show that linear perturbations on this solution describe either a massless graviton, or a massive graviton and a scalar, which are free of ghosts and tachyons for certain choices of boundary conditions. The obtained linearized expressions suggest that nonlinear interactions should, for certain boundary conditions, be strongly coupled, although this issue is not studied here. The full nonlinear Hamiltonian of the theory is shown to be positive for the selfaccelerated solution, while in general, it reduces to surface terms in our and auxiliary dimensions.     

Simulation of <Emphasis Type="Italic">Z</Emphasis> plus graviton/unparticle production at the LHC

Theories with extra dimensions have gained much interest in recent years as candidates for a possible extension of the SM. The observation of large extra dimensions through real graviton emission is one of the most popular related new phenomena. The main experimental signatures from graviton emission are production of single jet and single photon events, which have been studied in great detail. This work describes the implementation of graviton production together with either a Z or a photon in Pythia 8. The potential of using Z plus graviton production at the LHC as a complementary channel is also studied. For completeness, this work also includes the more recently proposed scenario of unparticle emission, since the effective theory of unparticles to some extent represents a generalization of the large extra dimension model.     

Minimal metagravity versus dark matter and/or dark energy

The minimal metagravity theory, explicitly violating the general covariance but preserving the unimodular one, is applied to study the evolution of the isotropic homogeneous Universe. The massive scalar graviton, contained in the theory in addition to the massless tensor one, is treated as a source of dark matter and/or dark energy. The modified Friedmann equation for the scale factor of the Universe is derived. The question whether the minimal metagravity can emulate the LCDM concordance model, valid in General Relativity, is discussed. The text was submitted by the author in English.     

Identification of the origin of monojet signatures at the LHC

Several new physics scenarios can lead to monojet signatures at the LHC. If such events are observed above the Standard Model background it will be important to identify their origin. In this Letter we compare and contrast these signatures as produced in two very different pictures: vector or scalar unparticle production in the scale-invariant/conformal regime and graviton emission in the Arkani-Hamed, Dimopoulos and Dvali extra-dimensional model. We demonstrate that these two scenarios can be distinguished at the LHC for a reasonable range of model parameters through the shape of their respective monojet and/or missing E_T distributions.     

Gravity localization in sine-Gordon braneworlds

In this work we study two types of five-dimensional braneworld models given by sine-Gordon potentials. In both scenarios, the thick brane is generated by a real scalar field coupled to gravity. We focus our investigation on the localization of graviton field and the behaviour of the massive spectrum. In particular, we analyse the localization of massive modes by means of a relative probability method in a Quantum Mechanics context. Initially, considering a scalar field sine-Gordon potential, we find a localized state to the graviton at zero mode. However, when we consider a double sine-Gordon potential, the brane structure is changed allowing the existence of massive resonant states. The new results show how the existence of an internal structure can aid in the emergence of massive resonant modes on the brane.     

Definitions and units in mechanics

With displacement, time, and force as basic undefined physical quantities, other physical quantities are defined as combinations of two vector quantities and one scalar quantity. Combinations include multiplication and division of vectors by vectors, scalars by vectors, and scalars by scalars. Defined quantities are vectors, scalars or quaternions, depending on directions of vectors in the definitions. Division of a vector by a vector is equivalent to multiplication of vectors divided by a scalar. The unit of a vector (or scalar) is itself a vector (or scalar) quantity. Thesquare meter (a vector) differs from meter ² (a scalar), and the cubic meter (a scalar) is different frommeter ³ . The characteristics of displacement, time, and force are considered known from experience.     

Brane effects on extra-dimensional scenarios: a tale of two gravitons

We analyze the propagation of a scalar field in multidimensional theories which include kinetic corrections in the brane, as a prototype for gravitational interactions in a four-dimensional brane located in a (nearly) flat extra-dimensional bulk. We regularize the theory by introducing an infrared cutoff given by the size of the extra dimensions, R, and a physical ultraviolet cutoff of the order of the fundamental Planck scale in the higher-dimensional theory, M. We show that, having implemented cutoffs, the radius of the extra dimensions cannot be arbitrarily large for M≳1 TeV. Moreover, for finite radii, the gravitational effects localized on the brane can substantially alter the phenomenology of collider and/or table-top gravitational experiments. This phenomenology is dictated by the presence of a massless graviton, with standard couplings to the matter fields, and a massive graviton which couples to matter in a much stronger way. While graviton KK modes lighter than the massive graviton couple to matter in a standard way, the couplings to matter of the heavier KK modes are strongly suppressed.