KK Graviton Research Articles

The dark universe: Primordial black hole ⇋ dark graviton gas connection

We study the possible correspondence between 5-dimensional primordial black holes and massive 5-dimensional KK gravitons as dark matter candidate within the recently proposed dark dimension scenario that addresses the cosmological hierarchy problem. First, we show that in the local universe a population of 5-dimensional black holes with MBH∼7×1013g would be practically indistinguishable from a KK tower of dark gravitons with mDM∼50keV. Second, we connect the mass increase of 5-dimensional black holes and the related temperature decrease with the cooling of the tower of massive spin-2 KK excitations of the graviton. The dark gravitons are produced at a mass ∼1−50GeV and the bulk of their mass shifts down to roughly 1−100keV today. The cooling of the system proceeds via decay to lighter gravitons without losing much total mass density, resembling the intra-tower decays that characterize the cosmological evolution of the dynamical dark matter framework. We associate the intra-tower decays of the graviton gas with the black hole growth through accretion. We also discuss that the primordial black hole ⇋ dark graviton gas connection can be nicely explained by the bound state picture of black holes in terms of gravitons.

Gravity at the tip of the throat

We study the gravitational signatures that arise from compactifying Type IIB supergravity on a compact space containing a Klebanov-Strassler warped throat. After reviewing the dimensional reduction of the 10d graviton and explicitly obtaining the equa- tions of motion for the 4d tensor hμν, vector hμn and scalar hmn modes, we find the masses and wavefunctions of the Kaluza-Klein tower of spin-2 states. We explore how the masses and wavefunctions depend on the balance between the strength of the warping and the size of the bulk, and how these relate to the range and strength of the interactions which correct the Newtonian gravitational potential. By computing the modified Newtonian potential for sources on a brane somewhere along the throat, and applying consistency constraints on the Klebanov-Strassler parameters, we obtain predictions for the phenomenological pa- rameter space. In the case of a fully warped throat, and depending on where the brane is along the throat, these predictions are narrow in range and consistent with current obser- vational and experimental constraints. We also begin an exploration of gravitational wave signatures of KK gravitons in warped throats, finding that strong warping can bring the corresponding frequencies down to the windows of current and proposed experiments.

5-dimensional Chern-Simons gauge theory on an interval: Massive spin-2 theory from symmetry breaking via boundary conditions

In this note, we revisit the 4-dimensional theory of massive gravity through compactification of an extra dimension and geometric symmetry breaking. We dimensionally reduce the 5-dimensional topological Chern-Simons gauge theory of (anti) de Sitter group on an interval. We apply non-trivial boundary conditions at the endpoints to break all of the gauge symmetries. We identify different components of the gauge connection as invertible vierbein and spin-connection to interpret it as a gravitational theory. The effective field theory in four dimensions includes the dRGT potential terms and has a tower of Kaluza-Klein states without massless graviton in the spectrum. The UV cut of the theory is the Planck scale of the 5-dimensional gravity l−1. If ζ is the scale of symmetry breaking and L is the length of the interval, then the masses of the lightest graviton m and the level n (for n<Ll−1) KK gravitons mKK(n) are determined as m=(ζL−1)12≪mKK(n)=nL−1. The 4-dimensional Planck mass is mPl∼(Ll−3)12 and we find the hierarchy ζ<m<L−1<l−1<mPl.

Holography of massive M2-brane theory: non-linear extension

We investigate the gauge/gravity duality between the mathcal{N} = 6 mass-deformed ABJM theory with hbox {U}_k(N)times hbox {U}_{-k}(N) gauge symmetry and the 11-dimensional supergravity on LLM geometries with SO(2,1)times SO(4)/{mathbb {Z}}_ktimes SO(4)/{mathbb {Z}}_k isometry, in terms of a KK holography, which involves quadratic order field redefinitions. We establish the quadratic order KK mappings for various gauge invariant fields in order to obtain the canonical 4-dimensional gravity equations of motion and to reduce the LLM solutions to an asymptotically AdS_4 gravity solutions. The non-linearity of the KK maps indicates that we can observe the true purpose of the non-linear KK holography of the LLM solutions. We read the vacuum expectation value of conformal dimension two operator from the asymptotically AdS_4 gravity solutions. For the LLM solutions which are represented by square-shaped Young diagrams, we compare the vacuum expectation value obtained from the holographic procedure with the result obtained from the field theory, which is given by langle mathcal{O}^{(Delta =2)}rangle =sqrt{k}N^{frac{3}{2}}f_{(Delta =2)}+mathcal{O}(N), where f_{Delta } is independent of N. Based on this result, we examine the gauge/gravity duality in the large N limit and finite k. We also show that the vacuum expectation values of the massive KK graviton modes are vanishing as expected by the supersymmetry.

High-density QCD phase transitions inside neutron stars: Glitches and gravitational waves

We discuss physics of exotic high baryon density QCD phases which are believed to exist in the core of a neutron star. This can provide a laboratory for exploring exotic physics such as axion emission, KK graviton production etc. Much of the physics of these high-density phases is model-dependent and not very well understood, especially the densities expected to occur inside neutron stars. We follow a different approach and use primarily universal aspects of the physics of different high-density phases and associated phase transitions. We study effects of density fluctuations during transitions with and without topological defect production and study the effect on pulsar timings due to changing moment of inertia of the star. We also discuss gravitational wave production due to rapidly changing quadrupole moment of the star due to these fluctuations.

Kaluza-Klein gravitons at LHC2

In this work we study constraints from new searches for heavy particles at the LHC on the allowed masses and couplings of a KK Graviton in a holographic composite Higgs model. Keeping new electroweak states heavy such that electroweak precision tests are satisfied, we control the mass of the lightest KK graviton using a brane kinetic term. With this we study KK graviton masses from 0.5-3 TeV. In our analysis we also employ Little Randall-Sundrum (RS) Models, characterised by a lower UV scale in the 5D model which in turn implies modified couplings to massless bulk fields. Viewing this scenario as a strongly coupled 4D theory with a composite Higgs boson, the KK graviton is interpreted as a composite spin-2 state and the varying UV scale corresponds to a varying intermediate scale between the cutoff of the low energy effective theory and the Planck scale. We find that KK gravitons with masses in the range 0.5-3 TeV are compatible with current collider constraints, where the most promising channels for detecting these states are the di-photon and ZZ channels. A detection is more likely in the little RS models, in which the dual gauge theory has a larger number of colours than in traditional RS models.

Lowest Order Mass of KK Graviton Revisited and How It May Affect the Blue Spectrum for Gravitons

The lowest order mass for a KK graviton, as a non-zero product of two branes interacting via a situation similar to Steinhardt’s ekpyrotic universe is obtained, as to an alternative to the present dogma specifying that gravitons must be massless. The relative positions as to the branes give a dynamical picture as to how lowest order KK gravitons could be affected by contraction and then subsequent expansion. Initially we have bulk gravitons as a vacuum state. The massless condition is just one solution to a Stern Liuouville operator equation we discuss, which with a non-zero lowest order mass for a KK graviton permits modeling of gravitons via a dynamical Casmir effect which we generalize using Ruser and Duerrer’s 2007 work. In particular the blue spectrum for (massless gravitons), is revisited, with consequences for observational astrophysics.

Does Entropy Manufacture Impacts DM Density Profiles and How Well Does the Scientific Community Understand If or Not Gravity Is always Either a Classical and/or Quantum Phenomenon at Its Genesis over 13.7 Billion Years Ago?

In the 12th Marcel Grossmann Meeting, July 9th, 2009, the author raised the issue of whether early graviton production could affect non-Gaussian contributions to DM density profiles. Specifically, does a first-order phase transition, in the formation of GW also lead to variation in density fluctuations of space plasma production? and curvature perturbations? We submit that the answer to this question will lead to quantifying fluctuations in space time which affect the stability and formation of DM halos and DM density profiles. Furthermore, we look at whether or not there is a relationship between DM and DE, and gravitons. This is suggested by a modification of Randal Sundrum brane world models, which may be used to admit a very small four-dimensional standard space time non-zero graviton mass. Non zero graviton mass in 4 dimensional space time, as well as modification of existing KK graviton theories will lead to a speed-up of cosmological expansion when the red shift was approximately z ≈ 0.5 − 0.55, i.e., about a billion years ago. Finally, the issue of if gravity is a quantum phenomenon will be brought up in the context of understanding if or not squeezing of coherent states is mandatory at the onset of inflation.

Planckian Interacting Massive Particles as Dark Matter

The standard model could be self-consistent up to the Planck scale according to the present measurements of the Higgs boson mass and top quark Yukawa coupling. It is therefore possible that new physics is only coupled to the standard model through Planck suppressed higher dimensional operators. In this case the weakly interacting massive particle miracle is a mirage, and instead minimality as dictated by Occam's razor would indicate that dark matter is related to the Planck scale, where quantum gravity is anyway expected to manifest itself. Assuming within this framework that dark matter is a Planckian interacting massive particle, we show that the most natural mass larger than 0.01M_{p} is already ruled out by the absence of tensor modes in the cosmic microwave background (CMB). This also indicates that we expect tensor modes in the CMB to be observed soon for this type of minimal dark matter model. Finally, we touch upon the Kaluza-Klein graviton mode as a possible realization of this scenario within UV complete models, as well as further potential signatures and peculiar properties of this type of dark matter candidate. This paradigm therefore leads to a subtle connection between quantum gravity, the physics of primordial inflation, and the nature of dark matter.

The diphoton resonance as a gravity mediator of dark matter

We consider the possibility of interpreting the recently reported diphoton excess at 750 GeV as a spin-two massive particle (such as a Kaluza-Klein graviton in warped extra-dimensions) which serves as a mediator to Dark Matter via its gravitational couplings to the dark sector and to the Standard Model (SM). We model non-universal couplings of the resonance to gauge bosons in the SM and to Dark Matter as a function on their localization in the extra dimension. We find that scalar, fermion or vector dark matter can saturate the dark matter relic density by the annihilation of dark matter into a pair of the SM particles or heavy resonances, in agreement with the diphoton resonance signal strength. We check the compatibility of our hypothesis with other searches for the KK graviton. We show that the invisible decay rate of the resonance into a pair of dark matter is subdominant in the region of the correct relic density, hence leading to no constraints from the mono-jet bound at 8 TeV via the gluon coupling. We also discuss the kinematic features of the decay products of a KK graviton to distinguish the KK graviton from the SM backgrounds or a scalar particle interpretation of the diphoton resonance.

The structure of f(R)-brane model

Recently, a family of interesting analytical brane solutions were found in $f(R)$ gravity with $f(R)=R+\alpha R^2$ in Ref. [Phys. Lett. B 729, 127 (2014)]. In these solutions, inner brane structure can be turned on by tuning the value of the parameter $\alpha$. In this paper, we investigate how the parameter $\alpha$ affects the localization and the quasilocalization of the tensorial gravitons around these solutions. It is found that, in a range of $\alpha$, despite the brane has an inner structure, there is no graviton resonance. However, in some other regions of the parameter space, although the brane has no internal structure, the effective potential for the graviton KK modes has a singular structure, and there exists a series of graviton resonant modes. The contribution of the massive graviton KK modes to the Newton's law of gravity is discussed shortly.

Tensor perturbations of Palatinif(R)branes

We investigate the thick brane model in Palatini $f(\mathcal{R})$ gravity. The brane is generated by a real scalar field with a scalar potential. We solve the system analytically and obtain a series of thick brane solutions for the $f(\mathcal{R})=\mathcal{R}+\alpha \mathcal{R}^2$-brane model. It is shown that tensor perturbations of the metric are stable for $df({\mathcal{R}})/d{\mathcal{R}}>0$. For nonconstant curvature solutions, the graviton zero mode can be localized on the brane, which indicates that the four-dimensional gravity can be recovered on the brane. Mass spectrum of graviton KK modes and their corrections to the Newtonian potential are also discussed.

Constraints on Randall-Sundrum model from the events of dijet production with QCD next-to-leading order accuracy at the LHC

We study the dijet production in Randall-Sundrum model at the LHC with QCD next-to-leading(NLO) order accuracy. Our results show that the QCD NLO corrections can increase the total cross sections by more than $80\%$ and reduce the scale dependence. We also explore in detail several important kinematic distributions at the NLO level. Moreover, we discuss the upper limits of the KK graviton excluded mass range and the allowed parameter space for the coupling constant and KK graviton mass, using the experiment data.

Stability and (quasi)localization of gravitational fluctuations in an Eddington-inspired Born-Infeld brane system

The stability and localization of the gravitational perturbations for a special brane system in Eddington-inspired Born-Infeld gravity were studied in Liu et al. [Phys. Rev. D 85, 124053 (2012)]. In this paper, we show that the gravitational perturbations for a general brane system are stable, the four-dimensional graviton (massless KK graviton) can be localized on the brane, and the mass spectra of massive KK gravitons are gapless and continuous. Two models are constructed as examples. In the first model, which is a generalization of Liu et al. [Phys. Rev. D 85, 124053 (2012)], the brane has no inner structure and there is no gravitational resonance (quasilocalized KK gravitons). In the second one, the background scalar field is a double kink when the parameter in the model approaches its critical value. Correspondingly, the brane has inner structure and some gravitational resonances appear.

Higher curvature gravity at the LHC

We investigate brane-world models in different viable $F(R)$ gravity theories where the Lagrangian is an arbitrary function of the curvature scalar. Deriving the warped metric for this model, resembling Randal-Sundrum (RS)-like solutions, we determine the graviton KK modes. The recent observations at the LHC, which constrain the RS graviton KK modes to a mass range greater than 3 TeV, are incompatible with RS model predictions. It is shown that the models with $F(R)$ gravity in the bulk address the issue, which in turn constrains the $F(R)$ model itself.

Gravity-mediated (or composite) Dark Matter confronts astrophysical data

We consider the astrophysical bounds on a new form of dark matter, the so called Gravity-mediated Dark Matter. In this scenario, dark matter communicates with us through a mediator sector composed of gravitational resonances, namely a new scalar (radion) and a massive spin-two resonance (massive graviton). We consider specific models motivated by natural electroweak symmetry breaking or weak-scale dark matter in the context of models in warped extra-dimensions and their composite duals. The main Dark Matter annihilation mechanism is due to the interactions of KK gravitons to gauge bosons that propagate in bulk. We impose the bounds on monochromatic or continuum photons from Fermi-LAT and HESS. We also explore scenarios in which the Fermi gamma-ray line could be a manifestation of Gravity-mediated Dark Matter.

Anomalous gauge couplings from composite Higgs and warped extra dimensions

We examine trilinear and quartic anomalous gauge couplings (AGCs) generated in composite Higgs models and models with warped extra dimensions. We first revisit the SU(2)_L x U(1)_Y effective Lagrangian and derive the charged and two-photon neutral AGCs. We derive the general perturbative contributions to the pure field-strength operators from spin 0, 1/2, 1 resonances by means of the heat kernel method. In the composite Higgs framework, we derive the pattern of expected deviations from typical SO(N) embeddings of the light composite top partner. We then study a generic warped extra dimension framework with AdS_5 background, recasting in few parameters the features of models relevant for AGCs. We also present a detailed study of the latest bounds from electroweak and Higgs precision observables, with and without brane kinetic terms. For vanishing brane kinetic terms, we find that the S and T parameters exclude KK gauge modes of the RS custodial [non-custodial] scenario below 7.7 [14.7] TeV, for a brane Higgs and below 6.6 [8.1] TeV for a Pseudo Nambu-Goldstone Higgs, at 95% CL. These constraints can be relaxed in presence of brane kinetic terms. The leading AGCs are probing the KK gravitons and the KK modes of bulk gauge fields in parts of the parameter space. In these scenarios, the future CMS and ATLAS forward proton detectors could be sensitive to the effect of KK gravitons in the multi-TeV mass range.

Scale-invariant resonance tagging in multijet events and new physics in Higgs pair production

Abstract We study resonant pair production of heavy particles in fully hadronic final states by means of jet substructure techniques. We propose a new resonance tagging strategy that smoothly interpolates between the highly boosted and fully resolved regimes, leading to uniform signal efficiencies and background rejection rates across a broad range of masses. Our method makes it possible to efficiently replace independent experimental searches, based on different final state topologies, with a single common analysis. As a case study, we apply our technique to pair production of Higgs bosons decaying into $ b\overline{b} $ pairs in generic New Physics scenarios. We adopt as benchmark models radion and massive KK graviton production in warped extra dimensions. We find that despite the overwhelming QCD background, the 4b final state has enough sensitivity to provide a complementary handle in searches for enhanced Higgs pair production at the LHC.

Top quark phenomenology of the Arkani-Hamed–Dimopoulos–Dvali model and the minimal length scenario

We study top-(anti)quark pair production at the Tevatron and Large Hadron Collider (LHC) in the context of the Minimal Length Scenario (MLS) of the Arkani-Hamed, Dimopoulos and Dvali (ADD) model of extra dimensions (XDs). We show that sizable effects onto both the integrated and differential cross section due to graviton mediation are expected for a String scale, M_S, of O(1-10TeV) and several XDs, \delta, all compatible with current experimental constraints. Potential limits on M_S are extracted. We also highlight clear phenomenological differences between a simple ADD scenario and its modification based on using the MLS as a natural regulator for divergent amplitudes of virtual KK graviton exchange.

KK gravitons and unitarity violation in the Randall–Sundrum model

We show that perturbative unitarity for W L + W L − → W L + W L − scattering places significant constraints on the Randall–Sundrum theory with two 3-branes, with matter confined to the TeV brane. The exchange of massive 4D Kaluza–Klein gravitons leads to amplitudes growing linearly with the CM energy squared. Summing over KK gravitons up to a scale Λ ¯ and testing unitarity at s = Λ ¯ , one finds that unitarity is violated for Λ ¯ below the ‘naive dimensional analysis’ scale, Λ NDA . We evaluate Λ ¯ as a function of the curvature ratio m 0 / m Pl for the pure gravity theory. We then demonstrate that unitarity need not be violated at Λ ¯ in the presence of a heavy Higgs boson. In fact, much larger Higgs masses are consistent with unitarity than if no KK gravitons are present. Observation of the mass and width (or cross section) of one or more KK gravitons at the LHC will directly determine m 0 / m Pl and the scale Λ ˆ W specifying the couplings of matter to the KK gravitons. With this information in hand and a measurement of the Higgs boson mass, one can determine the precise scale Λ ¯ below which unitarity will remain valid.