In large extra dimensional Kaluza-Klein (KK) scenario, where the usual Standard Model (SM) matter is confined to a 3+1-dimensional hypersurface called the 3-brane and gravity can propagate to the bulk (D=4+d, d being the number of extra spatial dimensions), the light graviton KK modes can be produced inside the supernova core due to the usual nucleon-nucleon bremstrahlung, electron-positron and photon-photon annihilations. This photon inside the supernova becomes plasmon due to the plasma effect. In this paper, we study the energy-loss rate of SN 1987A due to the KK gravitons produced from the plasmon-plasmon annihilation. We find that the SN 1987A cooling rate leads to the conservative bound $M\_D$ > 22.9 TeV and 1.38 TeV for the case of two and three space-like extra dimensions.
We show that the LHC will be able to differentiate between a four-dimensional model with quantum gravity at ~1 TeV where the (massless) graviton becomes strongly coupled to standard model particles at 1 TeV and brane world type models with a large extra-dimensional volume and massive Kaluza-Klein gravitons. We estimate that the 14 TeV LHC could put a limit of the order of ~5 TeV on the four dimensional Planck mass in a model independent way.
We review the capability of $e^+e^-$ and $e^-e^-$ colliders to detect the virtual exchange of Kaluza-Klein towers of gravitons within the large extra dimension scenario of Arkani-Hamed, Dimopoulos and Dvali and in the localized gravity model of Randall and Sundrum with non-factorizable geometry.
We consider the production of gravitons via two photon fusion in Kaluza-Klein theories which allow TeV scale gravitational interactions. We find that the processes l+ l- to l+ l- + graviton, with l=electron or muon can put quite stringent bounds on such theories. For example, with two extra dimensions at the Next Linear Collider with a center of mass energy of 500 (1000) GeV attainable bounds on the scale of the gravitational interactions can reach about 6 (9) TeV.
We study Drell-Yan production at the LHC in low-scale quantum gravity models with extra dimensions. Asymptotic safety implies that the ultra-violet behavior of gravity is dictated by a fixed point. We show how the energy dependence of Newton's coupling regularizes the gravitational amplitude using a renormalization group improvement. We study LHC predictions and find that Kaluza-Klein graviton signals are well above Standard Model backgrounds. This leaves a significant sensitivity to the energy scale Lambda_T where the gravitational couplings cross over from classical to fixed point scaling.
We study the single graviton production at the CERN LHC using the $k_T$-factorization approach of QCD. We consider the Arkani-Hamed-Dimopoulos-Dvali scenario and Randall-Sundrum model with one warped extra-dimension and derive the production amplitudes for spin-$2$ (Kaluza-Klein excitation of the graviton) and spin-$0$ (radion) states, including subsequent graviton decay into the dilepton or diphoton pairs. We use the transverse momentum dependent (unintegrated) parton densities in a proton obtained from Ciafaloni-Catani-Fiorani-Marchesini (CCFM) evolution equation, which resums the leading lo…
We study linearized graviton in the presence of a four-dimensional cosmological constant in two brane models with a warped extra dimension. In explicit models including bulk scalar fields, we calculate the masses of Kaluza-Klein modes of graviton and their interactions with matter on the visible brane. It is shown that the effects of the cosmological constant contribute by the equivalent size to the warp factor, masses and couplings and that bulk scalar fields can increase the effects. This is examined further independently of the forms of scalar potentials. Then it is found how the masses and…
In the large extra dimensional ADD scenario, Z bosons undergo a one-loop decay into a photon and Kaluza-Klein towers of gravitons/gravi-scalars. We calculate such a decay width, extending previous arguments about the general form of the four-dimensional on-shell amplitude. The amplitudes calculated are relevant to processes in other extra dimensional models where the Standard Model fields are confined to a 4-brane.
We consider the production of gravitons via two photon and electron-photon fusion in Kaluza-Klein theories which allow TeV scale gravitational interactions. We show that at electron-positron colliders, the processes l+l- -> l+ l- graviton, with l=e, mu, can lead to a new signal of low energy gravity of the form l+l- -> l+l- + missing energy which is well above the Standard Model background. For example, with two extra dimensions at the Next Linear Collider with a center of mass energy of 500 or 1000 GeV, hundreds to thousands such l+ l- graviton events may be produced if the scale of the gravi…
An experimental search for signatures of Kaluza-Klein graviton states at the 500 GeV e+e- linear collider, in which the graviton states are produced in association with a photon, is presented. The study of the signal extraction is performed with the help of Monte Carlo simulations
The Standard Model problems lead to the new theories of extra dimensions: Randall-Sundrum model, Arkani-Hamed-Dimopoulos-Dvali model and TeV$^{-1}$ model. In the framework of these models with the help of computer program Pythia8.2 were calculated the production cross sections for Kaluza-Klein particles at various energies at the LHC. The generation of monojet events from scalar graviton emission was considered for number of extra dimensions, n=2, 4, 6, for the energy at the LHC 14 TeV. Also are studied the graviton production processes through the gluon-gluon, quark-gluon and quark-quark fusi…
Interaction of bulk gravitons to Standard Model particles is examined in the scenario of warped extra dimension. It is found that the length of the extra dimension is of physical importance as it determines the decay widths of graviton Kaluza-Klein modes. We show that cosmology as well as collider signals of the Kaluza-Klein modes are very different for different choices of the length of the fifth dimension.
We consider the phenomenology of the decay of a Z boson into a photon and a Kaluza-Klein excitation of the graviton in the ADD model. Using LEP data, we obtain an upper bound on the branching ratio corresponding to this process of ~10^-11. We also investigate energy profiles of the process.
We consider a generalised two brane Randall Sundrum model where the branes are endowed with non-zero cosmological constant. In this scenario, we re-examine the modulus stabilisation mechanism and the nature of Kaluza Klein (KK) graviton modes. Our result reveals that while the KK mode graviton masses may change significantly with brane cosmological constant, the Goldberger-Wise stabilisation mechanism, which assumes negligible backreaction on the background metric, continues to hold even when the branes have large cosmological constant. The possibility of having a global minimum for the modulu…
The small curvature option of the Randall-Sundrum model with two branes is considered which has almost continuous spectrum of low-mass Kaluza-Klein gravitons. It is shown that gravity effects related with these excitations can be detected in double diffractive events at the LHC and in inclined air showers induced by interactions of cosmic neutrinos with atmospheric nucleons at ultra-high energies.
We report on a search for direct Kaluza-Klein graviton production in a data sample of 84 ${pb}^{-1}$ of \ppb collisions at $\sqrt{s}$ = 1.8 TeV, recorded by the Collider Detector at Fermilab. We investigate the final state of large missing transverse energy and one or two high energy jets. We compare the data with the predictions from a $3+1+n$-dimensional Kaluza-Klein scenario in which gravity becomes strong at the TeV scale. At 95% confidence level (C.L.) for $n$=2, 4, and 6 we exclude an effective Planck scale below 1.0, 0.77, and 0.71 TeV, respectively.
We review the possibilities that the Kaluza-Klein excitations of graviton states induce electroweak symmetry breaking and that electroweak symmetry breaking could have a large impact on KK phenomenology.
In a supersymmetric large extra dimension scenario, the production of Kaluza-Klein gravitinos accompanied by a photino at e^+ e^- colliders is studied. We assume that a bulk supersymmetry is softly broken on our brane such that the low-energy theory resembles the MSSM. Low energy supersymmetry breaking is further assumed as in GMSB, leading to sub-eV mass shift in each KK mode of the gravitino from the corresponding graviton KK mode. Since the photino decays within a detector due to its sufficiently large inclusive decay rate into a photon and a gravitino, the process e^+ e^- -> photino + grav…
In search of extra dimensions in the ongoing LHC experiments, signatures of Randall-Sundrum (RS) lightest KK graviton have been one of the main focus in recent years. The recent data from the dilepton decay channel at the LHC has determined the experimental lower bound on the mass of the RS lightest Kaluza-Klein (KK) graviton for different choices of underlying parameters of the theory. In this work we explore the effects of the backreaction of the bulk scalar field, which is employed to stabilise the RS model, in modifying the couplings of the lightest KK graviton with the standard model (SM)…
In this paper we study the role of the 5D Gauss-Bonnet corrections and two loop higher genus contribution to the gravity action in type IIB string theory inspired low energy supergravity theory in the light of gravidilatonic interactions on the lightest Kaluza-Klein graviton mass spectrum. From the latest constraints on the lightest Kaluza-Klein graviton mass as obtained from the ATLAS dilepton search in 7 TeV proton-proton collision, we have shown that due to the presence of Gauss-Bonnet and string loop corrections, the warping solution in an ${\bf AdS_{5}}$ bulk is quite distinct from Randal…
It is pointed out in a class of models with large extra dimensions that the cross section of processes with virtual Kaluza-Klein graviton exchanges becomes either much smaller or much larger by many orders of magnitude than what is expected from that of the on-shell production of the Kaluza-Klein gravitons. We demonstrate how the problem arises using a toy model. The cause of this new problem lies in the fact that we do not have momentum conservation in the extra dimensions. To search for the signal of the large extra dimensions with high energy collider experiments, we need more care in inter…
We study the phenomenology of a massive graviton $G$ with non-universal couplings to the Standard Model (SM) particles. Such a particle can arise as a warped Kaluza-Klein graviton from a framework of the Randall-Sundrum extra-dimension model. In particular, we consider a case in which $G$ is top-philic, i.e., $G$ interacts strongly with the right-handed top quark, resulting in the large top-loop contributions to its production via the gluon fusion and its decays to the SM gauge bosons. We take into account the constraints from the current 13 TeV LHC data on the channels of $t\bar{t}$, $γγ$, $j…
Stable particle dark matter may well originate during the decay of long-lived relic particles, as recently extensively examined in the cases of the axino, gravitino, and higher-dimensional Kaluza-Klein (KK) graviton. It is shown that in much of the viable parameter space such dark matter emerges naturally warm/hot or mixed. In particular, decay produced gravitinos (KK-gravitons) may only be considered cold for the mass of the decaying particle in the several TeV range, unless the decaying particle and the dark matter particle are almost degenerate. Such dark matter candidates are thus subject …
We investigate contributions of Kaluza-Klein (KK) graviton in extra dimension models to the process $pp \to pγp \to pγj X$, where a proton emits a quasireal photon and is detected by using the very forward detectors planned at the LHC. In addition to the $γq$ initial state as in the Compton scattering in the standard model, the $γg$ scattering contributes through the $t$-channel exchange of KK gravitons. Taking account of pileup contributions to the background and examining viable kinematical cuts, constraints on the parameter space of both the ADD (Arkani-Hamed, Dimopoulos and Dvali) model an…
A generic prediction of scenarios with extra dimensions accessible in TeV-scale collisions is the existence of Kaluza-Klein excitations of the graviton. For a broad class of strongly-warped scenarios one expects to initially find an isolated resonance, whose phenomenology in the simplest cases is described by a simplified model with two parameters, its mass, and a constant $Λ$ with units of mass parameterizing its coupling to the Standard Model stress tensor. These parameters are in turn determined by the geometrical configuration of the warped compactification. We explore the possibility that…
The best-studied version of the RS1 model has all the Standard Model particles confined to the TeV brane. However, recent variants have the Standard Model fermions and gauge bosons located in the bulk five-dimensional spacetime. We study the potential reach of the LHC in searching for the lightest KK partner of the graviton in the most promising such models in which the right-handed top is localized very near the TeV brane and the light fermions are localized near the Planck brane. We consider both detection and the establishment of the spin-2 nature of the resonance should it be found.
We analyze the structure of scattering amplitudes of the Kaluza-Klein (KK) gravitons and of the KK gravitational Goldstone bosons in the compactified 5d General Relativity (GR). Using a general $R_ξ$ gauge-fixing, we study the geometric Higgs mechanism for the massive spin-2 KK gravitons. We newly propose and prove a Gravitational Equivalence Theorem (GRET) to connect the scattering amplitudes of longitudinal KK gravitons to that of the KK gravitational Goldstone bosons, which formulates the geometric gravitational Higgs mechanism at the scattering $S$-matrix level. We demonstrate that the GRE…
Direct production of Kaluza-Klein states in the TeV range is studied for the experimental environment at the multi-TeV $e^+e^-$ collider CLIC. The sensitivity of such data to model parameters is discussed for the Randall-Sundrum(RS) and TeV scale extra dimensional models.
We explore the possibility that the Kaluza-Klein graviton states induce electroweak symmetry breaking. We also demonstrate that electroweak symmetry breaking could have a large impact on KK phenomenology.
Models with large extra dimensions predict the existence of Kaluza-Klein graviton resonances. We compute the next-to-leading order QCD corrections to graviton plus jet hadro-production, which is an important channel for graviton searches at the Tevatron and the LHC. The QCD corrections are sizable and lead to a significant reduction of the scale dependence. We present numerical results for cross sections and distributions, and discuss the uncertainty from parton distribution functions and the ultraviolet sensitivity of the theoretical prediction.
We study for the first time the case in which Dark Matter (DM) is made of Feebly Interacting Massive Particles (FIMP) interacting just gravitationally with the standard model particles in an extra-dimensional Randall-Sundrum scenario. We assume that both the dark matter and the standard model are localized in the IR-brane and only interact via gravitational mediators, namely the graviton, the Kaluza-Klein gravitons and the radion. We found that in the early Universe DM could be generated via two main processes: the direct freeze-in and the sequential freeze-in. The regions where the observed D…
In extra dimensional models with Kaluza-Klein graviton states that are well separated in mass, such states may be observed as resonances in collider experiments. We extend previous works on such scenarios by considering the one-loop resonant production of a Z boson in association with a photon. We find the production rate to be negligible in conservative scenarios, and sufficiently small for observation to be very difficult even for reasonable luminosity in less conservative scenarios.
Recently, Barger {\em et al.} computed energy losses into Kaluza Klein modes from astrophysical plasmas in the approximation of zero density for the plasmas. We extend their work by considering the effects of finite density for two plasmon processes. Our results show that, for fixed temperature, the energy loss rate per cm$^3$ is constant up to some critical density and then falls exponentially. This is true for transverse and longitudinal plasmons in both the direct and crossed channels over a wide range of temperature and density. A difficulty in deriving the appropriate covariant interactio…
We calculate the tree-level open-string amplitudes for the scattering of four massless particles with diphoton final states. These amplitudes are required to reproduce those of standard model at the tree level in the low energy limit. After low energy stringy corrections, we found that they have similar form to the same processes induced by exchange of the Kaluza-Klein(KK) excitations of graviton in ADD scenario. Using this similarity, we apply constraints on the KK mass scale $M_D$ to the string scale $M_S$. The results are consistent with constraints from the 4-fermion scattering, about $0.6…
We study the structure of scattering amplitudes of the Kaluza-Klein (KK) gravitons and of the gravitational KK Goldstone bosons in the compactified 5d General Relativity (GR). We analyze the geometric "Higgs" mechanism for mass-generation of KK gravitons under compactification with a general $R_ξ$ gauge-fixing, which is free from the vDVZ discontinuity. Then, we formulate the Gravitational Equivalence Theorem (GRET) to connect the longitudinal KK graviton amplitudes to the KK Goldstone amplitudes, which is a manifestation of the geometric Higgs mechanism at $S$-matrix level. We directly comput…
We discuss photon Bremsstrahlung induced by virtual graviton exchange in proton-proton interactions at hadronic colliders, resulting from the exchange of Kaluza-Klein excitations of the graviton. The relevant subprocesses, gg to G to e^+e^-gamma and q barq to e^+e^-gamma are discussed in both the ADD and the RS scenarios. Although two-body final states (or real graviton emission) would presumably be the main discovery channels, a search for three-body final states could be worthwhile since such events have characteristic features that could provide additional confirmation. In particular, the k…
We discuss the physics of Kaluza-Klein excitations of the Standard Model gauge bosons that can be explored by a high energy muon collider in the era after the LHC and TeV Linear Collider. We demonstrate that the muon collider is a necessary ingredient in the unraveling the properties of such states and, perhaps, proving their existence. The possibility of observing the resonances associated with the excited KK graviton states of the Randall-Sundrum model is also discussed.
We study the scattering amplitudes of massive Kaluza-Klein (KK) states of open and closed bosonic strings under toroidal compactification. We analyze the structure of vertex operators for the KK strings and derive an extended massive KLT-like relation which connects the $N$-point KK closed-string amplitude to the products of two KK open-string amplitudes at tree level. Taking the low energy field-theory limit of vanishing Regge slope, we derive double-copy construction formula of the $N$-point massive KK graviton amplitude from the sum of proper products of the corresponding KK gauge boson amp…
The discovery of Kaluza-Klein (KK) gravitons is a smoking gun of extra dimensions. Other scenarios, however, could give rise to spin-two resonances of a new strongly-coupled sector and act as impostors. In this paper we prove that a spin-two resonance does not couple to the Standard Model through dimension-four operators. We then show that the massive graviton and its impostor both couple to the Standard Model through the same dimension-five operators. Therefore the spin determination is identical. Nevertheless, we also show that one can use the ratio of branching ratios to photons and to jets…
We consider the effect of massive spin-2 gravitons that occur as Kaluza-Klein excitations of the graviton in a Weak scale Quantum Gravity scenario on the process $γγ\to ZZ$, which in the Standard Model can proceed through loop diagrams. For a wide range of parameters, we show that the massive gravitons leave behind signatures that should be verifiable in a TeV scale scattering experiment.
We study Kaluza-Klein (KK) graviton production in the large extra dimensions model via 2 jets plus missing transverse momentum signatures at the LHC. We make predictions for both the signal and the dominant Zjj and Wjj backgrounds, where we introduce missing P_T-dependent jet selection cuts that ensure the smallness of the 2-jet rate over the 1-jet rate. With the same jet selection cuts, the distributions of the two jets and their correlation with the missing transverse momentum provide additional evidence for the production of an invisible massive object.
We consider the Newton's force law for brane world consisting of periodic configuration of branes. We show that it supports a massless graviton. Furthermore, this massless mode is well separated from the Kaluza-Klein spectrum by a mass gap. Thus most of the problems in phenomenology coming from continuum of Kaluza-Klein modes without mass gap are potentially cured in such a model.
We compute the contribution of Kaluza-Klein graviton exchange to the cross section for photon-neutrino scattering. Unlike the usual situation where the virtual graviton exchange represents a small correction to a leading order electroweak or strong amplitude, in this case the graviton contribution is of the same order as the electroweak amplitude, or somewhat larger. Inclusion of the graviton contribution is not sufficient to allow high energy neutrinos to scatter from relic neutrinos in processes such as $ν\barν\toγγ$, but the photon-neutrino decoupling temperature is substantially reduced.
We study the process e+- e- -> e+- e- +- missing energy at a high-energy e+- e- collider, where the missing energy arises from the radiation of Kaluza-Klein gravitons in a model with large extra dimensions. It is shown that at a high-energy linear collider, this process can not only confirm the signature of such theories but can also sometimes be comparable in effectiveness to the commonly discussed channel e+- e- -> gamma +- missing energy, especially for a large number of extra dimensions and with polarized beams. We also suggest some ways of distinguishing the signals of a graviton tower fr…
We study the signature of dilepton and a hard jet ($\ell^+\ell^-j$) via heavy new gauge boson production in split universal extra dimension scenario where the Kaluza-Klein parity is conserved but the Kaluza-Klein number is not. A hard cut to the jet energy effectively removes virtually all possible backgrounds and provides a handle to search of new physics involving new neutral heavy states as the Kaluza-Klein $Z$ boson. The signature can be more generically used in search of other new states such as graviton and radion in warped extra dimension models.
We examine the axion model in the large extra dimensions scenario with TeV scale gravity. To obtain an intermediate-scale decay constant of the axion, the axion is assumed to live in a sub-spacetime (brane) of the whole bulk. In this model there appear Kaluza-Klein modes of the axion which have stronger interaction than those of the graviton. The axion brane plays a role of absorber of the graviton Kaluza-Klein modes. We discuss various cosmological constraints as well as astrophysical ones and show that the model is viable for certain choices of the dimensionality of the axion brane. The stru…
We consider the Kaluza-Klein (KK) graviton and its decays in the presence of the light radion, the modulus of extra dimension, appearing naturally light due to classical scale invariance in warped gravity. Due to the presence of a sizable wavefunction overlap in the extra dimension between the KK graviton and the radion, the KK graviton can decay largely into a pair of radions, each of which decays into a pair of collimated photons or photon-jets. Focusing on the setup where the KK graviton has suppressed couplings to the Higgs boson and fermions, we discuss the bounds on the light radion in t…
Tachyonic Kaluza-Klein modes normally appear from the compactification of extra timelike dimensions with scale $L$ and lead to some instabilities of physical systems. We calculate the contribution of tachyonic gravitons to the self energies of spherical massive bodies of radius $R$ and discuss their possible gravitational stability. We find that some spherical bodies can be stable at critical radii $R=2πL p$ for some positive integers $p$. We also prove the generic property of massive bodies that for the range $0<R\leqπL$ the gravitational force due to the ordinary massless graviton exchange i…
We study the feasibility of producing the graviton of the novel Kaluza-Klein theory in which there are d large compact dimensions in addition to the 4 dimensions of Minkowski spacetime. We calculate the cross section for producing such a graviton in nucleus-nucleus collisions via t-channel photon-photon fusion using the semiclassical Weizsacker-Williams method and show that it can exceed the cross section for graviton production in electron-positron scattering by several orders of magnitude.
The existing cosmological constraints on theories with large extra dimensions rely on the thermal production of the Kaluza-Klein modes of gravitons and radions in the early Universe. Successful inflation and reheating, as well as baryogenesis, typically requires the existence of a TeV-scale field in the bulk, most notably the inflaton. The non-thermal production of KK modes with masses of order 100 GeV accompanying the inflaton decay sets the lower bounds on the fundamental scale M_*. For a 1 TeV inflaton, the late decay of these modes distort the successful predictions of Big Bang Nucleosynth…
We present the calculations of the complete next-to-leading order(NLO) QCD corrections to the inclusive total cross sections for the Kaluza-Klein(KK) graviton and photon associated production process $pp \to γG_{KK} + X$ in the large extra dimensions(LED) model at the LHC. We show that the NLO QCD corrections in general enhance the total cross sections and reduce the dependence of the total cross sections on the factorization and renormalization scales. When jet veto is considered, the NLO corrections reduce the total cross sections. We also calculate some important differential cross sections…
A simple axion model is proposed in the scenario of large extra dimensions where gravity scale is as low as 1 TeV. To obtain an intermediate-scale decay constant of the axion, the axion is assumed to live in a sub-spacetime (brane) of the whole bulk. In this model there appear Kaluza-Klein modes of the axion which have stronger interaction than those of the graviton. The axion brane plays a role of absorber of the graviton Kaluza-Klein modes. Because of these reasons phenomenology and cosmology of the axion become highly non-trivial. We discuss various cosmological constraints as well as astro…
If the neutrinos are to be identified with the primary source of ultra-high energy cosmic rays(UHECR), their interaction on relic neutrinos is of great importance in understanding their long intergalactic journey. In theories with large compact dimensions, the exchange of a tower of massive spin-2 gravitons (Kaluza-Klein excitations) gives extra contribution to $ν\barν \longrightarrow f\bar{f}$ and $γγ$ processes along with the opening of a new channel for the neutrinos to annihilate with the relic cosmic neutrino background $ν\barν \longrightarrow G_{kk}$ to produce bulk gravitons in the extr…
