Nonsaturation of the J/psi suppression at large transverse energy in the comovers approach

We explore the phenomenology of the localized gravity model of Randall and Sundrum where a 5-dimensional nonfactorizable geometry generates the gauge hierarchy by an exponential function called a warp factor. The Kaluza-Klein (KK) tower of gravitons in this scenario has different properties from those in factorizable models. We derive the KK graviton interactions with the standard model fields and obtain constraints from their direct production at hadron colliders as well as from virtual KK exchanges. We study the KK spectrum in e(+)e(-) annihilation and show how to determine the model parameters if the first KK state is observed.     

Stringent neutron-star limits on large extra dimensions

Supernovae (SNe) are copious sources for Kaluza-Klein (KK) gravitons which are generic for theories with large extra dimensions. These massive particles are produced with average velocities approximately 0.5c so that many of them are gravitationally retained by the SN core. Every neutron star thus has a halo of KK gravitons which decay into nu(nu), e(+)e(-), and gammagamma on time scales approximately 10(9) years. The EGRET gamma-flux limits (E(gamma) approximately 100 MeV) for nearby neutron stars constrain the compactification scale for n = 2 extra dimensions to M > or = 500 TeV, and M > or = 30 TeV for n = 3. The requirement that neutron stars are not excessively heated by KK decays implies M > or = 1700 TeV for n = 2, and M > or = 60 TeV for n = 3.     

Dynamical casimir effect in braneworlds

In braneworld cosmology the expanding Universe is realized as a brane moving through a warped higher-dimensional spacetime. Like a moving mirror causes the creation of photons out of vacuum fluctuations, a moving brane leads to graviton production. We show that, very generically, Kaluza-Klein (KK) particles scale like stiff matter with the expansion of the Universe and can therefore not represent the dark matter in a warped braneworld. We present results for the production of massless and KK gravitons for bouncing branes in five-dimensional anti-de Sitter space. We find that for a realistic bounce the back reaction from the generated gravitons will be most likely relevant. This Letter summarizes the main results and conclusions from numerical simulations which are presented in detail in a long paper [M. Ruser and R. Durrer, arXiv:0704.0790].     

Universal torsion-induced interaction from large extra dimensions

We consider the Kaluza-Klein (KK) scenario in which only gravity exists in the bulk. Without the assumption of symmetric connection, the presence of brane fermions induces torsion. The result is a universal axial contact interaction that dominates those induced by KK gravitons. This enhancement arises from a large spin density on the brane. Using a global fit to Z-pole observables, we find the 3sigma bound on the scale of quantum gravity to be 28 TeV for n = 2. If Dirac or light sterile neutrinos are present, the data from SN1987A increase the bound to sqrt[n] M(S)>/=210 TeV.     

Effective contact interactions in a stabilized RS1 brane world model

We consider the effective Lagrangian due to the exchange of heavy Kaluza-Klein (KK) tensor graviton and scalar radion states in a stabilized Randall-Sundrum model (RS1) and compute explicitly the corresponding effective coupling constants. The Drell-Yan lepton pair production at the Tevatron and the LHC is analyzed in two situations, when the first KK resonance is too heavy to be directly detected at the colliders, and when the first KK resonance is visible but other states are still too heavy. In the first case the effective Lagrangian reduces to a contact interaction of Standard Model (SM) particles, whereas in the second case it includes a coupling of SM particles to the first KK mode and a contact interaction due to the exchange of all the heavier modes. It is shown that in both cases the contribution from the invisible KK tower leads to a modification of final particles distributions. In particular, for the second case a nontrivial interference between the first KK mode and the rest KK tower takes place. Expected 95% C.L. limits for model parameters for the Tevatron and the LHC are given. The numerical results are obtained by means of the CompHEP code, in which all new effective interactions are implemented providing a tool for simulation of corresponding events and a more detailed analysis.     

Cosmic Acceleration in a Model of Interacting Massive Gravitons Dark Energy

We propose an alternative understanding of gravity, resulting from the extension of N. Wu’s gauge theory of gravity with massive gravitons, which are minimally coupled to massless gravitons. Based on this, we derive the equations of state for massive gravitons. We study the dynamics of these massive gravitons in a flat, homogeneous and isotropic Friedmann-Robertson-Walker (FRW) universe. We calculate the critical points of the massive graviton dark energy interacting with background perfect fluid. These calculations may have crucial implications for the massive gravitons and dark energy theories. They could, therefore, have important repercussions for current cosmological problems.     

Some speculations on a causal unification of relativity,gravitation, and quantum mechanics

Some speculations on a causal model that could provide a common conceptual foundation for relativity, gravitation, and quantum mechanics are presented. The present approach is a unification of three theories, the first being the repulsive theory of gravitational forces first proposed by Lesage in the eighteenth century. Lesage attempted to explain gravitational forces from the principle of conservation of momentum of some hypothetical particles, which we shall call gravitons. These gravitons, whose density is assumed homogenous, are constantly colliding with objects. The gravitational force is caused by a shielding effect of bodies when they are near each other. One also can make a clear physical distinction between an accelerating and a nonaccelerating object from this viewpoint. The second of these theories is the Brownian motion theory of quantum mechanics or stochastic mechanics, which treats the nondeterministic nature of quantum mechanics as being due to a Brownian motion of all objects. This Brownian motion being caused by the statistical variation in the graviton flux. The above two theories are unified in this article with the causal theory of special relativity. Within the present context, the time dilations (and other effects) of relativity are explained by assuming that the rate of a clock is a function of the total number or intensity of gravitons and the average frequency or energy of the gravitons that the clock receives. Two clocks having some relative velocity in the same intensity gravitational field would then have a different rate because the average frequency of the gravitons would be different for each clock owing to the Doppler effect. That is, they would essentially be in different fields considering both the frequency and intensity. The special theory would then be the special case of the general theory where the intensity is constant but the average frequency varies. In all the previous it is necessary to assume a particular model of the creation of the universe, namely the Big Bang theory. This assumption gives us the existence of a preferred reference frame, the frame in which the Big Bang explosion was at rest. The above concepts of graviton distribution and real time dilations become meaningful by assuming the Big Bang theory along with this preferred frame. An experimental test is proposed.     

Search for universal extra dimensions in pp collisions

We present a search for Kaluza-Klein (KK) particles predicted by models with universal extra dimensions (UED) using a data set corresponding to an integrated luminosity of 7.3 fb(-1), collected by the D0 detector at a pp center-of-mass energy of 1.96 TeV. The decay chain of KK particles can lead to a final state with two muons of the same charge. This signature is used to set a lower limit on the compactification scale of R(-1)>260 GeV in a minimal UED model.     

Analysis of large angle p-d elastic scattering: 100–400 MeV

An analysis is presented of large angle proton-deuteron elastic scattering experiments at deuteron energies of 291, 362 and 433 MeV and proton energies of 140 and 316 MeVon the basis of the Kerman-Kisslinger (KK) model (first order). Further analysis is made using the KK model with second order corrections included. The object of the analysis is to determine quantitatively the sensitivity of large angle scattering to the D-state probability (P_D) in the deuteron. It is found that the KK model (first order and also second order corrections included) is not very successful in fitting the data at those energies when used with existing wavefunctions obtained from phenomenological potentials. A value of 6.7% for P_D gives the best fit when the model is used with the modified Moravcsik analytic fit to the Gartenhaus S-state wavefunction (the third approximation). The incoherent contributions of first and second order non-exchange processes are roughly estimated and found to be negligible. An investigation of the ambiguities in the S-state part of the deuteron wavefunction is also presented.     

Constraints on large-extra-dimensions model through 125 GeV Higgs pair production at the LHC

Based on the analysis of 5?fb^?1 of data at the LHC, the ATLAS and CMS collaborations have presented evidence for a Higgs boson with a mass in the 125 GeV range. We consider the 125 GeV neutral Higgs pair production process in the context of large-extra-dimensions (LED) model including the Kaluza?CKlein (KK) excited gravitons at the LHC. We consider the standard model (SM) Higgs pair production in gluon?Cgluon fusion channel and pure LED effects through graviton exchange as well as their interferences. It is shown that such interferences should be included; the LED model raises the transverse momentum (P _t ) and invariant mass (M _HH ) distributions at high scales of P _t and M _HH of the Higgs pair production. By using the Higgs pair production we could set the discovery limit on the cutoff scale M _S up to 6 TeV for ??=2 and 4.5 TeV for ??=6.     

Graviton-photon interaction

Amplitudes of photon-graviton scattering and the crossing process (annihilation of two photons into two gravitons and the reverse) are calculated. It is shown that the amplitudes are gradient invariant. It is also determined that upon scattering at any angle the spirality of photons and ravitons remains unchanged, and annihilation is possible only with identical spirality of photons (gravitons). The dependence of differential section on scattering angle is analyzed.     

Chiral vacuum fluctuations in quantum gravity

We examine tensor perturbations around a de?Sitter background within the framework of Ashtekar's variables and its cousins parameterized by the Immirzi parameter γ. At the classical level we recover standard cosmological perturbation theory, with illuminating insights. Quantization leads to real novelties. In the low energy limit we find a second quantized theory of gravitons which displays different vacuum fluctuations for right and left gravitons. Nonetheless right and left gravitons have the same (positive) energies, resolving a number of paradoxes suggested in the literature. The right-left asymmetry of the vacuum fluctuations depends on γ and the ordering of the Hamiltonian constraint, and it would leave a distinctive imprint in the polarization of the cosmic microwave background, thus opening quantum gravity to observational test.     

Gravitons from anomalous decay

The decay rate of the neutral pion into two gravitons is calculated from the gravitational anomaly in the axial current. Although this decay rate is negligible relative to the decay rate of the neutral pion into two photons, the rate of decay into gravitons is proportional to the seventh power of the mass of the decaying particle, and to the square of the gravitational constant. The possibility that a particle of very large mass, associated with an axial current anomaly, was present in the early universe is considered. Such a particle would decay at a significant rate into gravitons. As these gravitons would not be thermaiized, they would result in a (potentially observable) nonthermal spectrum of gravitational waves present today. The peak frequency of this gravitational wave spectrum would be indicative of the mass of the decaying particle. Alternatively, if the gravitational constant were large at early times, then the gravitational decay of the pion would be significant in the early universe, giving rise to a nonthermal gravitational wave spectrum.     

Holographic dual of de Sitter universe with AdS bubbles

We study the proposal that a de Sitter (dS) universe with an Anti-de Sitter (AdS) bubble can be replaced by a dS universe with a boundary CFT. To explore this duality, we consider incident gravitons coming from the dS universe through the bubble wall into the AdS bubble in the original picture. In the dual picture, this process has to be identified with the absorption of gravitons by CFT matter. We have obtained a general formula for the absorption probability in general d+1 spacetime dimensions. The result shows the different behavior depending on whether spacetime dimensions are even or odd. We find that the absorption process of gravitons from the dS universe by CFT matter is controlled by localized gravitons (massive bound state modes in the Kaluza-Klein decomposition) in the dS universe. The absorption probability is determined by the effective degrees of freedom of the CFT matter and the effective gravitational coupling constant which encodes information of localized gravitons. We speculate that the dual of (d+1)-dimensional dS universe with an AdS bubble is also dual to a d-dimensional dS universe with CFT matter.     

Finite-bandwidth Kramers-Kronig relations for acoustic group velocity and attenuation derivative applied to encapsulated microbubble suspensions

Kramers-Kronig (KK) analyses of experimental data are complicated by the conflict between the inherently bandlimited data and the requirement of KK integrals for a complete infinite spectrum of input information. For data exhibiting localized extrema, KK relations can provide accurate transforms over finite bandwidths due to the local-weighting properties of the KK kernel. Recently, acoustic KK relations have been derived for the determination of the group velocity (cg) and the derivative of the attenuation coefficient (alpha') (components of the derivative of the acoustic complex wave number). These relations are applicable to bandlimited data exhibiting resonant features without extrapolation or unmeasured parameters. In contrast to twice-subtracted finite-bandwidth KK predictions for phase velocity and attenuation coefficient (components of the undifferentiated wave number), these more recently derived relations for cg and alpha' provide stricter tests of causal consistency because the resulting shapes are invariant with respect to subtraction constants. The integrals in these relations can be formulated so that they only require the phase velocity and attenuation coefficient data without differentiation. Using experimental data from suspensions of encapsulated microbubbles, the finite-bandwidth KK predictions for cg and alpha' are found to provide an accurate mapping of the primary wave number quantities onto their derivatives.     

Search for dilepton resonances in pp collisions at √s=7 TeV with the ATLAS detector

This Letter reports on a search for narrow high-mass resonances decaying into dilepton final states. The data were recorded by the ATLAS experiment in pp collisions at √s=7 TeV at the Large Hadron Collider and correspond to a total integrated luminosity of 1.08 (1.21) fb(-1) in the e(+)e(-) (μ(+)μ(-)) channel. No statistically significant excess above the standard model expectation is observed and upper limits are set at the 95% C.L. on the cross section times branching fraction of Z' resonances and Randall-Sundrum gravitons decaying into dileptons as a function of the resonance mass. A lower mass limit of 1.83 TeV on the sequential standard model Z' boson is set. A Randall-Sundrum graviton with coupling k/M(Pl)=0.1 is excluded at 95% C.L. for masses below 1.63 TeV.     

Probing universal extra dimension at the international linear collider

We consider the UED scenario and study the detectability of the first KK electron-positron pair at the ILC. A few hundred GeV KK electron decays into a nearly degenerate KK photon, which carries away missing energy, and the standard electron. The mass splitting between the KK electron and KK photon is controlled by the bulk-and brane-induced radiative corrections. We look for the signal event e ⁺ e ⁻ + large missing energy for √s = 1 TeV and observe that with a few hundred fb⁻¹ luminosity the signal can be deciphered from the standard model background. We briefly outline how the UED signals may be distinguished from the supersymmetric signals. This talk is based on a work the author did with Paramita Dey, Anirban Kundu and Amitava Raychaudhuri [1].     

Efficient coannihilation process through strong Higgs self-coupling in LKP dark matter annihilation

We point out that the lightest Kaluza–Klein particle (LKP) dark matter in universal extra dimension (UED) models efficiently annihilates through the coannihilation process including the first KK Higgs bosons when the Higgs mass is slightly heavy as 200–230 GeV, which gives the large Higgs self-coupling. The large self-coupling naturally leads the mass degeneracy between the LKP and the first KK Higgs bosons and large annihilation cross sections of the KK Higgs bosons. These are essential for the enhancement of the annihilation of the LKP dark matter, which allows large compactification scale ∼1 TeV to be consistent with cosmological observations for the relic abundance of dark matter. We found that the thermal relic abundance of the LKP dark matter could be reconciled with the stringent constraint of electroweak precision measurements in the minimal UED model.     

Completing Lorentz violating massive gravity at high energies

Journal of Experimental and Theoretical Physics - Theories with massive gravitons are interesting for a variety of physical applications, ranging from cosmological phenomena to holographic modeling...