Narrow Results

We consider brane world models with interbrane separation stabilized by the Goldberger–Wise scalar field. For arbitrary background, or vacuum configurations of the gravitational and scalar fields in such models, we construct the second variation Lagrangian, study its gauge invariance, find the corresponding equations of motion and decouple them in a suitable gauge. We also derive an effective four-dimensional Lagrangian for such models, which describes the massless graviton, a tower of massive gravitons and a tower of massive scalars. It is shown that for a special choice of the background solution the masses of the graviton excitations may be of the order of 1 TeV, the radion mass of the order of 100 GeV, the inverse size of the extra dimension being 1 TeV. In this case the coupling of the radion to matter on the negative tension brane is approximately ten times weaker than in the unstabilized model with the same values of the fundamental five-dimensional energy scale and the interbrane distance.

In this note we study scalar and fermion zero modes on the brane arising from two scalar fields. The result is that there exist normalizable massless modes of scalar fields which can be localized on the brane. While, for spin 1/2 and spin 3/2 fermions, the corresponding zero modes are non-normalizable. Thus, some mechanism such as Yukawa coupling should be introduced for the localization of these fermionic fields on the thick brane.

The localization of the spin-3/2 gravitino field on thick branes with a Yukawa coupling is studied in this paper. We show that, for spin-3/2 fermionic field, there exist normalizable zero modes which can be localized on the flat thick branes under certain conditions.

We propose a theoretical scenario to solve the proton radius puzzle which recently arises from the muonic hydrogen experiment. In this framework, (4+n)-dimensional theory is incorporated with modified gravity. The extra gravitational interaction between the proton and muon at very short range provides an energy shift which accounts for the discrepancy between spectroscopic results from muonic and electronic hydrogen experiments. Assuming the modified gravity is a small perturbation to the existing electromagnetic interaction, we find the puzzle can be solved with stringent constraint on the range of the new force. Our result not only provides a possible solution to the proton radius puzzle but also suggests a direction to test new physics at very small length scale.

In this paper, we derive new modes for massive Dirac field in the background of a higher-dimensional Schwarzschild black hole. We use in our approach the Cartesian gauge defined in local frames. We work in the context of Arkani-Hamed, Dimopoulos and Dvali (ADD)-like theories, assuming that the Standard Model fields (fermions and bosons) live only on a (3+1)-dimensional brane and the extra dimensions of space can be large in size.

We examine the possibility of observing the Kaluza–Klein (KK) gluons in gauge-Higgs unification models at the LHC with the energy $\sqrt{s}$=14 TeV. We consider a benchmark model with the gauge symmetry SU(3)${}_C\times$SU(3)_W in five-dimensional spacetime, where SU(3)_C is the gauge symmetry of the strong interaction and SU(3)_W is that for the electroweak interaction and a Higgs doublet field. It is natural in general to introduce SU(3)_C gauge symmetry in five-dimensional spacetime as well as SU(3)_W gauge symmetry in gauge-Higgs unification (GHU) models. Since the fifth dimension is compactified to $S^1/Z_2$ orbifold, there are KK modes of gluons in low-energy effective theory in four-dimensional spacetime. We investigate the resonance contribution of the first KK gluon to dijet invariant mass distribution at the LHC, and provide signal-to-noise ratios in various cases of KK gluon masses and kinematical cuts. Although the results are given in a specific benchmark model, we discuss their application to general GHU models with KK gluons. GHU models can be verified or constrained through the physics of the strong interaction, though they are proposed to solve the naturalness problem in electroweak symmetry breaking.

In models with large extra dimensions, particle collisions with center-of-mass energy larger than the fundamental gravitational scale can generate nonperturbative gravitational objects such as black holes and branes. The formation and the subsequent decay of these super-Planckian objects would be detectable in particle colliders and high energy cosmic ray detectors, and have interesting implications in cosmology and astrophysics. In this paper we present a review of black hole and brane production in TeV-scale gravity.

We start by reviewing the existing literature on the creation of black holes during high-energy particle collisions, both in the absence and in the presence of extra, compact, spacelike dimensions. Then, we discuss in detail the properties of the produced higher-dimensional black holes, namely the horizon radius, temperature and life-time, as well as the physics that governs the evaporation of these objects, through the emission of Hawking radiation. We first study the emission of visible Hawking radiation on the brane: we derive a master equation for the propagation of fields with arbitrary spin in the induced-on-the-brane black hole background, and we review all existing results in the literature for the emission of scalars, fermions and gauge bosons during the spin-down and Schwarzschild phases of the life of the black hole. Both analytical and numerical results for the graybody factors and radiation spectra are reviewed and exact results for the number and type of fields emitted on the brane as a function of the dimensionality of space–time are discussed. We finally study the emission of Hawking radiation in the bulk: graybody factors and radiation spectra are presented for the emission of scalar modes, and the ratio of the missing energy over the visible one is calculated for different values of the number of extra dimensions.

A semiclassical picture of black hole production in trans-Planckian collisions is reviewed.

We give a brief introduction to the recent idea of Large eXtra Dimensions (LXDs). We give a motivation for the existence of a minimal length scale and show how to incorporate it into quantum theory. We derive first order corrections to high precision measurements such as transition frequencies in He⁺ and the muon gyromagnetic moment. The results clearly show that effects due to a minimal length have to be considered in models with LXDs.

Bekenstein–Hawking formalism of black hole thermodynamics should be modified to incorporate quantum gravitational effects. Generalized Uncertainty Principle (GUP) provides a suitable framework to perform such modifications. In this paper, we consider a general form of GUP to find black hole thermodynamics in a model universe with large extra dimensions. We will show that black holes radiate mainly in the four-dimensional brane. Existence of black holes remnants as a possible candidate for dark matter is discussed.

We study fermionic zero modes in the self-dual vortex background on an extra two-dimensional Riemann surface in 5+1 dimensions. Using the generalized Abelian Higgs model, we obtain the inner topological structure of the self-dual vortex and establish the exact self-duality equation with topological term. Then we analyze the Dirac operator on an extra sphere and the effective Lagrangian of four-dimensional fermions with the self-dual vortex background. Solving the Dirac equation, the fermionic zero modes on a sphere in two simple cases are obtained.

We present a model describing a single brane with tension embedded into a five-dimensional space–time with compact extra dimension, which can be easily stabilized. We examine the linearized gravity in the model and obtain an expression for the four-dimensional Planck mass on the brane in terms of the model parameters. It is also shown that the scalar sector of the effective four-dimensional theory contains a tachyonic mode, and we discuss the problem of stability of the model.

The framework of large extra dimensions provides a way to explain why gravity is weaker than the other forces in nature. A consequence of this model is the possible production of D-dimensional black holes in high energy p–p collisions at the Large Hadron Collider. The present work uses the CATFISH black hole generator to study quantitatively how these events could be observed in the hadronic channel at midrapidity using a particle-tracking detector.

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 interpreting the earlier results on the cross-sections of these processes.

The charged black hole thermodynamics is corrected in terms of the quantum gravity effects. Most of the quantum gravity theories support the idea that near the Planck scale, the standard Heisenberg uncertainty principle should be reformulated by the so-called Generalized Uncertainty Principle (GUP) which provides a perturbation framework to perform required modifications of the black hole quantities. In this paper, we consider the effects of the minimal length and maximal momentum as GUP type I and the minimal length, minimal momentum and maximal momentum as GUP type II on thermo dynamics of the charged TeV-scale black holes. We also generalized our study to the universe with the extra dimensions based on the ADD model. In this framework, the effect of the electrical charge on thermodynamics of the black hole and existence of the charged black hole remnants as a potential candidate for the dark matter particles are discussed.

The Generalized Uncertainty Principle (GUP) implies the existence of a physical minimum length scale $l_m$. In this scenario, black holes must have a radius larger than $l_m$. They are hotter and evaporate faster than in standard Hawking thermodynamics. We study the effects of the GUP on black hole production and decay at the LHC in models with large extra dimensions. Lower bounds on the fundamental Planck scale and the minimum black hole mass at formation are determined from black hole production cross-section limits by the CMS Collaboration. The existence of a minimum length generally decreases the lower bounds on the fundamental Planck scale obtained in the absence of a minimum length.

In this paper, we propose to compactify a single Large Extra Dimension (LED) on a star/rose graph with a large number of identical leaves/petals. The 5D Planck scale can be chosen to be ${\mathrm{\Lambda }}_P^{(5)}\sim {𝒪}(1)$ TeV which can provide a path to solve the gauge hierarchy problem. The leaf/petal length scale is of ${𝒪}(1/{\mathrm{\Lambda }}_{\mathrm{\text{EW}}})$, where ${\mathrm{\Lambda }}_{\mathrm{\text{EW}}}\sim 100$ GeV is the weak scale, without the large geometrical hierarchy of the traditional LED models to stabilize. The 4D fields of the SM are localized on a 3-brane at the central vertex of the star/rose graph. We predict a tower of feebly coupled weak scale Kaluza–Klein (KK) gravitons below a regime of strongly coupled gravitational phenomena above the TeV scale. Moreover, we reformulate in our setup the LED mechanism to generate light Dirac neutrinos, where the right-handed neutrinos are KK-modes of gauge singlet fermions propagating in the bulk. A large number of KK-gravitons and KK-neutrinos interact only gravitationally and thus constitute a hidden sector.

The analyticity properties of the scattering amplitude for a massive scalar field are reviewed in this paper where the space–time geometry is $R^{3,1}\otimes S^1$, i.e. one spatial dimension is compact. Khuri investigated the analyticity of scattering amplitude in a nonrelativistic potential model in three dimensions with an additional compact dimension. He showed that under certain circumstances, the forward amplitude is nonanalytic. He argued that in high energy scattering if such a behavior persists it would be in conflicts with the established results of quantum field theory and LHC might observe such behaviors. We envisage a real scalar massive field in flat Minkowski space–time in five dimensions. The Kaluza–Klein (KK) compactification is implemented on a circle. The resulting four-dimensional manifold is $R^{3,1}\otimes S^1$. The LSZ formalism is adopted to study the analyticity of the scattering amplitude. The nonforward dispersion relation is proved. In addition the Jin–Martin bound and an analog of the Froissart–Martin bound are proved. A novel proposal is presented to look for evidence of the large-radius-compactification scenario. A seemingly violation of Froissart–Martin bound at LHC energy might hint that an extra dimension might be decompactified. However, we find no evidence for violation of the bound in our analysis.

We consider the effects of extra dimensions on the thermodynamics of classical ideal gases, Bose–Einstein gases and Fermi–Dirac gas. Assuming a q-dimensional torus for the extra dimensions, we compute the thermodynamic functions such as the equation of state, the average energy and the specific heat at constant volume for the three systems. We show that the corrections due to the extra dimensions are small, proportional to .