Kaluza-Klein States Research Articles

Higher curvature effects in Arkani-Hamed-Dimopoulos-Dvali and Randall-Sundrum models

We explore the collider phenomenology of terascale extra-dimensional models with gravitational actions that contain higher curvature terms. In particular, we examine how the classic collider signatures of the models of Arkani-Hamed, Dimopoulos and Dvali (ADD) and of Randall and Sundrum (RS) are altered by these modifications to the usual Einstein-Hilbert (EH) action. Not only are the detailed signatures for gravitationally induced processes altered but new contributions are found to arise due to the existence of additional scalar Kaluza-Klein (KK) states in the spectrum.

Spinless photon dark matter from two universal extra dimensions

We explore the properties of dark matter in theories with two universal extra dimensions,where the lightest Kaluza–Klein state is a spin-0 neutral particle, representing asix-dimensional photon polarized along the extra dimensions. Annihilation of this ‘spinlessphoton’ proceeds predominantly through Higgs boson exchange, and is largely independentof other Kaluza–Klein particles. The measured relic abundance sets an upper limit on thespinless photon mass of 500 GeV, which decreases to almost 200 GeV if the Higgs boson islight. The phenomenology of this dark matter candidate is strikingly different fromKaluza–Klein dark matter in theories with one universal extra dimension. Elastic scatteringof the spinless photon with quarks is helicity suppressed, making its direct detectionchallenging, although possible at upcoming experiments. The prospects for indirectdetection with gamma rays and antimatter are similar to those of neutralinos. Therates predicted at neutrino telescopes are below the sensitivity of next-generationexperiments.

Fermions on spontaneously generated spherical extra dimensions

We include fermions to the model proposed in hep-th/0606021, and obtain a renormalizable 4-dimensional SU(N) gauge theory which spontaneously generates fuzzy extra dimensions and behaves like Yang-Mills theory on M^4 \times S^2. We find a truncated tower of fermionic Kaluza-Klein states transforming under the low-energy gauge group, which is found to be either SU(n), or SU(n_1) x SU(n_2) x U(1). The latter case implies a nontrivial U(1) flux on S^2, leading to would-be zero modes for the bifundamental fermions. In the non-chiral case they may pair up to acquire a mass, and the emerging picture is that of mirror fermions. We discuss the possible implementation of a chirality constraint in 6 dimensions, which is nontrivial at the quantum level due to the fuzzy nature of the extra dimensions.

Brane cosmology and Kaluza–Klein gravitinos

The cosmology of Kaluza–Klein (KK) gravitinos in models with extra dimensions is considered.The main result is that the production of such KK modes is not compatible with an epochof non-standard expansion after inflation. This is so because the big bang nucleosynthesis(BBN) constraint on the zero mode forces the reduced five-dimensional Planck massM5 down to values much smaller than the usual four-dimensional one yields,but this in turn implies that many KK states are available for a giventemperature. Once these states are taken into account one finds that there is noM5 for which the KK gravitinos produced satisfy BBN and overclosure constraints. Thisconclusion holds for both flat and warped models in which only gravity propagates in thefull spacetime.

Warped leptogenesis with Dirac neutrino masses

We show how leptogenesis can occur at the TeV scale with neutrinos that possess almost purely Dirac masses and negligible Majorana mass contributions as a consequence of the small wave-function overlap in a warped fifth dimension. Lepton-number violation at the Planck scale is introduced via a Majorana mass term on the Planck brane. Such a Majorana mass operator leads to the small mass splitting of otherwise degenerate Kaluza-Klein excited states on the TeV brane. This tiny mass splitting can compensate for the small Yukawa couplings to give a $CP$ asymmetry large enough to produce the sufficient baryon asymmetry from the decay of the nearly degenerate neutrino Kaluza-Klein states. In this way the standard baryogenesis via leptogenesis scenario can naturally occur at the TeV scale without the need for a high mass scale.

The little hierarchy in Universal Extra Dimensions

In the standard model in universal extra dimensions (UED) the mass of the Higgs field is driven to the cutoff of the higher-dimensional theory. This re-introduces a small hierarchy since the compactification scale 1/R should not be smaller than the weak scale. In this paper we study possible solutions to this problem by considering five-dimensional theories where the Higgs field potential vanishes at tree level due to a global symmetry. We consider two avenues: a Little Higgs model and a Twin Higgs model. An obstacle for the embedding of these four-dimensional models in five dimensions is that their logarithmic sensitivity to the cutoff will result in linear divergences in the higher dimensional theory. We show that, despite the increased cutoff sensitivity of higher dimensional theories, it is possible to control the Higgs mass in these two scenarios. For the Little Higgs model studied, the phenomenology will be significantly different from the case of the standard model in UED. This is due to the fact that the compactification scale approximately coincides with the scale where the masses of the new states appear. For the case of the Twin Higgs model, the compactification scale may be considerably lower than the scale where the new states appear. If it is as low as allowed by current limits, it would be possible to experimentally observe the standard model Kaluza-Klein states as well as a new heavy quark. On the other hand, if the compactification scale is higher, then the phenomenology at colliders would coincide with the one for the standard model in UED.

Renormalized masses of heavy Kaluza-Klein states

Several ways of computing the radiative corrections to the heavy boson masses in Kaluza-Klein theory are discussed. It is argued that only an intrinsically higher dimensional approach embodies all the desired physical properties. This contradicts earlier results in the literature.

Power law scaling in universal extra dimension scenarios

We study the power law running of gauge, Yukawa and quartic scalar couplings in the universal extra dimension scenario where the extra dimension is accessed by all the standard model fields. After compactifying on an S 1 / Z 2 orbifold, we compute one-loop contributions of the relevant Kaluza–Klein (KK) towers to the above couplings up to a cutoff scale Λ. Beyond the scale of inverse radius, once the KK states are excited, these couplings exhibit power law dependence on Λ. As a result of faster running, the gauge couplings tend to unify at a relatively low scale, and we choose our cutoff also around that scale. For example, for a radius R ∼ 1 TeV −1 , the cutoff is around 30 TeV. We then examine the consequences of power law running on the triviality and vacuum stability bounds on the Higgs mass. We also comment that the supersymmetric extension of the scenario requires R −1 to be larger than ∼ 10 10 GeV in order that the gauge couplings remain perturbative up to the scale where they tend to unify.

Light Kaluza–Klein states in Randall–Sundrum models with custodial [formula omitted

We consider Randall–Sundrum scenarios based on SU(2)L×SU(2)R and a discrete parity exchanging L with R. The custodial and parity symmetries can be used to make the tree level contribution to the T parameter and the anomalous couplings of the bottom quark to the Z very small. We show that the resulting quantum numbers typically induce a negative T parameter at one loop that, together with the positive value of the S parameter, restrict considerably these models. There are nevertheless regions of parameter space that successfully reproduce the fit to electroweak precision observables with light Kaluza–Klein excitations accessible at colliders. We consider models of gauge-Higgs unification that implement the custodial and parity symmetries and find that the electroweak data singles out a very well defined region in parameter space. In this region one typically finds light gauge boson Kaluza–Klein excitations as well as light SU(2)L singlet, and sometimes also doublet, fermionic states, that mix with the top quark, and that may yield interesting signatures at future colliders.

Superfield calculation of loop contributions in extra dimensional theories

Superfields provide a compact description of supersymmetry representations. Loop corrections with superfield formalism are simpler and much more manageable than the calculation in terms of component fields. In this paper we calculate the contribution of the Kaluza-Klein (KK) states, associated with extra dimensions, to the renormalization group beta function. These Kaluza-Klein particles circulate in the virtual loop, hence affecting the overall corrections at any order. We obtain the one-loop correction, which checks with the result previously obtained using the more laborious component field method. In addition, we calculate the two-loop correction coming from chiral KK states.

Top pair production in Randall-Sundrum models

If the lowest lying Kaluza-Klein states in Randall-Sundrum (RS1) models have masses in the 10-100 TeV range, direct production of these states at the LHC or ILC is impossible, and electroweak precision measurements may not be sufficiently sensitive. We address the possibility that high-precision measurements of top pair production at the ILC may provide the first evidence of these states. We consider RS1 models with fermions on and off the brane, with bulk left and right handed mass terms, discuss brane kinetic terms and calculate corrections to top pair production in these models.

Localization of 4D gravity on pure geometrical thick branes

We consider the generation of thick brane configurations in a pure geometric Weyl integrable 5D spacetime which constitutes a non-Riemannian generalization of Kaluza-Klein (KK) theory. In this framework, we show how 4D gravity can be localized on a scalar thick brane which does not necessarily respect reflection symmetry, generalizing in this way several previous models based on the Randall-Sundrum (RS) system and avoiding both, the restriction to orbifold geometries and the introduction of the branes in the action by hand. We first obtain a thick brane solution that preserves 4D Poincar\'e invariance and breaks ${Z}_{2}$-symmetry along the extra dimension which, indeed, can be either compact or extended, and supplements brane solutions previously found by other authors. In the noncompact case, this field configuration represents a thick brane with positive energy density centered at $y={c}_{2}$, whereas pairs of thick branes arise in the compact case. Remarkably, the Weylian scalar curvature is nonsingular along the fifth dimension in the noncompact case, in contraposition to the RS thin brane system. We also recast the wave equations of the transverse traceless modes of the linear fluctuations of the classical background into a Schr\"odinger's equation form with a volcano potential of finite bottom in both the compact and the extended cases. We solve Schr\"odinger equation for the massless zero mode ${m}^{2}=0$ and obtain a single bound wave function which represents a stable 4D graviton. We also get a continuum gapless spectrum of KK states with ${m}^{2}>0$ that are suppressed at $y={c}_{2}$ and turn asymptotically into plane waves.

Coupling Constant Dependence of the Kaluza-Klein Spectrum in Five-Dimensional SQCD on S1

We investigate the Kaluza-Klein (KK) spectrum of N=1 supersymmetric gauge theory compactified on a circle. We concentrate on a model with the gauge group SU(2) and four massless matter fields in the fundamental representation. We derive the exact mass formula of KK modes using Seiberg-Witten theory. From the mass formula and the D3-brane probe realization, we determine the spectrum of the KK modes of the matter fields and gauge fields. We find that the lightest KK state of the gauge fields is stable in the entire vacuum moduli space, while the lightest KK state of the matter fields decays more readily than other KK states in one region of the moduli space. This region becomes small as we decrease the five-dimensional gauge coupling constant g 5 , and vanishes in the limit g 5 → 0. This result continuously connects the known KK spectrum in the weak coupling limit and that in the strong coupling limit.

Indirect detection of Dirac right-handed neutrino dark matter

We present the signatures and prospects for the indirect detection of a Dirac right-handed neutrino dark matter candidate in neutrino telescopes, cosmic positron experiments and gamma-ray telescopes. An example of such a dark matter candidate can be found in extra-dimensional models. In some constructions, Kaluza–Klein states with the gauge quantum numbers of a right-handed neutrino can have sizable gauge interactions with standard model particles. For instance, in 5D warped Grand Unified Theories, it has been shown that a Kaluza–Klein right-handed neutrino may be stable and otherwise a phenomenologically viable dark matter candidate. We find that the prospects for the indirect detection of such a WIMP are encouraging, particularly for neutrino telescopes and cosmic positron experiments.

Effective actions for massive Kaluza-Klein states onAdS3×S3×S3

We construct the effective supergravity actions for the lowest massive Kaluza-Klein states on the supersymmetric background AdS_3 x S^3 x S^3. In particular, we describe the coupling of the supergravity multiplet to the lowest massive spin-3/2 multiplet which contains 256 physical degrees of freedom and includes the moduli of the theory. The effective theory is realized as the broken phase of a particular gauging of the maximal three-dimensional supergravity with gauge group SO(4) x SO(4). Its ground state breaks half of the supersymmetries leading to 8 massive gravitinos acquiring mass in a super Higgs effect. The holographic boundary theory realizes the large N=(4,4) superconformal symmetry.

Searching for dark matter with future cosmic positron experiments

Dark matter particles annihilating in the Galactic halo can provide a flux of positrons potentially observable in upcoming experiments, such as PAMELA and AMS-02. We discuss the spectral features which may be associated with dark matter annihilation in the positron spectrum and assess the prospects for observing such features in future experiments. Although we focus on some specific dark matter candidates, neutralinos and Kaluza-Klein states, we carry out our study in a model independent fashion. We also revisit the positron spectrum observed by HEAT.

Publisher's Note: M theory model of a big crunch/big bang transition [Phys. Rev. D70, 106004 (2004)

We consider a picture in which the transition from a big crunch to a big bang corresponds to the collision of two empty orbifold planes approaching each other at a constant non-relativistic speed in a locally flat background space-time, a situation relevant to recently proposed cosmological models. We show that $p$-brane states which wind around the extra dimension propagate smoothly and unambiguously across the orbifold plane collision. In particular we calculate the quantum mechanical production of winding M2-branes extending from one orbifold to the other. We find that the resulting density is finite and that the resulting gravitational back-reaction is small. These winding states, which include the string theory graviton, can be propagated smoothly across the transition using a perturbative expansion in the membrane tension, an expansion which from the point of view of string theory is an expansion in {\it inverse} powers of $\alpha'$. We argue that interactions should be well-behaved because the string coupling tends to zero at the crunch. The production of massive Kaluza-Klein states should also be exponentially suppressed for small collision speeds. We contrast this good behavior with that found in previous studies of strings in Lorentzian orbifolds.

M theory model of a big crunch/big bang transition

We consider a picture in which the transition from a big crunch to a big bang corresponds to the collision of two empty orbifold planes approaching each other at a constant nonrelativistic speed in a locally flat background space-time, a situation relevant to recently proposed cosmological models. We show that $p$-brane states which wind around the extra dimension propagate smoothly and unambiguously across the orbifold plane collision. In particular we calculate the quantum mechanical production of winding M2-branes extending from one orbifold to the other. We find that the resulting density is finite and that the resulting gravitational backreaction is small. These winding states, which include the string theory graviton, can be propagated smoothly across the transition using a perturbative expansion in the membrane tension, an expansion which from the point of view of string theory is an expansion in inverse powers of ${\ensuremath{\alpha}}^{\ensuremath{'}}$. The conventional description of a crunch based on Einstein general relativity, involving Kasner or mixmaster behavior is misleading, we argue, because general relativity is only the leading order approximation to string theory in an expansion in positive powers of ${\ensuremath{\alpha}}^{\ensuremath{'}}$. In contrast, in the M theory setup we argue that interactions should be well behaved because of the smooth evolution of the fields combined with the fact that the string coupling tends to zero at the crunch. The production of massive Kaluza-Klein states should also be exponentially suppressed for small collision speeds. We contrast this good behavior with that found in previous studies of strings in Lorentzian orbifolds.

Massive gravity on a brane

At present no theory of a massive graviton is known that is consistent with experiments at both long and short distances. The problem is that consistency with long distance experiments requires the graviton mass to be very small. Such a small graviton mass however implies an ultraviolet cutoff for the theory at length scales far larger than the millimeter scale at which gravity has already been measured. In this paper we attempt to construct a model which avoids this problem. We consider a brane world setup in warped AdS spacetime and we investigate the consequences of writing a mass term for the graviton on a the infrared brane where the local cutoff is of order a large (galactic) distance scale. The advantage of this setup is that the low cutoff for physics on the infrared brane does not significantly affect the predictivity of the theory for observers localized on the ultraviolet brane. For such observers the predictions of this theory agree with general relativity at distances smaller than the infrared scale but go over to those of a theory of massive gravity at longer distances. A careful analysis of the graviton two-point function, however, reveals the presence of a ghost in the low energy spectrum. A mode decomposition of the higher dimensional theory reveals that the ghost corresponds to the radion field. We also investigate the theory with a brane localized mass for the graviton on the ultraviolet brane, and show that the physics of this case is similar to that of a conventional four dimensional theory with a massive graviton, but with one important difference: when the infrared brane decouples and the would-be massive graviton gets heavier than the regular Kaluza--Klein modes, it becomes unstable and it has a finite width to decay off the brane into the continuum of Kaluza-Klein states.

Semiclassical string spectrum in a string model dual to large N QCD

We explore the string spectrum in the Witten QCD 4 model by considering classical string configurations, thereby obtaining energy formulas for quantum states with large excitation quantum numbers representing glueballs and Kaluza–Klein states. In units of the string tension, the energies of all states increase as the 't Hooft coupling λ is decreased, except the energies of glueballs corresponding to strings lying on the horizon, which remain constant. We argue that some string solutions can be extrapolated to the small λ regime. We also find the classical mechanics description of supergravity glueballs in terms of point-like string configurations oscillating in the radial direction, and reproduce the glueball energy formula previously obtained by solving the equation for the dilaton fluctuation.