Kaluza-Klein Excitations Research Articles

Controlling chaos through compactification in cosmological models with a collapsing phase

We consider the effect of compactification of extra dimensions on the onset of classical chaotic "Mixmaster" behavior during cosmic contraction. Assuming a universe that is well-approximated as a four-dimensional Friedmann-Robertson--Walker model (with negligible Kaluza-Klein excitations) when the contraction phase begins, we identify compactifications that allow a smooth contraction and delay the onset of chaos until arbitrarily close the big crunch. These compactifications are defined by the de Rham cohomology (Betti numbers) and Killing vectors of the compactification manifold. We find compactifications that control chaos in vacuum Einstein gravity, as well as in string theories with N = 1 supersymmetry and M-theory. In models where chaos is controlled in this way, the universe can remain homogeneous and flat until it enters the quantum gravity regime. At this point, the classical equations leading to chaotic behavior can no longer be trusted, and quantum effects may allow a smooth approach to the big crunch and transition into a subsequent expanding phase. Our results may be useful for constructing cosmological models with contracting phases, such as the ekpyrotic/cyclic and pre-big bang models.

Search with the CMS detector for Randall-Sundrum excitations of gravitons decaying into electron pairs

The sensitivity of the CMS experiment to the resonant production of massive Kaluza-Klein excitations of gravitons, expected in the framework of the Randall-Sundrum model, is studied. Full simulation and reconstruction are used to investigate this production followed by graviton decay to an ${\rm e^ + e^-}$ pair. For a Randall-Sundrum model with coupling parameter c = 0.01, the graviton excitations have weak couplings to Standard Model particles. For an integrated luminosity of 100 fb-1, resonances can be discovered at the $5\sigma$ level for masses up to 1.8 TeV/c 2. Heavier resonances are accessible for larger values of the c parameter, with a mass reach of 3.8 TeV/c 2 for c = 0.1.

Single Kaluza-Klein production in universal extra dimensions

In the universal extra-dimensions models, Kaluza-Klein excitations of matter are generaly produced in pairs. However, if matter lives on a fat brane embedded in a larger space, gravity-matter interactions do not obey KK number-conservation, thus making possible the production of single KK excitations at colliders. We evaluate the production rates for such excitations at the Tevatron and LHC colliders, and look for ways to detect them.

Searches for solar Kaluza–Klein axions with gas TPCs

In theories with n extra dimensions beyond the normal 3+1, axions may be able to propagate in these extra dimensions and hence acquire Kaluza–Klein excitations. We investigate the possibility of using a low pressure gas time projection chamber (TPC) to search for the two-photon decays of Kaluza–Klein axions produced in the solar interior and subsequently trapped into Earth-crossing orbits. A simulation of the background in a generic 1m3 TPC due to coincident photon events from radioactive decay in the detector and surrounding laboratory walls was performed. The results of these simulations are discussed with regard to the sensitivity of the TPC to the axion–photon coupling constant ga γγ and local axion number density n0. We find that sensitivities to solar Kaluza–Klein models consistent with limits on exotic solar energy loss are achievable.

6D Higgsless Standard Model

We present a six-dimensional Higgsless Standard Model with a realistic gauge sector. The model uses only the Standard Model gauge group SU(2)L×U(1)Y with the gauge bosons propagating in flat extra dimensions compactified on a rectangle. The electroweak symmetry is broken by boundary conditions, and the correct splitting between the W and Z gauge boson masses can be arranged by suitable choice of the compactification scales. The higher Kaluza–Klein excitations of the gauge bosons decouple from the effective low-energy theory due to dominant brane kinetic terms. The model has the following two key features compared to five-dimensional models. The dimensional couplings in the bulk Lagrangian, responsible for electroweak symmetry breaking using mixed boundary conditions, are of order the electroweak scale. Moreover, with respect to “oblique” corrections, the agreement with the precision electroweak parameters is improved compared to five-dimensional warped or flat space models. We also argue that the calculability of Higgsless models can be ameliorated in more than five dimensions.

Higgs production in association with top quark pair at e+e- colliders in theories of higher dimensional gravity

Models with large extra compact dimensions predict exciting phenomenological consequences with gravitational interactions becoming strong at the TeV scale. Such theories can be tested at the existing and future colliders. In this paper, we study the contribution of virtual Kaluza-Klein excitations in the process e + e - →ttH at a future linear collider. The exchange of virtual KK gravitons is found to modify the cross-section σ(e + e - →ttH) from its Standard Model value to a very significant extent. The consequent sensitivity to the effective string scale M S depends (weakly) on the number of extra-dimensions n and (strongly) on the center-of-mass energy of the collider. For n = 3, M S ⋍ 920 GeV (8 TeV) could be probed at machines working at √s = 500 GeV (3 TeV). More importantly, this process can serve to distinguish such models from other sources of new physics.

Accelerating cosmologies from exponential potentials

An exponential potential of the form V ∼ exp(−2cφ/Mp) arising from the hyperbolic or flux compactification of higher-dimensional theories is of interest for getting short periods of accelerated cosmological expansions. Using a similar potential but derived for the combined case of hyperbolic–flux compactification, we study the four-dimensional flat (and open) FLRW cosmologies and give analytic (and numerical) solutions with exponential behaviour of scale factors. We show that, for the M-theory motivated potentials, the cosmic acceleration of the universe can be eternal if the spatial curvature of the 4d spacetime is negative, while the acceleration is only transient for a spatially flat universe. We also briefly comment on the size of the internal space and its associated geometric bounds on massive Kaluza–Klein excitations.

Similarity between Kaluza–Klein and Open-string amplitudes in Diphoton Production

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 $0.6-0.9$ TeV.

Fermionic and bosonic stabilizing effects for type I and type II dimension bubbles

We consider two types of "dimension bubbles", which are viewed as 4d nontopological solitons that emerge from a 5d theory with a compact extra dimension. The size of the extra dimension varies rapidly within the domain wall of the soliton. We consider the cases of type I (II) bubbles where the size of the extra dimension inside the bubble is much larger (smaller) than outside. Type I bubbles with thin domain walls can be stabilized by the entrapment of various particle modes whose masses become much smaller inside than outside the bubble. This is demonstrated here for the cases of scalar bosons, fermions, and massive vector bosons, including both Kaluza-Klein zero modes and Kaluza-Klein excitation modes. Type II bubbles expel massive particle modes but both types can be stabilized by photons. Plasma filled bubbles containing a variety of massless or nearly massless radiation modes may exist as long-lived metastable states. Furthermore, in contrast to the case with a "gravitational bag", the metric for a fluid-filled dimension bubble does not exhibit a naked singularity at the bubble's center.

Physics reach with CMS at high and super-high luminosities

The physics reach of the Compact Muon Solenoid, under construction to study proton-proton collisions at a centre-of-mass energy of 14 TeV, is presented at design luminosity of 1034cm–2s–1 and beyond (1035cm–2s–1). The sensitivity for detection of the standard-model Higgs boson in the channels qqH (W fusion), WH, and tH is discussed with the result that the Higgs boson is observable in multiple decay modes over entire mass range, 0.1-1 TeV/c2. Higgs boson searches for decays involving taus in the context of the Minimal Supersymmetric Standard Model result in a limit of about 0.6 TeV/c2 at tanβ=25. Sparticle reconstruction for decays containing leptons and jets results in a squark/gluino mass reach in the range 2.5-3 TeV/c2. Limits on Kaluza-Klein excitations of the graviton or a new heavy vector boson are in the 5-6 TeV/c2 range. The scattering of vector bosons at high energy and discovery potential for compositeness is described. PACS: 11.30.Pb – 12.38.Qk; 12.60.Fr – 12.60.Fr – 12.60.Jv – 12.60.Rc – 14.60.Cd – 14.60.Ef – 14.60.Fg – 14.65.Fy – 14.65.Ha – 14.80.Bn – 14.80.Cp – 14.80.Ly – 14.70.Fm – 14.70.Hp – 14.70.Pw

A bulk effect to SUSY effective potential in a 5D super-Yang–Mills model

Supersymmetric effective potential of a 5D super-Yang–Mills model compactified on S1/Z2, i.e., on an interval l of extra dimension, is estimated at the 1-loop level by the auxiliary field tadpole method. For the sake of infinite towers of Kaluza–Klein excitation modes of bulk fields involved in the tadpoles, there arises a definite bulk effect of linear growth of the effective potential along with the cutoff Λ which is greatly suppressed by l to produce a finite contribution. Incorporating the tree potential and a Fayet–Iliopoulos D-term, the effective potential is minimized at a specific value of l, corresponding to an intermediate mass scale 1011–14 GeV, where the supersymmetry is restored.

Flavor violation in warped extra dimensions and CP asymmetries in B decays

We show that CP asymmetries in b {yields} s hadronic decays are potentially affected by the presence of massive color-octet particles strongly coupled to the third generation quarks. Theories with warped extra dimensions provide natural candidates in the Kaluza-Klein excitations of gluons in scenarios where flavor-breaking by bulk fermion masses results in the localization of fermion wave-functions. Topcolor models, in which a new gauge interaction leads to top-condensation and a large top mass, also result in the presence of these color-octet states with TeV masses. We find that large effects are possible in modes such as B {yields} {phi}K{sub s}, B {yields} {eta}{prime}K{sub s} and B {yields} {pi}{sup 0}K{sub s} among others.

Flavor violation in warped extra dimensions and CP asymmetries in B decays

We show that CP asymmetries in b→s hadronic decays are potentially affected by the presence of massive color–octet particles strongly coupled to the third generation quarks. Theories with warped extra dimensions provide natural candidates in the Kaluza–Klein excitations of gluons in scenarios where flavor-breaking by bulk fermion masses results in the localization of fermion wave-functions. Topcolor models, in which a new gauge interaction leads to top-condensation and a large top mass, also result in the presence of these color–octet states with TeV masses. We find that large effects are possible in modes such as B→φKs, B→η′Ks and B→π0Ks among others.

Universal extra dimensions and Kaluza-Klein bound states

We study the bound states of the Kaluza-Klein (KK) excitations of quarks in certain models of universal extra dimensions. Such bound states may be detected at future lepton colliders in the cross section for the pair production of KK quarks near threshold. For typical values of model parameters, we find that ``KK quarkonia'' have widths in the 10--100 MeV range, and production cross sections of the order of a few picobarns for the lightest resonances. Two body decays of the constituent KK quarks lead to distinctive experimental signatures. We point out that such KK resonances may be discovered before any of the higher KK modes.

Phenomenology of a 5D orbifoldSU(3)Wunification model

We study the phenomenology of a 5D $SU(3)_W$ model on a $S_1/(Z_2\times Z'_2)$ orbifold in which the minimal scalar sector plays an essential role of radiatively generating neutrino Majorana masses without the benefits of right-handed singlets. We carefully examine how do the exotic scalars affect the renormalization group (RG) equations for the gauge couplings and the 5D $SU(3)_W$ unification. We found that the compactification scale of extra dimension is in the range of $1/R\sim 1.5-5$ TeV. The possibility of the existence of relatively low mass Kaluza-Klein excitations makes the phenomenology of near term interest. Some possible bilepton signatures can be searched for in future colliders and in neutrino scattering experiments with intense neutrino beams. The low energy constraints from muon physics and lepton number violating decay process induced by bilepton are also discussed. These constraints can provide new information on the structure of Yukawa couplings which might be useful for future model building.

Homotopy structure of 5d vacua

It is shown that flat zero-energy solutions (vacua) of the 5d Kaluza–Klein theory admit a nontrivial homotopy structure generated by certain Kaluza–Klein excitations. These vacua consist of an infinite set of homotopically different space–times denoted by M5(n), among which M5(0) and M5(1) are especially identified as M4×S1 and M5, the vacuum states of the 5d Kaluza–Klein theory and the 5d general relativity, respectively (where Mk represents the k-dimensional Minkowski space).

Prospects for the detection of Kaluza-Klein excitations of gauge bosons in the ATLAS detector at the LHC

Kaluza-Klein excitations of the gauge bosons are a notable feature of theories with “small” (~ 1 TeV) extra dimensions. The leptonic decays of the excitations of γ and Z bosons provide a striking signature which can be detected at the LHC. We investigate the reach for these signatures through a parametrized simulation of the ATLAS detector. With an integrated luminosity of 100 fb–1 a peak in the lepton-lepton invariant mass will be detected if the compactification scale (M c ) is below 5.8 TeV. If no peak is observed, with an integrated luminosity of 300 fb–1 a limit of M c <12–13.5 TeV can be obtained from a detailed study of the shape of the lepton-lepton invariant mass distribution. If a peak is observed, the study of the angular distribution of the two leptons will allow to distinguish the KK excitations from alternative models yielding the same signature. PACS: 11.10Kk – 11.25Mj – 13.85-t

Prospects for observing the Kaluza-Klein excitations of the W boson in the ATLAS detector at the LHC

Kaluza-Klein excitations of the gauge bosons are a notable feature of theories with “small” (~ 1 TeV) extra dimensions. The leptonic decays of the excitations of the W boson provide at the LHC the striking signature of events containing an isolated high P T lepton accompanied by a high transverse momentum imbalance. We investigate the reach for these signatures through a parametrized simulation of the ATLAS detector. With an integrated luminosity of 100 fb–1 a peak in the transverse invariant mass of the lepton-neutrino system will be detected if the compactification scale (M c ) is below 6 TeV. If no signal is observed, with an integrated luminosity of 100 fb–1 a limit of M c >11.7 TeV can be obtained from the study of the lepton-neutrino transverse mass distribution below the peak. If a peak is detected, a measurement of the couplings of the boson to leptons and quarks can be performed for M c up to ~5 TeV. PACS: 11.10Kk – 11.25Mj – 13.85-t

Potentials from fluxes

We discuss the compactification of type IIB supergravity with fluxes to generate a potential for the moduli. In particular we resolve an apparent conflict with the no-go theorem for de Sitter space. It is shown that a positive potential for certain moduli is possible in situations where the volume modulus has no critical point. We also point out that the derivation of the potential is strictly valid only for a trivial warp factor. To go beyond that seems to require the inclusion of all the Kaluza-Klein excitations. We end with a discussion of the stabilization of the volume modulus.

Large extra dimensions and decaying Kaluza-Klein recurrences

We suggest the possibility that in Arkani-Hamed--Dimopoulos--Dvali (ADD)-type brane-world scenarios the higher Kaluza-Klein (KK) excitations of the graviton may decay to lower ones owing to a breakdown of the conservation of extra dimensional ``momenta'' and study its implications for astrophysics and cosmology. We give an explicit realization of this idea with a bulk scalar field $\ensuremath{\Phi},$ whose nonzero KK modes acquire vacuum expectation values. This scenario helps to avoid constraints on large extra dimensions that come from gamma ray flux bounds in the direction of nearby supernovae as well as those coming from a diffuse cosmological gamma ray background. It also relaxes the very stringent limits on the reheat temperature of the Universe in ADD models.