Extra Dimension Scenario Research Articles

Collider implications of a nonuniversal Higgs boson

We consider in detail the possibility that the Higgs is wholly or partially excluded from propagating into one otherwise universal extra dimension. This exclusion of the Higgs from propagating into an otherwise universal extra dimension violates tree-level Kaluza-Klein number conservation in the Yukawa interactions. As a consequence, there is inter-mode mixing between fermions. For example, zero-mode fermions mix with their associated Kaluza-Klein excitations. This is in contrast to the original universal extra dimensions scenario, in which conservation of Kaluza-Klein number prohibits such inter-mode mixing. Inter-mode mixing is especially significant for the top quark, since its mass ($171.4\ifmmode\pm\else\textpm\fi{}2.1\text{ }\text{ }\mathrm{GeV}$) is approximately one-half the current Tevatron mass bound ($\ensuremath{\sim}350\char21{}400\text{ }\text{ }\mathrm{GeV}$) for Kaluza-Klein excitations of quarks propagating into universal extra dimensions. We compute the effects that mixing among the zero-modes and lowest-lying Kaluza-Klein excitations has on the lightest third-generation charge $2/3$ quark mass eigenvalue in the nonuniversal Higgs model with one otherwise universal extra dimension. Another consequence of the inter-mode mixing is that the Kaluza-Klein excitations of the fermions can decay to a zero-mode Higgs and a corresponding zero-mode fermion. As a result, the pair production of Kaluza-Klein excitations of the top quark would lead to two zero-mode Higgs bosons plus a zero-mode top quark/antiquark pair. We compute the cross section that the nonuniversal Higgs model contributes to Higgs production at the Large Hadron Collider. The effect is quite large: For example, the Kaluza-Klein contribution to Higgs production is comparable to or larger than the Standard Model contribution, depending on the Higgs mass, for compactification scales up to about 600 GeV.

Direct detection of dark matter rates for various wimps

The event rates for the direct detection of dark matter candidates, originating from the universal extra dimension scenario, are evaluated for a number of nuclear targets. Realistic form factors as well as spin ME and response functions are employed. Due to LR + RL helicities contribution, the proton amplitude is found to be dominant. Various other non-susy dark matter candidates are examined at the end.

Microscopic primordial black holes and extra dimensions

We examine the production and evolution of microscopic black holes in the early universe in the large extra dimensions scenario. We demonstrate that, unlike in the standard four-dimensional cosmology, in large extra dimensions absorption of matter from the primordial plasma by the black holes is significant and can lead to rapid growth of the black hole mass density. This effect can be used to constrain the conditions present in the very early universe. We demonstrate that this constraint is applicable in regions of parameter space not excluded by existing bounds.

Using Muonic Hydrogen in Optical Spectroscopy Experiment to Detect Extra Dimensions

Considering that gravitational force might deviate from Newton's inverse-square law (ISL) and become much stronger in small scale, we propose a kind of optical spectroscopy experiment to detect this possible deviation and take electronic, muonic and tauonic hydrogen atoms as examples. This experiment might be used to indirectly detect the deviation of ISL down to nanometer scale and to explore the possibility of three extra dimensions in ADD's model, while current direct gravity tests cannot break through micron scale and go beyond two extra dimensions scenario.

Charged shells in Lovelock gravity: Hamiltonian treatment and physical implications

Using a Hamiltonian treatment, charged thin shells, static and dynamic, in spherically symmetric spacetimes, containing black holes or other specific types of solutions, in d dimensional Lovelock-Maxwell theory are studied. The free coefficients that appear in the Lovelock theory are chosen to obtain a sensible theory, with a negative cosmological constant appearing naturally. Using an Arnowitt-Deser-Misner (ADM) description, one then finds the Hamiltonian for the charged shell system. Variation of the Hamiltonian with respect to the canonical coordinates and conjugate momenta, and the relevant Lagrange multipliers, yields the dynamic and constraint equations. The vacuum solutions of these equations yield a division of the theory into two branches, namely d-2k-1>0 (which includes general relativity, Born-Infeld type theories, and other generic gravities) and d-2k-1=0 (which includes Chern-Simons type theories), where k is the parameter giving the highest power of the curvature in the Lagrangian. There appears an additional parameter {chi}=(-1){sup k+1}, which gives the character of the vacuum solutions. For {chi}=1 the solutions, being of the type found in general relativity, have a black hole character. For {chi}=-1 the solutions, being of a new type not found in general relativity, have a totally naked singularity character. Since there is a negative cosmologicalmore » constant, the spacetimes are asymptotically anti-de Sitter (AdS), and AdS when empty (for zero cosmological constant the spacetimes are asymptotically flat). The integration from the interior to the exterior vacuum regions through the thin shell takes care of a smooth junction, showing the power of the method. The subsequent analysis is divided into two cases: static charged thin shell configurations, and gravitationally collapsing charged dust shells (expanding shells are the time reversal of the collapsing shells). In the collapsing case, into an initially nonsingular spacetime with generic character or an empty interior, it is proved that the cosmic censorship is definitely upheld. Physical implications of the dynamics of such shells in a large extra dimension world scenario are also drawn. One concludes that, if such a large extra dimension scenario is correct, one can extract enough information from the outcome of those collisions as to know, not only the actual dimension of spacetime, but also which particular Lovelock gravity, general relativity or any other, is the correct one at these scales, in brief, to know d and k.« less

LEPTON NUMBER VIOLATION VIA INTERMEDIATE BLACK HOLE PROCESSES

Black holes at the TeV scale are investigated in the extra large dimension scenario. We interpret the lightest black hole excitation as a singlet scalar field, and show how interaction terms can be appended to the standard model at the dimension five non-renormalizable level. Lepton family number violation is natural in this model. Muon magnetic moment, and neutrino masses are investigated. We also present a quantization scheme in n dimensions.

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.

Exploring Extra Dimensions in Spectroscopy Experiments

We propose an idea in spectroscopy to search for extra spatialdimensions as well as to detect the possible deviation from Newton'sinverse-square law at small scale, and we take high-Z hydrogenicsystems and muonic atoms as illustrations. The relevant experimentsmight help to explore a more than two extra dimensions scenario in thebrane world model proposed by Arkani-Hamed, Dimopoulos, Dvali (ADD)and to set constraints for fundamental parameters such as the size ofextra dimensions.

Search for Large Extra Dimensions in the Production of Jets and Missing Transverse Energy inpp¯Collisions ats=1.96 TeV

We present the results of a search for new physics in the jets plus missing transverse energy data sample collected from 368 pb(-1) of pp collisions at square root of s = 1.96 TeV recorded by the Collider Detector at Fermilab. We compare the number of events observed in the data with a data-based estimate of the standard model backgrounds contributing to this signature. We observe no significant excess of events, and we interpret this null result in terms of lower limits on the fundamental Planck scale for a large extra dimensions scenario.

Monojet and single photon signals from universal extra dimensions

The usual universal extra dimensions scenario does not allow for single production of first level Kaluza-Klein (KK) excitations of matter due to the KK number conservation. However, if the matter fields are localized on a fat brane embedded in a higher dimensional space, matter-gravitation interactions violate KK number, and the production of single KK excitations becomes possible. In this paper we analyze the production of a single KK matter excitation together with a graviton in the final state, and study the potential for discovery at the Tevatron and Large Hadron Collider.

Probing universal extra dimension at the International Linear Collider

In the context of an universal extra-dimensional scenario, we consider production of the first Kaluza–Klein electron positron pair in an e+e− collider as a case-study for the future International Linear Collider. The Kaluza–Klein electron decays into a nearly degenerate Kaluza–Klein photon and a standard electron, the former carrying away missing energy. The Kaluza–Klein electron and photon states are heavy with their masses around the inverse radius of compactification, and their splitting is controlled by radiative corrections originating from bulk and brane-localised interactions. 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 will be readily detectable over the standard model background. We comment on how this signal may be distinguished from similar events from other new physics.

Large-volume flux compactifications: moduli spectrum and D3/D7 soft supersymmetry breaking

We present an explicit calculation of the spectrum of a general class of string models, corresponding to Calabi-Yau flux compactifications with h_{1,2}>h_{1,1}>1 with leading perturbative and non-perturbative corrections, in which all geometric moduli are stabilised as in hep-th/0502058. The volume is exponentially large, leading to a range of string scales from the Planck mass to the TeV scale, realising for the first time the large extra dimensions scenario in string theory. We provide a general analysis of the relevance of perturbative and non-perturbative effects and the regime of validity of the effective field theory. We compute the spectrum in the moduli sector finding a hierarchy of masses depending on inverse powers of the volume. We also compute soft supersymmetry breaking terms for particles living on D3 and D7 branes. We find a hierarchy of soft terms corresponding to `volume dominated' F-term supersymmetry breaking. F-terms for Kahler moduli dominate both those for dilaton and complex structure moduli and D-terms or other de Sitter lifting terms. This is the first class of string models in which soft supersymmetry breaking terms are computed after fixing all geometric moduli. We outline several possible applications of our results, both for cosmology and phenomenology and point out the differences with the less generic KKLT vacua.

New instability for rotating black branes and strings

The evolution of small perturbations around rotating black branes and strings, which are low energy solutions of string theory, are investigated. For simplicity, we concentrate on the Kerr solution times transverse flat extra dimensions, possibly compactified, but one can also treat other branes composed of any rotating black hole and extra transverse dimensions, as well as analogue black hole models and rotating bodies in fluid mechanics systems. It is shown that such a rotating black brane is unstable against any massless (scalar, vectorial, tensorial or other) field perturbation for a wide range of wavelengths and frequencies in the transverse dimensions. Since it holds for any massless field it can be considered, in this sense, a stronger instability than the one studied by Gregory and Laflamme. Accordingly, it has also a totally different physical origin. The perturbations can be stabilized if the extra dimensions are compactified to a length smaller than the minimum wavelength for which the instability settles in, resembling in this connection the Gregory–Laflamme case. Likewise, this instability will have no effect for astrophysical black holes. However, in the large extra dimensions scenario, where TeV scale black holes can be produced, this instability should be important. It seems plausible that the endpoint of this instability is a static, or very slowly rotating, black brane and some outgoing radiation at infinity.

Topcolor breaking through boundary conditions

The nontrivial boundary conditions (BC's) for the topcolor breaking are investigated in the context of the TeV-scale extra dimension scenario. In the gauge symmetry breaking mechanism via the BC's we do not need to incorporate a dynamical mechanism for the topcolor breaking into the model. Moreover, the topcolor breaking can be realized without introducing explicitly a (composite) scalar field. We present a six dimensional model where the top and bottom quarks in the bulk have the topcolor charge while the other quarks in the bulk do not. We also put the electroweak gauge interaction in the six dimensional bulk. The bottom quark condensation is naturally suppressed owing to the powerlike running of the bulk $\mathrm{U}(1{)}_{Y}$ interaction, so that only the top condensation is expected to take place. We explore such a possibility based on the ladder Schwinger-Dyson equation and show the cutoff to make the model viable.

“Footballs,” conical singularities, and the Liouville equation

We generalize the football shaped extra dimensions scenario to an arbitrary number of branes. The problem is related to the solution of the Liouville equation with singularities, and explicit solutions are presented for the case of three branes. The tensions of the branes do not need to be tuned with each other but only satisfy mild global constraints.

Inflationary solution to the strong CP and μ problems

We show that the vacuum expectation value of the inflaton at the Peccei–Quinn axion scale can generate the supersymmetric Higgs mass μ term. This provides an inflationary simultaneous solution to the strong CP problem and the μ problem of the minimal supersymmetric Standard Model, and gives a testable prediction for the μ parameter: μ2≈(0.25–0.5)m02, where m0 is the soft Higgs scalar mass. Our model involves a very small Yukawa coupling of order 10−10, which could originate from an extra-dimensional scenario or type I string theory.

THE MINIMAL LENGTH AND LARGE EXTRA DIMENSIONS

Planck scale physics represents a future challenge, located between particle physics and general relativity. The Planck scale marks a threshold beyond which the old description of spacetime breaks down and conceptually new phenomena must appear. Little is known about the fundamental theory valid at Planckian energies, except that it necessarily seems to imply the occurrence of a minimal length scale, providing a natural ultraviolet cutoff and a limit to the possible resolution of spacetime. Motivated by String Theory, the models of large extra dimensions lower the Planck scale to values soon accessible. These models predict a vast number of quantum gravity effects at the lowered Planck scale, among them the production of TeV-mass black holes and gravitons. Within the extra dimensional scenario, the minimal length also comes into the reach of experiment and sets a fundamental limit to short distance physics. We review the status of Planck scale physics in these effective models.

MSLED: a minimal supersymmetric large extra dimensions scenario

We propose a framework for the low-energy realization of supersymmetry which is very predictive, but differs radically in its phenomenological implications from the supersymmetric Standard Model (minimal or otherwise). The proposal consists of a supersymmetric version of the large-extra-dimensions scenario, with the Standard Model living on a 3-brane, coupled to a bulk sector consisting of six-dimensional supergravity. This picture is motivated by a promising recent attempt ( hep-th/0304256) to naturally understand the observed dark energy density, and this connection with dark energy prevents making the extra dimensions smaller than of order 5 μm. The resulting inability to change this size makes the model very predictive, and easily falsifiable within the near future. Being supersymmetric, it may plausibly be embedded into a more fundamental theory such as string theory, in which case an additional 4 compact dimensions may also be present having inverse radii at the TeV scale or higher. The model is close to, but consistent with, current experimental constraints. We outline possible phenomenological implications for particle physics (both at accelerators and elsewhere), for precision tests of gravity, for astrophysics and for cosmology.

SIGNATURES OF QUANTIZED TeV SCALE BLACK HOLES IN SCATTERING PROCESSES

In this paper we shall study the phenomenology of a doubly charged and neutral exchange black hole in an (n+3) extra-dimensional scenario, where the black hole shall be treated as a normal quantum field.

Search for branons at LEP

We search, in the context of extra-dimension scenarios, for the possible existence of brane fluctuations, called branons. Events with a single photon or a single Z-boson and missing energy and momentum collected with the L3 detector in e+e− collisions at centre-of-mass energies 2=189–209 GeV are analysed. No excess over the Standard Model expectations is found and a lower limit at 95% confidence level of 103 GeV is derived for the mass of branons, for a scenario with small brane tensions. Alternatively, under the assumption of a light branon, brane tensions below 180 GeV are excluded.