Universal Extra Dimensions Research Articles

Indirect dark matter search with the ANTARES neutrino telescope

Using the ANTARES neutrino telescope, the largest neutrino telescope in the Northern hemisphere, from its first configuration with 5 lines of photodetectors to the actual nominal one corresponding to a total of 12 lines, we have studied our ability to search indirectly an evidence of Dark Matter annihilations in heavy astrophysical objects as the Sun. First limits have been obtained using the data recorded by ANTARES in 2007 and 2008, and compared with neutrino fluxes predicted within a minimal supersymmetric extension of the Standard Model with supersymmetry-breaking scalar and gaugino masses constrained to be universal at the GUT scale, the CMSSM, as well as a minimal Universal Extra-Dimensions scenario with one extra compact dimension where all the Standard Model fields propagate into the bulk, the mUED. The current limits over the neutrino/muon fluxes coming from the dark matter self-annihilations, as well as the spin-dependent and spin-independent cross-sections, are presented.

Cosmological model with nonminimal derivative coupling of scalar fields in five dimensions

We study a nonminimal derivative coupling (NMDC) of scalar field, where the scalar field is coupled to curvature tensor in the five dimensional universal extra dimension model. We apply the Einstein equation and find its solution. First, we consider a special case of pure free scalar field without NMDC and we find that for static extradimension, the solution is equivalent to the standard cosmology with stiff matter. For a general case of pure free scalar field with NMDC, we find that the de Sitter solution is the solution of our model. For this solution, the scalar field evolves linearly in time. In the limit of small Hubble parameter, the general case give us the same solution as in the pure free scalar field. Finally, we perform a dynamical analysis to determine the stability of our model. We find that the extradimension, if it exist, can not be static and always shrinks with the expansion of four dimensional spacetime.

Testing minimal universal extra dimensions using Higgs boson searches at the LHC

Large Hadron Collider (LHC) searches for the SM Higgs boson provide a powerful limit on models involving Universal Extra Dimensions (UED) where the Higgs production is enhanced. We have evaluated all one-loop diagrams for Higgs production from gluon fusion and decay to two photons within "minimal" UED (mUED), independently confirming previous results, and we have evaluated enhancement factors for Higgs boson production and decay over the mUED parameter space. Using these we have derived limits on the parameter space, combining data from both ATLAS and CMS collaborations for the most recent 7 TeV and 8 TeV LHC data. We have performed a rigorous statistical combination of several Higgs boson search channels which is important because mUED signatures from the Higgs boson are not universally enhanced. We have found that 1/R < 500 GeV is excluded at 95% CL, while for larger 1/R only a very narrow (\pm1-4 GeV) mass window around m_h = 125 GeV and another window (up to 2 GeV wide for 1/R > 1000 GeV) around m_h = 118 GeV are left. The latter is likely to be excluded as more data becomes available whereas the region around 125 GeV is where the recently discovered Higgs-like particle was observed and therefore where the exclusion limit is weaker. It is worth stressing that mUED predicts an enhancement for all channels for Higgs production by gluon fusion and decay while the vector boson fusion process WW/ZZ -> h -> AA is generically suppressed and WW/ZZ -> h -> WW*/ZZ* is standard. Therefore, as more 8 TeV LHC data becomes available, the information on individual Higgs boson production and decay processes provided by the CMS and ATLAS experiments can be effectively used to favour mUED or exclude it further.

Dark Matter in a twisted bottle

Abstract The real projective plane is a compact, non-orientable orbifold of Euler characteristic 1 without boundaries, which can be described as a twisted Klein bottle. We shortly review the motivations for choosing such a geometry among all possible two-dimensional orbifolds, while the main part of the study will be devoted to dark matter study and limits in Universal Extra Dimensional (UED) models based on this peculiar geometry. In the following we consider such a UED construction based on the direct product of the real projective plane with the standard four-dimensional Minkowski space-time and discuss its relevance as a model of a weakly interacting Dark Matter candidate. One important difference with other typical UED models is the origin of the symmetry leading to the stability of the dark matter particle. This symmetry in our case is a remnant of the six-dimensional Minkowski space-time symmetry partially broken by the compactification. Another important difference is the very small mass splitting between the particles of a given Kaluza-Klein tier, which gives a very important role to co-annihilation effects. Finally the role of higher Kaluza-Klein tiers is also important and is discussed together with a detailed numerical description of the influence of the resonances.

Direct bound on the minimal universal extra dimension model from thett¯resonance search at the Tevatron

In the minimal Universal Extra Dimension (mUED) model, the second Kaluza-Klein (KK) gluon $g^{(2)}$ has loop-induced vertices with the standard model quarks, mediated by the first KK modes of the quark and the gluon/Higgs boson. With a top quark pair, this vertex is enhanced by the cooperation of the strong coupling of a gluon and the large Yukawa coupling of a top quark, leading to substantial branching ratio of $Br(g^{(2)} \to t \bar{t}) \approx 7%-8%$. As the $g^{(2)}$ coupling with two gluons appears via dimension-6 operator, $q\bar{q}\to g^{(2)}\to t\bar{t}$ is the golden mode for the mUED model. Hence the best channel is the $t\bar{t}$ resonance search in $p\bar{p}$ collisions. The recent Tevatron data at $\sqrt{s}=1.96$ TeV with an integrated luminosity of 8.7 fb$^{-1}$ are shown to give the first direct bound on the $g^{(2)}$ mass above 800 GeV. The implication and future prospect at the LHC are discussed also.

Non-minimal universal extra dimensions: the strongly interacting sector at the Large Hadron Collider

We work out the strongly interacting sector of a non-minimal Universal Extra Dimension (nmUED) scenario with one flat extra spatial dimension orbifolded on S^1/Z_2 in the presence of brane-localized kinetic and Yukawa terms. On compactification, these terms are known to have significant, nontrivial impact on the masses and the couplings of the Kaluza-Klein (KK) excitations. We study the masses of the level `1' KK gluon and the quarks and find the modified strong interaction vertices involving these particles. The scenario conserves KK parity. Possibility of significant level-mixing among the quarks from different KK-levels is pointed out with particular reference to the top quark sector. Cross sections for various generic final states involving level `1' KK-gluon and KK-quarks from first two generations are estimated at the Large Hadron Collider (LHC) via an implementation of the scenario in MadGraph-5 with the help of FeynRules. The decay branching fractions of both strong and weakly interacting KK excitations are studied to estimate yields in various different final states involving jets, leptons and missing energy. These are used to put some conservative constraints on the nmUED parameter space using the latest LHC data. Nuances of the scenario are elucidated with reference to the minimal Universal Extra Dimension (mUED) and Supersymmetry (SUSY) and their implications for the LHC are discussed.

Search for diphoton events with large missing transverse momentum in 7 TeV proton–proton collision data with the ATLAS detector

A search for diphoton events with large missing transverse momentum has been performed using proton–proton collision data at s=7 TeV recorded with the ATLAS detector, corresponding to an integrated luminosity of 4.8 fb−1. No excess of events was observed above the Standard Model prediction and model-dependent 95% confidence level exclusion limits are set. In the context of a generalised model of gauge-mediated supersymmetry breaking with a bino-like lightest neutralino of mass above 50 GeV, gluinos (squarks) below 1.07 TeV (0.87 TeV) are excluded, while a breaking scale Λ below 196 TeV is excluded for a minimal model of gauge-mediated supersymmetry breaking. For a specific model with one universal extra dimension, compactification scales 1/R<1.40 TeV are excluded. These limits provide the most stringent tests of these models to date.

Possible suppression of resonant signals for split universal extra dimensions by mixing at the LHC

The mixing of the imaginary parts of the transition amplitudes of nearby resonances via the breakdown of the Breit-Wigner approximation has been shown to lead to potentially large modifications in the signal rates for new physics at colliders. In the case of suppression, this effect may be significant enough to lead to some new physics signatures being initially missed in searches at, e.g., the LHC. Here we explore the influence of this `width mixing' on the production of the nearly degenerate, level-2 Kaluza-Klein (KK) neutral gauge bosons present in Split-UED. We demonstrate that in this particular case large cross section modifications in the resonance region are necessarily absent and explain why this is so based on the group theoretical structure of the SM.

Improved vacuum stability in a 5D extra-dimension model

In this paper we study the renormalization effects of the quark flavor mixings and the Higgs self-coupling in a five-dimensional model where the boson fields are propagating in the bulk while the matter fields are localized to the brane. We first explore the evolution behaviors for the Cabibbo-Kobayashi-Maskawa matrix in this scenario. Then, in light of the recent LHC bounds on the Higgs mass, we find that the Higgs self-coupling evolution has an improved vacuum stability condition, which is in contrast with that of Standard Model and the Universal Extra Dimension scenario, where the theory has a much lower ultraviolet cutoff.

Search for leptonic decays of W′ bosons in pp collisions at $ \sqrt {s} = {7} $ TeV

Abstract A search for a new heavy gauge boson W′ decaying to an electron or muon, plus a low mass neutrino, is presented. This study uses data corresponding to an integrated luminosity of 5.0 fb−1, collected using the CMS detector in pp collisions at a centre-of-mass energy of 7 TeV at the LHC. Events containing a single electron or muon and missing transverse momentum are analyzed. No significant excess of events above the standard model expectation is found in the transverse mass distribution of the lepton-neutrino system, and upper limits for cross sections above different transverse mass thresholds are presented. Mass exclusion limits at 95% CL for a range of W′ models are determined, including a limit of 2.5 TeV for right-handed W′ bosons with standard-model-like couplings and limits of 2.43–2.63 TeV for left-handed W′ bosons, taking into account their interference with the standard model W boson. Exclusion limits have also been set on Kaluza-Klein WKK states in the framework of split universal extra dimensions.

Higgs dark matter in UEDs: A good WIMP with bad detection prospects

We study the first Kaluza–Klein excitation of the Higgs boson in universal extra dimensions as a dark matter candidate. The first-level Higgs boson could be the lightest Kaluza–Klein particle, which is stable due to the conservation of Kaluza–Klein parity, in non-minimal models where boundary localized terms modify the mass spectrum. We calculate the relic abundance and find that it agrees with the observed dark matter density if the mass of the first-level Higgs boson is slightly above 2 TeV, not considering coannihilations and assuming no relative mass splitting among the first-level Kaluza–Klein modes. In the case of coannihilations and a non-zero mass splitting, the mass of the first-level Higgs boson can range from 1 TeV to 4 TeV. We study also the prospects for detection of this dark matter candidate in direct as well as indirect detection experiments. Although the first-level Higgs boson is a typical weakly interacting massive particle, an observation in any of the conventional experiments is very challenging.

Theories of particle dark matter

This brief review outlines some of the most attractive theoretical motivations for particle dark matter, and illustrates how they fit into the bigger context of physics beyond the Standard Model. Particular emphasis is given to the generic properties of theories of dark matter, and how the mechanism by which it interacts with the Standard Model particles influences its phenomenology. Brief descriptions of the most popular models, including supersymmetric theories and theories with universal extra dimensions are discussed.

Lower limits on the strengths of gamma ray lines from WIMP dark matter annihilation

We study the spectra of gamma ray signals that arise from dark matter annihilation in the universe. We focus on the large class of theories where the photon spectrum includes both continuum spectrum of gamma rays that arise from annihilation into Standard Model states at tree level, as well as monochromatic gamma rays arising from annihilation directly into two photons at the one loop level. In this class of theories we obtain lower bounds on the ratio of the strength of the gamma ray line relative to the gamma ray continuum as a function of the dark matter mass and spin. These limits are obtained from the unitarity relation between the tree level amplitude of the primary annihilation channel and the imaginary part of the loop level amplitude for annihilation directly into photons, with the primary decay products running in the loop. These results are exact in the limit that dark matter annihilation is exclusively to a single Standard Model species, occurs through the lowest partial wave and respects CP. Away from this limit the bounds are approximate. Our conclusions agree with the known results in the literature in the case of the Minimal Supersymmetric Standard Model (MSSM). We use the Fermi-LAT observations to translate these limits into upper bounds on the dark matter annihilation cross section into any specific Standard Model state.

Study ofBc→Ds*ℓ+ℓ−in a single universal extra dimension

The rare semileptonic Bc-> D_s^* \ell^+ \ell^- decay is studied in the scenario of the universal extra dimension model with a single extra dimension in which inverse of the compactification radius R is the only new parameter. The sensitivity of differential branching ratio, total branching ratio, polarization and forward-backward asymmetries of final state leptons, both for muon and tau, to the compactification parameter is presented. For some physical observables uncertainty on the form factors and resonance contributions have been considered in the calculations. Obtained results, compared with the available data, show that there appear new contributions due to the extra dimension.

Earthly probes of the smallest dark matter halos

Dark matter kinetic decoupling involves elastic scattering of dark matter off of leptons and quarks in the early universe, the same process relevant for direct detection and for the capture rate of dark matter in celestial bodies; the resulting size of the smallest dark matter collapsed structures should thus correlate with quantities connected with direct detection rates and with the flux of high-energy neutrinos from dark matter annihilation in the Sun or in the Earth. In this paper we address this general question in the context of two widely studied and paradigmatic weakly-interacting particle dark matter models: the lightest neutralino of the minimal supersymmetric extension of the Standard Model, and the lightest Kaluza-Klein particle of Universal Extra Dimensions (UED). We argue and show that while the scalar neutralino-nucleon cross section correlates poorly with the kinetic decoupling temperature, the spin-dependent cross section exhibits a strong correlation in a wide range of models. In UED models the correlation is present for both cross sections, and is extraordinarily tight for the spin-dependent case. A strong correlation is also found, for both models, for the flux of neutrinos from the Sun, especially for fluxes large enough to be at potentially detectable levels. We provide analytic guidance and formulae that illustrate our findings.

Bounds on the Fermion-Bulk masses in models with universal extra dimensions

In models with extra dimensions, vectorlike Dirac masses for fermion fields are generically allowed. These masses are independent of electroweak symmetry breaking and do not contribute to the known masses for the quarks and leptons. They control the profile of the bulk wave functions, the mass spectra of Kaluza-Klein modes, and interactions that could be tested in experiments. In this article, we study the effects of bulk masses in electroweak precision measurements and in dark matter and collider searches, to set bounds on the bulk mass parameters in models with a flat universal extra dimension, namely, Split-UED. We find the current bound on the universal bulk-mass to be smaller than (0.2-0.3)/R, where R is the radius of the extra dimension. Similar but slightly relaxed bounds are obtained in the non-universal bulk mass case. The LHC is expected to play an important role in constraining the remaining parameter space.

Constraints on universal extra dimension models with gravity mediated decays from ATLAS diphoton search

We discuss the collider phenomenology of Universal Extra Dimension models with gravity mediated decays. We concentrate on diphoton associated with large missing transverse energy signature. At the collider, level-1 Kaluza-Klein (KK) particles are produced in pairs due to the conservation of KK-parity. Subsequently, KK-particles decay via cascades involving lighter KK-particles until reaching the lightest KK-particle (LKP). Finally, gravity induced decay of the LKP into photons gives rise to the diphoton signature. The search for diphoton events with large missing transverse energy was recently communicated by the ATLAS collaboration for 7 TeV center-of-mass energy and 3.1 inverse femtobarn integrated luminosity of the Large Hadron Collider. Above the Standard Model background prediction, no excess of such events was reported. We translate the absence of any excess of the diphoton events to constrain the model parameters, namely, the radius of compactification (R) and the fundamental Planck mass ($M_D$).

RG running in a minimal UED model in light of recent LHC Higgs mass bounds

We study how the recent ATLAS and CMS Higgs mass bounds affect the renormalization group running of the physical parameters in universal extra dimensions. Using the running of the Higgs self-coupling constant, we derive bounds on the cutoff scale of the extra-dimensional theory itself. We show that the running of physical parameters, such as the fermion masses and the CKM mixing matrix, is significantly restricted by these bounds. In particular, we find that the running of the gauge couplings cannot be sufficient to allow gauge unification at the cutoff scale.

B→Kη(′)γdecays in the standard model and in scenarios with universal extra dimensions

We study the radiative $B\ensuremath{\rightarrow}K{\ensuremath{\eta}}^{(\ensuremath{'})}\ensuremath{\gamma}$ decays, which are important to investigate $CP$ violation, and are also relevant to assess the role of the exclusive modes induced by the $b\ensuremath{\rightarrow}s\ensuremath{\gamma}$ transition to saturate the inclusive $B\ensuremath{\rightarrow}{X}_{s}\ensuremath{\gamma}$ decay rate. Moreover, these channels do not display the same hierarchy as $B\ensuremath{\rightarrow}K{\ensuremath{\eta}}^{(\ensuremath{'})}$ modes, for which the decay into ${\ensuremath{\eta}}^{\ensuremath{'}}$ is enhanced with respect to one into $\ensuremath{\eta}$. The three-body radiative decays reverse the role: we find that this experimentally observed behavior (although affected by a large uncertainty in the case of the ${\ensuremath{\eta}}^{\ensuremath{'}}$) is reproduced in the theoretical analysis. We compute a ${B}^{*}\ensuremath{\rightarrow}K$ form factor, needed for this study, using light cone QCD sum rules, and discuss a relation expected to hold in the large energy limit for the light meson. Finally, we examine $B\ensuremath{\rightarrow}K\ensuremath{\eta}\ensuremath{\gamma}$ in two extensions of the standard model with universal extra dimensions, to investigate the sensitivity of this rare mode to such a kind of new physics effects.

Updated status of the global electroweak fit and constraints on new physics

We present an update of the Standard Model fit to electroweak precision data. We include newest experimental results on the top quark mass, the W mass and width, and the Higgs boson mass bounds from LEP, Tevatron and the LHC. We also include a new determination of the electromagnetic coupling strength at the Z pole. We find for the Higgs boson mass (91 +30 -23) GeV and (120 +12 -5) GeV when not including and including the direct Higgs searches, respectively. From the latter fit we indirectly determine the W mass to be (80.360 +0.014 -0.013) GeV. We exploit the data to determine experimental constraints on the oblique vacuum polarisation parameters, and confront these with predictions from the Standard Model (SM) and selected SM extensions. By fitting the oblique parameters to the electroweak data we derive allowed regions in the BSM parameter spaces. We revisit and consistently update these constraints for a fourth fourth fermion generation, two Higgs doublet, inert Higgs and littlest Higgs models, models with large, universal or warped extra dimensions and technicolour. In most of the models studied a heavy Higgs boson can be made compatible with the electroweak precision data.