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.

No abstract

Besides supersymmetry, the other prime candidate of physics beyond the standard model (SM), crying out for verification at the CERN Large Hadron Collider (LHC), is extra-dimension. To hunt for effects of Kaluza-Klein (KK) excitations of known fermions and bosons is very much in the agenda of the LHC. These KK states arise when the SM particles penetrate in the extra space-like dimension(s). In this paper, we consider a 5d scenario, called 'Universal Extra Dimension', where the extra space coordinate, compactified on an orbifold S 1 /Z 2 , is accessed by all the particles. The KK number (n) is conserved at all tree level vertices. This entails the production of KK states in pairs and renders the lightest KK particle stable, which leaves the detector carrying away missing energy. The splitting between different KK flavors is controlled by the zero mode masses and the bulk-and brane-induced one-loop radiative corrections. We concentrate on the production of an n = 1 KK electroweak gauge boson in association with an n = 1 KK quark. This leads to a signal consisting of only one jet, one or more leptons and missing p T . For definiteness we usually choose the inverse radius of compactification to be R −1 = 500 GeV, which sets the scale of the lowest lying KK states. We show on a case-by-case basis (depending on the number of leptons in the final state) that with 10 fb −1 integrated luminosity at the LHC with √ s = 14 TeV this signal can be detected over the SM background by imposing appropriate kinematic cuts. We record some of the expectations for a possible intermediate LHC run at √ s = 10 TeV and also exhibit the integrated luminosity required to obtain a 5σ signal as a function of R −1 .

We study implications of recent data on neutrino mixing from T2K, MINOS, Double Chooz and µ → eγ from MEG for the Zee model. The simplest version of this model has been shown to be ruled out by experimental data some time ago. The general Zee model is still consistent with recent data. We demonstrate this with a constrained Zee model based on naturalness consideration. In this constrained model, only inverted mass hierarchy for neutrino masses is allowed, and θ 13 must be non-zero in order to have correct ratio for neutrino mass-squared differences and for mixing in solar and atmospherical neutrino oscillations. The best-fit value of our model for θ 13 is 8.91 • from T2K and MINOS data, very close to the central value obtained by Double Chooz experiment. There are solutions with non-zero CP violation with the Jarlskog parameter predicted in the range ±0.039, ±0.044 and ±0.048 respectively for a 1σ, 2σ and 3σ ranges of other input parameters. However, without any constraint on the θ 13 -parameter above respective ranges become ±0.049, ±0.053 and ±0.056. We analyse different cases to obtain a branching ratio for µ → eγ close to the recent MEG bound. We also discuss other radiative as well as the charged trilepton flavour violating decay modes of the τ -lepton.

We explore the discovery potential of doubly charged Higgs bosons (ξ ±± )

An effective theory for dark matter has recently been proposed. The key assumption is that the dark matter particle which is a Dirac fermion is protected from decaying by a global U(1) symmetry. We point out that quantum gravity effects will violate this symmetry and that the dark matter candidate thus decays very fast. In order to solve that problem, we propose to consider a local gauge symmetry which implies a new force in the dark matter sector. It is likely that this new local U(1) symmetry will need to be spontaneously broken leading for a range of the parameters of the model to a Sommerfeld enhancement of the annihilation cross-sections which is useful to explain the Pamela and ATIC results using a weakly interacting massive particle with a mass in the TeV range.

The upper limit on the mass of the lightest CP-even neutral Higgs in the minimal supersymmetric standard model is around 135 GeV for soft supersymmetry breaking masses in the 1 TeV range. We demonstrate that this upper limit may be sizably relaxed if supersymmetry is embedded in extra dimensions. We calculate, using the effective potential technique, the radiative corrections to the lightest Higgs mass induced by the Kaluza-Klein towers of quarks and squarks with one and two compactified directions. We observe that the lightest Higgs may comfortably weigh around 200 GeV (300 GeV) with one (two) extra dimension(s).

No abstract