Universal Extra Dimensions Research Articles

W′ at the LHC with √s = 14 TeV: Split universal extra dimension model

We study the search of new charged gauge boson W′ in the split universal extra dimension model by considering pp → W′ → lve with √s = 14 TeV at the Large Hadron Collider. The interference between the W′ and the W boson of the Standard Model can be used to probe W′ from the distribution shape of the transverse mass between the lepton and the neutrino from the decay of W′. We show that the LHC can cover a rather large range of masses of the Kaluza-Klein W boson for various values of the couplings.

Direct detection of vector dark matter

In this paper we complete formulae for the elastic cross section of general vector dark matter with nucleon in the direct detection at the leading order of the strong coupling constant, assuming that the dark matter is composed of vector particles. As an application of our formulae, the direct detection of the first Kaluza-Klein photon in the minimal universal extra dimension model is discussed. It is found that the cross section is larger than those in the previous works by up to a factor of ten.

XQCAT: eXtra Quark Combined Analysis Tool

XQCAT (eXtra Quark Combined Analysis Tool) is a tool aimed at determining exclusion confidence levels for scenarios of new physics characterised by the presence of one or multiple heavy extra quarks which interact through Yukawa couplings with any of the Standard Model quarks. The code uses a database of efficiencies for pre-simulated processes of QCD-induced pair production of extra quarks and their subsequent on-shell decays. In the version 1.2 of XQCAT the efficiencies have been computed for a set of seven publicly available search results by the CMS experiment. The input for the code is a text file in which masses, branching ratios and dominant chirality of the couplings of the new quarks are provided. The output of the code is the exclusion confidence levels of the test point for each implemented experimental analysis considered individually and, when possible, in statistical combination. Program summaryProgram title: XQCATCatalogue identifier: AEXS_v1_0Program summary URL:http://cpc.cs.qub.ac.uk/summaries/AEXS_v1_0.htmlProgram obtainable from: CPC Program Library, Queen’s University, Belfast, N. IrelandLicensing provisions: Standard CPC licence, http://cpc.cs.qub.ac.uk/licence/licence.htmlNo. of lines in distributed program, including test data, etc.: 84420No. of bytes in distributed program, including test data, etc.: 1959913Distribution format: tar.gzProgramming language: Perl and C++.Computer: Personal Computer.Operating system: Any OS where Perl, C++ and ROOT are installed.RAM: Around 2.5 MbytesClassification: 11.1, 11.6.External routines: C++, Perl and ROOTSubprograms used:Cat IdTitleReferenceAEFA_v2_0ROOTCPC 182(2011)1384Nature of problem: Experimental searches of new heavy extra quarks (XQs) usually consider minimal extensions of the Standard Model (SM) with only one XQ representation which couples only to the third generation SM quarks or only to the SM light quark families. In contrast, various theoretically-motivated scenarios of new physics predict a new quark sector, i.e. more than one new quark, with general couplings to SM quarks. Notable examples are composite Higgs models or universal extra-dimensions. Hence, recasting experimental limits for these scenarios can be a challenging task. To avoid time-consuming simulations and dedicated searches for scenarios which can already be excluded by current data, we present a tool for reinterpretation of existing experimental analyses, including those not made for XQs searches, in terms of exclusion confidence levels (eCLs) for XQ models. Our tool should serve as a useful preliminary approach to understand in a quick way the regions of validity of scenarios of new physics.Solution method: The core of the tool consists in a database of pre-simulated efficiencies (ϵ), defined as the ratio of signal events which survive a given set of experimental cuts over the total number of signal events. These efficiencies have been computed simulating the process of pair production and decay of XQs with masses in the range 400–2000 GeV and implementing the selection and kinematics cuts of a set of experimental searches at 7 and 8 TeV. The tool uses the database to reconstruct any scenario where XQs couple to SM quarks through Yukawa interactions and gives as output the eCL of the test point, characterised by values of the XQ masses and their branching ratios (BRs) into specific final states, for all the implemented searches. It also provides eCLs for combinations of experimental searches when search bins are uncorrelated. The method has been validated against experimental analyses.Restrictions: The efficiency database has been built under the following hypotheses: QCD induced pair production of quarks with masses from 400 GeV to 2000 GeV with steps of 100 GeV; the electro-weak (EW) couplings of XQs with SM states have a dominant chirality, according to the hypothesis that new quarks are vector-like and that a new chiral generation is excluded with high confidence level (see main text for more details); in v1.2 the number of searches implemented is limited: four supersymmetric (SUSY) inspired CMS searches for final states with jets, missing transverse energy and variable number of leptons at 7 TeV [1-4], two SUSY-inspired CMS searches at 8 TeV (updates of two of the implemented 7 TeV searches) [5,6] and one CMS direct search at 8 TeV of a vector-like t′ (a top quark partner) coupling to third generation SM quarks [7]. The code also relies on the possibility of reproducing experimental results by using a cut-and-count analysis technique and applying a eCL procedure.Running time: Around 30 seconds with two XQs and with 100k toy Monte Carlo (MC) experiments yielding specific numbers of signal and background events to determine the eCL (tested on a DELL Precision M4700 laptop with a Kubuntu Linux 12.04 distribution).

Semi-leptonic [formula omitted] decays in the standard model and in the universal extra dimension model

In this article, we assume the two nonets of scalar mesons below and above 1 GeV are all q¯q states, and study the semi-leptonic decays B→Sℓ−ν¯ℓ, B→Sℓ+ℓ− and B→Sν¯ν both in the standard model and in the universal extra dimension model using the B–S form-factors calculated by the light-cone QCD sum rules in our previous work. We obtain the partial decay widths and decay widths, which can be confronted with the experimental data in the future to examine the natures of the scalar mesons and constrain the basic parameter in the universal extra dimension model, the compactification scale 1/R.

Search for physics beyond the standard model in final states with a lepton and missing transverse energy in proton-proton collisions ats=8 TeV

A search for new physics in proton-proton collisions having final states with an electron or muon and missing transverse energy is presented. The analysis uses data collected in 2012 with the CMS detector, at an LHC center-of-mass energy of 8 TeV, and corresponding to an integrated luminosity of 19.7 inverse femtobarns. No significant deviation of the transverse mass distribution of the charged lepton-neutrino system from the standard model prediction is found. Mass exclusion limits of up to 3.28 TeV at a 95% confidence level for a W' boson with the same couplings as that of the standard model W boson are determined. Results are also derived in the framework of split universal extra dimensions, and exclusion limits on Kaluza-Klein W[KK,2] states are found. The final state with large missing transverse energy also enables a search for dark matter production with a recoiling W boson, with limits set on the mass and the production cross section of potential candidates. Finally, limits are established for a model including interference between a left-handed W' boson and the standard model W boson, and for a compositeness model.

Status report on universal extra dimensions after LHC8

Although they do not address the hierarchy problem, models with Universal Extra Dimensions have attracted a lot of attention as simple benchmark models characterized by small mass splittings and a dark matter (DM) WIMP played by the Lightest Kaluza–Klein particle (LKP). We review their status, with emphasis on minimal implementation in five dimensions (MUED) in which the LKP is a massive hypercharge gauge boson. In this case, the mass range accounting for the correct DM abundance (around 1.4 TeV) remains untouched by LHC8 and is out of reach of present DM direct detection experiments. However, LHC14 can probe the relevant region in the 3-lepton channel.

Bounds on Kaluza–Klein states from EWPT and direct searches at the LHC

We review the present bounds on Kaluza–Klein (KK)-excitations of Standard Model gauge bosons, predicted by TeV size extra dimensions, which have been set by the ElectroWeak Precision Test (EWPT) and recently by the direct searches performed at the CERN Large Hadron Collider (LHC). Concerning the theoretical framework we present results for the Non-Universal Extra Dimension (NUED) model with matter localized at the boundaries and all gauge bosons propagating into the bulk and acquiring KK-excitations. We also discuss its simplified version, NUED(EW), where only the ElectroWeak SM gauge bosons are allowed to propagate in the extra dimension, and its next-to-minimal version ElectroWeak Universal Extra Dimension (UED)(EW) where SU(3) is localized on the brane while the SU(2)×U(1) particle content fully propagates into the bulk.

Search for squarks and gluinos in events with isolated leptons, jets and missing transverse momentum at s = 8 $$ \sqrt{s}=8 $$ TeV with the ATLAS detector

The results of a search for supersymmetry in final states containing at least one isolated lepton (electron or muon), jets and large missing transverse momentum with the ATLAS detector at the Large Hadron Collider (LHC) are reported. The search is based on proton-proton collision data at a centre-of-mass energy $\sqrt{s} = 8$ TeV collected in 2012, corresponding to an integrated luminosity of 20 fb$^{-1}$. No significant excess above the Standard Model expectation is observed. Limits are set on the parameters of a minimal universal extra dimensions model, excluding a compactification radius of $1/R_c=950$ GeV for a cut-off scale times radius ($\Lambda R_c$) of approximately 30, as well as on sparticle masses for various supersymmetric models. Depending on the model, the search excludes gluino masses up to 1.32 TeV and squark masses up to 840 GeV.

Z → b b ¯ $$ Z\to b\overline{b} $$ in non-minimal Universal Extra Dimensional Model

We calculate the effective $$ Zb\overline{b} $$ coupling at one loop level, in the framework of non-minimal Universal Extra Dimensional (nmUED) model. Non-minimality in Universal Extra Dimensional (UED) framework is realized by adding kinetic and Yukawa terms with arbitrary coefficients to the action at boundary points of the extra space like dimension. A recent estimation of the Standard Model (SM) contribution to $$ Zb\overline{b} $$ coupling at two loop level, points to a 1.2σ discrepancy between the experimental data and the SM estimate. We compare our calculation with the difference between the SM prediction and the experimental estimation of the above coupling and constrain the parameter space of nmUED. We also review the limit on compactification radius of UED in view of the new theoretical estimation of SM contribution to $$ Zb\overline{b} $$ coupling. For suitable choice of coefficients of boundary-localized terms, 95% C.L. lower limit on R −1 comes out to be in the ballpark of 800 GeV in the framework of nmUED; while in UED, the lower limit on R −1 is 350 GeV which is a marginal improvement over an earlier estimate.

A review on non-minimal universal extra dimensions

We report on the current status of non-minimal universal extra dimension (NMUED) models. Our emphasis is on the possible extension of the minimal UED (MUED) model by allowing bulk masses and boundary localized terms. We take into account the data from the Large Hadron Collider (LHC) as well as direct and indirect searches of dark matter (DM) and electroweak (EW) precision measurements.

Constraining bosonic supersymmetry from Higgs results and 8 TeV ATLAS multi-jets plus missing energy data

The collider phenomenology of the models with Universal Extra Dimensions (UED) is surprisingly similar to that of supersymmetric (SUSY) scenarios. For each level-1 bosonic (fermionic) Kaluza-Klein (KK) state, there is a fermionic (bosonic) analog in SUSY and thus UED scenarios are often known as bosonic supersymmetry. The minimal version of UED (mUED) gives rise to a quasi-degenerate particle spectrum at each KK-level and thus, can not explain the enhanced Higgs to diphoton decay rate hinted by the ATLAS collaboration of the Large Hadron Collider (LHC) experiment. However, in the non-minimal version of the UED (nmUED) model, the enhanced Higgs to diphoton decay rate can be easily explained via the suitable choice of boundary localized kinetic (BLK) terms for higher dimensional fermions and gauge bosons. BLK terms remove the degeneracy in the KK mass spectrum and thus, pair production of level-1 quarks and gluons at the LHC gives rise to hard jets, leptons and large missing energy in the final state. These final states are studied in details by the ATLAS and CMS collaborations in the context of SUSY scenarios. We find that the absence of any significant deviation of the data from the Standard Model (SM) prediction puts a lower bound of about 2.1 TeV on equal mass excited quarks and gluons.

Radiative decay in SM and BSM

Using transition form factors calculated via light cone QCD sum rules in full theory, we comparatively analyze the rare radiative decay in the standard model (SM) and models with one or two universal extra dimensions, such as beyond the SM scenarios. We estimate the total decay width and branching ratio associated with this decay channel in the SM and compare the obtained results with those of scenarios with one or two universal extra dimensions. We discuss how the results of universal extra dimensional models approach the SM predictions when the compactification factor of extra dimension is increased.

Yang-Mills theories with an arbitrary number of compactified extra dimensions

The well-known Yang-Mills theory with one $ S^{1} / Z_{2}$ universal extra dimension (UED) is generalized to an arbitrary number of spatial extra dimensions through a novel compactification scheme. In this paper, the Riemannian flat based manifold under consideration contains $ n $ spatial extra dimensions defined by $ n $ copies of the orbifold $ S^{1} / Z_{2}$. In this approach, we present the gauge structure and the mass spectrum of the effective four-dimensional theory. We introduce the concept of standard and nonstandard gauge transformations of the effective theory, and explicitly identify the emergence of massive vector fields in the same number as massless ('pseudo-Goldstone') scalars in the compactified theory, verifying that a Higgs-like mechanism operates in the compactification process. It is found that, in contrast with the one UED scenario, in cases with two or more UEDs there emerge massive scalar fields. Besides, at phase-space level, the Hamiltonian analysis yields that the higher-dimensional and compactified theories are classically equivalent using the fundamental concept of canonical transformation. This work lays the ground for a wider study on these theories concerning their quantization and predictive power at the level of quantum fluctuations.

Higgs boson decay constraints on a model with a universal extra dimension

We investigate the impact of the latest data on Higgs boson branching ratios on the minimal model with a Universal Extra Dimension (mUED). Combining constraints from vacuum stability requirements with these branching ratio measurements we are able to make realistic predictions for the signal strengths in this model. We use these to find a lower bound of 1.3 TeV on the size parameter $R^{-1}$ of the model at 95% confidence level, which is far more stringent than any other reliable bound obtained till now.

Matter matters in asymptotically safe quantum gravity

We investigate the compatibility of minimally coupled scalar, fermion and gauge fields with asymptotically safe quantum gravity, using nonperturbative functional renormalization group methods. We study $d=4,5$ and 6 dimensions and within certain approximations find that for a given number of gauge fields there is a maximal number of scalar and fermion degrees of freedom compatible with an interacting fixed point at positive Newton coupling. The bounds impose severe constraints on grand unification with fundamental Higgs scalars. Supersymmetry and universal extra dimensions are also generally disfavored. The standard model and its extensions accommodating right-handed neutrinos, the axion and dark-matter models with a single scalar are compatible with a fixed point.

AMS-02 and next-to-minimal universal extra dimensions

The anomaly detected by AMS-02 and PAMELA in the cosmic-ray positron flux when interpreted as arising from dark matter annihilation suggests that dark matter may interact differently with hadrons and leptons so as to remain compatible with cosmic-ray antiproton data. Such a scenario is readily accommodated in models with extra spatial dimensions. We study indirect detection of Kaluza–Klein (KK) dark matter in universal extra dimensions with brane-localized terms and fermion bulk masses: next-to-minimal universal extra dimensions. So that an excess of antiprotons is not produced in explaining the positron anomaly, it is necessary that the KK bulk masses in the lepton and hadron sectors be distinct. Even so, we find that cosmic-ray data disfavor a heavy KK photon dark matter scenario. Also, we find these scenarios with flavor-universal bulk masses to be in conflict with dijet and dilepton searches at the LHC.

Direct detection of vector dark matter

We evaluate the elastic scattering cross section of vector dark matter with nucleon based on the method of effective field theory. The dark matter is assumed to behave as a vector particle under the Lorentz transformation and to interact with colored particles including quarks in the Standard Model. After formulating general formulae for the scattering cross sections, we apply them to the case of the first Kaluza–Klein photon dark matter in the minimal universal extra dimension model. The resultant cross sections are found to be larger than those calculated in previous literature.

Dark matter in minimal universal extra dimensions with a stable vacuum and the “right” Higgs boson

The recent discovery of a Higgs boson with mass of about 125 GeV, along with its striking similarity to the prediction from the standard model, informs and constrains many models of new physics. The Higgs mass exhausts one out of three input parameters of the minimal, five-dimensional version of universal extra dimension models, the other two parameters being the Kaluza-Klein (KK) scale and the cutoff scale of the theory. The presence of KK fermions with large coupling to the Higgs implies a short-lived electroweak vacuum, unless the cutoff scale is at most a few times higher than the KK mass scale, providing an additional tight constraint to the theory parameter space. Here, we focus on the lightest KK particle as a dark matter candidate, and investigate the regions of parameter space where such particle has a thermal relic density in accord with the cosmological dark matter density. We find the paradoxical result that, for low enough cutoff scales consistent with vacuum stability, larger than previously thought KK mass scales become preferred to explain the dark matter abundance in the Universe. We explain this phenomenon by pinpointing the additional particles which, at such low cutoffs, become close enough in mass to the dark matter candidate to coannihilate with it. We make predictions for both collider and direct dark matter searches that might soon close in on all viable theory parameter space.

Universal extra dimensions : life with BLKTs

In universal extra dimension (UED) models with one compactified extra dimension, a Z2 symmetry, termed KK-parity, ensures the stability of the lightest Kaluza-Klein particle (LKP) which could be a viable dark matter candidate. This symmetry leads to two fixed points in the extra space like direction. In non-minimal versions of UED boundary-localized kinetic terms (BLKT) of same strength at both fixed points induce a new Z2 symmetry which ensures the stability of LKP. The precision of the dark matter measurements severely correlates and restricts the BLKT parameters of gauge bosons and fermions. Furthermore, BLKT parameters of different strengths at the fixed would induce a non-consevation of KK-parity. We examine, in the presence of such terms, single production and decay of Kaluza-Klein excitations of the neutral electroweak gauge bosons in the context of LHC.

Non-minimal Universal Extra Dimensions with Brane Local Terms: the top quark sector

We study the physics of Kaluza-Klein (KK) top quarks in the framework of a non-minimal Universal Extra Dimension (nmUED) with an orbifolded (S1/Z2) flat extra spatial dimension in the presence of brane-localized terms (BLTs). In general, BLTs affect the masses and the couplings of the KK excitations in a non-trivial way including those for the KK top quarks. On top of that, BLTs also influence the mixing of the top quark chiral states at each KK level and trigger mixings among excitations from different levels with identical KK parity (even or odd). The latter phenomenon of mixing of KK levels is not present in the popular UED scenario known as the minimal UED (mUED) at the tree level. Of particular interest are the mixings among the KK top quarks from level `0' and level `2' (driven by the mass of the Standard Model (SM) top quark). These open up new production modes in the form of single production of a KK top quark and the possibility of its direct decays to Standard Model (SM) particles leading to rather characteristic signals at the colliders. Experimental constraints and the restrictions they impose on the nmUED parameter space are discussed. The scenario is implemented in MadGraph 5 by including the quark, lepton, the gauge-boson and the Higgs sectors up to the second KK level. A few benchmark scenarios are chosen for preliminary studies of the decay patterns of the KK top quarks and their production rates at the LHC in various different modes. Recast of existing experimental analyzes in scenarios having similar states is found to be not so straightforward for the KK top quarks of the nmUED scenario under consideration.