Minimal Universal Extra Dimension Model Research Articles

Updated LHC bounds on MUED after run 2

We present updated LHC limits on the minimal universal extra dimensions (MUEDs) model from the Run 2 searches. We scan the parameter space against a number of searches implemented in the public code CheckMATE and derive up-to-date limits on the MUED parameter space from 13[Formula: see text]TeV searches. The strongest constraints come from a search dedicated to squarks and gluinos with one isolated lepton, jets and missing transverse energy. In the procedure, we take into account initial state radiation and stress its importance in the MUED searches, which is not always appreciated.

Renormalization and ultraviolet sensitivity of gauge vertices in universal extra dimensions

When computing radiative corrections in models with compactified extra dimensions, one has to sum over the entire tower of Kaluza-Klein excitations inside the loops. The loop corrections generate a difference between the coupling strength of a zero-mode gauge boson and the coupling strength of its Kaluza-Klein excitation, although both originate from the same higher-dimensional gauge interaction. Furthermore, this discrepancy will in general depend on the cutoff scale and assumptions about the UV completion of the extra-dimensional theory. In this article, these effects are studied in detail within the context of the minimal universal extra dimension model (MUED). The broad features of the cutoff scale dependence can be captured through the solution of the functional flow equation in five-dimensional space. However, an explicit diagrammatic calculation reveals some modifications due to the compactification of the extra dimension. Nevertheless, when imposing a physical renormalization condition, one finds that the UV sensitivity of the effective Kaluza-Klein gauge-boson vertex is relatively small and not very important for most phenomenological purposes. Similar conclusions should hold in a larger class of extra-dimensional models besides MUED.

LHC collider phenomenology of minimal universal extra dimensions

We discuss the collider phenomenology of the model of Minimal Universal Extra Dimensions (MUED) at the Large hadron Collider (LHC). We derive analytical results for all relevant strong pair-production processes of two level 1 Kaluza–Klein partners and use them to validate and correct the existing MUED implementation in the fortran version of the Pythia event generator. We also develop a new implementation of the model in the C++ version of Pythia. We use our implementations in conjunction with the Checkmate package to derive the LHC bounds on MUED from a large number of published experimental analyses from Run 1 at the LHC. Program summaryProgram title:Pythia6 MUED and Pythia8 MUEDProgram Files doi:http://dx.doi.org/10.17632/fkvcgdw9j6.1Licensing provisions: CC0 1.0Programming language: Fortran and C++Journal reference of previous version: Comput. Phys. Comm. 181 (2010) 122–127Does the new version supersede the previous version?: YesReasons for new version: The Minimal Universal Extra Dimension (MUED) model was implemented in the Pythia6 event generator from version 6.4.18 onwards. The new version now allows for different masses for various level 1 KK excitations, modified and corrected subroutines to handle the kinematics and squared matrix elements. A new production process has been added. Additionally the model is now made available in the Pythia8 event generator.Summary of revisions: The Minimal Universal Extra Dimension (MUED) model implementation in the Pythia6 event generator now allows for different masses for various level 1 KK excitations. These may appear both in the final states and in the propagators of t∕u channel contributions. Routines handling the kinematics and squared matrix elements are suitably modified to incorporate correct kinematics and ensure proper interferences of diagrams. For some processes, corrections in the expressions for the existing squared matrix elements have been made. A new subprocess qq̄→g1∗g1∗ has been added. A couple of production modes (which originally had some subprocesses lumped together) are now split to handle different masses of doublet and singlet KK excitations.Nature of problem: The ongoing run of the Large Hadron Collider (LHC) at CERN continues to look for new physics Beyond the Standard Model (BSM). For many years, the only complete models which were seriously investigated by the LHC collaborations, were different versions of low energy supersymmetry: mSUGRA, gauge-mediated SUSY, anomaly-mediated SUSY, etc. The MUED model provides an interesting and motivated alternative to supersymmetry, with unique and challenging collider phenomenology. In order to study the MUED model, it was implemented in the fortran version Pythia6 general purpose event generator from version 6.4.18 onwards. The MUED model is not available in the C++ version of Pythia8.Solution method: The new implementation validates and fixes the backward compatibility and some issues in the current Pythia6 version. The model has now been implemented in the Pythia8 event generator.

Constraining compressed versions of MUED and MSSM using soft tracks at the LHC

A compressed spectrum is an anticipated hideout for many beyond standard model scenarios. Such a spectrum naturally arises in the minimal universal extra dimension framework and also in supersymmetric scenarios. Low pT leptons and jets are characteristic features of such situations. Hence, a monojet with has been the conventional signal at the Large Hadron Collider (LHC). However, we stress that inclusion of pT -binned track observables from such soft objects provide very efficient discrimination of new physics signals against various SM backgrounds. We consider two benchmark points each for minimal universal extra dimension (MUED) and minimal supersymmetric standard model (MSSM) scenarios. We perform a detailed cut-based and multivariate analysis (MVA) to show that the new physics parameter space can be probed in the ongoing run of LHC at 13 TeV center-of-mass energy with an integrated luminosity ∼ 20-50 fb−1. When studied in conjunction with the dark matter relic density constraint assuming standard cosmology, we find that compressed MUED (with ΛR = 2) can be already excluded from the existing data. Also, MVA turns out to be a better technique than regular cut-based analysis since tracks provide uncorrelated observables which would extract more information from an event.

Current LHC constraints on minimal universal extra dimensions

In this letter, we present LHC limits on the minimal universal extra dimension (MUED) model from LHC Run 1 data and current limits from searches of the ongoing Run 2. Typical collider signals of the Kaluza–Klein (KK) states mimic generic degenerate supersymmetry (SUSY) missing transverse momentum signatures since the KK particles cascade decay into jets, leptons and the lightest KK particle which is stable due to KK parity and evades detection. We test the parameter space against a large number of supersymmetry based missing energy searches implemented in the public code CheckMATE. We demonstrate the complementarity of employing various searches which target a large number of final state signatures, and we derive the most up to date limits on the MUED parameter space from 13 TeV SUSY searches.

Electroweak Kaluza-Klein dark matter

In models with universal extra dimensions (UED), the lightest Kaluza-Klein excitation of neutral electroweak gauge bosons is a stable, weakly interacting massive particle and thus is a candidate for dark matter thanks to Kaluza-Klein parity. We examine concrete model realizations of such dark matter in the context of non-minimal UED extensions. The boundary localized kinetic terms for the electroweak gauge bosons lead to a non-trivial mixing among the first Kaluza-Klein excitations of the SU(2)W and U(1)Y gauge bosons and the resultant low energy phenomenology is rich. We investigate implications of various experiments including low energy electroweak precision measurements, direct and indirect detection of dark matter particles and direct collider searches at the LHC. Notably, we show that the electroweak Kaluza-Klein dark matter can be as heavy as 2.4 TeV, which is significantly higher than 1.3 TeV as is indicated as an upper bound in the minimal UED model.

Bounds on universal extra dimension from LHC run I and II data

We discuss the collider bounds on minimal Universal Extra Dimension (mUED) model from LHC Run-I and II data. The phenomenology of mUED is determined by only two parameters namely, the compactification scale ($R^{-1}$) of the extra dimension and cutoff scale ($\Lambda$) of the theory. The characteristic feature of mUED is the occurrence of nearly degenerate mass spectrum for the Kaluza-Klein (KK) particles and hence, soft leptons, soft jets at the collider experiments. The degree of degeneracy of KK-mass spectrum crucially depends on $\Lambda$. The strongest direct bound on $R^{-1}$ ($\sim $950 GeV for large $\Lambda$) arises from a search for a pair of soft dimuons at the Large Hadron Collider (LHC) experiment with 8 TeV center-of-mass energy and $20~{\rm fb}^{-1}$ integrated luminosity. However, for small $\Lambda$ and hence, small splitting within the first KK-level, the bounds from the dimuon channel is rather weak. On the other hand, the discovery of 126 GeV Higgs boson demands small $\Lambda$ to prevent the scalar potential form being unbounded from below. We discuss LHC monojet searches as a probe of low $\Lambda$ region of mUED parameter space. We also compute bounds on the mUED parameter space from 13 TeV multijets results.

Search for Strongly-Produced Supersymmetric Particles in Decays with Two Leptons at [formula omitted

This contribution presents a search for squarks and gluinos in final states containing two isolated electrons or muons using the 20.3 fb-1 of s=8 TeV proton-proton collisions recorded by the ATLAS detector at the LHC during 2012. The search uses a set of variables carrying information on the event kinematics both transverse and parallel to the beam line. No excess above the Standard Model expectation is observed, therefore exclusion limits are set on sparticle masses for various simplified model scenarios and a minimal universal extra dimensions model.

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.

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.

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.

Universal extra dimensions after Higgs discovery

We show bounds on five- and six-dimensional universal extra dimension (UED) models from the latest results of the Higgs searches at the LHC and from the electroweak precision data for the S and T parameters. We consider the minimal UED model in five dimensions and the ones in six dimensions. The highest possible ultraviolet cutoff scale for each UED model is evaluated from the electroweak vacuum stability by solving the renormalization group equation of the Higgs self-coupling. This scale turns out to be lower than the conventional one obtained from the perturbativity of the gauge coupling. The resultant 95% C.L. lower bounds on the first Kaluza-Klein scale from the LHC results and from the S, T analysis are 600 and 700 GeV in the minimal UED model, while those in the six-dimensional UED models are 800-1300 GeV and 900-1500 GeV, respectively.

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.

Search for Universal Extra Dimensions inpp¯Collisions

We present a search for Kaluza-Klein (KK) particles predicted by models with universal extra dimensions (UED) using a data set corresponding to an integrated luminosity of 7.3 fb(-1), collected by the D0 detector at a pp center-of-mass energy of 1.96 TeV. The decay chain of KK particles can lead to a final state with two muons of the same charge. This signature is used to set a lower limit on the compactification scale of R(-1)>260 GeV in a minimal UED model.

Enriching the exploration of the mUED model with event shape variables at the CERN LHC

We propose a new search strategy based on the event shape variables for new physics models where the separations among the masses of the particles in the spectrum are small. Collider signature of these models, characterized by low pT leptons/jets and low missing pT, are known to be difficult to look for. The conventional search strategies involving hard cuts may not work in such situations. As a case study, we have investigated the hitherto neglected jets+missing ET signature – known to be a challenging one – arising from the pair productions and decay of n=1 KK-excitations of gluons and quarks in the minimal Universal Extra Dimension (mUED) model. Judicious use of the event shape variables enables us to reduce the Standard Model backgrounds to a negligible level. We have shown that in mUED, R−1 up to 850 GeV can be explored or ruled out with 12 fb−1 of integrated luminosity at the 7 TeV run of the LHC. We also discuss the prospects of employing these variables for searching other beyond Standard Model physics with compressed or partially compressed spectra.

Implications on the minimal universal extra dimension model from the early LHC data onℓ+E̸Tsignal

Recently, the ATLAS and CMS collaborations reported their search for a new heavy gauge boson ${W}^{\ensuremath{'}}$ with one lepton plus missing transverse momentum. We find that ${W}^{(2)}$, the second Kaluza-Klein (KK) state of the $W$ boson in the minimal universal extra dimension (mUED) model, can be a good candidate for this signal, as its branching ratio into $\ensuremath{\ell}\ensuremath{\nu}$ is sizable. Moreover, nearly degenerate KK mass spectra in the mUED model yield generically very soft standard model particles accompanying ${W}^{(2)}$ from the subsequent decays of the second KK quarks and gluons. In a hadron collider, this indirect ${W}^{(2)}$ production is difficult to distinguish from the ${W}^{(2)}$ single production. The involved strong interactions make it more important than the single production. The early LHC data on $\ensuremath{\ell}+{\mathrm{E\ensuremath{\llap{\not\;}}}}_{T}$ signal for $1.1\text{ }\text{ }{\mathrm{fb}}^{\ensuremath{-}1}$ integrated luminosity is shown insufficient to limit our model. However, the results show that the present LHC $5.6\text{ }\text{ }{\mathrm{fb}}^{\ensuremath{-}1}$ data can cover most of the reasonable parameter space of the mUED model.

The second Kaluza–Klein mode of CP-odd neutral Higgs boson in the minimal universal extra dimension model

Loop-induced decays of a neutral standard model (SM) Higgs boson into a pair of gluons or photons are very suppressed if the Higgs boson is heavy (≳500 GeV). In the minimal universal extra dimension model, these radiative decays can be significant for the second Kaluza–Klein (KK) mode of the CP-odd Higgs boson, χ(2). We find that the CP-even KK Higgs boson has vanishing decay rate of h(2)→gg at one-loop level: the h(2) production at the LHC is very suppressed. On the contrary, the process gg→χ(2)→γγ in an optimal scenario can be observed with manageable SM backgrounds at the LHC.

Improved discovery of a nearly degenerate model: Minimal universal extra dimension model usingMT2at the LHC

We study the discovery potential of the minimal universal extra dimension model (MUED) and improve it by utilizing the $\mathrm{\text{multijet}}+\mathrm{\text{lepton}}$ mode at the LHC. Since the MUED has a nearly degenerate spectrum, most events only have soft jets and small ${E}_{T}^{\mathrm{miss}}$. The signature is challenging to search. We apply ${M}_{T2}$ for the event selection and set the invisible particle mass of ${M}_{T2}$ (test mass) to zero. The test mass is much smaller than the invisible particle mass of MUED. In that case, ${M}_{T2}$ of the signal can be large depending on up-stream radiation which includes initial state radiation. On the other hand, ${M}_{T2}$ of the background is mainly below the top quark mass. Hence, the signal is extracted from the background in the high ${M}_{T2}$ region. Since we use the leading jets for ${M}_{T2}$, there is a combinatorics effect. We find that the effect also enhances the signal to background ratio for high ${M}_{T2}$. We perform a detailed simulation with the matrix element correction to the QCD radiations. The discovery potential of the MUED is improved by the ${M}_{T2}$ cut, and the improvement is especially significant for the most degenerate parameter we consider, $\ensuremath{\Lambda}R=10$.

Indirect Search of Dark Matter with the ANTARES Neutrino Telescope

Indirect search for Dark Matter trapped inside celestial bodies is one of the main physics goals of neutrino telescopes. The expected flux coming from supersymmetric Dark Matter annihilations in the Sun and the sensitivity of the ANTARES and KM3NeT detectors to such a signal are presented. The ANTARES detector has been taking data during its construction phase in 2007 with five lines operational. This allowed to set a first limit on the neutrino flux coming from Dark Matter annihilations in the Sun with this experiment. A limit on Dark Matter to proton cross section in the framework of Minimal Universal Extra Dimension model is also presented.

Scaling of the Higgs self-coupling and bounds on the extra dimension

In this paper we study the one-loop evolution equation of the Higgs quartic coupling $\ensuremath{\lambda}$ in the minimal universal extra dimension model, and find that there are certain bounds on the extra dimension due to the singularity and vacuum stability conditions of the Higgs sector. In the range $250\text{ }\text{ }\mathrm{GeV}\ensuremath{\sim}{R}^{\ensuremath{-}1}\ensuremath{\sim}80\text{ }\text{ }\mathrm{TeV}$ of the compactification radius, we notice that for a given initial value $\ensuremath{\lambda}({M}_{Z})$, there is an upper limit on ${R}^{\ensuremath{-}1}$ for a Higgs mass of $183\text{ }\text{ }\mathrm{GeV}\ensuremath{\sim}{m}_{H}({M}_{Z})\ensuremath{\sim}187\text{ }\text{ }\mathrm{GeV}$; where any other compactification scales beyond that have been ruled out for theories where the evolution of $\ensuremath{\lambda}$ does not develop a Landau pole and become divergent in the whole range (that is, from the electroweak scale to the unification scale). Likewise, in the range of the Higgs mass $152\text{ }\text{ }\mathrm{GeV}\ensuremath{\sim}{m}_{H}({M}_{Z})\ensuremath{\sim}157\text{ }\text{ }\mathrm{GeV}$, for an initial value $\ensuremath{\lambda}({M}_{Z})$, we are led to a lower limit on ${R}^{\ensuremath{-}1}$; any other compactification scales below that will be ruled out for theories where the evolution of $\ensuremath{\lambda}$ does not become negative and destabilize the vacuum between the electroweak scale and the unification scale. For a Higgs mass in the range $157\text{ }\text{ }\mathrm{GeV}<{m}_{H}({M}_{Z})<183\text{ }\text{ }\mathrm{GeV}$, the evolution of $\ensuremath{\lambda}$ is finite and the theory is valid in the whole range (from the electroweak scale to the unification scale) for $250\text{ }\text{ }\mathrm{GeV}\ensuremath{\sim}{R}^{\ensuremath{-}1}\ensuremath{\sim}80\text{ }\text{ }\mathrm{TeV}$.