arXiv subjects
Publications and source records attributed to Thomas Flacke.
We report on the current status of non-minimal universal extra dimension (UED) models. Our emphasis is on the possible extension of the minimal UED model by allowing bulk masses and boundary localized terms. We take into account the data from the Large Hadron Collider as well as direct and indirect searches of dark matter and electroweak precision measurements.
In composite Higgs models, the generation of quark masses requires the standard model-like quarks to be partially or fully composite states which are accompanied by composite quark partners. The composite quark partners decay into a standard model-like quark and an electroweak gauge boson or Higgs boson, which can be searched for at the LHC. In this article, we study the phenomenological implications of composite quarks in the minimal composite Higgs model based on the coset $SO(5)/SO(4)$. We focus on light quark partners which are embedded in the $SO(4)$ singlet representation. In this case, a dominant decay mode of the partner quark is into a Higgs boson and a jet, for which no experimental bounds have been established so far. The presence of $SO(4)$ singlet partners leads to an enhancement of the di-Higgs production cross section at the LHC. This will be an interesting experimental signature in the near future, but, unfortunately, there are no direct bounds available yet from the experimental analyses. However, we find that the currently available standard model-like Higgs searches can be used in order to obtain the first constraints on partially and fully composite quark models with light quark partners in the $SO(4)$ singlet. We obtain a flavor- and composition parameter independent bound on the quark partner mass of $M_{U_h} > 310 \mbox{ GeV}$ for partially composite quark models and $M_{U_h} > 212 \mbox{ GeV}$ for fully composite quark models.
We study the implications of a large degree of compositeness for the light generation quarks in composite pseudo-Nambu-Goldstone-boson Higgs models. We focus in particular on viable scenarios where the right-handed up-type quarks have a sizable mixing with the strong dynamics. For concreteness we assume the latter to be characterized by an SO(5)/SO(4) symmetry with fermionic resonances in the SO(4) singlet and fourplet representations. Singlet partners dominantly decay to a Higgs boson and jets. As no dedicated searches are currently looking for these final states, singlet partners can still be rather light. Conversely, some fourplet partners dominantly decay to an electroweak gauge boson and a jet, a signature which has been analyzed at the LHC. To constrain the parameter space of this scenario we have reinterpreted various LHC analyses. In the limit of first two generation degeneracy, as in minimal flavor violation or U(2)-symmetric flavor models, fourplet partners need to be relatively heavy, with masses above 1.8 TeV, or the level of compositeness needs to be rather small. The situation is rather different in models that deviate from the first two generation degeneracy paradigm, as the charm parton distribution functions are suppressed relative to the up quark ones. The right-handed charm quark can be composite and its partners being as light as 600 GeV, while the right-handed up quark needs either to be mostly elementary or to have its partners as heavy as 2 TeV. Models with fully composite singlet fermions are also analyzed, leading to similar conclusions. Finally, we consider the case where both the fourplet and the singlet states are present. In this case the bounds could be significantly weaken due to a combination of smaller production rates and the opening of new channels including cascade processes.
Discovery of a Higgs boson and precise measurements of its properties open a new window to test physics beyond the standard model. Models with Universal Extra Dimensions are not exception. Kaluza-Klein excitations of the standard model particles contribute to the production and decay of the Higgs boson. In particular, the parameters associated with third generation quarks are constrained by Higgs data, which are relatively insensitive to other searches often involving light quarks and leptons. We investigate implications of the 126 GeV Higgs in Next-to-Minimal Universal Extra Dimensions, and show that boundary terms and bulk masses allow a lower compactification scale as compared to in Minimal Universal Extra Dimensions.
Models with universal extra dimensions predict that each Standard Model particle is accompanied by a tower of Kaluza-Klein resonances. Canonical searches for the production and cascade decays of first Kaluza-Klein modes through missing transverse momentum signatures suffer in general from low detection efficiencies because of the rather compressed Kaluza-Klein particle mass spectrum. Here, instead we analyze signatures from the production of second Kaluza-Klein states which can decay into Standard Model particles and thus do not result in any missing transverse momentum. Such signatures provide a strong sensitivity, and are of particular interest as they would allow for a clear distinction between extra dimension models and other models of new physics like supersymmetry. We constrain the production of second Kaluza-Klein particles from recent LHC searches for dilepton resonances, and place limits on the compactification scale to be larger than 715GeV, and on the masses of the second Kaluza-Klein particles to be larger than 1.4TeV.
We present a general model with universal extra dimensions in the presence of the bulk fermion masses and boundary localized kinetic terms, which are generically allowed by symmetries of five dimensional gauge theory. We provide a comprehensive analysis for a general UED model, including Kaluza-Klein mass spectra, their interactions with the SM particles, and constraints from LHC, electroweak tests, and dark matter experiments. Finally we show current bounds on the size of allowed universal bulk mass and universal brane-localized terms.
We obtain contraints on three Universal Extra Dimensional models utilizing limits from the CMS Collaboration on W' production and decay into a single-top-quark final state. We find a weak constraint on the Minimal Universal Extra Dimensions model due to small Kaluza-Klein number violating terms. In contrast, the W' search puts a strong limit on the size of the Dirac mass term of the quarks in Split Universal Extra Dimension models. In Non-minimal Universal Extra Dimension models the W' search constrains the splitting between the boundary localized kinetic terms of the gauge bosons and the quarks. Each of these bounds can be translated into constraints on the mass splitting between the Kaluza-Klein excitations of the SU(2) charged quarks and the Klauza-Klein excitations of the W boson.
We present strongly improved electroweak precision constraints on the split-UED model. We find that the dominating effect arises from contributions to the muon decay rate by the exchange of even-numbered W-boson Kaluza-Klein modes at tree-level, which so far have not been discussed in the context of UED models. The constraints on the split-UED parameter space are translated into bounds on the mass difference of the first Kaluza-Klein mode of fermions and the lightest Kaluza-Klein mode, which will be tested is the LHC.
In models with one universal extra dimension (UED), the first Kaluza-Klein excitations of the hypercharge gauge boson, B^(1), and the neutral component of isospin gauge boson, W^3(1), are each viable dark matter candidates. In either case, such particles are predicted to accumulate in the core of the Sun, where they annihilate to generate a potentially observable flux of high energy neutrinos. In this article, we calculate the flux of neutrinos produced in this model and determine the constraints that can be placed on the UED parameter space from current IceCube data. For the case of B^(1) dark matter, we find that the present limits from IceCube are stronger than those from direct dark matter detection experiments such as CDMS and XENON10. For W^3(1) dark matter, the present IceCube data provides a constraint slightly weaker than direct detection experiments. In addition, we also present the projected regions of UED parameter space that can be probed by IceCube/DeepCore in the near future and compare them to the prospects for future direct detection experiments.
In this paper we investigate the phenomenological implications of boundary localized terms (BLTs) in the model of Universal Extra Dimensions (UED). In particular, we study the electroweak Kaluza-Klein mass spectrum resulting from BLTs and their effect on electroweak symmetry breaking via the five dimensional Higgs mechanism. We find that the addition of BLTs to massive five dimensional fields induces a non-trivial extra dimensional profile for the zero and non-zero Kaluza-Klein (KK) modes. Hence BLTs generically lead to a modification of Standard Model parameters and are therefore experimentally constrained, even at tree level. We study Standard Model constraints on three representative non-minimal UED models in detail and find that the constraints on BLTs are weak. On the contrary, non-zero BLTs have a major impact on the spectrum and couplings of non-zero KK modes. For example, there are regions of parameter space where the Lightest Kaluza-Klein particle (LKP) is either the Kaluza-Klein Higgs boson or the first KK mode of the W^3.
Motivated by multi-throat considerations, we study the phenomenological implications of a bulk axion in a slice of AdS_5 with a large extra dimension: k~0.01 eV, kR > 1. In particular, we compare axion physics with a warped geometry to axions in flat compactifications. As in flat compactification scenarios, we find that the mass of the axion can become independent from the underlying Peccei-Quinn scale. Surprisingly, we find that in warped extra dimensions the axion's invisibility, cosmological viability, and basic phenomenology remain essentially unaltered in comparison to axions in flat compactifications.
We study a number of realizations of axions existing in a multi-`throat' generalization of the warped throat geometry of a Randall-Sundrum slice of $AdS_5$. As argued by previous authors, the problem of generating a suitable, phenomenologically allowed Peccei-Quinn scale is simply and elegantly solved by the warping. In compactifications with two or more throats it is possible to simultaneously solve the Standard Model hierarchy problem by the Randall-Sundrum mechanism while implementing interesting warped axion models. The constructions discussed are related to holographic duals of previously studied models of composite axions arising from strongly coupled four-dimensional dynamics.
We report on recent constraints on models with a flat ``universal'' extra dimension in which all Standard Model fields propagate in the bulk. A significantly improved constraint on the compactification scale is obtained from the extended set of electroweak precision observables accurately measured at LEP1 and LEP2. We find a lower bound of 1/R > 700 (800) GeV at the 99% (95%) confidence level. Comparison of this constraint with the relic density of Kaluza-Klein dark matter for the Minimal UED model points towards the necessity of including non-minimal boundary terms which motivates studying alternative Kaluza-Klein dark matter candidates. Results for the one-loop induced magnetic dipole moment for Kaluza-Klein neutrino dark matter are presented. This talk is based on Phys.Rev.D73:095002,2006 and hep-ph/0601161.
Generically, universal extra dimension (UED) extensions of the standard model predict the stability of the lightest Kaluza-Klein (KK) particle and hence provide a dark matter candidate. For UED scenarios with one extra dimension, we model-independently determine the size of the induced dimension-five magnetic dipole moment of the KK-neutrino, $ν^{(1)}$. We show that current observational bounds on the interactions of dipole dark matter place constraints on UED models with KK-neutrino dark matter.
We study constraints on models with a flat "Universal'' Extra Dimension in which all Standard Model fields propagate in the bulk. A significantly improved constraint on the compactification scale is obtained from the extended set of electroweak precision observables accurately measured at LEP1 and LEP2. We find a lower bound of M_c = R^{-1} > 700 (800) GeV at the 99% (95%) confidence level. We also discuss the implications of this constraint on the prospects for the direct and indirect detection of Kaluza-Klein dark matter in this model.
We consider a U(1) gauge theory on the five dimensional orbifold $\mathcal{M}_4\times S^1/Z_2$, where $A_5$ has even $Z_2$ parity. This leads to a light pseudoscalar degree of freedom $W(x)$ in the effective 4D theory below the compactification scale arising from a gauge-invariant brane-to-brane Wilson line. As noted by Arkani-Hamed et al in the non-supersymmetric $S^1$ case the 5D bulk gauge-invariance of the underlying theory together with the non-local nature of the Wilson line field leads to the protection of the 4D theory of $W(x)$ from possible large global-symmetry violating quantum gravitational effects. We study the $S^1/Z_2$ theory in detail, in particular developing the supersymmetric generalization of this construction, involving a pseudoscalar Goldstone field (the `axion') and its scalar and fermion superpartners (`saxion' and `axino'). The global nature of $W(x)$ implies the absence of independent Kaluza-Klein excitations of its component fields. The non-derivative interactions of the (supersymmetric) Wilson line in the effective 4D theory arising from U(1) charged 5D fields $Φ$ propagating between the boundary branes are studied. We show that, similar to the non-supersymmetric $S^1$ case, these interactions are suppressed by $\exp(-πR m_Φ)$ where $πR$ is the size of the extra dimension.