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Possible low energy manifestations of strings and gravity
https://cds.cern.ch/record/1359203
Lowering the string scale in the TeV region provides a theoretical framework for solving the mass hierarchy problem and unifying all interactions. The apparent weakness of gravity can then be accounted by the existence of large internal dimensions, in the submillimeter region, and transverse to a braneworld where our universe must be confined. I review the main properties of this scenario and its implications for observations at both particle colliders, and in non-accelerator gravity experiments. I also discuss the warped case and localization of gravity in the presence of infinite size extra dimensions.Antoniadis, IThu, 16 Jun 2011 09:18:05 GMThttps://cds.cern.ch/record/1359203Alternative electroweak symmetry breaking models
https://cds.cern.ch/record/1352765
Grojean, CTue, 24 May 2011 08:56:46 GMThttps://cds.cern.ch/record/1352765Possible low energy manifestations of strings and gravity
https://cds.cern.ch/record/1352711
Lowering the string scale in the TeV region provides a theoretical framework for solving the mass hierarchy problem and unifying all interactions. The apparent weakness of gravity can then be accounted by the existence of large internal dimensions, in the submillimeter region, and transverse to a braneworld where our universe must be confined. The author reviews the main properties of this scenario and its implications for observations at both particle colliders, and in non-accelerator gravity experiments.Antoniadis, IMon, 23 May 2011 15:30:46 GMThttps://cds.cern.ch/record/1352711Physics from extra dimensions
https://cds.cern.ch/record/1352694
Antoniadis, IMon, 23 May 2011 15:30:44 GMThttps://cds.cern.ch/record/1352694Aspects of string phenomenology
https://cds.cern.ch/record/1352136
Antoniadis, IThu, 19 May 2011 15:48:35 GMThttps://cds.cern.ch/record/1352136FCNC Effects in a Minimal Theory of Fermion Masses
https://cds.cern.ch/record/1352083
As a minimal theory of fermion masses we extend the SM by heavy vectorlike fermions, with flavor-anarchical Yukawa couplings, that mix with chiral fermions such that small SM Yukawa couplings arise from small mixing angles. This model can be regarded as an effective description of the fermionic sector of a large class of existing flavor models and thus might serve as a useful reference frame for a further understanding of flavor hierarchies in the SM. Already such a minimal framework gives rise to FCNC effects through exchange of massive SM bosons whose couplings to the light fermions get modified by the mixing. We derive general formulae for these corrections and discuss the bounds on the heavy fermion masses. Particularly stringent bounds, in a few TeV range, come from the corrections to the Z couplings.Grojean, ChristopheThu, 19 May 2011 11:28:15 GMThttps://cds.cern.ch/record/1352083Non-perturbative transitions among intersecting-brane vacua
https://cds.cern.ch/record/1351789
We investigate the transmutation of D-branes into Abelian magnetic backgrounds on the world-volume of higher-dimensional branes, within the framework of global models with compact internal dimensions. The phenomenon, T-dual to brane recombination in the intersecting-brane picture, shares some similarities to inverse small-instanton transitions in non-compact spaces, though in this case the Abelian magnetic background is a consequence of the compactness of the internal manifold, and is not ascribed to a zero-size non-Abelian instanton growing to maximal size. We provide details of the transition in various supersymmetric orientifolds and non-supersymmetric tachyon-free vacua with Brane Supersymmetry Breaking, both from brane recombination and from a field theory Higgs mechanism viewpoints.Condeescu, CezarWed, 18 May 2011 11:27:56 GMThttps://cds.cern.ch/record/1351789On Fluxed Instantons and Moduli Stabilisation in IIB Orientifolds and F-theory
https://cds.cern.ch/record/1351551
We study the superpotential induced by Euclidean D3-brane instantons carrying instanton flux, with special emphasis on its significance for the stabilisation of Kahler moduli and Neveu-Schwarz axions in Type IIB orientifolds. Quite generally, once a chiral observable sector is included in the compactification, arising on intersecting D7-branes with world-volume flux, resulting charged instanton zero modes prevent a class of instantons from participating in moduli stabilisation. We show that instanton flux on Euclidean D3-branes can remove these extra zero modes and helps in reinstating full moduli stabilisation within a geometric regime. We comment also on the F-theoretic description of this effect of alleviating the general tension between moduli stabilisation and chirality. In addition we propose an alternative solution to this problem based on dressing the instantons with charged matter fields which is unique to F-theory and cannot be realised in the weak coupling limit.Kerstan, MaxWed, 18 May 2011 11:27:15 GMThttps://cds.cern.ch/record/1351551Forward-backward asymmetries of the bottom and top quarks in warped extra-dimensional models: LHC predictions from the LEP and Tevatron anomalies
https://cds.cern.ch/record/1351430
Within the paradigm of warped extra dimensions, third generation quarks are expected to be the most sensitive to effects beyond the Standard Model. The anomalies observed at the LEP and Tevatron colliders in the forward-backward asymmetries of the bottom (A_FB^b) and top (A_FB^t) quarks can thus be seen as early signatures of warped extra-dimensional scenarios. We propose a realization of such a scenario, with a gauge custodial symmetry in the bulk, which allows to address simultaneously the A_FB^b anomaly and the discrepancies observed recently on A_FB^t at high top quark rapidities and ttbar invariant masses. We also show that the various phenomenological constraints arising from LEP, Tevatron and LHC can be satisfied within the considered model. The model predicts new features, induced by a Kaluza-Klein excitation of the gluon at a mass ~1.5-2 TeV, in top quark pair production at the 7 TeV LHC.Moreau, GTue, 17 May 2011 11:12:51 GMThttps://cds.cern.ch/record/1351430Mapping Anomalous Currents in Supersymmetric Dualities
https://cds.cern.ch/record/1351200
In many strongly-coupled systems, the infrared dynamics is described by different degrees of freedom from the ultraviolet. It is then natural to ask how operators written in terms of the microscopic variables are mapped to operators composed of the macroscopic ones. Certain types of operators, like conserved currents, are simple to map, and in supersymmetric theories one can also follow the chiral ring. In this note, we consider supersymmetric theories and extend the mapping to anomalous currents (and gaugino bilinears). Our technique is completely independent of subtleties associated with the renormalization group, thereby shedding new light on previous approaches to the problem. We demonstrate the UV/IR mapping in several examples with different types of dynamics, emphasizing the uniformity and simplicity of the approach. Natural applications of these ideas include the effects of soft breaking on the dynamics of various theories and new models of electroweak symmetry breaking.Buican, MatthewTue, 17 May 2011 11:12:16 GMThttps://cds.cern.ch/record/1351200One-loop adjoint masses for non-supersymmetric intersecting branes
https://cds.cern.ch/record/1348674
We consider breaking of supersymmetry in intersecting D-brane configurations by slight deviation of the angles from their supersymmetric values. We compute the masses generated by radiative corrections for the adjoint scalars on the brane world-volumes. In the open string channel, the string two-point function receives contributions only from the infrared and the ultraviolet limits. The latter is due to tree-level closed string uncanceled NS-NS tadpoles, which we explicitly reproduce from the effective Born-Infeld action. On the other hand, the infrared region reproduces the one-loop mediation of supersymmetry breaking in the effective gauge theory, via messengers and their Kaluza-Klein excitations. In the toroidal set-up considered here, it receives contributions only from broken N=4 and N=2 supersymmetric configurations, and thus always leads at leading order to a tachyonic direction, in agreement with effective field theory expectations.Antoniadis, IWed, 04 May 2011 09:08:21 GMThttps://cds.cern.ch/record/1348674Warped 5D Standard Model Consistent with EWPT
https://cds.cern.ch/record/1347544
For a 5D Standard Model propagating in an AdS background with an IR localized Higgs, compatibility of bulk KK gauge modes with EWPT yields a phenomenologically unappealing KK spectrum (m > 12.5 TeV) and leads to a "little hierarchy problem". For a bulk Higgs the solution to the hierarchy problem reduces the previous bound only by sqrt(3). As a way out, models with an enhanced bulk gauge symmetry SU(2)_R x U(1)_(B-L) were proposed. In this note we describe a much simpler (5D Standard) Model, where introduction of an enlarged gauge symmetry is no longer required. It is based on a warped gravitational background which departs from AdS at the IR brane and a bulk propagating Higgs. The model is consistent with EWPT for a range of KK masses within the LHC reach.Cabrer, Joan AFri, 29 Apr 2011 08:38:29 GMThttps://cds.cern.ch/record/1347544Improving Naturalness in Warped Models with a Heavy Bulk Higgs
https://cds.cern.ch/record/1345361
A Standard-Model-like Higgs boson should be light in order to comply with electroweak precision measurements from LEP. We consider warped models as UV completions of the Standard Model with a heavy Higgs. Provided the Higgs propagates in the 5D bulk, the KK modes of the gauge bosons can compensate for the Higgs contribution to oblique parameters while their masses lie within the range of the LHC reach.von Gersdorff, GeroTue, 19 Apr 2011 07:56:55 GMThttps://cds.cern.ch/record/1345361New physics: Theoretical developments
https://cds.cern.ch/record/1344476
Grojean, ChristopheThu, 14 Apr 2011 05:11:22 GMThttps://cds.cern.ch/record/1344476An effective approach to same sign top pair production at the LHC and the forward-backward asymmetry at the Tevatron
https://cds.cern.ch/record/1343880
We study the phenomenology of same sign top pair production at the LHC in a model-independent way. The complete set of dimension six operators involving two top (or anti-top) quarks is introduced and the connection with all possible t- or s-channel particle exchanges is established. Only in the former case, same and opposite sign top pair production can be related. We find that while current Tevatron data disfavor t-channel models, other production mechanisms are viable and can be tested at the LHC.Gerard, Jean-MarcTue, 12 Apr 2011 14:23:43 GMThttps://cds.cern.ch/record/1343880General Aspects of Gauge Mediation
https://cds.cern.ch/record/1342828
We describe some new, model-independent, results in gauge mediation [1, 2].Buican, MThu, 07 Apr 2011 04:00:17 GMThttps://cds.cern.ch/record/1342828Anomaly driven signatures of extra U(1)'s
https://cds.cern.ch/record/1342827
Anomaly cancellation between different sectors of a theory may mediate new interactions between gauge bosons. Such interactions lead to observable effects both at precision laboratory experiments and at accelerators. Such experiments may reveal the presence of hidden sectors or hidden extra dimensions.Boyarsky, AlexeyThu, 07 Apr 2011 04:00:17 GMThttps://cds.cern.ch/record/1342827Implications of the ATLAS and CMS searches in the channel $pp \to Higgs \to \tau^+\tau^-$ for the MSSM and SM Higgs bosons
https://cds.cern.ch/record/1341768
We discuss the implications of the recent constraints on the Higgs sector of the Minimal Supersymmetric extension of the Standard Model obtained by the ATLAS and CMS collaborations at the lHC with $\sqrt s=7$ TeV and 36 pb$^{-1}$ of data. The main production and detection channel that is relevant in these analyses is the gluon--gluon and bottom quark fusion mechanisms leading to neutral Higgs bosons which subsequently decay into tau lepton pairs, $gg, b\bar b \to Higgs \to \tau^+\tau^-$. In this note, we show that: i) the exclusion limits are in fact more general than indicated by the ATLAS and CMS analyses and are essentially independent of the scenario for the supersymmetric particle spectrum; ii) when the exclusion limits are applied to the lowest theory prediction for the Higgs production cross section times branching ratio, when all theoretical uncertainties are taken into account, the bounds are somewhat less stringent; iii) the exclusion limits from the $pp \to Higgs \to \tau^+ \tau^-$ process are so strong that only a modest improvement would be possible when other MSSM Higgs detection channels are considered, even with femtobarn level accumulated data. Finally and most important, we point out that the prospects for the search for the Standard Model Higgs boson in the inclusive $gg \to H \to \tau^+\tau^-$ channel, that is not currently considered by the ATLAS and CMS collaborations, turn out to be very promising and wit h a few inverse femtobarn data it might provide a convincing discovery signal in the difficult 115--135 GeV mass range for the standard Higgs boson.Djouadi, AbdelhakFri, 01 Apr 2011 13:16:12 GMThttps://cds.cern.ch/record/1341768Classicalization of Gravitons and Goldstones
https://cds.cern.ch/record/1341481
We establish a close parallel between classicalization of gravitons and derivatively-coupled Nambu-Goldstone-type scalars. We show, that black hole formation in high energy scattering process represents classicalization with the classicalization radius given by Schwarzschild radius of center of mass energy, and with the precursor of black hole entropy being given by number of soft quanta composing this classical configuration. Such an entropy-equivalent is defined for scalar classicalons also and is responsible for exponential suppression of their decay into small number of final particles. This parallel works in both ways. For optimists that are willing to hypothesize that gravity may indeed self-unitarize at high energies via black hole formation, it illustrates that the Goldstones may not be much different in this respect, and they classicalize essentially by similar dynamics as gravitons. In the other direction, it may serve as an useful de-mystifier of via-black-hole-unitarization process and of the role of entropy in it, as it illustrates, that much more prosaic scalar theories essentially do the same. Finally, it illustrates that in both cases classicalization is the defining property for unitarization, and that it sets-in before one can talk about accompanying properties, such as entropy and thermality of static classicalons (black holes). These properties are by-products of classicalization, and their equivalents can b e defined for non-gravitational cases of classicalization.Gomez, CesarThu, 31 Mar 2011 12:57:26 GMThttps://cds.cern.ch/record/1341481Conformal Invariance, Dark Energy, and CMB Non-Gaussianity
https://cds.cern.ch/record/1337830
We show that in addition to simple scale invariance, a universe dominated by dark energy naturally gives rise to correlation functions possessing full conformal invariance. This is due to the mathematical isomorphism between the conformal group of certain three dimensional slices of de Sitter space and the de Sitter isometry group SO(4,1). In the standard homogeneous, isotropic cosmological model in which primordial density perturbations are generated during a long vacuum energy dominated de Sitter phase, the embedding of flat spatial R^3 sections in de Sitter space induces a conformal invariant perturbation spectrum and definite prediction for the shape of the non-Gaussian CMB bispectrum. In the case in which the density fluctuations are generated instead on the de Sitter horizon, conformal invariance of the S^2 horizon embedding implies a different but also quite definite prediction for the angular correlations of CMB non-Gaussianity on the sky. Each of these forms for the bispectrum is intrinsic to the symmetries of de Sitter space, and in that sense, independent of specific model assumptions. Each is different from the predictions of single field slow roll inflation models, which rely on the breaking of de Sitter invariance. Thus detection of non-Gaussian correlations in the CMB of one of these bispectral shape functions can both pinpoint the origins of primordial density fluctuations, and distinguish between different dyna mical models of cosmological vacuum dark energyMazur, Pawel OWed, 23 Mar 2011 09:25:19 GMThttps://cds.cern.ch/record/1337830A weakly constrained $W'$ at the early LHC
https://cds.cern.ch/record/1336088
We study, within an effective approach, the phenomenology of a charged W' vector which transforms as an isosinglet under the Standard Model gauge group. We discuss bounds from present data, finding that these are quite weak for suitable choices of the right-handed quark mixing matrix. Then we study the resonant production at the early LHC of such a weakly constrained W'. We start discussing the reach in the dijet final state, which is one of the channels where the first W' signal would most likely appear, and then we analyse prospects for the more challenging discovery of W' decays into W{\gamma} and WZ. We show in particular that the former can be used to gain insight on the possibly composite nature of the resonance.Salvioni, EnnioTue, 15 Mar 2011 08:45:59 GMThttps://cds.cern.ch/record/1336088Extensions of the Poincare group
https://cds.cern.ch/record/1335824
We construct an extension of the Poincare group which involves a mixture of internal and space-time supersymmetries. The resulting group is an extension of the superPoincare group with infinitely many generators which carry internal and space-time indices. It is a closed algebra since all Jacobi identities are satisfied and it has therefore explicit matrix representations. We investigate the massless case and construct the irreducible representations of the extended symmetry. They are divided into two sets, longitudinal and transversal representations. The transversal representations involve an infinite series of integer and half-integer helicities. Finally we suggest an extension of the conformal group along the same line.Brink, LarsTue, 15 Mar 2011 08:45:26 GMThttps://cds.cern.ch/record/1335824Suppressing Electroweak Precision Observables in 5D Warped Models
https://cds.cern.ch/record/1334625
We elaborate on a recently proposed mechanism to suppress large contributions to the electroweak precision observables in five dimensional (5D) warped models, without the need for an extended 5D gauge sector. The main ingredient is a modification of the AdS metric in the vicinity of the infrared (IR) brane corresponding to a strong deviation from conformality in the IR of the 4D holographic dual. We compute the general low energy effective theory of the 5D warped Standard Model, emphasizing additional IR contributions to the wave function renormalization of the light Higgs mode. We also derive expressions for the S and T parameters as a function of a generic 5D metric and zero-mode wave functions. We give an approximate formula for the mass of the radion that works even for strong deviation from the AdS background. We proceed to work out the details of an explicit model and derive bounds for the first KK masses of the various bulk fields. The radion is the lightest new particle although its mass is already at about 1/3 of the mass of the lightest resonances, the KK states of the gauge bosons. We examine carefully various issues that can arise for extreme choices of parameters such as the possible reintroduction of the hierarchy problem, the onset of nonperturbative physics due to strong IR curvature or the creation of new hierarchies near the Planck scale. We conclude that a KK scale of 1 TeV is compatible with all these constr aints.von Gersdorff, GeroWed, 09 Mar 2011 08:29:11 GMThttps://cds.cern.ch/record/1334625Phenomenology of TeV Little String Theory from Holography
https://cds.cern.ch/record/1330864
We study the graviton phenomenology of TeV Little String Theory by exploiting its holographic gravity dual five-dimensional theory. This dual corresponds to a linear dilaton background with a large bulk that constrains the Standard Model fields on the boundary of space. The linear dilaton geometry produces a unique Kaluza-Klein graviton spectrum that exhibits a ~ TeV mass gap followed by a near continuum of narrow resonances that are separated from each other by only ~ 30 GeV. Resonant production of these particles at the LHC is the signature of this framework that distinguishes it from large extra dimensions where the KK states are almost a continuum with no mass gap, and warped models where the states are separated by a TeV.Arvanitaki, AsiminaTue, 22 Feb 2011 06:52:45 GMThttps://cds.cern.ch/record/1330864On R-symmetric Fixed Points and Superconformality
https://cds.cern.ch/record/1328761
An important unanswered question in quantum field theory is to understand precisely under which conditions scale invariance implies invariance under the full conformal group. While the general answer in two dimensions has been known for over twenty years, a precise non-perturbative relation between scale and conformal invariance in higher dimensions has been lacking. In this note, we specialize to four dimensions and give a full quantum mechanical proof that certain unitary R-symmetric fixed points are necessarily superconformal. Among other consequences, this result implies that the infrared fixed points of N=1 supersymmetric quantum chromodynamics are superconformal.Buican, MatthewMon, 14 Feb 2011 20:26:27 GMThttps://cds.cern.ch/record/1328761