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Asymptotic safety and the gauged SU(N) nonlinear sigma-model
https://cds.cern.ch/record/1297895
We study the beta functions of the leading, two-derivative terms of the left-gauged SU(N) nonlinear sigma-model in d dimensions. In d>2, we find the usual Gaussian ultraviolet fixed point for the gauge coupling and an attractive non-Gaussian fixed point for the Goldstone boson coupling. The position of the latter fixed point controls the chiral expansion, unitarity and the strength of the tree-level Goldstone boson scattering amplitudes. For large N the model is weakly coupled, unitary at all energies and well described by the lowest order of chiral perturbation theory. Attention is payed to the gauge- and scheme-dependence of the results.Fabbrichesi, MWed, 06 Oct 2010 06:03:27 GMThttps://cds.cern.ch/record/1297895The quantum vacuum of the minimal SO(10) GUT
https://cds.cern.ch/record/1297362
We reexamine the longstanding no-go excluding all potentially viable SO(10) -> SU(3)_c x SU(2)_L x U(1)_Y symmetry breaking patterns within the minimal renormalizable non-supersymmetric SO(10) GUT framework featuring the 45-dimensional adjoint representation in the Higgs sector. A simple symmetry argument indicates that quantum effects do change the vacuum structure of the model dramatically. A thorough analysis of the one-loop effective potential reveals that the phenomenologically favoured symmetry breaking chains passing through the SU(4)_C x SU(2)_L x U(1)_R or SU(3)_c x SU(2)_L x SU(2)_R x U(1)_B-L intermediate stages are, indeed, supported at the quantum level. This brings the class of minimal non-supersymmetric SO(10) GUTs back from oblivion, providing a new ground for a potentially realistic model building.Bertolini, StefanoTue, 05 Oct 2010 05:23:50 GMThttps://cds.cern.ch/record/1297362A Unified Theory of Matter Genesis: Asymmetric Freeze-In
https://cds.cern.ch/record/1296499
We propose a unified theory of dark matter (DM) genesis and baryogenesis. It explains the observed link between the DM density and the baryon density, and is fully testable by a combination of collider experiments and precision tests. Our theory utilises the "thermal freeze-in" mechanism of DM production, generating particle anti-particle asymmetries in decays from visible to hidden sectors. Calculable, linked, asymmetries in baryon number and DM number are produced by the feeble interaction mediating between the two sectors, while the out-of-equilibrium condition necessary for baryogenesis is provided by the different temperatures of the visible and hidden sectors. An illustrative model is presented where the visible sector is the MSSM, with the relevant CP violation arising from phases in the gaugino and Higgsino masses, and both asymmetries are generated at temperatures of order 100 GeV. Experimental signals of this mechanism can be spectacular, including: long-lived metastable states late decaying at the LHC; apparent baryon-number or lepton-number violating signatures associated with these highly displaced vertices; EDM signals correlated with the observed decay lifetimes and within reach of planned experiments; and a prediction for the mass of the dark matter particle that is sensitive to the spectrum of the visible sector and the nature of the electroweak phase transition.Hall, Lawrence JMon, 04 Oct 2010 05:08:09 GMThttps://cds.cern.ch/record/1296499Yukawa couplings and fermion mass structure in F-theory GUTs
https://cds.cern.ch/record/1296038
The calculation of Yukawa couplings in F-theory GUTs is developed. The method is applied to the top and bottom Yukawa couplings in an SU(5) model of fermion masses based on family symmetries coming from the SU(5)_\perp factor in the underlying E(8) theory. The remaining Yukawa couplings involving the light quark generations are determined by the Froggatt Nielsen non-renormalisable terms generated by heavy messenger states. We extend the calculation of Yukawa couplings to include massive states and estimate the full up and down quark mass matrices in the SU(5) model. We discuss the new features of the resulting structure compared to what is usually assumed for Abelian family symmetry models and show how the model can give a realistic quark mass matrix structure. We extend the analysis to the neutrino sector masses and mixing where we find that tri-bi-maximal mixing is readily accommodated. Finally we discuss mechanisms for splitting the degeneracy between the charged leptons and the down quarks and the doublet triplet splitting in the Higgs sector.Leontaris, G KFri, 01 Oct 2010 03:34:39 GMThttps://cds.cern.ch/record/1296038Bounds in 4D Conformal Field Theories with Global Symmetry
https://cds.cern.ch/record/1295863
We explore the constraining power of OPE associativity in 4D Conformal Field Theory with a continuous global symmetry group. We give a general analysis of crossing symmetry constraints in the 4-point function <Phi Phi Phi* Phi*>, where Phi is a primary scalar operator in a given representation R. These constraints take the form of 'vectorial sum rules' for conformal blocks of operators whose representations appear in R x R and R x Rbar. The coefficients in these sum rules are related to the Fierz transformation matrices for the R x R x Rbar x Rbar invariant tensors. We show that the number of equations is always equal to the number of symmetry channels to be constrained. We also analyze in detail two cases - the fundamental of SO(N) and the fundamental of SU(N). We derive the vectorial sum rules explicitly, and use them to study the dimension of the lowest singlet scalar in the Phi x Phi* OPE. We prove the existence of an upper bound on the dimension of this scalar. The bound depends on the conformal dimension of Phi and approaches 2 in the limit dim(Phi)-->1. For several small groups, we compute the behavior of the bound at dim(Phi)>1. We discuss implications of our bound for the Conformal Technicolor scenario of electroweak symmetry breaking.Rattazzi, RiccardoThu, 30 Sep 2010 03:19:27 GMThttps://cds.cern.ch/record/1295863On Moduli Stabilisation and de Sitter Vacua in MSSM Heterotic Orbifolds
https://cds.cern.ch/record/1293698
We study the problem of moduli stabilisation in explicit heterotic orbifold compactifications, whose spectra contain the MSSM plus some vector-like exotics that can be decoupled. Considering all the bulk moduli, we obtain the 4D low energy effective action for the compactification, which has contributions from various, computable, perturbative and non-perturbative effects. Hidden sector gaugino condensation and string worldsheet instantons result in a combination of racetrack, KKLT and cusp-form contributions to the superpotential, which lift all the bulk moduli directions. We point out the properties observed in our concrete models, which tend to be missed when only "generic" features of a model are assumed. We search for interesting vacua and find several de Sitter solutions, but -- so far -- they all turn out to be unstable.Parameswaran, Susha LThu, 23 Sep 2010 00:58:03 GMThttps://cds.cern.ch/record/1293698Lifshitz solutions in supergravity and string theory
https://cds.cern.ch/record/1293002
We derive Lifshitz configurations in string theory for general dynamical exponents z \geq 1. We begin by obtaining simple Li x Omega solutions to supergravities in diverse dimensions, with Omega a compact constant curvature manifold. Then we uplift the solutions to ten dimensions, providing configurations that correspond to warped compactifications in Type II string theory.Gregory, RuthMon, 20 Sep 2010 23:32:26 GMThttps://cds.cern.ch/record/1293002Strongly Scale-dependent Non-Gaussianity
https://cds.cern.ch/record/1292549
We discuss models of primordial density perturbations where the non-Gaussianity is strongly scale-dependent. In particular, the non-Gaussianity may have a sharp cut-off and be very suppressed on large cosmological scales, but sizeable on small scales. This may have an impact on probes of non-Gaussianity in the large-scale structure and in the cosmic microwave background radiation anisotropies.Riotto, AntonioFri, 17 Sep 2010 22:27:18 GMThttps://cds.cern.ch/record/1292549Central Charge Bounds in 4D Conformal Field Theory
https://cds.cern.ch/record/1291833
We derive model-independent lower bounds on the stress tensor central charge C_T in terms of the operator content of a 4-dimensional Conformal Field Theory. More precisely, C_T is bounded from below by a universal function of the dimensions of the lowest and second-lowest scalars present in the CFT. The method uses the crossing symmetry constraint of the 4-point function, analyzed by means of the conformal block decomposition.Rattazzi, RiccardoWed, 15 Sep 2010 18:54:21 GMThttps://cds.cern.ch/record/1291833Note on a Differential-Geometrical Construction of Optimal Directions in Linearly-Constrained Systems
https://cds.cern.ch/record/1290126
This note presents an analytic construction of the optimal unit-norm direction hat(x) = x/|x| that maximizes or minimizes the objective linear expression, B . hat{x}, subject to a system of linear constraints of the form [A] . x = 0, where x is an unknown n-dimensional real vector to be determined up to an overall normalization constant, 0 is an m-dimensional null vector, and the n-dimensional real vector B and the m\times n-dimensional real matrix [A] (with m < n and n >= 2) are given. The analytic solution to this problem can be expressed in terms of a combination of double wedge and Hodge-star products of differential forms.Ellis, JohnWed, 08 Sep 2010 11:09:07 GMThttps://cds.cern.ch/record/1290126Chameleon Induced Atomic Afterglow
https://cds.cern.ch/record/1290019
The chameleon is a scalar field whose mass depends on the density of its environment. Chameleons are necessarily coupled to matter particles and will excite transitions between atomic energy levels in an analogous manner to photons. When created inside an optical cavity by passing a laser beam through a constant magnetic field, chameleons are trapped between the cavity walls and form a standing wave. This effect will lead to an afterglow phenomenon even when the laser beam and the magnetic field have been turned off, and could be used to probe the interactions of the chameleon field with matter.Brax, PhilippeTue, 07 Sep 2010 10:39:39 GMThttps://cds.cern.ch/record/1290019On Climbing Scalars in String Theory
https://cds.cern.ch/record/1289851
In string models with "brane supersymmetry breaking" exponential potentials emerge at (closed-string) tree level but are not accompanied by tachyons. Potentials of this type have long been a source of embarrassment in flat space, but can have interesting implications for Cosmology. For instance, in ten dimensions the logarithmic slope |V'/V| lies precisely at a "critical" value where the Lucchin--Matarrese attractor disappears while the scalar field is \emph{forced} to climb up the potential when it emerges from the Big Bang. This type of behavior is in principle perturbative in the string coupling, persists after compactification, could have trapped scalar fields inside potential wells as a result of the cosmological evolution and could have also injected the inflationary phase of our Universe.Kitazawa, NTue, 07 Sep 2010 10:39:18 GMThttps://cds.cern.ch/record/1289851Direct dark matter detection: The diurnal variation in directional experiments
https://cds.cern.ch/record/1289612
We present some theoretical results relevant to the direct dark matter detection experiments, paying particular attention to directional experiments, i.e. experiments in which, not only the energy but the direction of the recoiling nucleus is observed. In directional experiments the detection rate depends on the angle between the line observation and the sun's direction of motion. Since, however, the direction of observation is fixed with respect the earth, while the Earth is rotating around its axis, in a directional experiment the angle between the direction of observation and the Sun's direction of motion will change during the day. So the observed signal in such experiments will exhibit a very interesting and characteristic periodic diurnal variation.Vergados, J DMon, 06 Sep 2010 09:49:07 GMThttps://cds.cern.ch/record/1289612Summary report of MINSIS workshop in Madrid
https://cds.cern.ch/record/1289343
Recent developments on tau detection technologies and the construction of high intensity neutrino beams open the possibility of a high precision search for non-standard {\mu} - {\tau} flavour transition with neutrinos at short distances. The MINSIS - Main Injector Non-Standard Interaction Search- is a proposal under discussion to realize such precision measurement. This document contains the proceedings of the workshop which took place on 10-11 December 2009 in Madrid to discuss both the physics reach as well as the experimental requirements for this proposal.Alonso, RodrigoFri, 03 Sep 2010 21:44:28 GMThttps://cds.cern.ch/record/1289343Signals of single particle production at the earliest LHC
https://cds.cern.ch/record/1288422
Based on simple phenomenological Lagrangians, fulfilling reasonable consistency conditions, we consider under which circumstances the production of a single particle might be an early signal of new physics at the LHC. Effective final states are $\gamma \gamma $ and $\gamma +jet$ already with tens of inverse picobarns of integrated luminosity at 7 TeV.Barbieri, RiccardoWed, 01 Sep 2010 20:28:15 GMThttps://cds.cern.ch/record/1288422Non-singular string cosmology in a 2d Hybrid model
https://cds.cern.ch/record/1288209
The existence of non-singular string cosmologies is established in a class of two-dimensional supersymmetric Hybrid models at finite temperature. The left-moving sector of the Hybrid models gives rise to 16 real (N_4=4) spacetime supercharges as in the usual superstring models. The right-moving sector is non-supersymmetric at the massless level, but is characterized by MSDS symmetry, which ensures boson/fermion degeneracy of the right-moving massive levels. Finite temperature configurations, which are free of Hagedorn instabilities, are constructed in the presence of non-trivial "gravito-magnetic" fluxes. These fluxes inject non-trivial winding charge into the thermal vacuum and restore the thermal T-duality symmetry associated with the Euclidean time circle. Thanks to the unbroken right-moving MSDS symmetry, the one-loop string partition function is exactly calculable beyond any alpha'-approximation. At the self-dual point new massless thermal states appear, sourcing localized spacelike branes, which can be used to connect a contracting thermal Universe to an expanding one. The resulting bouncing cosmology is free of any curvature singularities and the string coupling remains perturbative throughout the cosmological evolution.Florakis, IoannisTue, 31 Aug 2010 20:08:27 GMThttps://cds.cern.ch/record/1288209Anomaly Mediation in Superstring Theory
https://cds.cern.ch/record/1287375
We study anomaly mediated supersymmetry breaking in type IIB string theory and use our results to test the supergravity formula for anomaly mediated gaugino masses. We compute 1-loop gaugino masses for models of D3-branes on orbifold singularities with 3-form fluxes by calculating the annulus correlator of 3-form flux and two gauginos in the zero momentum limit. Consistent with supergravity expectations we find both anomalous and running contributions to 1-loop gaugino masses. For background Neveu-Schwarz H-flux we find an exact match with the supergravity formula. For Ramond-Ramond flux there is an off-shell ambiguity that precludes a full matching. The anomaly mediated gaugino masses, while determined by the infrared spectrum, arise from an explicit sum over UV open string winding modes. We also calculate brane-to-brane tree-level gravity mediated gaugino masses and show that there are two contributions coming from the dilaton and from the twisted modes, which are suppressed by the full T^6 volume and the untwisted T^2 volume respectively.Goodsell, MarkFri, 27 Aug 2010 19:15:27 GMThttps://cds.cern.ch/record/1287375Higher-Dimensional Unified Theories with Fuzzy Extra Dimensions
https://cds.cern.ch/record/1284800
Theories defined in higher than four dimensions have been used in various frameworks and have a long and interesting history. Here we review certain attempts, developed over the last years, towards the construction of unified particle physics models in the context of higher-dimensional gauge theories with non-commutative extra dimensions. These ideas have been developed in two complementary ways, namely (i) starting with a higher-dimensional gauge theory and dimensionally reducing it to four dimensions over fuzzy internal spaces and (ii) starting with a four-dimensional, renormalizable gauge theory and dynamically generating fuzzy extra dimensions. We describe the above approaches and moreover we discuss the inclusion of fermions and the construction of realistic chiral theories in this context.Chatzistavrakidis, AthanasiosFri, 13 Aug 2010 12:40:32 GMThttps://cds.cern.ch/record/1284800SuperB Progress Reports - Physics
https://cds.cern.ch/record/1284223
SuperB is a high luminosity e+e- collider that will be able to indirectly probe new physics at energy scales far beyond the reach of any man made accelerator planned or in existence. Just as detailed understanding of the Standard Model of particle physics was developed from stringent constraints imposed by flavour changing processes between quarks, the detailed structure of any new physics is severely constrained by flavour processes. In order to elucidate this structure it is necessary to perform a number of complementary studies of a set of golden channels. With these measurements in hand, the pattern of deviations from the Standard Model behavior can be used as a test of the structure of new physics. If new physics is found at the LHC, then the many golden measurements from SuperB will help decode the subtle nature of the new physics. However if no new particles are found at the LHC, SuperB will be able to search for new physics at energy scales up to 10-100 TeV. In either scenario, flavour physics measurements that can be made at SuperB play a pivotal role in understanding the nature of physics beyond the Standard Model. Examples for using the interplay between measurements to discriminate New Physics models are discussed in this document. SuperB is a Super Flavour Factory, in addition to studying large samples of B_{u,d,s}, D and tau decays, SuperB has a broad physics programme that includes spectroscopy both in terms of t he Standard Model and exotica, and precision measurements of sin^2theta_W. In addition to performing CP violation measurements at the Y(4S) and phi(3770), SuperB will test CPT in these systems, and lepton universality in a number of different processes. The multitude of rare decay measurements possible at SuperB can be used to constrain scenarios of physics beyond the Standard Model. ...O'Leary, BTue, 10 Aug 2010 11:39:05 GMThttps://cds.cern.ch/record/1284223Low-scale warped extra dimension and its predilection for multiple top quarks
https://cds.cern.ch/record/1283555
Within warped extra dimension models that explain flavor through geometry, flavor changing neutral current constraints generally force the Kaluza-Klein scale to be tens of TeV. This creates tension with a natural electroweak scale. On the other hand, a much lower scale compatible with precision electroweak and flavor changing neutral current constraints is allowed if we decouple the Kaluza-Klein states of Standard Model gauge bosons from light fermions $c_{\rm light}\simeq c_b\simeq 0.5$ bulk mass parameters). The main signature for this approach is four top quark production via the Kaluza-Klein excitations' strong coupling to top quarks. We study single lepton, like-sign dilepton, and trilepton observables of four-top events at the Large Hadron Collider. The like-sign dilepton signature typically has the largest discovery potential for a strongly coupled right-handed top case ($M_{KK} \sim 2-2.5 TeV$), while single lepton is the better when the left-handed top couples most strongly ($M_{KK} \sim 2 TeV$). We also describe challenging lepton-jet collimation issues in the like-sign dilepton and trilepton channels. An alternative single lepton observable is considered which takes advantage of the many bottom quarks in the final state. Although searches of other particles may compete, we find that four top production via Kaluza-Klein gluons is most promising in a large region of this parameter space.Wells, James DFri, 06 Aug 2010 10:02:31 GMThttps://cds.cern.ch/record/1283555Gravitational Atom in Compactified Extra Dimensions
https://cds.cern.ch/record/1283386
We consider quantum mechanical effects of the modified Newtonian potential in the presence of extra compactified dimensions. We develop a method to solve the resulting Schroedinger equation and determine the energy shifts caused by the Yukawa-type corrections of the potential. We comment on the possibility of detecting the modified gravitational bound state Energy spectrum by present day and future experiments.Floratos, E GThu, 05 Aug 2010 09:42:04 GMThttps://cds.cern.ch/record/1283386Higgs Boson Masses in the MSSM with Heavy Majorana Neutrinos
https://cds.cern.ch/record/1282605
We present a full diagrammatic computation of the one-loop corrections from the neutrino/sneutrino sector to the renormalized neutral CP-even Higgs boson self-energies and the lightest Higgs boson mass, Mh, within the context of the so-called MSSM-seesaw scenario. This consists of the Minimal Supersymmetric Standard Model with the addition of massive right handed Majorana neutrinos and their supersymmetric partners, and where the seesaw mechanism is used for the lightest neutrino mass generation. We explore the dependence on all the parameters involved, with particular emphasis in the role played by the heavy Majorana scale. We restrict ourselves to the case of one generation of neutrinos/sneutrinos. For the numerical part of the study, we consider a very wide range of values for all the parameters involved. We find sizeable corrections to Mh, which are negative in the region where the Majorana scale is large (10^{13}-10^{15} GeV) and the lightest neutrino mass is within a range inspired by data (0.1-1 eV). For some regions of the MSSM-seesaw parameter space, the corrections to Mh are larger than the anticipated Large Hadron Collider precision.Heinemeyer, STue, 03 Aug 2010 07:31:40 GMThttps://cds.cern.ch/record/1282605Flavour in supersymmetry: horizontal symmetries or wave function renormalisation
https://cds.cern.ch/record/1282250
We compare theoretical and experimental predictions of two main classes of models addressing fermion mass hierarchies and flavour changing neutral currents (FCNC) effects in supersymmetry: Froggatt-Nielsen (FN) U(1) gauged flavour models and Nelson-Strassler/extra dimensional models with hierarchical wave functions for the families. We show that whereas the two lead to identical predictions in the fermion mass matrices, the second class generates a stronger suppression of FCNC effects. We prove that, whereas at first sight the FN setup is more constrained due to anomaly cancelation conditions, imposing unification of gauge couplings in the second setup generates conditions which precisely match the mixed anomaly constraints in the FN setup. Finally, we provide an economical extra dimensional realisation of the hierarchical wave functions scenario in which the leptonic FCNC can be efficiently suppressed due to the strong coupling (CFT) origin of the electron mass.von Gersdorff, GeroFri, 30 Jul 2010 21:09:46 GMThttps://cds.cern.ch/record/1282250One-loop Yukawa Couplings in Local Models
https://cds.cern.ch/record/1282194
We calculate the one-loop Yukawa couplings and threshold corrections for supersymmetric local models of branes at singularities in type IIB string theory. We compute the corrections coming both from wavefunction and vertex renormalisation. The former comes in the IR from conventional field theory running and in the UV from threshold corrections that cause it to run from the winding scale associated to the full Calabi-Yau volume. The vertex correction is naively absent as it appears to correspond to superpotential renormalisation. However, we find that while the Wilsonian superpotential is not renormalised there is a physical vertex correction in the 1PI action associated to light particle loops.Goodsell, MarkFri, 30 Jul 2010 21:09:41 GMThttps://cds.cern.ch/record/1282194Mixed dark matter from technicolor
https://cds.cern.ch/record/1281730
We study natural composite cold dark matter candidates which are pseudo Nambu-Goldstone bosons (pNGB) in models of dynamical electroweak symmetry breaking. Some of these can have a significant thermal relic abundance, while others must be mainly asymmetric dark matter. By considering the thermal abundance alone we find a lower bound of MW on the pNGB mass when the (composite) Higgs is heavier than 115 GeV. Being pNGBs, the dark matter candidates are in general light enough to be produced at the LHC.Belyaev, AlexanderThu, 29 Jul 2010 20:21:04 GMThttps://cds.cern.ch/record/1281730