Lorentz Center - Universe in a Box: LHC, Cosmology and Lattice Field Theory from 24 Aug 2009 through 28 Aug 2009
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### Universe in a Box: LHC, Cosmology and Lattice Field Theory from 24 Aug 2009 through 28 Aug 2009

 Abstracts Abstracts   Anselmi Title: Standard Model and high energy Lorentz violation   Abstract: We show that if Lorentz symmetry is violated at high energies, interactions that are usually non-renormalizable can become renormalizable by weighted power counting. We present a CPT invariant, Lorentz violating extension of the Standard Model containing two scalar-two fermion interactions (which can explain neutrino masses) and four fermion interactions (which can explain proton decay). The presence of four fermion vertices allows us to argue that the known low energy physics can be reproduced also if the elementary scalars are suppressed, in the Nambu--Jona-Lasinio spirit, avoiding the ambiguities of common non-renormalizable approaches. Using a large-Nc expansion, we study the dynamical symmetry breaking in the scalarless model, and show that the effective potential has a Lorentz invariant minimum and that the Lorentz violation does not reverberate down to low energies. The mechanism generates fermion masses, gauge-boson masses and scalar bound states, to be identified with composite Higgs bosons. Moreover, it predicts relations among the parameters of the Standard Model.     Catterall Title: Exact lattice supersymmetry   Abstract: I will review the recent constructions of lattice theories which retain one or more exact supersymmetries at non-zero lattice spacing with particular emphasis on N=4 super Yang-Mills. Applications to AdSCFT will be discussed and recent results from numerical simulations presented.     Del Debbio Title: IRFP on the lattice   Abstract: I will discuss the current evidence for IRFP on the lattice, focussing on the techniques used in numerical simulations and their limitations.     Deuzeman: Title: Traces of a fixed point: Unravelling the phase diagram at large Nf   Abstract: With a sufficiently high number of fundamental fermionic flavours present, Yang-Mills theory develops an infrared fixed point and becomes (quasi-)conformal in nature. The range of flavour numbers for which this occurs defines the conformal window, the lower limit of which has yet to be determined. We studied the phase diagram of SU(3) Yang-Mills theory with twelve flavours of staggered fermions. Here we present evidence for the occurrence of a bulk transition towards a chirally broken phase and the existence of a Coulomb phase on the symmetric side of this transition, using results of measurements of the sign of the beta function along lines of constant physics. Since such a phase can only occur in the presence of an attractive fixed point in the renormalization group flow and an associated conformal phase, this implies the existence of the conformal window and sets a bound on its lower end.     Di Chiara Title: The Limits of Custodial Symmetry   Abstract: I introduce a toy model implementing the proposal of using a custodial symmetry to protect the Zbb coupling from large corrections. This "doublet-extended standard model" adds a weak doublet of fermions (including a heavy partner of the top quark) to the particle content of the standard model in order to implement an O(4) x U(1)_X = SU(2)_L x SU(2)_R x P_{LR} x U(1)_X symmetry that protects the Zbb coupling. This symmetry is softly broken to the gauged SU(2)_L x U(1)_Y electroweak symmetry by a Dirac mass M for the new doublet; adjusting the value of M allows one to explore the range of possibilities between the O(4)-symmetric (M to 0) and standard-model-like (M to infinity) limits. In this simple model, I find that the experimental limits on the Zbb coupling favor smaller M while the presence of a potentially sizable negative contribution to T strongly favors large M. A fit to all precision electroweak data shows that the heavy partner of the top quark must be heavier than about 3.4 TeV, making it difficult to search for at LHC.     Farakos Title: Higher Dimensional Models on the Lattice: The case of the Layer Phase   Abstract: T.b.c.     Fleming Title: Condensate Enhancement in SU(3) Yang-Mills   Abstract: T.b.c.     Foadi Title: Unitarity in Walking Technicolor   Abstract: We investigate the longitudinal WW scattering in models of technicolor featuring spin-one vector and axial-vector resonances and a spin-zero isospin-zero state. We show how the walking dynamics constrains the interplay of these states in the unitarization of the scattering amplitudes"     Frandsen Title: Technicolor Dark Matter   Abstract: Dark Matter candidates are natural in Technicolor theories. I will discuss signals of Technicolor Dark Matter at LHC and constraints from earth based experiments such as CDMS and XENON.     Giedt Title:  Lattice epsilon regime and minimal walking technicolor   Abstract: We discuss how lattice data with small values of mpi*L can be described using lattice chiral perturbation theory in the epsilon regime. Some open questions are highlighted. A comparison to on-going lattice simulations of minimal walking Technicolor is made.     Hasenfratz Title: Monte Carlo Renormalization Group calculation for many-fermion models   Abstract: Monte Carlo Renormalization Group methods were designed to study critical behavior in statistical systems and quantum field theories. They are particularly powerful in determining phase structure and critical indexes. In this talk I outline how the 2-lattice MCRG matching can be used to determine the bare beta function of many fermion systems. I will discuss models with fermion numbers 0,4,12 and 16, moving from the clearly QCD like to conformal models.     Holland Title: Running coupling measurements in technicolor models   Abstract: The renormalized coupling, and its running, is one of the fundamental properties of a gauge theory, and plays an important role in potential walking technicolor models. We describe how to calculate the renormalized coupling non-perturbatively via lattice simulations, by measuring Wilson loop ratios. We present results for pure SU(3) gauge theory and for fermions in the fundamental representation inside and outside the conformal window.     Matti Järvinen Title: Electroweak phase transition in walking technicolor   Abstract: First order temperature-dependent electroweak phase transitions may arise in walking technicolor models. I analyze the transitions in minimal walking technicolor and in ultra minimal technicolor by using the effective potential. In minimal walking technicolor, the phase transition is sufficiently strong for electroweak baryogenesis in a significant region of the parameter space. In ultra minimal technicolor the interplay of two transitions leads to a rich phase diagram with the possibility of a restoration and an extra breaking of the electroweak symmetry.     Kuti Title: Studies of gauge theories in finite volume and the conformal window   Abstract: We report new results on nearly conformal gauge theories with fermions in the fundamental representation of the SU(3) color gauge group as the number of fermion flavors is varied in the Nf = 4-16 range. To unambiguously identify the chirally broken phase below the conformal window we apply a comprehensive lattice tool set in finite volumes which includes the test of Goldstone pion dynamics, the spectrum of the fermion Dirac operator, and eigenvalue distributions of random matrix theory. We also discuss the theory inside the conformal window and beyond. The importance of  finite volume zero momentum gauge field dynamics is explained.      Lucini Title: Glueball masses and string tension in SU(2) gauge theory with adjoint fermions   Abstract: In a recent work, we have pointed out that a clean signal for the existence of an infrared fixed point in a gauge theory with fermions can be obtained by looking for signatures in the gluonic sector. In this talk, we shall describe the technical details of our calculations and discuss possible systematic errors. We shall show that, although those measurements are technically difficult, they can be kept under good control even with a limited number of configurations.         Michielse Title: The PRACE Project - Applications, Benchmarks and Prototypes   Abstract: I can give an overview of PRACE, what it is aiming at, what kind of opportunities / difficulties there are, what kind of prototype systems, what about access, what about benchmarking etc.     Miransky Title: Conformal phase transition in QCD and beyond   Abstract: I describe the main characteristics of the conformal phase transition. The examples are the phase transition with respect to the quark flavor number in QCD and the phase transition with respect to the coupling constant in grapheme like dynamics.     Patella Title: Comparing mesonic and gluonic sectors in SU(2) with two adjoint fermions.   Abstract: The masses of the lowest-lying states in the meson and in the gluonic sector of an SU(2) gauge theory with two Dirac flavors in the adjoint representation are compared on the lattice at a fixed $\beta = 2.25$ for values of the bare fermion mass $m_0$ that span a range between the quenched regime and the massless limit. Even for light constituent fermions, the spectrum shows a well-defined hierarchy: the lightest glueballs are found to be lighter than the lightest mesons. I will discuss the implications of these findings, combined with the results presented in the talks of Pica, Rago and Lucini. A strategy for discriminating between the (near-)conformal and the confining scenario is outlined.     Pica Title: Mesonic spectrum of SU(2) with two Adjoint Dirac fermions   Abstract: I will report on our recent accurate computation of the low-lying mesonic states of the SU(2) gauge theory with two adjoint fermions. We performed lattice simulations focusing on the chiral regime of the theory while keeping the systematic errors under control by using a sequence of lattices of increasing size. Results for the pseudoscalar and vector meson masses, the pseudoscalar decay constant and the chiral condensate, obtained on the largest lattices and smallest quark masses available to date, will be discussed. The relevance of our findings for the existence of an IR fixed point in the theory will be clarified.     Pickup Title: Investigating the Scaling of SU(2) with two Adjoint Fermions   Abstract SU(2) with two adjoint fermions is an interesting candidate theory for Walking Technicolour. I will present our recent lattice results on the running of the coupling and the mass anomalous dimension in this theory, using the Schr\"odinger functional scheme.     Rago Title: Infrared effective dynamics of SU(2) with adjoint fermions   Abstract: In this talk I will present the result of a recent lattice study of a SU(2) model with two adjoint fermions. I will focus the presentation on the infrared behaviour of the theory, and I will investigate the possibility of comparing the dynamical data to suitabbly choosen quenced simulations.     Rummukainen Title: Infrared fixed point in SU(2) gauge theory with 2 adjoint representation fermions   Abstract: T.b.c.     Sakuma Title: Minimal Flavor Constraints for Technicolor   Abstract: We introduce a new set of minimal flavor constraints valid for a general class of models of dynamical electroweak symmetry breaking. We show that these constraints are important and cannot be neglected.     Sannino Title: Phases of Gauge Theories and QCD Duals   Abstract: I will present the state-of-the-art of the phase diagrams for strongly coupled gauge theories as function of the number of flavors, colors and matter representation for SU, Sp and SO gauge theories. I will also argue that different nonsupersymmetric gauge theories can be nontrivially related, in their respective conformal windows, via an electro-magnetic duality transformation.       Sarkar Title: Discovering dark matter   Abstract: T.b.c.     Shamir Title: Cohomology of supersymmetric gauge theories revisited   Abstract: Using Algebraic-Renormalization techniques we study the consistency conditions pertaining to supersymmetric abelian gauge theories, finding a new cohomologically non-trivial solution.  This implies that supersymmetry may be anomalous in certain gauge theories. While a full loop calculation has yet to be done, we examine the implications of some anomalous supersymmetry Ward identities in a concrete model.     Smit Title: The crumpled phase in the dynamical triangulation approach to quantum gravity.   Abstract: Numerical simulations in the dynamical triangulation formulation of quantum gravity have shown the existence of an elongated phase' and a crumpled phase', which have unphysical features for coupling values far from the crtitical coupling separating these phases. We attempt to give a physical interpretation of these phenomea, with emphasis on the crumpled phase for which we present old unpublished results.     Soni Title: Lattice Weak Matrix Elements & CP Violation: Standard Model Model and beyond.   Abstract: T.b.c.     Svetisky Title: Sextet quarks: at the sill of the conformal window?   Abstract: I will present recent numerical results for the SU(3) gauge theory with two flavors of sextet quarks that indicate that if it is conformal, it is barely over the edge into the window.  I will also discuss peculiarities of the Aoki phase.     Tuominen Title: From hierarchy problem to unification and dark matter.   Abstract: The electroweak hierarchy problem has provided a paradigm for model building for decades. Technicolor with its various incarnations provides a natural solution. However, various other model building paradigms can be addressed within technicolor as well. In this talk I will discuss some concrete examples, like how fourth generation of ordinary matter may arise, and how simple technicolor model can also provide unification of the three Standard Model coupling constants and lead to viable dark matter candidates.     van Baal Title: Progress on Calorons   Abstract: T.b.c.     Wijewardhana Title: Black branes in Einstein-Gauss-Bonnet gravity   Abstract: For his presentation, click here     Yamada Title: Study of the running coupling constant in 10-flavor QCD with the Schrödinger functional method   Abstract: The electroweak gauge symmetry is allowed to be spontaneously broken by the strongly interacting vector-like gauge dynamics, especially provided the gauge coupling runs slowly in a wide range of energy scale. This may open up the possibility that the origin of all masses may be traced back to the gauge theory. We use the Schrödinger functional method to study the scale dependence of the gauge coupling of 10-flavor QCD. Some preliminary results are presented.     Yamawaki Title: Conformal Higgs, or Techni-dilaton - Composite Higgs at Conformal Phase Transition   Abstract: Walking/Conformal technicolor near the Banks-Zaks conformal fixed point is discussed in terms of conformal phase transition (CPT) which is characterized by the essential singularity scaling, breakdown of the Ginzburg-Landau effective theory, and large anomalous dimension. In terms of the gauged Nambu-Jona-Lasinio model, the CPT takes place as a fusion of infrared fixed point and ultraviolet fixed point with \gamma_m =1. As a remnant of conformal symmetry there exists a light scalar, techni-dilaton, in the broken phase, while no light spectra exist in the symmetric phase (conformal window). The techni-dilaton may be discovered in LHC.        [Back]