Seminars 2012

DEPARTMENT OF PHYSICS / HIP JOINT COLLOQUIA / SEMINARS 2012

  • Thursday 5 January 2012 at 10.15 in A315: Lusaka Bhattacharya (Saha Institute of Nuclear Physics, Kolkata, India) 
    Photons from relativistic heavy ion collisions 
    Abstract: One of the most important issues that arises in the study of relativistic heavy-ion collisions is that of the creation of a new state of matter, quark-gluon-plasma (QGP). Since the plasma life time and volume are small, various “probes” of QGP detection have been proposed, such as jet-quenching, photon and dilepton production e.t.c. In this talk the prospect of photons as a possible probe will be discussed.
  • Thursday 12 January 2012 at 10.15 in A315: Particle theory 2-minute meeting. 
    Abstract: Everybody working in theoretical particle physics has up to two minutes to present his/her activities.
    Blackboard, transparencies, the local computer or none of those can be used (remember the strictly enforced time limit).
  • Tuesday 17 January 2012 at 10.15 in E204: Lauri Wendland (Helsinki) 
    Latest news from the Higgs front 
    Abstract: The ATLAS and CMS collaborations presented their latest results in the search for the standard model Higgs boson at a public seminar on 13.12.2011. The two experiments report to have narrowed down the Higgs boson mass to a range of 115-130 GeV (ATLAS) and 114-127 GeV (CMS) at 95% confidence level with a small (~2 sigma) excess at 126 GeV (ATLAS) and 124 GeV (CMS) observed in independent decay channels. The results are discussed and an outlook is presented for what can be expected to be achieved with this year’s data.
    CMS results are here and Atlas results here. 
  • Tuesday 24 January 2012 at 10.15 in E204: Priyotosh Bandyopadhyay (Helsinki) 
    Probing Higgs in Type III Seesaw at the LHC 
    Abstract: We show that the type III seesaw mechanism opens up a promising possibility of searching the Higgs boson in the b-bbar channel through the Higgs production associated with a charged lepton coming from the decay of the triplet fermions. In particular we look for the 2b signals with trileptons and same-sign dileptons to construct the Higgs and the triplet fermion mass and calculate the reach with the integrated luminosity of 10 1/fb at the 14 TeV LHC.
  • Tuesday 14 February 2012 at 10.15 in E204: Mark Hindmarsh (Helsinki) 
    Cosmic Strings, Inflation and the Cosmic Microwave Background 
    Abstract: Theories of physics beyond the Standard Model predict the existence of relativistic strings, either as composite objects, or as fundamental constituents of matter. In a class of well-motivated models of the early Universe, inflation ends by producing cosmic strings, which will still be present at a low density today. This talk reviews the status of cosmic strings in inflationary cosmology, and describes the latest constraints from the Cosmic Microwave Background data.
  • Thursday 23 February 2012 at 11.00 (Note time!) in A315: Dirk Rischke (Frankfurt) 
    Recent results from chiral effective models 
    Abstract: In this talk, I present results from an effective model based on the linear representation of the chiral U(N_f)_r x U(N_f)_l symmetry of QCD. It is demonstrated that a reasonable fit of the mass parameters and coupling constants of the model to hadron vacuum properties is possible. This fit can contribute to answering the question about the quark content of the scalar isoscalar mesons. The ultimate goal is to use this model to investigate signatures for chiral symmetry restoration at nonzero temperatures and densities.
  • Tuesday 28 February 2012 at 10.15 in E204: Stephan Huber (Sussex University, Brighton, UK) 
    Models for a strong electroweak phase transition 
    Abstract: I will briefly review the generation of possible relics from a strong electroweak phase transition, such as the baryon asymmetry and gravitational waves. I will discuss the real time history of the transition, in particular the expansion velocity of the nucleating bubbles. In the second part I will present models, with and without supersymmetry, which do lead to a strong first-order phase transition.
  • Tuesday 20 March 2012 at 10.15 in E204: Sergey Ketov (Tokyo Metropolitan University) 
    Higgs inflation vs. Starobinsky inflation in gravity and supergravity 
    Abstract: Inflationary slow-roll dynamics in the Einstein gravity with non-minimal scalar-curvature coupling (known as Higgs inflation) is shown to be equivalent to that in the f(R) modified gravity theory (known as Starobinsky inflation). I give a proof of the correspondence and extend it to N=1 supergravity. The non-minimal coupling in supergravity is reformulated in terms of the standard (minimal) N=1 matter-coupled supergravity by using curved superspace. The equivalence relation between the supergravity theory with the nonminimal scalar-curvature coupling and the recently constructed F(R) supergravity (which is the N=1 locally supersymmetric extension of f(R) gravity) during slow-roll inflation is established in the manifestly supersymmetric way. The equivalence does not hold after inflation during reheating. The main reference is arXiv:1201.2239.
  • Monday 26 March 2012 at 12.15 in D114 (Note time and place!): Martin Kunz (Geneva) 
    Observing the Darkness 
    Abstract: In my talk I will briefly review the dark energy problem and possible explanations. I will then discuss how cosmological observations can characterize the properties of the dark energy, what our current knowledge is, and what we can expect to learn in the coming decade.
  • Tuesday 27 March 2012 at 10.15 in E204: Dan-Olof Riska (Helsinki) 
    HIP 2000-2010 and some research career highlights 
    Abstract: I’ll describe the challenges and lucky breaks at HIP during my tenure as director and some fortuitous career forming research discoveries.
  • Thursday 12 April 2012 at 10.15 in A315: Kimmo Tuominen (Jyväskylä) 
    Thermodynamics of quasi-conformal gauge theories and gauge/gravity duality 
    Abstract: Thermodynamics of a generic almost conformal theory, specified by its beta function, is studied using gauge/gravity duality. The 5-dimensional gravity dual is a metric with a black hole and a scalar field, dilaton, acting as a source of F_mn^2. Three different phases are identified: a high temperature phase of massless partons, an intermediate quasi-conformal phase and a low temperature confining phase. The transitions between the phases are of first order or continuous, depending on the parameters of the beta function. These results will be compared with the preliminary results from a model containing also a second scalar, tachyon, acting as the source of quark condensate <qqbar>.
  • Wednesday 18 April 2012 at 14.15 in A315: Valery Khoze (Durham; St. Petersburg) 
    Central exclusive production processes at hadron colliders 
  • Tuesday 7 May 2012 at 10.15 in A315: Kim Splittorff (Copenhagen) 
    The Aoki phase versus the Sharpe-Singleton scenario 
    Abstract: We will discuss the new insights on the phase structure of lattice QCD with Wilson fermions which has emerged from the exact computation of spectrum of the Wilson Dirac operator at nonzero lattice spacing. In addition to the spontaneous breaking of chiral symmetry, new phase structures known as the Aoki phase and the Sharpe-Singleton scenario can dominate. The new phases arise due to the interplay between the continuum and the chiral limit in lattice QCD with Wilson fermions and are essential for the study of non perturbative QCD at physical values of the pion masses. In particular, we will explain a long standing puzzle between the phase structure observed in quenched and unquenched lattice simulations.
  • Tuesday 15 May 2012 at 10.15 in E204: Tuukka Meriniemi (Helsinki) 
    Gravitational waves produced after inflation 
    Abstract: Several possible gravitational wave production schemes in the early Universe have been studied before, like bosonic preheating and phase transitions. We will introduce for the first time the spectrum of gravitational waves produced by fermions. Preheating and other particle production phenomena in the early Universe can give rise to high-energy out-of-equilibrium fermions. These fermions develop a source for gravitational waves, an anisotropic stress. We will present a formalism to regularize the source and to calculate the spectrum of gravitational waves from this process.
  • Tuesday 29 May 2012 at 10.15 in E204: Anindya Datta (Calcutta) 
    Universal Extra Dimensions and its signature at the LHC 
    Abstract: In universal extra-dimensional models a conserved Z_2 parity ensures the stability of the lightest Kaluza-Klein particle, a potential dark-matter candidate. We show here that boundary-localized kinetic terms, in general, do not preserve this symmetry. We examine the single production of a Kaluza-Klein excitation of the photon and its decay to zero-mode fermion-antifermion pairs in the presence of such terms. We explore how experiments at the Large Hadron Collider at CERN can help constrain the boundary-localized kinetic terms for different choices of the compactification radius.
  • Tuesday 5 June 2012 at 10.15 in A315: Anupam Mazumdar (Lancaster, Copenhagen) 
    Towards Asymptotic Freedom of Gravity 
    Abstract: I will present the most general covariant ghost-free gravitational action in a Minkowski vacuum. Apart from the much studied f(R) models, this includes a large class of non-local actions with improved UV behavior, which nevertheless recover Einstein?s general relativity in the IR.
  • Thursday 7 June 2012 at 10.15 in A315: Alexandru Jipa (Bucharest) 
    From nuclear matter to Big Bang and back. New results on the nuclear matter dynamics in relativistic and ultrarelativistic nuclear collisions 
    Abstract: The nucleus-nucleus collisions at relativistic and ultrarelativistic energies offer a unique opportunity to obtain high excited and dense nuclear matter. A number of phase transitions, from normal nuclear matter to the quark-gluon plasma, are possible in such matter. The formation of the quark-gluon plasma in these conditions can be discussed in the terms of the cosmological scenarios on the formation and evolution of the Universe. The present work presents a few new experimental results, as well as a few simulation results on the behaviour of high excited and dense nuclear matter formed in such collisions. The experimental results, as well as the simulation codes predictions, are obtained in the framework of a few international collaborations where the team members from the Nuclear Matter in Extreme Conditions Research Center are involved, namely: SKM 200, MARUSYA at JINR Dubna (Russia), BRAHMS at RHIC-BNL (USA) and CBM-FAIR at GSI Darmstadt (Germany).
  • Monday 11 June 2012 at 14.15 in A315: Veikko Karimäki (Helsinki) 
    Farewell seminar: Forty-five years of High Energy Physics 
  • Tuesday 19 June 2012 at 10.15 in A315: Emidio Gabrielli (Tallinn) 
    Fermiophobic Higgs scenarios at the LHC 
    Abstract: After reviewing the present status of Higgs boson searches at the LHC, I will focus on fermiophobic Higgs boson scenarios, where the standard-model Higgs couplings to fermions vanish at tree level. One-loop corrections will in general affect the tree-level predictions by generating radiative fermionic (Yukawa) couplings. Effective Higgs Yukawa couplings are studied in a general theoretical framework, giving an improved description of a large class of fermiophobic Higgs-boson scenarios. The impact of these scenarios at the LHC is discussed in the light of the recent anomalous excess of events observed by both ATLAS and CMS collaborations in the 125 GeV diphoton invariant mass region. I will eventually consider the theoretical and phenomenological implications of a fermiophobic Higgs boson with mass of 125 GeV in supersymmetry.
  • Tuesday 26 June 2012 at 10.15 in A315: Matti Järvinen (Heraclion, Crete) 
    Holographic models for QCD in the Veneziano limit 
    Abstract: I discuss holographic bottom-up models for QCD in the Veneziano limit of large N_f and N_c with fixed x=N_f/N_c (see arXiv:1112.1261). The models are constructed by putting together holographic models of Yang-Mills theory (improved holographic QCD), with a Sen-type tachyon actions inspired by brane constructions, and by considering full backreaction. At zero temperature one finds, as a function of x=N_f/N_c, a phase diagram, which meets the expectations from QCD, including a conformal transformation for zero quark mass at a critical value x=x_c. Other important features are “walking” behavior of the QCD coupling in the region near and below x_c, Miransky scaling as x -> x_c, and Efimov-like saddle points.
  • Tuesday 3 July 2012 at 10.15 in A315: O.W.Greenberg (Maryland) 
    Haag expansion and covariant bound state amplitudes 
    Abstract: I discuss a framework for the calculation of covariant, yet single-time, amplitudes for bound states, both at rest and in motion, based on the Haag expansion in asymptotic fields.
  • Tuesday 14 August 2012 at 10.15 in A315: Aleksi Vuorinen (Bielefeld) 
    Holographic photon and dilepton production in a thermalizing plasma 
    Abstract: I will discuss a recent AdS/CFT calculation aimed at determining the production rates of prompt photons and dileptons in strongly coupled N = 4 Super Yang-Mills plasma out of thermal equilibrium. Thermalization is described via the gravitational collapse of a thin shell of matter in AdS_5 space and the subsequent formation of a black hole. We evaluate the spectral functions relevant for the two processes as well as the quasinormal spectrum of the corresponding U(1) vector field, which display interesting signatures prior to thermalization.
  • Thursday 16 August 2012 at 10.15 in A315: Kazuo Fujikawa (RIKEN Nishina Center, Japan) 
    Universally valid Heisenberg uncertainty relation 
    Abstract: The original formulation of the uncertainty relation by Heisenberg, which is based on a thought experiment with an emphasis on measurement processes, lacked a simple mathematical basis compared to the widely accepted relations of Kennard and Robertson. In fact, a commonly assumed form of the Heisenberg-type relation has been recently invalidated by spin-measurements at Vienna. On the other hand, the analysis of measurement processes was missing in the relations of Kennard and Robertson. Here we suggest to reformulate the Heisenberg uncertainty relation in such a manner that it incorporates both of the intrinsic quantum fluctuations and the effects of measurement, and yet with the same mathematical rigor as the relations of Kennard and Robertson and thus universally valid. This relation, which assumes the form delta x * delta p ~ hbar (instead of hbar/2) when written in a popular notation, is regarded as a combination of the past works on the uncertainty relation by Arthurs and Kelly, who emphasized the role of measurement apparatus, and by Ozawa who clarified the mathematical structure.
  • Tuesday 21 August 2012 at 10.15 in A315: Steinar Stapnes (CERN) 
    The Compact Linear Collider study 
    Abstract: The Compact Linear Collider study (CLIC) is in the process of completing a Conceptual Design Report (CDR) for a multi-TeV linear electron-positron collider. Such a machine would open up for detailed studies of many of main physics questions that are currently occupying the particle physics community. The CLIC concept is based on high gradient normal-conducting accelerating structures. The RF power for the acceleration of the colliding beams is produced by a novel two beam acceleration scheme, where power is extracted from a high current drive beam that runs parallel with the main linac. A summary of the concept, progress and status of the corresponding studies will be given in this talk, as well as an outline of the preparation and work towards an implementation plan by 2016 for CLIC.
  • Tuesday 28 August 2012 at 11.15 in A315: Gautam Bhattacharyya (Saha Institute, Kolkata) Note delayed beginning due to SAB meeting! 
    Electroweak Symmetry Breaking Beyond the Standard Model 
    Abstract: I shall discuss two key issues related to electroweak symmetry breaking: First, how fine-tuned different models are that trigger this phenomenon? Second, is the Higgs boson necessarily elementary or can it be composite as well?
  • Wednesday 5 September 2012 at 10.15 in A315: Stefan Stricker (Wien) Note day! 
    Bootstraping gravity solutions 
    Abstract: We present an algorithm that allows one to construct all stationary axi-symmetric solutions of 3-dimensional Einstein gravity with self-interacting scalar field. We discuss the most general asymptotically AdS boundary conditions and show how the theory can be holographically renormalized and calculate the Brown-York stress tensor as well as the scalar response function. We give several examples, including asymptotically flat hairy black holes and novel asymptotically AdS solutions and discuss potential condensed matter applications using the AdS/CFT correspondence.
  • Tuesday 18 September 2012 at 10.15 in A315: Stan Brodsky (SLAC) 
    AdS/QCD, Light-Front Holography, and Color Confinement 
    Abstract: Gauge/gravity duality leads to a simple, analytical, and phenomenologically compelling nonperturbative approximation to the full light-front QCD Hamiltonian. This approach, called “Light-Front Holography”, successfully describes the spectroscopy of light-quark meson and baryons, their elastic and transition form factors, and other hadronic properties. The bound-state Schrodinger and Dirac equations of the soft-wall AdS/QCD model predict linear Regge trajectories which have the same slope in orbital angular momentum L and radial quantum number n for both mesons and baryons. Light-front holography connects the fifth-dimensional coordinate of AdS space z to an invariant impact separation variable zeta in 3+1 space at fixed light-front time. A key feature is the determination of the frame-independent light-front wavefunctions of hadrons — the relativistic analogs of the Schrodinger wavefunctions of atomic physics which allow one to compute form factors, transversity distributions, spin properties of the valence quarks, jet hadronization, and other hadronic observables. AdS/QCD and Light-Front Holography provide a remarkable window into the dynamics and spectroscopy of hadrons, as well as color confinement. This approach also gives a new perspective on the correct definition of the vacuum and the interpretation of condensates in relativistic quantum field theory, thus resolving the 10^{45} conflict with the empirical value of the cosmological constant.
  • Tuesday 25 September 2012 at 10.15 in A315: Lauri Wendland (HIP) 
    Progress on standard model Higgs boson searches at the LHC 
    Abstract: An observation of a new boson in standard model Higgs boson searches was announced by the ATLAS and CMS collaborations on the 4th of July. The new boson was found to decay to gamma gamma and to ZZ at a local P-value of above 4 and 3 sigma, respectively. Signs of decay to WW were also found at a local P-value of above 2 sigma. The observed number of events in each decay channel, the measured branching ratios, and the mass of ~125 GeV render the new boson compatible with the standard model Higgs boson hypothesis within statistical precision.
    The results (arXiv:1207.7214, arXiv:1207.7235) will be discussed and an outlook will be give$ determining the spin and parity of the new boson.
  • Tuesday 2 October 2012 at 10.15 in A315: Dilip Kumar Ghosh (IACS, India) 
    The Standard Model Higgs coupling measurement at the LHC, ILC and LHeC 
    Abstract: The LHC has found a new resonance with mass close to 125 GeV. This new resonance resembles the SM Higgs boson. However, to confirm this new boson to be the SM Higgs, one needs to measure its couplings to other SM particles, its spin and parity. In this talk I will review some of these issues.
  • Tuesday 9 October 2012 at 10.15 in A315: Anne Mykkänen (Helsinki) 
    Properties of QCD strings from lattice Monte Carlo 
    Abstract: In the confining regime of SU(N) gauge theories, the flux lines between well separated color sources are expected to be squeezed in a thin, stringlike tube, and the interaction between the sources can be described by an effective string theory. One of the consequences of the effective string description at zero temperature is the presence of the Lüscher term – a Casimir effect ~ -1/r due to the finiteness of the interquark distance – in the long distance interquark potential. We study the static quark potential and the Lüscher term through lattice simulations, implementing an efficient ‘multilevel’ algorithm proposed by Lüscher and Weisz. We study SU(3) and SU(4) Yang-Mills theories in 2+1 and 3+1 dimensions, with the generic Wilson action and with a tree-level improved action, and compare the results with the predictions of bosonic string theory.
  • Tuesday 16 October 2012 at 10.15 in A315: Stefano Di Chiara (HIP) 
    A Perturbative Realization of Miransky Scaling 
    Abstract: In this talk I show that a simple extension of quantum chromodynamics, featuring a meson-like scalar degree of freedom as well as an adjoint Weyl fermion, at the two loop order generates several fixed points, of which one is stable in the infrared. An interesting property of the model is that this fixed point is lost, within the perturbatively trustable regime, by merging with another fixed point when varying the number of quark flavors. In the vicinity of this fixed point I determine that the relation between the UV and IR scales of the theory follows, in first approximation, the Miransky scaling. Furthermore I define precisely the region of the parameter space where the theory features walking dynamics and, within such a region, estimate the anomalous dimension of the fermion masses.
  • Thursday 18 October 2012 at 10.15 in A315: K. Kajantie (HIP) 
    Hot QCD in the limit of large number of colors and flavors 
    Abstract: Finite temperature QCD can be discussed in various versions. The most interesting is _the_ QCD with quark masses which lead to the observed hadron spectrum. One can also set Nf=0 and study pure glue, Yang-Mills theory, at any Nc. Further, Nc = Nf = 3 is an interesting case. On the theoretical level, an important approximation is the ‘t Hooft limit, Nc->infty with g^2Nc fixed. The topic of this talk is the Veneziano limit, one takes the ‘t Hooft limit but further Nf->infty with xf=Nf/Nc=const. What is the phase structure on the (xf,T) plane? One knows that asymptotic freedom will be lost for xf>11/2, there is a conformal window below this at xc < xf < 11/2 and below xc there most probably are deconfining and chiral symmetry restoring transitions. What is xc, what happens when xf approaches xc, how are deconfining and chiral transitions related, what are the possible phase structures? Lattice Monte Carlo will answer these questions but, since Nc and g^2Nc are large, holography is also a natural tool. We apply a 5-dimensional holographic model with two scalars as the sources of the two operators F^2 and qbarq and with full inclusion of the gravity interactions between gluon and quark degrees of freedom. One more step in the search of a gravity dual of QCD – and useful techniques in the study of new beyond-the-SM theories.
  • Tuesday 6 November 2012 at 10.15 in A315: Tommi Markkanen (FL/HIP) 
    Quantum Corrections to Inflaton and Curvaton Dynamics 
    Abstract: The effective action (potential) has for a long time been one of the standard tools for studying the dynamics of inflation. However, often this approach is used in a simple Minkowski space setting neglecting the curved space contributions to the quantum corrections. In this talk I will present how to compute the fully renormalized one-loop effective action for two interacting and self-interacting scalar fields in curved space. I will then derive and solve the quantum corrected equations of motion both for fields that dominate the energy density (such as an inflaton) and fields that do not (such as a subdominant curvaton) in FRW spacetime. I will also introduce quantum corrected Friedmann equations that determine the evolution of the scale factor.
  • Thursday 8 November 2012 at 10.15 in A315: Heikki Arponen (Mathematics Dept, Helsinki) 
    Generalizing the Brown-Henneaux type gauge/gravity duality to higher dimensions 
    Abstract: In three and two dimensions the asymptotic symmetry groups of anti-de Sitter spaces are infinite dimensional and correspond to boundary conformal transformations. Further insight into this property can be gained by noting the relations AdS3 ≅ SL(2) and AdS2 ≅ SL(2)/SO(2), i.e. that the asymptotic symmetries are in fact that of the Lie group SL(2). I will briefly review the duality between asymptotically AdS3 gravity and the boundary Liouville conformal field theory from this Lie group theoretic point of view. I will then talk about my own work in generalizing this duality to the cases SL(3) and SL(3)/SO(3).
  • Tuesday 13 November 2012 at 10.15 in A315: Antti Gynther (TU Wien) 
    Modelling thermodynamics of anisotropic quark-gluon plasma 
    Abstract: Quark-gluon plasma created with heavy-ion collider experiments is initially very far from equilibrium and may contain substantial pressure anisotropies over its entire lifetime. At weak coupling, such anisotropic plasma exhibits instabilities which may play a crucial role in thermalization and isotropization of the plasma. It is therefore of considerable interest to develop a more complete understanding of the effects of anisotropies in both weakly and strongly coupled plasmas.
    In this talk, I will review our recent study of the thermodynamics and phase diagram of an anisotropic plasma, described by a Chern-Simons deformed gauge theory, and compare its weak and strong coupling limits.
  • Friday 16 November 2012 at 10.15 in A315: York Schröder (Bielefeld) Note day! 
    The Debye screening mass of hot QCD 
    Abstract: In analogy to the screening of electric fields within an electromagnetic plasma, chromo-electric fields within a quark-gluon plasma exhibit a characterictic screening length as well. Its inverse, the Debye screening mass, can be mapped onto a matching coefficient within dimensionally reduced effective theories. We report on an evaluation of this coefficient to 3-loop order, and point out how it contributes to the thermodynamic pressure of hot QCD.
  • Tuesday 20 November 2012 at 10.15 in A315: Juha Jäykkä (Nordita) 
    Dynamics and properties of Hopfions 
    Abstract: Several materials, such as ferromagnets, spinor Bose-Einstein condensates and some topological insulators, are now believed to support knotted structures. One of the most successful base-models having stable knots is the Faddeev- Skyrme model and it is expected to be contained in some of these experimentally relevant models. The taxonomy of knotted topological solitons (Hopfions) of this model is known. In this talk, we describe the basic properties of static Hopfions, known for quite a long time before discussing some aspects of the dynamics of Hopfions, how the static properties survive in the dynamical situation, and show that they indeed behave like particles: during scattering the Hopf charge is conserved and bound states are formed when the dynamics allows it.
  • Tuesday 27 November 2012 at 10.15 in A315: Tuula Mäki (HIP) 
    TOTEM experiment: Physics results and future 
    Abstract: TOTEM experiment (TOTal Elastic and diffractive cross section Measurement) is one of the seven detector experiments at the LHC. It focuses on forward physics by measuring the total pp cross-section, elastic scattering, diffraction and forward event topologies. This seminar discusses the recent TOTEM physics results and the plan forward to combine data with the CMS experiment.
  • Tuesday 4 December 2012 at 10.15 in A315: Rose Lerner (HIP) 
    Curvaton Decay by Resonant Production of the Standard Model Higgs 
    Abstract: In the curvaton scenario the primordial density perturbations originate from a second scalar field, rather than the inflaton. We investigate in detail a model where the curvaton is coupled only to the Standard Model Higgs boson. In such a case, one would expect a fast non-perturbative decay of the curvaton, so that the curvaton would not have time to build up the curvature perturbation. However, we show that this is not the case, and that the curvaton decay may be delayed even down to the electroweak symmetry breaking scale. This delay is due to the thermal background generated by the inflaton decay into Standard Model degrees of freedom. Contrary to expectations, it is possible to obtain the observed curvature perturbation for large values of the higgs-curvaton coupling.
  • Tuesday 11 December 2012 at 10.15 in A315: Ray Rivers (Imperial College) 
    The consequences of causality for tunable condensates undergoing rapid magnetic field quenches 
    Abstract: We discuss the consequences of causality for rapid magnetic field quenches of tunable cold Fermi gases like Li6 as they are driven between BCS and Bose-Einstein Condensate regimes. We suggest [1] that, with current experimental techniques, the constraints of causal horizons can lead to the spontaneous creation of vortices in fast quenches from the BEC to the BCS regime by a method akin to that for the creation of topological defects in the very early universe. On the other hand, in rapid quenches from the BCS to the BEC regime, we discuss [2] to what extent quasi-particle production in the condensate mimics that of particle production in Freedman-Robinson-Walker (FRW) metrics in the early universe, as proposed by several authors (e.g. see [3]).
    1. Lee, D-S, Lin, C-Y and Rivers, RJ, Spontaneous Vortex Production in Driven Condensates with Narrow Feshbach Resonances, Phys. Rev. A84 013623 (2011)
    2. Lee, D-S, Lin, C-Y and Rivers, RJ, Phonon Production in Tunable Fermi gas condensates; Galilean Invariance Fights Back, arXiv:1205.0133 .
    3. P. Jain, S. Weinfurtner, M. Visser and C. W. Gardiner, Analogue model of a FRW universe in Bose-Einstein condensates: Application of the classical field method, Phys. Rev. A 76 033616 (2007)
  • Thursday 20 December 2012 at 10.15 in A315: Niko Jokela (Santiago de Compostela) 
    Holographic flavors in Chern-Simons matter theories 
    Abstract: We review the holographic dual of N = 6 Chern-Simons matter theory and analyze the addition of unquenched flavors and the modification of the supergravity dual that they induce. We will then construct the corresponding flavored black hole and study the thermodynamic properties of both massive and massless brane probes and in particular the meson melting transition that they undergo at a certain critical temperature.