Seminars 2007



    • Friday 24 August at 10.15 in HIP seminar room A315: Shaaban Khalil (Cairo)
      TeV scale B-L extension of the standard model
      Abstract: The fact that neutrinos are massive indicates that the Standard Model (SM) requires extension. We propose a low energy (less than TeV) B-L extension of the SM, which is based on the gauge group SU(3)_C x SU(2)_L x U(1)_Y x U(1)_{B-L}. We show that this model provides a natural explanation for the presence of three right-handed neutrinos in addition to an extra gauge boson and a new scalar Higgs. Therefore, it can lead to very interesting phenomenological implications different from the SM results which can be tested at the LHC.
    • Monday 27 August at 10.15 in HIP seminar room A315: Per Kraus (UCLA)
      Stringy black holes in five dimensions
      Informal blackboard review talk
    • Tuesday 28 August at 10.15 in HIP seminar room A315: Kazuya Koyama (Portsmouth)
      Primordial perturbations in the new ekpyrotic model
      Abstract: A scale-invariant spectrum of isocurvature perturbations is generated during collapse in the ekpyrotic scaling solution in models where multiple fields have steep negative exponential potentials. The scale invariance of the spectrum is realized by a tachyonic instability in the isocurvature field. This instability drives the scaling solution to the late time attractor that is the old ekpyrotic collapse dominated by a single field. We show that the transition from the scaling solution to the single field dominated ekpyrotic collapse automatically converts the initial isocurvature perturbations about the scaling solution to comoving curvature perturbations about the late-time attractor. We calculate the spectrum and amplitude of curvature perturbations. It is also shown that large non-Gaussianity is generated during the transition.
    • Thursday 30 August at 10.15 in HIP seminar room A315: Jorma Louko (Nottingham)
      How often does an accelerated particle detector click?
      Abstract: It has been known since the seventies that a uniformly-accelerated particle detector in Minkowski vacuum becomes excited thermally, in a temperature proportional to the acceleration. We discuss generalisations of this result to arbitrary detector motions and to curved spacetimes. In particular: (i) For a pointlike detector in non-stationary motion, the instantaneous transition rate is ill-defined without regularisation; (ii) Spatial or temporal smearings lead to a well-defined transition rate that is causal and allows the extraction of various asymptotic properties. (References: gr-qc/0606067, gr-qc/0611067).
    • Friday 14 September 2007 at 14.15 in A315: Vesa Muhonen (HIP) [cosmo seminar]
      Isocurvature in the CMB?
      Abstract: The concordance model of the universe takes the primordial perturbations to be adiabatic and scale-invariant. However, even as the pure isocurvature case is ruled out, the data does allow a small deviation from adiabaticity. I will discuss the case where we allow a correlated cold dark matter isocurvature component to be present and what are the observational constraints for this kind of model based on the currently available CMB and large-scale structure data.
    • Friday 21 September 2007 at 14.15 in A315: Diana Battefeld (HIP) [cosmo seminar]
      Magnetogenesis from Cosmic String Loops
    • Tuesday 25 September at 10.15 in E204: Gudrun Hiller (Dortmund)
      Minimal Flavor violation and the LHC
      Abstract: Over the recent years studies in Kaon-, charm- and B-physics lead to the picture that minimal flavor violation (MFV), that is, all flavor violation is due to the Yukawa coulings as in the Standard Model, could be a viable organizing principle of flavor physics within and beyond the Standard Model. I review the concept of MFV and point out potential challenges. I discuss first steps to access flavor also with high p_T collider observables. As an example, charged Higgs production in pp-collisions dependent on flavor physics (hep-ph/0708.0940) is discussed. This opens up the possibility to test MFV at the LHC.
    • Friday 28 September at 10.15 in D114: Martin Schnabl (IAS, a recipient of 2007 EURYI award) [string seminar]
      Prospects in String Field Theory
      Abstract: Open string field theory is a very good tool to study the dynamics of unstable D-brane systems and perhaps other phenomena. I will review its present status and outline few possible directions for years to come.
    • Friday 5 October 2007 at 14.15 in A315: Jim Virdee (CERN, Spokesman of the CMS experiment):
      The CMS Experiment at the Large Hadron Collider: Status and Prospects
      Abstract: The current status of the LHC machine and the CMS experiment will be given. The preparations for the physics run in 2008 will be outlined. The prospects for physics, with an emphasis on the first two years of machine operation, will be described.
    • Tuesday 9 October 2007 at 10.15 in E204: Michael Doser (CERN):
      Experiments on Antihydrogen: status and outlook
      Abstract: Several years after the first production of antihydrogen atoms, several experiments at the Antiproton Decellerator at CERN are now taking the next steps towards using these systems to test CPT and gravity. An overview of the current status will be given in the context of the general low-energy antiproton physics program at CERN, pointing out what has been learned, and where the main difficulties remain. Particular emphasis will be given to a newly proposed experiment that will represent the first measurement of the gravitational interaction of antimatter.
    • Wednesday 10 October at 16.15 in A315: Nobuchika Okada (Theory Division, KEK, Tsukuba, Japan) [string seminar]
      Economically deflected anomaly mediation
      Abstract: We discuss the so-called deflected anomaly mediation scenario, in which the tachyonic slepton problem in pure anomaly mediation scenario can be fixed through threshold corrects of the messenger fields. We propose an economical setup of this scenario, where the messengers play another important role for the see-saw scenario in neutrino sector. The lightest sparticle is mostly B-ino and can be a good candidate for the dark matter.
    • Tuesday 30 October 2007 at 10.15 in E204: Charanjit Aulakh (Chandigarh, India)
      Deciphering Ourobouros : Pinning down the NMSGUT
      Abstract: We trace the emergence of the “ New Minimal” supersymmetric SO(10) GUT (NMSGUT) out of the debris created by our demonstration that the MSGUT is falsified by the data. It has only spontaneous CP violation and Type I seesaw. With only 23 real superpotential parameters it is the simplest model capable of accommodating the fermion mass data set. We show that superheavy threshold corrections in the New Minimal Supersymmetric GUT based on the SO(10) Higgs system 210 + 126 + \overline{126} + 10 + 120 can comfortably correct the prediction for the value alpha_3(M_Z) from the relatively large value predicted by the two loop RG equations to the central value determined by the current world average. The unification scale is raised above the one loop value over almost all of the viable parameter space. We show that generic 10 + 120 + \overline{126} fits of fermion masses and mixings, overdetermine the superpotential parameters (by one extra constraint). Therefore fits should properly be done by generating the 24 generic fit parameters from the 23 parameters of the NMSGUT superpotential, given tan beta as input. Each numerical fit then fully specifies the parameters of the NMSGUT, offering the possibility of a confrontation between the scale of gauge unification and the fit to fermion masses due to their extractable common dependence on the NMSGUT parameters.
    • Tuesday 20 November 2007 at 10.15 in E204: Tuula Mäki (University of Helsinki and Helsinki Institute of Physics):
      Top quark mass measurement in dilepton channel
      Abstract: The top quark is the heaviest elementary particle. It was discovered in 1995 at Fermilab which still remains the only place where top quarks have been produced. The top quark mass is interesting as a fundamental parameter of the standard model, an important input to precision electroweak tests, and it places constraints on various extensions of the standard model. In this seminar, a top quark mass measurement in the dilepton channel will be discussed.
    • Tuesday 27 November 2007 at 10.15 in E204: Arttu Rajantie (Imperial College):
      Lattice calculation of non-Gaussianity from preheating
      Abstract: If light scalar fields are present at the end of inflation, their non-equilibrium dynamics such as parametric resonance or a phase transition can produce non-Gaussian density perturbations, which would be observable in the cosmic microwave background radiation. I show how this non-Gaussianity can be calculated using non-linear lattice field theory simulations and the separate universe approximation, and present numerical results for the massless preheating model, which rule out some parts of the parameter space. I argue that preheating can be an important factor in assessing the viability of inflationary models.
    • Monday 3 December 2007 at 14.15 in D101: Frank Wilczek (MIT and Nordita, Nobel laureate 2004):
      The Universe is a Strange Place
      Abstract: Over the course of the twentieth century we have constructed a very successful fundamental theory of the behavior of matter. Viewed from this perspective, the world looks very different from our everyday reality. It is a very strange place, and a beautiful one — in particular, we’ve come to understand that the building blocks of matter appear as notes in a Music of the Void. I’ll describe this using a combination of facts, pictures, and jokes. Finally I’ll discuss some recent discoveries indicating that the world is even stranger than we’ve understood so far, and how we’re rising to the challenge. At about 15.45 in D101:
      Anticipating a New Golden Age (particle physics talk)
      Abstract: The standard model of fundamental interactions is remarkably successful, but it leaves an unfinished agenda. Several major questions seem ripe for exploration in the near future. I anticipate that the coming decade will be a Golden Age of discovery in fundamental physics.
    • Tuesday 4 December 2007 at 10.15 in E204: Alexei A. Starobinsky (Landau Institute for Theoretical Physics):
      Scalar-tensor and f(R) models of dark energy
      Abstract: Recent progress in construction of viable dark energy models in scalar-tensor and f(R) gravity satisfying laboratory, Solar system and cosmological tests and containing no ghosts and instabilities is discussed. Such models can admit phantom behaviour of dark energy. Further problems and most critical tests of these models are outlined.
    • Tuesday 11 December 2007 at 10.15 in E204: Teppo Mattsson (HIP):
      Dark energy as a mirage
      Abstract: The evidence for dark energy is based on the assumption that the effects of the nonlinear clustering of matter are averaged out at cosmological distances. I argue that this assumption is too crude: Due to the forming nonlinear structures, the regions the observable light traverses get emptier and emptier compared to the average. As space expands the faster the lower the local matter density, the expansion can then accelerate along our line of sight without local acceleration. This phenomenon provides both a natural physical interpretation and a quantitative match for the current cosmological observations without dark energy, resulting in a concordant model with 90% dark matter and 10% baryons.
    • Friday 14 December 2007 at 14.15 in A315: Jussi Väliviita (IGC, Portsmouth) [cosmo seminar]

Unexpected blow-up of perturbations in coupled dark energy and matter fluid models
Abstract: We consider fluid models of Dark Energy interacting with Dark Matter. After correcting some previous mistakes in literature, we find that in several cases the perturbations grow very fast. This rules out a large class of coupled models where the equation of state parameter of dark energy is constant.


    • Tuesday 18 December 2007 at 10.15 in A315 (note room!): Tuomas Lappi (Saclay):
      The initial state of the little bang at RHIC and LHC
      Abstract: The early stages of an ultrarelativistic heavy ion collision, such as seen at the Relativistic Heavy Ion Collider (RHIC) or the Large Hadron Collider (LHC) consist of a high energy density, mostly gluonic, matter. The system then rapidly cools in an initially one dimensional Hubble flow. Both the relevant small x parts of the nuclear wavefunctions and the earliest stages of the collision process can be understood in terms of classical gluon fields in a picture known as the color glass condensate. This talk will discuss some applications of these ideas to RHIC and LHC phenomenology and their connections to DIS experiments.