DEPARTMENT OF PHYSICS / HIP JOINT COLLOQUIA / SEMINARS 2009
Thursday 8 January 2009 at 10.15 in A315: Matti Järvinen (Odense) The Electroweak Phase Transition in Nearly Conformal Technicolor
Abstract: I will briefly introduce Minimal Walking Technicolor (MWT) and Ultra Minimal Technicolor (UMT) which are viable candidates for extensions of the standard model. I go on discussing the temperature-dependent electroweak phase transition in these models by studying the effective potential in their low energy effective field theories. The phase transition in MWT is seen to be sufficiently strong for electroweak baryogenesis in a sizeable region of the parameter space [arXiv:0808.1512]. UMT has two coupled chiral transitions which may lead to a nontrivial structure of the induced electroweak transition.
Tuesday 13 January 2009 at 10.15 in E204: Paula Eerola (FL and HIP) First physics at LHC when and what?
Abstract: The LHC accelerator and the physics data taking were expected to start in 2008. Proton beams were successfully injected into and circulated around the LHC in September 2008, but the machine, however, broke shortly thereafter, and the reparations and the required improvements will take some time. The restart has now been scheduled in summer-autumn 2009. I will first briefly review the accelerator design, the September 2008 incident, and the current plans for the restart, as well as the expected luminosity build-up and the centre-of-mass energy. Then the physics programme for the first years will be described as a function of the luminosity and energy. Finally, the status of the detectors is summarized.
Wednesday 14 January and Friday 16 January at 10-12 in the HIP Multifunctional Room A311: Matthias Gaberdiel (ETH Zurich) An overview of logarithmic conformal field theory
Abstract: This is a minilecture series, introducing logarithmic conformal field theory.
Thursday 15 January 2009 at 10.15 in A315: Virginia Azzolini (FL and HIP) Study of Charmless Inclusive Semileptonic B Decays and Measurement of the CKM Matrix Element |Vub| with the BaBar Detector
Abstract: The determination of the element |Vub| of the Cabibbo-Kobayashi-Maskawa (CKM) quark-mixing matrix plays a central role in the search for flavour and CP violation beyond the Standard Model. In this seminar, we will present measurements of partial branching fractions for inclusive charmless semileptonic decays, B -> Xu l nu, in limited regions of phase space and the corresponding values of |Vub|, as extracted using several theoretical calculations. The invariant mass of the hadronic system, Mx, the squared invariant mass of the lepton pair, q2, and the variable P+ = Ex-|Px|, or one of their combinations, in the process B -> Xu l nu are used as discriminating variables to suppress semileptonic decays with charm. Partial branching fractions are measured as functions of the cuts on the above variables. Different theoretical models are used to compute acceptances and related uncertainties, thereby allowing to extract |Vub|. These studies are performed on a sample of 383 million BB events collected at the Υ(4S) resonance, with the BaBar detector at the PEP-II e+e storage rings.
Cosmo seminar: Friday 6 February 2009 at 14.15 in A315: Keijo Kajantie (FL and HIP) The big black hole in the center of the Milky Way
Abstract: I review the properties of and evidence for the 4 million solar mass black hole in the center of the Milky Way. A comparison with Valtonen’s two-black hole-system OJ 287 is carried out.
Tuesday 17 February 2009 at 11.00 in E204: Dirk Rischke (Frankfurt)
Note time! From kinetic theory to dissipative fluid dynamics
Abstract: First-order dissipative fluid dynamics due to Landau and Eckart is unstable and leads to acausal signal propagation. The origin of this can be traced to the assumption that the energy-momentum tensor reacts instantaneously to forces exerted by deviations from thermodynamical equilibrium. In order to remedy this, second-order dissipative fluid-dynamical theories have been proposed, which take into account a nonzero relaxation time for the fluid response to fluid-dynamical forces. In this talk, starting from kinetic theory and using Grad’s 14-moment expansion, I present the derivation of the second-order theory due to Israel and Stewart. Working consistently to second order in the Knudsen number, I show that in previous derivations of the Israel-Stewart equations several second-order terms were missed. I also demonstrate that, in the absence of bulk viscous pressure and heat flux relative to energy flux, the resulting equations reduce to the set of second-order equations which were recently suggested by Baier, Romatschke, Son, Starinets and Stephanov for conformal theories in the context of the AdS/CFT correspondence.
Tuesday 24 February 2009 at 10.15 in E204: Jari Laamanen (Dortmund) Relic density and SUSY GUT models with non-universal gaugino masses
Abstract: Non-universal boundary conditions in grand unified theories can lead to non-universal gaugino masses at the unification scale. In R-parity preserving theories the lightest supersymmetric particle is a natural candidate for the dark matter. The composition of the lightest neutralino and implications on the dark matter is studied, when non-universal gaugino masses come from representations of SU(5) or SO(10). In these cases, the thermal relic density compatible with WMAP observations is found.
Cosmo seminar: Friday 27 February 2009 at 14.15 in A315: Andrea Ferrantelli (HIP) Scattering of massive W bosons into gravitinos and tree unitarity in broken supergravity
Abstract: The WW scattering into gravitino and gaugino is investigated in the broken phase, by using both gauge and mass eigenstates. Differently from what is obtained for unbroken gauge symmetry, we find in the scattering amplitudes new structures, which can lead to violation of unitarity above a certain scale. This happens because, in the annihilation diagram, the longitudinal degrees of freedom in the propagator of the gauge bosons disappear from the amplitude, by virtue of the SUGRA vertex. We show that the longitudinal polarizations of the on-shell W become strongly interacting in the high energy limit, and that the inclusion of diagrams with off-shell scalars of the MSSM does not cancel the divergences.
Tuesday 3 March 2009 at 10.15 in E204: Tuomas Lappi (Saclay) Initial conditions of heavy ion collisions and high energy factorization
Abstract: The “Color Glass Condensate” is an effective theory description for the small momentum fraction (x) degrees of freedom in a high energy hadron or nucleus, which can be understood in terms of strong classical gluon fields. I will discuss the resulting picture of the initial conditions in a relativistic heavy ion collision. I describe recent work to show that the leading logarithms of the collision energy can be factorized into the renormalization group evolution of the small x wavefunction. I will then show how this framework could be used to understand the long range rapidity correlations observed by the RHIC experiments.
Tuesday 10 March 2009 at 10.15 in E204: Flyura Djurabekova (FL and HIP) Multiscale modelling of sparking in the Compact Linear Collider components
Abstract: Sparks near metal surfaces cause a considerable damage to metal parts in high field gradient electric devices. The design of the Compact LInear Collider (CLIC) meets high expectations in the particle physics field, providing collision energy of 3 TeV for e^- — e^+ beams, thanks to the newly designed high frequency (~12 GHz) accelerating rf-structures with very high gradient electric fields (~100 MV/m). Unfortunately, the upper energy limit of the beams is strongly restricted by the significant probability of electrical breakdowns (sparks) inside of the rf-structures, though, the surfaces of the inner parts are thoroughly treated and operated in ultra-high vacuum. The insight to the triggering of electrical breakdown could help the efficiency of the present design of CLIC and reason the costs of its exploitation in future. I will give an overview on the computational model we develop to explain the triggering phenomenon, including as well the successive formation of a near-surface plasma, where ions can be accelerated towards the surface and cause further surface damage by sputtering. I will also show some preliminary results, which can be compared to experiments on surface damage due to sparks.
Cosmo seminar: Friday 20 March 2009 at 14.15 in A315: Matts Roos (FL) Dark matter: The evidence from astronomy, astrophysics and cosmology
Abstract: Dark matter has been introduced to explain many independent gravitational effects at different astronomical scales, even at cosmological scales. This review describes more than ten such effects. It is intended for an audience with little or no knowledge of astrophysics or cosmology.
Tuesday 24 March 2009 at 10.15 in E204: Valeri Khoze (IPPP, Durham) Studying the BSM Higgs sector with forward protons at the LHC.
Abstract: The prospects for central exclusive diffractive (CED) production of the MSSM Higgs bosons at the LHC are reviewed. These processes can provide important information on the CP-even Higgs bosons, allowing to probe important regions of the M_A-beta parameter plane. The sensitivity of the searches in the forward proton mode for the Higgs bosons in the so-called CDM-benchmark scenarios, the effects of fourth-generation models on the CED Higgs production and serching for the triplet Higgses are briefly discussed.
Thursday 26 March 2009 at 10.15 in A315: Franz von Feilitzsch (TUM, Munich) A new European large infrastructure for particle astrophysics at low energies: search for proton decay, low energy neutrino physics and neutrino astronomy
Abstract: In this talk I will report on the Laguna design study and the three proposed experimental infrastructures based on large scale detectors installed in deep underground laboratories. Particular emphasis will be given to the LENA large scale scintillation detector and the scientific research program.
Tuesday 31 March 2009 at 11.00 in E204: Kumar Rao (HIP)
Note time! Probing anomalous Higgs couplings at electron-positron colliders
Abstract: We investigate beyond the Standard Model contributions to the Higgs production process e+ e- -> Z H at the planned International Linear Collider (ILC). Couplings arising from New Physics are parametrised in terms of form factors constrained only by Lorentz invariance and include the possibility of CP violation. It is shown that transverse polarization is needed to observe an interesting CP violating part of the anomalous couplings, which otherwise would be invisible to unpolarized or logitudinally polarized beams. We construct angular distributions and construct various corelations to present constraints on the anomalous couplings.
Tuesday 14 April 2009 at 10.15 in E204: Zhi-zhong Xing (Institute of High Energy Physics, Chinese Academy of Sciences, Beijing) Neutrino masses via TeV seesaws
Abstract: I will give a brief overview of three typical seesaw mechanisms at the TeV scale: an attempt to bridge the gap between the origin of neutrino masses and collider signatures in the LHC era. The naturalness and testability of TeV seesaws, together with their possible low-energy consequences, will be discussed.
Tuesday 21 April 2009 at 10.15 in E204: Jonna Koponen (FL, Helsinki) Heavy-light mesons on a lattice
Abstract: I will report on a study of heavy-light meson excited states. Computer simulations, i.e. lattice QCD, allow us to extract both the energy spectrum and radial distributions of the mesons. In nature, the closest equivalent is the B_s meson. Only few of the excited states have been observed in experiments, and we are able to predict where some of the missing states should lie. The radial distributions are qualitatively what is to be expected from a model based on the Dirac equation.
Tuesday 28 April 2009 at 10.15 in E204: M. M. Sheikh-Jabbari (IPM, Tehran) A Realization of Cohen-Glashow Very Special Relativity on Noncommutative Space-Time
Abstract: The Cohen-Glashow Very Special Relativity (VSR) theory is shown to be realized as the part of the Poincare symmetry preserved on a noncommutative Moyal plane with light-like noncommutativity. Moreover, it is shown that the three subgroups relevant to the Cohen-Glashow VSR can also be realized in the noncommutative space-time setting. For all these three cases the noncommutativity parameter should be light-like. Some physical implications of this noncommutative realization of the Cohen-Glashow VSR will also be discussed.
Tuesday 12 May 2009 at 10.15 in E204: Mikko Vepsäläinen (FL, Helsinki) Heavy quarkonia in QCD plasma
Abstract: At high temperatures strongly interacting matter goes into a deconfined phase, forming a plasma of free color charges. This plasma can be experimentally studied in heavy ion collisions. Dissociation of heavy quark-antiquark bound states (quarkonia) is expected to signal the formation of plasma. In this talk I will review some analytical computations on the quarkonium melting, and compare with lattice and experiment.
Tuesday 19 May 2009 at 10.15 in E204: Oleg Antipin (HIP, Jyväskylä) Discriminating between technicolor and warped extra dimensional models via the pp -> ZZ channel
Abstract: We explore the possibility to discriminate between certain strongly-coupled technicolor (TC) models and warped extra-dimensional models where the Standard Model fields are propagating in the extra dimension. We consider a generic QCD-like TC model with running coupling as well as two TC models with walking dynamics. We argue that due to the different production mechanisms for the lowest-lying composite tensor state in these TC theories compared to the first Kaluza-Klein graviton mode of warped extra-dimensional case, it is possible to distinguish between these models based on the angular analysis of the reconstructed longitudinal Z bosons in the pp -> ZZ -> four charged leptons channel.
Tuesday 26 May 2009 at 10.15 in E204: Helga Timkó (HIP and CERN) “CLIC for the future” – The plasma physics of breakdowns
Abstract: The Compact Linear Collider (CLIC) study, currently under feasibility tests at CERN, is aiming at the development of a realistic technology for the post-LHC era. Driven by nanometer-scale phenomena, electrical breakdowns within RF accelerating structures influence strongly the efficiency of the 50 km machine. The talk will focus on a part of a multiscale model for breakdowns, namely on establishing a realistic model to describe the plasma physics of vacuum arcs. Considered will be also open questions regarding the build-up of plasma, such as its sensitivity to influencing factors and its adaptation to the external circuit.
Thursday 28 May 2009 at 10.15 in A315: Timo Lähde (University of Washington, Seattle) A new prospect for graphene-based electronics
Abstract: Graphene is a membrane of carbon atoms arranged in a hexagonal honeycomb lattice. Due to its remarkable mechanical and electronic properties, graphene shows great promise for a variety of applications in high-tech industries, although the semimetallic nature of graphene samples on a substrate is problematic for electronic applications. The observed absence of a gap is in line with band-structure calculations of graphene, although by analogy with benzene, strong electron-electron interactions could in principle render the material insulating. Based on recent Lattice Monte Carlo simulations of the low-energy theory of graphene, I will argue that such an insulating state is expected in suspended samples, where the electron-electron interaction is not screened by a dielectric substrate. With the advent of suspended graphene experiments, our understanding of this fascinating material may have to be revised.
Tuesday 2 June 2009 at 10.15 in A315: H. Kurki-Suonio (FL) Planck satellite and cosmology
Abstract: The Planck satellite of the European Space Agency was launched succesfully into space on May 14th. Planck’s mission is to measure the anisotropy and polarization of the cosmic microwave background to unprecedented accuracy. I will describe the Planck satellite and its operation, and what kind of cosmological information we hope to obtain from the observations. We are especially interested in the properties of primordial density perturbations, that we can deduce from Planck data. These primordial perturbations are the origin of all structure in the universe, but we do not yet know what caused them.
Thursday 4 June 2009 at 10.15 in A315: Emidio Gabrielli (CERN) Flavor Changing Fermion-Graviton Vertices
Abstract: We study the flavor-changing quark-graviton vertex that is induced at the one-loop level when gravitational interactions are coupled to the Standard Model. We show that flavor-changing interactions in gravity are local if the graviton is strictly massless while, if the graviton has a small mass, long-range interactions inducing a flavor-changing contribution in the Newton potential appear. Flavor-changing processes with massive spin-2 particles are also briefly discussed. Our results can be easily generalized to the case of lepton-graviton couplings.
Tuesday 9 June 2009 at 10.15 in A315: Zurab Berezhiani (Univ. L’Aquila) Baryogenesis and dark matter genesis: unified model
Abstract: We discuss the baryogenesis mechanism via B-L and CP violating scattering processes of the ordinary particles with the particles of the hidden parallel gauge sector. This mechanism allows to naturally explain the proportion between the baryonic and dark matter fractions in the Universe. Some possible phenomenological implications are also discussed.
Tuesday 16 June 2009 at 10.15 in A315: O. Kancheli (ITEP) Spontaneous Breaking of Lorentz-Invariance and Gravitons as Goldstone Particles
Abstract: We consider some aspects of spontaneous breaking of Lorentz Invariance in field theories, discussing the possibility that the certain tensor operators may condens in the ground state in which case the tensor Goldstone particles would appear. We analyze their dynamics and discuss to which extent such a theory could imitate gravity. We are also interested if the universality of coupling of such `gravitons’ with other particles can be achieved in the infrared limit. Then we address the more complicated models when such tensor Goldstones coexist with the usual geometrical gravitons. Finally, we examine the properties of possible cosmological scenarios in the case of Goldstone gravity coexisting with geometrical gravity.
Tuesday 23 June 2009 at 10.15 in A315: K. Kajantie (FL/HIP) Hot QCD matter: lattice, perturbation theory and AdS/QCD.
Abstract: I review the determination of the thermodynamics of finite temperature QCD matter using lattice Monte Carlo techniques and perturbation theory, concentrating on the interaction measure e(T)-3 p(T), which quantifies conformal invariance breaking, and the spatial string tension. The perturbative expansion at finite T goes in powers of g, not g^2, and contains log(g) terms. The coefficient of the g^6 term, the Linde term, is non-perturbative, sums an infinite set of loop diagrams. A discuss the set-up for determining it; one step is still missing. Determination of the same quantitities in AdS/QCD requires a model for conformal invariance breaking. I discuss a specific one and apply it to the particularly simple quantity, spatial string tension as a function of T.
Tuesday 11 August 2009 at 10.15 in A315: Akifumi Sako (Kushiro National College of Technology, Japan) Smooth Noncommutative Deformation of Instantons and the ADHM Construction
Abstract: We construct instanton solutions on noncommutative Euclidean 4-space, which are deformations of instanton solutions on commutative Euclidean 4-space. We show that the instanton numbers of these noncommutative instanton solutions coincide with the commutative solutions and conjecture that the instanton number in ${\mathbb R}^4$ is preserved for general noncommutative deformations. Next, we prove the existence of the Green’s function associated with the background of the noncommutative instantons. The Green’s functions are smoothly deformed from commutative one. Using this Green’s function, we derive the noncommutative ADHM equations that include the one introduced by Nekrasov and Schwarz. We also show a one-to-one correspondence between instantons on noncommutative ${\mathbb R}^4$ and ADHM up to zero modes of a Dirac operator with a commutative instanton background.
Thursday 13 August 2009 at 10.15 in A315: Tom DeGrand (University of Colorado, Boulder) Lattice Gauge Theories with an Infrared-Attractive Fixed Point
Abstract: In the last few years several lattice groups (including Kari Rummukainen and collaborators and me, Shamir and Svetitsky) have begun to study non-Abelian gauge theories coupled to fermions with many degrees of freedom. These systems might be candidates for beyond-Standard Model physics. They might also have “unparticle” phases, with no confinement, no chiral symmetry breaking and algebraic decay of correlation functions. I will introduce the physics of these systems as I understand it and describe the adventures we have had performing simulations with two flavors of fermions in the sextet representation, and an SU(N) gauge symmetry.
Friday 14 August 2009 at 10.15 in A315: Antti Niemi (Université de Tours and Uppsala University) Weinberg-Salam Model and its De Sitter Ground State
Abstract: We show how the Weinberg-Salam model can be interpreted in terms of a gravity theory, with the modulus of the Higgs field as a dilaton and the (anti)DeSitter space as its ground state
Tuesday 1 September 2009 at 10.15 in A315: Olli Taanila (FL and HIP) The subdominant curvaton
Abstract: The curvaton scenario is an alternative and an addition to the traditional inflationary scenario. It functions as an auxiliary field during and after inflation producing the observed primordial density fluctuations, which seed the formation of all observed structure in the universe. I will first introduce and review the curvaton model in general and then present new work on curvaton models with non-monomial potentials. A complete scan of the parameter space will be presented, as well new results on the magnitude of the non-gaussianity parameters of these models.
Tuesday 8 September 2009 at 10.15 in E204: Merab Gogberashvili (Institute of Physics and Tbilisi State University) Higher-Dimensional Models – Past and Future
Abstract: First part of the talk will be devoted to the history and various aspects of large extra-dimensional models, including the Randall-Sundrom scenario. Then some particular model of a universe considered as an expanding spherical brane in 5D will be presented. The Shell-Universe model allows us to explain the observed expansion rate of the universe without a dark energy component. It also provides a natural mechanism for local increasing of the brane tension leading to the modified Newton’s law alternative to galactic dark matter.
Thursday 10 September 2009 at 10.15 in A315: Vladimir Eremin (Ioffe Institute) Avalanche multiplication – a new bases for radiation hard silicon detectors?
Abstract: New developments for experiments on Large Hadron Collider at CERN require silicon detectors with sufficiently improved radiation hardness. A new effect observed in heavily irradiated silicon strip detectors – an unpredictable rise of the signal with the bias voltage – looks promising for the purpose, however the physics of the effect is not clear yet. A possible explanation of the effect and its applied perspectives will be discussed in the presentation.
Tuesday 29 September 2009 at 10.15 in E204: Jyrki Piilo (University of Turku) Econophysics: What can physicists say about financial markets?
Abstract: Since 1990’s a growing number of physicists has developed interest to make academic research on financial markets. On one hand, physics graduates have been hired already since 1970’s by financial institutions for quantitative finance purposes (quants). On the other hand, an academic physicists’ community with interest to financial markets coined the term econophysics in the last decade to describe their interdisciplinary activies. We will give a general overview about the development of econophysics during last 10 years or so, highlight some central research themes, and indicate how insight from physics can possibly help to increase the understanding of financial markets. We conclude with a brief description of the activities of the recently initiated joint econophysics project including researchers from the Universities of Palermo and Turku, and the Santa Fe Institute.
Tuesday 6 October 2009 at 10.15 in E204: Erik Heijne (CERN-PH Department) Developments in radiation sensors
Abstract: Innovative approaches in sensing and imaging are continuously sought after for scientific applications. With the ongoing miniaturization new possibilities are created for the integration of sensor elements, the signal processing and the data analysis. There is a bottleneck for the transfer of such new devices into industrial situations or even into consumer environment. It is needed to have intimate knowledge of practical and economic aspects for these target fields.
Wednesday 7 October 2009 at 10.15 in E206 (note place!): Valeri Khoze (IPPP, Durham) Physics of Heavy quarkonia: as seen through the eyes of Central Exclusive Production
Abstract: We discuss how the central exclusive production of heavy quarkonia and of the new exotic states could allow to study their quantities, and in particular, to serve as a spin-parity analyzer. A special attention is paid to the comparison between the theory and the new CDF results and, the prospects of further studies at the Tevatron and LHC are addressed.
Wednesday 7 October 2009 at 14.15 in E206 (note place!): Sergey Baranov (Lebedev Institute, Moscow) Production and polarization of Upsilon mesons at the Tevatron
Abstract: In the framework of the k_t-factorization approach, the production and polarization of Upsilon mesons at the Fermilab Tevatron is considered, and a comparision of the calculated double differential distributions and spin alignment parameter alpha with the experimental data is shown. We argue that measuring the double differential cross sections and polarization of upsilon mesones can serve as a crucial test discriminating competing theoretical approaches to the production of quarkonium states.
Thursday 8 October 2009 at 10.15 in A315: Yannis Burnier (University of Bielefeld) Effective theory for a five-dimensional domain wall and branon physics
Abstract: The idea of braneworlds put forward in the eighties as extension of the Standard Model has made a comeback as ingredient of higher dimensional theories like string theory. The conventional effective description of branes and their oscillations (branons) was obtained from geometrical arguments. We show by calculating the four-dimensional low energy action of a two scalar field domain wall model in five dimensions that the form of the effective action do not match the geometric derivation. Additional terms lead to new physical processes like the decay of the Higgs to branons. We shortly comment on the possibility to see branons in dark matter searches and at the LHC.
Tuesday 13 October 2009 at 10.15 in E204: Wolfgang Unger (University of Bielefeld) The Chiral Phase Transition in QCD: on Critical Scaling and Goldstone Fluctuations
Abstract: We analyze the quark mass dependence of the chiral condensate and chiral susceptibilities in QCD with two degenerate light quark masses and a strange quark mass close to its physical value. First we discuss the magnetic equation of state and show that the small quark masses indeed follow critical scaling. Then we provide evidence for the influence of thermal fluctuations of Goldstone modes on the chiral condensate at finite temperature. We show that at temperatures below but close to the chiral phase transition at vanishing quark mass this leads to a characteristic dependence of the light quark chiral condensate on the square root of the light quark mass m_l. As a consequence the chiral susceptibility shows a strong quark mass dependence for all temperatures below T_c and diverges like 1/sqrt{m_l} in the chiral limit. We separately examine the divergence of disconnected and connected parts of the light quark susceptibility and discuss the cut-off dependence of susceptibilities and chiral condensates.
Thursday 15 October 2009 at 10.15 in A315: Mauri Valtonen (University of Turku, HIP) Arrow of time in the classical three-Body problem
Abstract: It is well known that Arrow of Time can be defined in systems with large numbers of particles, using the concept of entropy. It is less well known that a similar definition applies already to the classical three body problem. Even though the problem is time-reversible in principle, certain type of evolution happens only in one direction, with zero or negligible probability in reverse direction. The actual direction of evolution may be used to define the forward direction of the Arrow of Time. More generally, the Kolmogorov- Sinai entropy also defines the Arrow of time in any strongly interacting three-body system. I will discuss the history of the study of the three body problem, leading to the current understanding of its nature.
Tuesday 20 October 2009 at 10.15 in E204: László Jenkovszky (Bogolyubov Institute for Theoretical Physics, Kiev) Diffraction at the LHC
Abstract: After a brief introduction to the theory of high-energy diffraction, new effects expected in elastic and inelastic diffractive processes at the LHC, will be presented. At small momentum transfers squared (|t|), the fine structure of the cone (Pomeron) should be scrutinized, where a break due to the two-pion threshold, required by t-channel unitarity, and possible small-period oscillations are expected. Of extreme interest are the details of the expected diffraction minimum in the differential cross section. Its position, expected in the interval 0.4<-t<1 GeV^2 cannot be predicted unambiguously, while its depth and the ratio between the minimum and the subsequent maximum are of great importance. The expected slow-down with increasing |t| of the shrinkage of the second cone (beyond the dip-bump), together with the transition from an exponential to a power decrease in -t, will be indicative of the transition from “soft” to “hard” physics. Explicit models are proposed to help in quantifying this transition. In a number of papers a limiting behaviour, or saturation of the black disc limit (BDL), was predicted. This controversial phenomenon shows that the BDL may not be the ultimate limit, instead a transition from shadow to antishadow scattering may by typical at the LHC. Low missing mass diffraction dissociation will be among the priorities of the LHC experiments. Preliminary results on the predictions for low mass diffraction dissociation at the LHC will be presented.
Thursday 22 October 2009 at 12.30 (note time!) in A315: Priyotosh Bandyopadhyay (Harish Chandra Research Institute, Allahabad, India) Higgs searches under Supersymmetric cascades with non-universal gaugino masses
Abstract: Cascade decays of Supersymmetric (SUSY) particles are likely to be prolific sources of Higgs bosons at the Large Hadron Collider (LHC). In this work, we explore, with the help of detailed simulation, the role of non-universal gaugino masses in the production of the Higgs bosons under SUSY cascades. The analysis is carried out by choosing an appropriate set of benchmark points with non-universal gaugino masses in the relevant SUSY parameter space and then contrasting the resulting observations with the corresponding cases having universal relationship among the same. It is shown that even of data at an early phase of the LHC-run with 10 fb$^{-1}$ one would be able to see, under favourable situations, the imprint of non-universal gaugino masses by reconstructing various Higgs boson resonances and comparing their rates. With increased accumulated luminosities, the indications would naturally become distinct over a larger region of the parameter space.
Monday 26 October 2009 at 13.00 (note time!) in A315: Jens Andersen (Norwegian University of Science and Technology, Trondheim) Convergent hard-thermal-loop resummation for thermal field theories
Abstract: In this talk, I will discuss the breakdown of perturbation theory for quantum field theories at high temperature and explain the necessity of resummation. The weak-coupling expansion for the pressure is poorly convergent and it is necessary to reorganize the perturbative series. I will discuss screened perturbation theory and hard-thermal-loop perturbation theory as one way of reorganizing perturbation theory for scalar and gauge theories, respectively. Comparison with other resummation schemes will be made.
Tuesday 27 October 2009 at 10.15 in E204: Durmus Demir (Izmir Institute of Technology) Search for an Extra Supersymmetric U(1) at the LHC CMS Experiment
Abstract: We discuss the reasons for and the LHC signatures of an additional Abelian symmetry in supersymmetry. The signatures of such extra force laws originate not only from their gauge bosons but also from their gauge fermions, which modify the decay patterns of scalar fermions. The scalar fermions and gluinos, to be produced copiously at the LHC, thus provide an alternative way of searching for extra forces at the LHC experiments. The talk will discuss the theoretical basis, simulation studies and reconstructed events for the CMS experiment.
Tuesday 3 November 2009 at 10.15 in E204: J. Alanen (FL and HIP) A gauge/gravity duality model for hot QCD matter: application to bulk thermodynamics and string tensions.
Abstract: A celebrated fact of the duality between AdS5 gravity with a black hole and hot N=4 conformal strongly coupled supersymmetric Yang-Mills theory is that the pressure is 3/4 of what one would expect of an ideal gas, the same theory with zero coupling. A conformal theory has no phase transitions and when trying to extend this duality to hot QCD matter the first problem is how to break conformal invariance. In QCD this happens via the appearance of a mass scale in the running coupling g^2(Q/Lambda). I discuss a model in which this is implemented on the gravity side by identifying g^2 = exp(phi(Lambda z)), where phi(z) is a scalar field, z is the extra dimensional coordinate and the energy scale is identified as Q ~ 1/z. By choosing the scalar potential V(phi) in the gravity action suitably a successful dual to SU(N) pure glue QCD is obtained, as I show for bulk thermodynamics and string tensions. So far this is bottom-up; the ultimate hope is to derive the model top-down from string theory.
Tuesday 10 November 2009 at 10.15 in E204: A. Tranberg (HIP and University of Oulu) Cold Electroweak Baryogenesis from Standard Model CP-violation
Abstract: We ask whether the observed matter/antimatter asymmetry in the Universe can be the result of the slight bias induced by Standard Model CP violation. The answer seems to be yes, provided the electroweak transition takes place at very low temperature T<<100GeV. This Cold Electroweak Baryogenesis scenario is realised by extending the Standard Model by one gauge singlet (the inflaton). Then electroweak symmetry breaking and post-inflationary reheating can be made to coincide, leading to successful baryogenesis.
Monday 23 November 2009 at 12.15 in A315 (note date and time!): Arttu Rajantie (Imperial College) Non-Gaussianity from resonant curvaton decay
Abstract: We calculate curvature perturbations produced when a light scalar field, known as the curvaton, decays into another scalar field via parametric resonance at the end of inflation in the early universe. This involves nonlinear nonequilibrium dynamics, and therefore standard perturbative calculation techniques fail. Instead, we use lattice field theory simulations and the separate universe approximation to calculate the curvature perturbation as a nonlinear function of the curvaton field. For the parameters tested, the generated perturbations are highly non-Gaussian and not well approximated by the usual fNL parameterisation. This shows that the resonance plays an important role in the curvaton scenario and can have a substantial effect on the resulting perturbations.
Tuesday 8 December 2009 at 10.15 in E204: Boris Arbuzov (Institute for Nuclear Research, Moscow State University) Application of Bogoliubov compensation principle to QCD and electroweak theory
Abstract: The Bogoliubov compensation principle is applied to the gauge electroweak interaction to demonstrate the spontaneous generation of an anomalous three-boson gauge invariant effective interaction. The nontrivial solution of the compensation equations uniquely defines the values of the parameters of the theory and the form factor of the anomalous interaction. The contribution of this interaction to the running EW coupling gives its observable value alpha_ew(Mw)=0.0374, in satisfactory agreement with experiment. The anomalous three-boson interaction gives a natural explanation of the well-known discrepancy in the muon g-2.
Tuesday 15 December 2009 at 12.00 (note time!) in the HIP Multifunctional Room A311: Arthur Chernin (Sternberg Astronomical Institute, Moscow University and Tuorla Observatory, Turku) Dark energy in local cosmology
Abstract: The Hubble Space Telescope data on the Local Group and other groups of galaxies provide evidence for dark energy dynamical domination on the spatial scale of a few megaparsec (arXiv: 0902.3871).
Thursday 17 December 2009 at 10.15 in A315: Aleksi Vuorinen (University of Bielefeld) Perturbative nuclear physics
Abstract: I will describe a new formulation of effective field theories for nucleon-nucleon (NN) interactions that treats pion interactions perturbatively and seems to converge satisfactorily for all partial waves considered. Starting with the Kaplan-Savage-Wise (KSW) expansion about the nontrivial fixed point corresponding to infinite NN scattering length, we cure the convergence problems with by modifying the short distance pion interaction, resumming those contributions in the contact interactions. This method makes it possible to perform a host of analytic few-body calculations in nuclear physics.
Tuesday 22 December 2009 at 10.15 in E204: Aleksi Kurkela (ETH, Zürich) Cold quark matter
Abstract: I will discuss various issues related to cold but dense QCD matter, concentrating on our current knowledge on the phase structure of the theory, the physical systems where these conditions may be realized, as well as the computational tools we have available to describe the system. In particular, I will present results from a recent perturbative calculation of the QCD equation of state at zero temperature and finite quark number density, including two light and one massive quark flavor. These results can be used to address questions such as the existence of stable strange quark matter, the mass-radius relationships of quark stars, as well as the breakdown of the Color-Flavor-Locked phase of color superconductivity.
