Seminars 2016


  • Friday 15 January 2016 at 10.15 in A315: Tapio Rantala (Tampere, Note day!)
    Path integral quantum Monte Carlo simulation of atomic matter
    Abstract: Feynman path integral approach to quantum mechanics and Monte Carlo simulations allow straightforward study of quantum many-body systems. Propagation of a quantum system in imaginary time (DMC, PIMC) can be used to find eigenstates or simulate thermal equilibrium, for example. I will present novel applications of PIMC to first-principles calculations of small molecules and simulation of a dissociation/recombination chemical reaction. Propagation in real time (RTPI), on the other hand, leads to conventional coherent quantum dynamics. Recently, we also found the incoherent propagation as a novel numerical tool for finding stationary states. I will present our first simulations of model systems in the way towards atoms and molecules. With Monte Carlo simulations the “fermion sign problem” arises as the major obstacle for simulations of large atomic systems. This and other development topics including possible extensions will be discussed.

  • Tuesday 9 February 2016 at 10.15 in A315: Fabian Rennecke (Giessen)
    From quarks and gluons to hadrons: chiral symmetry breaking in QCD
    Abstract: The strong interactions are characterized by very different degrees of freedom at different energy scales. While the high energy regime of QCD is governed by quark-gluon dynamics, hadrons are the relevant degrees of freedom at low energies. The associated complex phase structure raises many fundamental questions, both experimentally and theoretically. In this talk I will address the question how chiral symmetry breaking and the spectrum of the light mesons emerge from the underlying quark-gluon dynamics. To this end, I employ functional renormalization group techniques, which will be reviewed briefly. As an application, I will present results on the scaling of vector meson masses towards the chiral symmetry breaking scale. If time permits, I will also show new results on the influence of the gauge sector of QCD on the curvature of the chiral phase boundary.
  • Tuesday 16 February 2016 at 10.15 in A315: Mikko Möttönen (Aalto)
    Tying Quantum Knots
    Abstract: Knots are familiar entities that appear at a captivating nexus of art, technology, mathematics and science. Following a long period of theoretical investigation and development, they have recently attracted great experimental interest in classical contexts ranging from knotted DNA and nanostructures to vortex knots in fluids. In our work, we demonstrate the controlled creation and detection of knot solitons in the quantum-mechanical order parameter of a spinor Bose-Einstein condensate. Images of the superfluid reveal the circular shape of the soliton core and its associated linked rings. Our observations of the knot soliton establish an experimental foundation for future studies of their stability, dynamics and applications within quantum systems.

  • Tuesday 23 February 2016 at 10.15 in A315: Sven Moch (Hamburg)
    Top-quark production at the LHC: Theory status and perspectives
    Abstract: The current state of precision predictions for top-quark production at the LHC will be reviewed. Special emphasis will be put on the definition and the determination of the top-quark mass as a fundamental parameter of the Standard Model. We will motivate, why precision determinations of the top-quark mass are important in the current high-energy run of the LHC and discuss the prerequisites in theory for the extraction of a well-defined mass parameter in a given renormalization scheme. We also discuss the implications for the stability of the Higgs potential and the electroweak vacuum.

  • Tuesday 1 March 2016 at 10.15 in A315: K. Kajantie (HIP)
    Physics of gravitational radiation
    Abstract: The LIGO Laser Interferometer signal GW150914 was the first ever direct observation of gravitational radiation. This talk will review how you get gravitational radiation and black holes from general relativity and discuss the magnitudes of relevant physical parameters.

  • Tuesday 8 March 2016 at 10.15 in A315: Jarno Rantaharju (Odense)
    Lattice Model of Ideal Walking
    Abstract: We present preliminary studies of the SU(2) gauged NJL model with 2 flavors of fermions in the adjoint representation. The gauge model is infrared conformal and an additional NJL-type four fermion interaction, at large coupling, induces a chirally broken phase. In the symmetric phase the four fermion interaction is expected to influence the dynamics of the infrared fixed point and there may be a second order transition to the chirally broken phase. We study chiral symmetry breaking and the mass anomalous dimension at the infrared fixed point using the mode number of the Dirac operator.

  • Tuesday 15 March 2016 at 10.15 in A315: Rauno Lauhakangas (HIP)
    To the galaxy with the bubble chamber
    Abstract: A few words about measurements from bubble chamber era to the large hadron colliders.

  • Monday 4 April 2016 at 10.15 in A315: Mirko Berretti (HIP/Totem) Note Day!
    Exclusive processes with TOTEM and CT-PPS: results, perspectives and experimental challenges
    Abstract: The latest results and the physics potential of the TOTEM experiment at the LHC will be presented. This include searches for glueballs and new physics together with CMS and a deeper understanding of elastic scattering. For LHC RUN-2, a joint CMS-TOTEM project (CT-PPS) has been approved to study exclusive particle production at the highest LHC luminosity. With the recent indication by the CMS and ATLAS experiments of a possible resonance in the 750 GeV mass region, the CT-PPS, initially designed to search for anomalous gauge boson quartic couplings, will give a relevant contribution in a possible confirmation and study of this new resonance. I will review the CT-PPS status and plans for 2016 LHC running.

    In the second part of the seminar I will concentrate on the new detectors designed to precisely measure the time-of-flight of the scattered protons produced in such exclusive processes at medium and high luminosity to be able to reject pile-up. Timing detectors based on diamond sensors have been developed by TOTEM and will be used in the first phase of the CT-PPS project. I will summarize the detector development, performance and perspective for this promising technology.

  • Tuesday 5 April 2016 at 10.15 in A315: Kirill Boguslavski (Heidelberg)
    Universality classes far from equilibrium: from heavy-ion collisions to superfluid Bose systems
    This talk is cancelled!

  • Tuesday 12 April 2016 at 10.15 in A315: Louis Lyons (Imperial College)
    Statistical Issues in Searches for New Physics
    Abstract: Given the cost, both financial and even more importantly in terms of human effort, in building High Energy Physics accelerators and detectors and running them, it is important to use good statistical techniques in analysing data. This talk covers some of the statistical issues that arise in searches for New Physics. They include topics such as: Blind Analysis. How should we deal with the `Look Elsewhere Effect’? Should we insist on the 5 sigma criterion for discovery claims? Significance P(A|B) is not the same as P(B|A). The meaning of p-values. What is Wilks’ Theorem and when does it not apply? Dealing with systematics such as background parametrisation. Coverage: What is it and does my method have the correct coverage? Upper Limits. The use of p_0 vs p_1 plots. Higgs search: Discovery and Spin.

  • Thursday 14 April 2016 at 10.15 in A315: Guy Moore (Darmstadt)
    Relating the Axion Mass and Dark Matter Density
    Abstract: QCD appears to allow for large parity and time-reversal violating effects, which are in fact unmeasurably small. The simplest dynamical model to explain this predicts a new particle, the Axion, which is also an excellent dark matter candidate. Under reasonable assumptions it should be possible to predict the relation between the axion’s mass and its dark matter abundance. I will discuss the interesting physics we need to make this prediction concrete — axionic string networks and topological susceptibility.

  • Tuesday 19 April 2016 at 10.15 in A315: Aurora Meroni (Odense)
    Neutrino physics: status and quests for the future
    Abstract: Neutrino physics has entered the precision era. Nevertheless many questions still remain without an answer. We know that the SM cannot be the ultimate theory, since a so-called “elusive” sector is completely missing: neutrinos are not properly included since we cannot describe their mass. Moroever, the nature, Dirac or Majorana, of the three light active neutrinos nuj (j = 1,2,3) with definite mass mj is unknown. I will review unknown properties of neutrinos and how possibly detect some of them. In particular I will define a theoretical framework and deduce the conditions under which multi-messenger astronomy can constrain neutrino masses and unveil their ordering. The framework uses time differences between the arrival of neutrinos and the other two light messengers, i.e. light and gravitational waves, emitted by astrophysical catastrophes.

  • Tuesday 26 April 2016 at 10.15 in A315: Thomas Konstandin (Desy)
    Effective actions in particle physics and cosmology
    Abstract: Effective actions are an invaluable tool in particle physics and cosmology. For example, they are used to determine properties of the Higgs or the stability of the vacuum. Other applications include the sphaleron rate in the early universe or the characteristics of the electroweak phase transition. In this talk, I will give an extensive introduction to the topic and finally touch on some advanced questions as infrared problems or gauge-dependence.

  • Tuesday 17 May 2016 at 10.15 in A315: Mads Frandsen (Odense)
    Electroweak symmetry breaking, dark matter and the diphoton excess
    Abstract: I will discuss some interpretations of the putative LHC diphoton excess at 750 GeV in the light of models of dynamical electroweak symmetry breaking and models of dark matter.

  • Thursday 19 May 2016 at 10.15 in A315: Tobias Zingg (HIP)
    How I learned to stop worrying and love fractional spin: A systematic approach to holographic anyonization
    Abstract: Anyons are a special type of particle in 2+1 dimensions that can have fractional spin quantum number and have garnered substantial interest theoretically as well as experimentally. However, they have a highly non-trivial configuration space of multiparticle states, compared to bosons or fermions, which often impedes a direct approach via quantum statistics, even in the most simple cases.

    Holography provides a way to evade some of these issues. Within this framework, I will formulate a general method to obtain an effective physical description of strongly correlated anyonic systems via an alternative quantization of asymptotic electromagnetic degrees of freedom in a gravitational dual, and demonstrate how this prescription can be employed to compute the equation of state and various transport coefficients.

  • Tuesday 31 May 2016 at 10.15 in A315: Santosh Kumar Rai (Allahabad)
    Revisiting compressed SUSY at LHC
    Abstract: Recently a compressed mass spectrum has been thought as an explanation for the elusiveness of low-energy supersymmetry (SUSY). Some characteristic signals at the Large Hadron Collider, such as mono-jet + missing transverse energy (MET), had been propounded as its trademark signals. However, later investigations suggested that lower limits on the supersym- metric particle masses would be quite stringent in spite of compression. Also, most compressed SUSY scenarios studied so far are only partially compressed. By keeping the level of compression in the entire spectrum as high as possible we study a broad class of benchmark spectra, ensuring consistency with the observed Higgs mass as well as the dark matter constraints. We show that of both the multi-jet +MET and mono-jet + MET final states, the former is still more efficient to reveal a compressed SUSY spectrum first, while the latter can serve as a useful confirmatory channel.

  • Thursday 2 June 2016 at 14.15 in A315: Ritva Kinnunen (HIP)
    My Experiences in Large Experiments
    Abstract: I have worked in two large high energy physics experiments, UA1 and CMS. I will talk about some personal experiences, indicating also important milestones of particle physics achieved in these experiments.

    Coffee is served after the talk in the HIP coffee room.

  • Monday 6 June 2016 at 10.15 in A315: Juan Pedraza (Amsterdam) (Note day!)
    Spread of entanglement in holographic theories
    Abstract: In this talk I will present recent results of the propagation of entanglement entropy after a global quench in the context of AdS/CFT. I will start by reviewing the heuristic picture for entanglement propagation dubbed as ‘entanglement tsunami’, and explain why this interpretation fails for general theories and entangling regions. In the second part of the talk I will present an analytic perturbative calculation for small subregions and show that in this regime the spread of entanglement exhibit some distinct features: i) the instantaneous rate of growth is not constrained by causality, but rather its time average, and ii) the saturation is always continuous, regardless the shape of the entangling region. I will also comment on the generalization of these results for non-relativistic scale invariant theories in some generic examples (1602.05934).

  • Tuesday 7 June 2016 at 10.15 in A315: Ilpo Vattulainen (Helsinki)
    Cholesterol, tiny but tough! How membranes sense changes in cholesterol structure.
    Abstract: Cholesterol is one of the vital components in regulating the physical properties of animal cell membranes. Further, there are membrane proteins whose function is dependent on cholesterol, however the mechanisms and physical principles used by cholesterol to modulate protein function remain unknown. What makes cholesterol exceptionally intriguing is the fact that other sterols are not able to replace cholesterol, thus its structure is unique in a manner that is not yet understood. In this talk, we discuss how cell membranes sense cholesterol and changes in its structure. We consider synthetic sterols non-existent in nature to elucidate the roles of cholesterol’s individual structural elements. This brings out the critical components in cholesterol structure that are critical to its function. To clarify how reactive oxygen species affect cholesterol and its role in cell function, we also discuss how oxysterols based on oxidation of cholesterol affect membrane properties that turn out to be distinct from those induced by cholesterol. We further discuss how cholesterol is able to govern cellular signaling by modulating the structure and dynamics of membrane receptors that manage the signaling between the outside and the inside of cells. The data emerged from molecular simulations as well as experiments provide a basis to better understand why cholesterol is indeed unique in modulating membrane properties and membrane protein function, and the insight found by simulations can possibly be used to predict new synthetic sterols with applications in biotechnology.

  • Thursday 9 June 2016 at 14.15 in A315: Kai Schmidt-Hoberg (Desy) (Note time!)
    The case for dark matter self interactions – evidence in Abell 3827?
    Abstract: I will review motivations for the existence of self interacting dark matter and discuss possible astrophysical observables. Self-interactions of dark matter particles can potentially lead to an observable separation between the dark matter halo and the stars of a galaxy moving through a region of large dark matter density. Such a separation has recently been observed in a galaxy falling into the core of the galaxy cluster Abell 3827. I discuss the DM self-interaction cross section needed to reproduce the observed effects.

  • Tuesday 14 June 2016 at 10.15 in A315: Carl Carlson (College of William and Mary, Virginia)
    The proton charge radius puzzle
    Abstract: There is a proton charge radius puzzle because the proton charge radius appears different when measured with electrons than when measured with muons. Explanations broadly fit into two categories. “Ordinary” explanations include problems with the extrapolations or theoretical corrections involved in the measurements, and “exotic” explanations include such beyond the standard model ideas as a breakdown of electron-muon universality. We will discuss something of how the measurements are done, and discuss possible explanations in both the “ordinary” and “exotic” categories.

  • Tuesday 21 June 2016 at 10.15 in A315: Michael Gronau (Technion, Haifa)
    Precise perturbative flavor symmetry breaking in D decays
    Abstract: Flavor SU(3) has been known to describe adequately hadronic charmed meson decay amplitudes with SU(3) breaking corrections of 20-30%. I will describe a new approach treating perturbatively high order SU(3) breaking. I will focus on predicted amplitude relations affected by tiny fourth order SU(3) breaking terms varying between 10^{-3} and 10^{-4}. SU(3) relations failing at such high precision could provide evidence for new physics in the flavor sector.

  • Tuesday 5 July 2016 at 10.15 in A315: Aleksi Vuorinen (Helsinki)
    Quark matter inside neutron stars
    Abstract: I will describe recent advances in the theoretical description of the cold and dense deconfined matter possibly found inside the cores of neutron stars. Novel attempts to understand the bulk thermodynamic behavior of this exotic matter using on one hand perturbative QCD and on the other hand the gauge/gravity duality are introduced, and the implications of the new results on the observable properties of neutron stars are discussed.

  • Tuesday 30 August 2016 at 14.15 in E204: Mikko Sainio (HIP)
    From loops to knots – physics to bureaucracy

  • Tuesday 20 September 2016 at 10.15 in A315: Tyler Gorda (Helsinki)
    Global properties of rotating neutron stars with QCD equations of state
    Abstract: This talk will discuss a numerical study of global properties of rotating neutron stars using the allowed band of QCD equations of state derived by Kurkela et al. (2014). This band is constrained by chiral effective theory at low densities and perturbative QCD at high densities, and is thus, in essence, a controlled constraint from first-principles physics. Previously, this band of equations of state was used to investigate non-rotating neutron stars only; now these results are extended to any rotation frequency below the mass-shedding limit. Mass-radius curves, allowed mass-frequency regions, radius-frequency curves for a typical 1.4-solar-mass star, and the values of the moment of inertia of the double pulsar PSR J0737-3039A are computed. I also present limits on observational data coming from these constraints, and identify values of observationally relevant parameters that would further constrain the allowed region for the QCD equation of state.

  • Tuesday 27 September 2016 at 10.15 in A315: Christian Ecker (TU Wien)
    Exploring nonlocal observables in shock wave collisions
    Abstract: We study the time evolution of 2-point functions and entanglement entropy in holographic shock wave collisions which are frequently used as toy models for heavy ion collisions. We discriminate between three classes of initial conditions corresponding to wide, intermediate and narrow shocks and show that they exhibit different phenomenology with respect to the nonlocal observables that we determine. Surprisingly, we found that 2-point functions can be sensitive to the inside of the black hole apparent horizon on the gravity side, while we did not find such cases for the entanglement entropy. This talk is based on arXiv:hep-th/1609.03676.

  • Tuesday 18 October 2016 at 10.15 in A315: Carlos Hoyos (Oviedo)
    Towards a simpler description of holographic nuclear matter
    Abstract: Baryonic matter is notoriously difficult to deal with in the large-N limit, as baryons become operators of very large dimension with N fields in the fundamental representation. This issue is also present in gauge/gravity duals as baryons are described by very heavy localized objects. There are however alternative large-N extrapolations of QCD where small baryonic operators exist and can be treated on an equal footing to mesons. We explore the possibility of turning on a finite density of “light” baryons in a theory with a hadronic mass gap using a gauge/gravity construction based on the D3/D7 intersection

  • Tuesday 25 October 2016 at 10.15 in A315: Luca Visinelli (Stockholm)
    Axion cosmology
    Abstract: The axion is a hypothetical pseudo-scalar particle which might constitute 100% of the cold dark matter observed. We revise its properties, the current observation bounds, and the prospects of detection.

  • Tuesday 1 November 2016 at 10.15 in A315: Tapio Ala-Nissilä (Aalto)
    The physics of this year’s Nobel prize in physics – a personal point of view
    Abstract: The Nobel Prize in Physics in 2016 was awarded to David J. Thouless, F. Duncan M. Haldane, and J. Michael Kosterlitz “for theoretical discoveries of topological phase transitions and topological phases of matter”. In this talk I will briefly describe the historical development and the key findings of the Nobelists from the topological excitations of the Kosterlitz-Thouless transition to the novel topological phases of matter unraveled by Thouless and Haldane.

  • Friday 11 November 2016 at 13.00-15.20 in D101 Helsinki Institute of Physics 20 years
    Talks by Vattulainen, Eskola, Oinonen, Heikkurinen, Haeggström, Björkroth on their experiences with HIP. A reception follows.

  • Tuesday 15 November 2016 at 10.15 in A315: Aurora Meroni (HIP)
    A Radiatively induced elementary Goldstone Higgs
    Abstract: We investigate the pseudo-Goldstone nature of the Higgs boson in an elementary realisation that at the same time provides an ultraviolet completion. The renormalizability of the model together with the perturbative corrections determine dynamically the direction of vacuum of the theory and the corresponding Higgs chiral symmetry breaking scale f ~ 14 TeV. The Higgs boson is radiatively generated and the scalar mass spectrum, together with a second massive Higgs boson, lies in the multi-TeV range.

  • Tuesday 22 November 2016 at 10.15 in A315: Wilfried Buchmüller (Desy)
    Grand Unification and the Early Universe
    Abstract: Grand unified theories can provide a complete picture of early universe cosmology. This includes inflation, baryogenesis and the production of dark matter. We discuss some observable consequences with emphasis on the cosmic microwave background and the nature of dark matter.

  • Thursday 24 November 2016 at 10.15 in A315: Harri Waltari (Helsinki)
    Collider signatures of sneutrino dark matter in left-right symmetric supersymmetry
    Abstract: A right-handed sneutrino is a viable dark matter candidate in supersymmetry in addition to the more conventional neutralino option. Right-handed sneutrinos are a natural part of left-right symmetric supersymmetric models, where the gauge sector is extended with right-handed weak interactions. We studied the sneutrino dark matter option in left-right supersymmetry and its signatures at the LHC. We find that we may satisfy the constraints from relic density, low-energy observables and direct SUSY searches. The easiest way to produce the sneutrino would be via the right-handed gauge sector, where the decays of W_R to sleptons lead to multilepton final states. We compare some benchmarks to the case of a neutralino LSP. We may get a detectable signal with high luminosities even with the right-handed W-boson being around 3.5 TeV.

  • Tuesday 29 November 2016 at 10.15 in A315: Viljami Leino (Helsinki)
    The gradient flow running coupling in SU(2)
    Abstract: For SU(N) gauge field theories coupled to fermions, there exists a range in the number of fermion flavors where the beta-function has a non-trivial zero in the infrared (IRFP, infrared fixed point). These conformal theories have applications in beyond the standard model physics. We discuss our recent results on SU(2) gauge teory with 6 and 8 massless fundamental representation Dirac fermions. They are seen to feature an IRFP.

  • Thursday 8 December 2016 at 10.15 in A315: Henning Kirschenmann (CERN)
    Searches of new physics at CMS
    Abstract: We discuss direct and indirect new physics searches at CMS, directly looking for SUSY and indirectly placing constraints on the new physics with the top quark mass. The main experimental limitations come from reconstruction of jets and tail in missing-ET. We review current results and discuss future improvements with up to 100 fb-1 of data to be collected by 2018.

  • Thursday 8 December 2016 at 14.15 in D112: Yohei Ema (Tokyo)
    Dynamics of Higgs during preheating epoch
    Abstract: In the first part, I will discuss the implication of the electroweak (EW) vacuum metastability during the preheating epoch. The EW vacuum may be metastable in light of the current experimental data, and it may have a tension with high-scale inflation. In order to overcome this problem, Higgs-inflaton/-curvature couplings are often introduced. However, after inflation, the additional interaction term oscillates, and it may destabilize the EW vacuum via resonant production of Higgs. In this talk, I will study whether the Higgs-inflaton/-curvature coupling can save the EW vacuum by taking account of Higgs production during the preheating stage. In particular, I will put upper bounds on the Higgs-inflaton/-curvature coupling.
    In the second part, I will discuss the preheating dynamics of the Higgs inflation model. I will find that the Higgs dynamics possesses a very fast time scale during the inflaton oscillation regime, and the preheating dynamics can be much more violent than previously thought due to this time scale. In particular, possibility of unitarity violation will be discussed.

  • Tuesday 13 December 2016 at 10.15 in A315: Thorben Graf (Nantes)
    Quark mass effects in perturbative thermodynamics
    Abstract: Results for several thermodynamic quantities within the next-to-leading order calculation of the thermodynamic potential in perturbative QCD at finite temperature and chemical potential including non-vanishing quark masses are presented. These results are compared to lattice data and to higher-order optimized perturbative calculations to investigate the trend brought about by mass corrections.

  • Tuesday 13 December 2016 at 14.15 in A315: Howard Haber (Santa Cruz)
    Extended Higgs sectors and the alignment limit
    Abstract: After the discovery of the first elementary scalar particle–the Higgs boson–it is natural to wonder if additional elementary scalar particles exist in nature. Indeed, given the multiplicity of fermions and vector bosons that make up the Standard Model of particle physics, it would be somewhat surprising if the Higgs sector was of a minimal form, as posited by the Standard Model (SM). However, the current Higgs data suggest that the properties of the observed Higgs boson are very close to those expected in the Standard Model. In this talk, I discuss the required properties of an extended Higgs sector such that one Higgs scalar is approximately SM-like. This can be achieved if one of the scalar mass-eigenstates is nearly aligned in field space with the scalar vacuum expectation value (the so-called alignment limit). Implications of the alignment limit for a variety of Higgs sectors, including supersymmetric extensions of the Standard Model, are examined, and some of the phenomenological implications are considered.

  • Wednesday 14 – Friday 16 December 2016 in E204 or E207: Helsinki Higgs Forum is taking place
  • Tuesday 20 December 2016 at 10.15 in A315: Matti Järvinen (Paris)
    Inverse magnetic catalysis in holographic QCD
    Abstract: Lattice simulations have shown recently that, contrary to expectations, the chiral condensate is suppressed with growing magnetic field near the chiral/deconfinement transition temperature of QCD. This phenomenon is known as “Inverse Magnetic Catalysis”. I will demonstrate that holographic V-QCD reproduces this effect, and provides a good qualitative match with lattice results for the condensate and related observables. In particular, the inverse catalysis is enhanced with increasing number of flavors, in agreement with lattice analysis.