Seminars 2017


  • Monday 9 January 2017 at 14.15 in A315: Albert De Roeck (CERN)
    Searching for exotic long lived particles with dedicated experiments at the LHC
    Abstract: The Large Hadron Collider has opened a new energy frontier for searches for new physics. Initial results of the 13 TeV run have not yet revealed signals for new physics in ATLAS or CMS. Do these detectors allow us to search at all places where new physics could show up? In this presentation we look at some scenarios where small dedicated experiments will allow to considerably extend our search horizon. The explicate examples of the proposed MilliQan experiment – a search for millicharge particles- and the already approved and running MoEDAL experiment – a search for monopoles – will be presented. In addition there are even more recent ideas for new detection techniques at the LHC for new physics.

  • Tuesday 10 January 2017 at 10.15 in A315: Teemu Ojanen (Aalto)
    Topological matter for pedestrians
    Abstract: The last decade has witnessed a tremendous success in identifying novel phases of matter classified by the topological properties of their spectrum. Topological quantum matter comes in three incarnations, consisting of topological insulators, metals and superconductors. I will give (mostly) a non-technical introduction to this enormous research field which combines ideas from condensed-matter physics, high-energy physics and mathematics. Topological materials exhibit quantized responses, exotic emergent quantum particles and offer new platforms for future technology.

  • Monday 16 January 2017 at 14.15 in E206: Matthew Lippert (Long Island University) Note new time and place!
    Shining Light on Quantum Gravity with Pulsar-Black Hole Binaries
    Abstract: Pulsars are some of the most accurate clocks found in nature, while black holes offer a unique arena for the study of quantum gravity. As such, pulsar-black hole (PSR-BH) binaries provide ideal astrophysical systems for detecting effects of quantum gravity. With the success of aLIGO and the advent of instruments like the SKA and eLISA, the prospects for discovery of such PSR-BH binaries are very promising. We argue that PSR-BH binaries can serve as ready-made testing grounds for proposed resolutions to the black hole information paradox. We propose using timing signals from a pulsar beam passing through the region near a BH event horizon as a probe of quantum gravitational effects. In particular, we demonstrate that fluctuations of the geometry outside a black hole lead to an increase in the measured root-mean-square deviation of arrival times of pulsar pulses traveling near the horizon. This allows for a clear observational test of the nonviolent nonlocality proposal for black hole information escape. For a series of pulses traversing the near-horizon region, this model predicts an rms in pulse arrival times of ~30 mus for a 3 M_sun black hole, ~ 0.3 ms for a 30 M_sun black hole, and ~ 40 s for Sgr A*. The current precision of pulse time of arrival measurements is sufficient to discern these rms fluctuations. This work is intended to motivate observational searches for PSR-BH systems as a means of testing models of quantum gravity.

  • Thursday 9 February 2017 at 10.15 in A315: Timo Alho (Reykjavik)
    Monopole correlation functions and holographic phases of matter in 2+1 dimensions
    Abstract: The strong coupling dynamics of a 2+1 dimensional U(1) gauge theory coupled to charged matter can be holographically modeled via a top-down construction with intersecting D3- and D5-branes. I will talk about our recent paper 1607.04059, where we calculate the correlation functions of monopole operators, dual to magnetically charged particles in the bulk theory, in such a model. We explore the resulting phase diagram when the model is taken to a finite temperature and charge density.

  • Tuesday 14 February 2017 at 10.15 in A315: Blaise Goutéraux (Nordita)
    Bad Metals from Density Waves
    Abstract: So-called ‘bad metals’ present a long-standing conundrum to theory. In particular, their electric resistivity is too high to be accounted for by weakly coupled quasiparticles as in conventional metals. In this talk, I will present a theory of hydrodynamic transport with spontaneous translation symmetry breaking, applicable to density waves and Wigner crystals, which have been detected in regions in close proximity to the bad metallic regime. I will argue that melting of these states by proliferating defects allows to reproduce bad metallic phenomenology and suggests that quantum fluctuations play an important role. I’ll conclude by mentioning how gauge/gravity duality can be used to efficiently perform calculations in the quantum critical regime.

  • Tuesday 21 February 2017 at 10.15 in A315: Anupam Mazumdar (Lancaster)
    Infinite derivative ghost free and singularity free theory of gravity
    Abstract: I will discuss how to construct ghost free and singularity free theory of gravity which can also ameliorate quantum aspects of ultraviolet gravity.

  • Thursday 23 February 2017 at 10.15 in A315: Jorma Louko (Nottingham)
    Waiting for Unruh
    Abstract: How long does a uniformly accelerated observer need to interact with a quantum field in order to record thermality in the Unruh temperature? In the limit of large excitation energy, the answer turns out to be sensitive to whether (i) the switch-on and switch-off periods are stretched proportionally to the total interaction time T, or whether (ii) T grows by stretching a plateau in which the interaction remains at constant strength but keeping the switch-on and switch-off intervals of fixed duration. For a pointlike Unruh-DeWitt detector, coupled linearly to a massless scalar field in four spacetime dimensions and treated within first order perturbation theory, we show that letting T grow polynomially in the detector’s energy gap E suffices in case (i) but not in case (ii), under mild technical conditions. These results limit the utility of the large E regime as a probe of thermality in time-dependent versions of the Hawking and Unruh effects, such as an observer falling into a radiating black hole. They may also have implications on the design of prospective experimental tests of the Unruh effect. Based on arXiv:1605.01316.

  • Monday 27 February 2017 at 14.15 in E206: Nora Brambilla (TU München)
    Quarkonium with Effective field theories
    Abstract: Quantum Chromodynamics (QCD) is the sector of the Standard Model of particle physics that describes the strong interaction, deceptively simple to formulate but notoriously difficult to solve. Heavy quarkonium is a multiscale system that probes the different energy regimes of QCD, from the high-energy region, where an expansion in the coupling constant is possible and precision studies may be done, to the low-energy region, dominated by confinement and the many manifestations of the nonperturbative strong dynamics. Properties of production and absorption of quarkonium in a medium are also crucial for the study of QCD at high density and temperature. On the theoretical side, the construction of new nonrelativistic effective field theories for quarkonium has recently revolutionized the field providing both a conceptual framework and a powerful calculational tool. On the experimental side, the diversity, quantity and accuracy of the data collected in the last few years at B and tau-charm factories and at RHIC and LHC experiments is impressive, featuring the observation of new states and new unexpected processes. I will discuss these theoretical and experimental advancements and their implications for our understanding of strong interactions.

  • Tuesday 28 February 2017 at 10.15 in A315: Antonio Vairo (TU München)
    Heavy Majorana neutrino production and decay in the hot early universe
    Abstract: We compute thermal corrections to the production rate and CP asymmetry of heavy Majorana neutrinos in leptogenesis models of the early universe. We consider temperatures larger than the electroweak scale but smaller than the neutrino masses so that the computation may be performed in a non-relativistic effective field theory framework. We discuss different arrangements of the Majorana neutrino masses.

  • Tuesday 14 March 2017 at 10.15 in A315: Najmul Haque (Giessen)
    Resummed QCD thermodynamics at finite temperature and chemical potential
    Abstract: The thermodynamics of QCD at finite temperature and density is of great interest for the heavy ion collision experiments. In this talk I will discuss about the various thermodynamic quantities calculated within Hard thermal Loop approximation at finite temperature and finite chemical potential. I will also discuss about the possible extensions of the current results to make it more reliable in heavy-ion collision experiments.

  • Thursday 16 March 2017 at 10.15 in A315: Risto Paatelainen (Jyväskylä)
    Towards higher order accuracy in LCPT
    Abstract: Hamiltonian perturbation theory in the light cone form (LCPT) has become a standard tool in understanding hadronic scattering processes within a first principles QCD approach. The calculational inconvenience of LCPT compared to standard covariant perturbation theory is balanced by several features that make its physical interpretation more transparent. Due to the more complicated mathematical structure resulting from the breaking of explicit rotational symmetry, LCPT has never been the formulation of choice for higher order loop calculations. More recently, however, calculations of small-x dilute-dense scattering processes in the Color Glass Condensate (CGC) picture have been approaching the NLO level, for example in the small-x evolution equation and inclusive deep inelastic scattering cross sections. In this talk I will discuss our latest work (T. Lappi, R. Paatelainen arXiv:1611.00497), in which we formulate the LCPT rules in helicity space, independently of the spinor representation. This presents a major technological improvement for loop calculations by replacing the Dirac algebra by simple helicity sums. I also demonstrate how to apply this framework to other LCPT calculations.

  • Tuesday 21 March 2017 at 10.15 in A315: Blagoje Oblak (ETH, Zürich)
    BMS Particles in Three Dimensions
    Abstract: In this talk I will sketch the relation between unitary representations of the BMS3 (Bondi-Metzner-Sachs) group and three-dimensional, asymptotically flat gravity. After defining BMS in 3D, I will argue that its unitary representations are classified by orbits of CFT (conformal field theory) stress tensors under conformal transformations. This will provide a natural relation between BMS particles and 3D quantum gravity. I will also show how one can compute BMS characters, which coincide with gravitational one-loop partition functions in thermal 3D flat space.

  • Tuesday 28 March 2017 at 10.15 in A315: Brandon DiNunno (Austin)
    Relaxation of non-local probes in AdS/CFT
    Abstract: I will discuss the late-time evolution of non-local observables in an expanding, boost-invariant strongly coupled plasma via Holography. Focusing on first and second order dissipative Bjorken hydrodynamics, we compute the late-time behavior of two-point functions, Wilson loops and entanglement entropies analytically. We find universal formulae for the relaxation of such probes in conformal field theories with a gravity dual in the limit of infinite coupling. We then generalize our findings to finite coupling by studying Gauss-Bonnet gravity as well as alpha’ corrections.

  • Thursday 27 April 2017 at 10.15 in A315: Jens Andersen (Trondheim)
    QCD in strong magnetic fields
    Abstract: QCD in strong magnetic fields is relevant for compact stars, heavy-ion collisions, and the early universe. In this talk I will discuss our current understanding of the thermodynamics of QCD in a constant magnetic background. I will focus on magnetic catalysis at T=0 and inverse magnetic catalysis around the chiral transition in the context of low-energy models (Nambu-Jona-Lasinio and quark-meson models with and without the Polyakov loop) and lattice QCD.

  • Tuesday 2 May 2017 at 17.00 in E204: Gia Dvali (Munich) Note time and place!
    The secret quantum life of black holes
    Abstract: TBA

  • Thursday 4 May 2017 at 10.15 in A315: Hannu Paukkunen (Jyväskylä)
    Nuclear PDFs today
    Abstract: I will review the present status of global determination of nuclear PDFs, Parton Distribution Functions. A special emphasis will be given to the recent Eskola-Paakkinen-Paukkunen-Salgado (EPPS16) analysis, which is the first one to include constraints from the LHC proton-lead collisions.

  • Tuesday 9 May 2017 at 10.15 in A315: Jim Olsen (Princeton, CERN)
    Exploring the Energy Frontier: LHC at 13 TeV
    Abstract: The Large Hadron Collider (LHC) at CERN is the world’s largest and highest energy particle accelerator, which began operation in 2009 at a center of mass energy of 7 trillion electronvolts. The first ‘physics run’ of the LHC extended from 2010-2012, culminating in the discovery of a new particle whose properties appear to match those of the Higgs boson. In the current run, which began in 2015, the LHC has resumed proton collisions at a new record energy of 13 trillion electronvolts, and with double the interaction rate achieved in the previous run. As with many scienfitic discoveries, observation of the Higgs boson raises more questions than it answers, including why its mass is so far below the Planck mass. The standard model of particle physics has no answer to this question, nor does it provide a ready candidate for Dark Matter, let alone any explanation at all for Dark Energy. Such questions are driving the intensified search for new particles and new phenomena beyond those described by the standard model, using the unprecedented data currently being collected at the LHC. In this talk, I will summarize the near-term and far-term goals of the project, and possible future paths beyond the LHC.

  • Thursday 11 May 2017 at 10.15 in A315: Arttu Pönni (Helsinki)
    Holographic entanglement flows
    Abstract: We study the entanglement entropy and mutual information in a holographic QFT with a top-down gravity dual and propose a new quantity for measuring the extensivity properties of mutual information. I discuss how these quantities and two degree of freedom-measuring holographic objects behave under RG flow in our model.

  • Friday 12 May 2017 at 14.15 in A315: Phil Harris (CERN)
    Understanding the minutiae of the standard model with Dark Matter
    Abstract: Developments over the past year have demonstrated the power of the LHC to complement and, in some cases, extend direct detection and galactic searches for dark matter. We present a series of new searches for dark matter that represents the culmination of these developments. In addition to an order of magnitude improvement in sensitivity to dark matter, we demonstrate that these searches have lead to some of the most precise measurements of electroweak boson production to date. Finally, we explore the future of dark matter searches and present a new class of searches using hadronically decaying bosons. Can we make a definitive path to dark matter discovery?

  • Tuesday 16 May 2017 at 10.15 in A315: Mauri Valtonen (Turku)
    Post-Newtonian components of a gravitational wave
    Abstract: The direct detection of a gravitational wave from GW150914 in September 2015 opens up a new window to the study of the universe. Even though the effects of gravitational waves in astronomical systems have been indirectly observed since 1974, this was the first confirmation of their existence. I will describe the history of the method leading to the detection, and the properties of the merging binary black hole system in GW150914. One of the key issues in the analysis of gravitational wave events is the theoretical treatment of the Post-Newtonian components of the wave. Until now the lowest order Newtonian component has been enough, but in the analysis of black hole mergers one has take into account higher orders. I will discuss the situation in the binary black hole system OJ287 and show that it is necessary to include tails (scattering of the waves from themselves) while the memories of past waves can be neglected. Truncating the series at the first post-Newtonian order (as is often done), leads to a serious error.

  • Tuesday 16 May 2017 at 14.15 in A315: Alexander Rothkopf (Heidelberg)
    Improved real-time dynamics of thermal fields from lattice simulations
    Abstract: The determination of real-time information from lattice simulations at finite temperature is a central challenge in our quest to nonperturbatively connect first principles theory to experimental measurements. In the context of relativistic heavy-ion collisions the shear viscosity of the quark-gluon plasma is one pertinent example, which with standard simulation methods is exponentially hard to obtain. In this talk I will discuss the challenges of computing real-time quantities via the extraction of spectral functions from standard lattice simulations and introduce a recent proposal of how to possibly circumvent these. In it, thermal fields are simulated on a lattice in imaginary frequency space, which allows one to resolve correlation functions in between the conventional Matsubara frequencies. Results from a (0+1)d proof-of-principles simulation are presented, which show that an exponential improvement in the reconstruction of spectral features may be achieved (arXiv:1610.09531).

  • Tuesday 30 May 2017 at 10.15 in A315: Tommaso Dorigo (Padova)
    Controversial Phenomena in Collider Data and the Five Sigma Criterion in HEP
    Abstract: Extraordinary claims require extraordinary evidence. The p < 0.000029% criterion used in HEP and astro-HEP does not appear adequate to cover all experimental situations. The seminar will start with a short history of anomalies found in HEP data and their resolution, and then focus on the statistical problem of defining a proper discovery level for new phenomena and on the non-trivial issues it entails.
  • Tuesday 30 May 2017 at 14.15 in A315: Oscar Henriksson (Boulder)
    Holographic studies of ABJM theory at finite density
    Abstract: TBA

  • Wednesday 31 May 2017 at 10.15 in A315: Marco Panero (Torino)
    Non-equilibrium theorems from statistical mechanics and their applications in lattice QCD
    Abstract: In statistical mechanics, Jarzynski’s and Crooks’ theorems relate the free-energy difference between an initial and a final statistical ensemble (both at equilibrium), to the distribution of work done on the system, when, starting from a configuration of the initial ensemble, it is driven towards the final one, through a sequence of transformations out of equilibrium. In this talk, I will discuss how these theorems can be applied in numerical simulations of QCD and QCD-like theories on a lattice.

  • Thursday 1 June 2017 at 10.15 in A315: Malak Khouchen (Brno)
    Fundamental strings and D1 branes on deformed AdS3 x S3 background
    Abstract: In this talk I describe results derived in two of my papers that were published in Phys. Review D and JHEP. In the first one we analyzed dynamics of fundamental string in deformed AdS3 x S3 space-time where we find giant magnon solutions for strings moving in this background which reproduces the celebrated Hofman-Maldacena dispersion relation in the limit when the deformation parameter goes to zero. In the second paper we analyzed D1-brane as a natural probe in the deformed AdS3 x S3 background with non-trivial Ramond-Ramond two form. We find static and time-dependent solutions of D1-brane equations of motion. We find that the behavior of these solutions crucially depends on the value of the deformation parameter and we discuss their relations to Anti-de Sitter D-branes found by K. Bachas.

  • Tuesday 6 June 2017 at 10.15 in A315: Daniel Fernández (Reykjavik)
    Entanglement entropy at non-equilibrium in holography
    Abstract: In recent years, holographic models have proved to be successful at studying far-from-equilibrium physics. This provides a new approach to studying quantum quenches in strongly coupled systems. In this talk, based on ArXiv:1705.04696, I will focus on the local quench-like time evolution obtained by joining two 1+1 dimensional heat baths at different temperatures. I will present results for the entanglement entropy of different entangling regions obtained by adapting the time-dependent Hubeny-Rangamani-Takayanagi prescription. The interest of this study relies on the presence of emergent collective behavior, which can provide insight into the interplay between quantum effects and out of equilibrium physics.

  • Thursday 8 June 2017 at 10.15 in A315: Mithat Kaya (Marmara)
    Jet measurements at CMS
    Abstract: We review the 7 TeV inclusive jet cross section measurement from CMS that has been widely used in global PDF fits, and compare to the new 8 TeV update that was just released in HEPData last week after several years of scrutiny. We also discuss the potential of the 13 TeV data from Run II and of the new quark-gluon identification tools for constraining PDFs, determining the running of the strong coupling alpha_s and testing the recently released NNLO pQCD predictions for jet production.

  • Friday 9 June 2017 at 10.15 in A315: David Rodríguez (Oviedo)
    Stiff phases in holography
    Abstract: If strongly coupled quark matter is present in the cores of neutron stars, it would demand a very stiff equation of state. In this talk, we summarize the progress so far in finding holographic models at finite density and UV fixed points which can accomplish this. We consider N=4 super Yang-Mills at finite R-charge density and a bottom-up construction, dual to an Einstein-Maxwell theory plus a scalar field in a charged black hole geometry. This is a sensible candidate to describe deconfined quark matter inside a neutron star. We also comment on possible future works on this matter.

  • Wednesday 14 June 2017 at 10.15 in A315: Kent Yagi (Princeton)
    Probing Fundamental Physics with Gravitational Waves from Compact Binary Coalescences
    Abstract: The binary black hole merger events recently discovered by the LIGO and Virgo Collaboration offer us excellent testbeds for exploring extreme (strong and dynamical-field) gravity that was previously inaccessible. In this talk, I will first review the current status of testing such gravity with GW150914 and GW151226, in particular, explaining how well one can probe various fundamental pillars in General Relativity. I will then describe what fundamental physics information can we learn if we detect gravitational waves from neutron star binaries. In particular, I will explain how approximate universal relations (such as the “I-Love-Q relations”) among certain neutron star observables that are almost insensitive to the unknown stellar internal structure help to extract such important physics from future gravitational wave observations. I will conclude with a summary of important future directions.

  • Thursday 15 June 2017 at 10.15 in A315: Tobias Zingg (Nordita)
    Holographic Renormalization via Background Subtraction
    Abstract: The aim is to provide an alternative and complementary approach to established procedures in holographic renormalization, aiming to facilitate explicit computations and forego complications that might potentially arise with methods that require a large number of counter-terms to be computed. An embedding into a higher-dimensional ambient manifold provides a controlled environment that allows for a more direct comparison with a reference solution – which, in principle, is even applicable if the latter is defined on a manifold with different topology than the one of interest. If the reference solution is an appropriately chosen vacuum/ground state, this procedure leads to a renormalized action that naturally preserves symmetries of the original action and leads to the correct thermodynamics for black hole space-times, respectively the field theory dual. If time permits, also potential applications towards calculating n-point functions, entanglement entropy and renormalization in cases where the asymptotics are less well behaved than in AdS and similar spaces with boundaries defined via asymptotic scaling, e.g. due to back-reaction with bulk fields beyond the BF bounds, will be discussed.

  • Tuesday 8 August 2017 at 10.15 in E204: Jean-Paul Blaizot (Saclay). Special Colloquium, note place!
    Bose-Einstein condensation in unusual circumstances
    Abstract: There is robust evidence from the Relativistic Heavy Ion Collider (RHIC) in the USA, and now from the Large Hadron Collider (LHC) at CERN, that the matter produced in ultra-relativistic heavy ion collisions reaches (nearly) local equilibrium. According to our present understanding, the initial state of this matter consists of gluons, the quanta of the gluon field responsible for the strong interactions of elementary particles. These gluons are bosons, and are too numerous, given their energy, to be accommodated by an ordinary thermal distribution. If their number remains approximately constant as they evolve toward equilibrium, that is, if inelastic processes are sufficiently slow, a natural, albeit controversial, possibility is that the excess gluons form a Bose-Einstein condensate. Aside from its potential relevance to the problem of thermalization of the quark-gluon plasma in ultra-relativistic heavy ions, the dynamical formation of such a condensate is an interesting problem in itself, with connections to diverse fields of physics, ranging from cosmology to cold atom systems. Several aspects of this problem will be addressed in the talk.

  • Tuesday 15 August 2017 at 10.15 in A315: Martin Krššák (Tartu)
    Modified teleparallel theories
    Abstract: One of the greatest challenges of modern theoretical physics is explanation of the accelerated expansion of the Universe. The usual approach is to introduce the Dark Energy, but recently another approach started to be increasingly popular, where the laws of gravity are reconsidered and modified. It turns out that it is possible to modify general relativity not only in its standard formulation, but also in the so-called teleparallel formulation. This leads to novel modified models, e.g. f(T) gravity. I will present some recent results in this field. In the first part, I will discuss some problems of f(T) gravity and how to overcome them, and then in the second part I will show some new ways to formulate novel models of gravity.

  • Tuesday 22 August 2017 at 10.15 in A315: Vasily Tarasov (Moscow State University)
    Physics on Fractals: Approaches and Problems
    Abstract: Fractals are measurable metric sets with non-integer dimensions. The basic property of the fractals is non-integer “mathematical” dimensions that should be observed at all scales. Fractal media can be defined as media (or distributions) that are characterized by non-integer “physical” dimensions. A short review of the five basic approaches to the description of fractal media will be suggested in this talk. The main differences between these approaches to describe fractal media, which are distributed in the integer-dimensional Euclidean space, will be described on the talk. The derivatives and integrals of non-integer orders, generalizations of differential operators of first orders (gradient, divergence, curl operators), the scalar and vector Laplacian will be considered. Analysis of these approaches and methods to described fractal physical phenomena will be presented.

  • Tuesday 29 August 2017 at 10.15 in E205 (Note place!): Stanislav Rusak (Nordita)
    Inflation, Higgs and EW vacuum stability
    Abstract: Today the universe appears to be occupying a metastable false vacuum with some more energetically favourable true vacuum existing at higher energies. This fact is puzzling in the light of early universe physics, particularly inflation which tends to push the universe into the true vacuum if the Standard Model remains valid up to the inflationary energy scale. I discuss extensions of the SM which ensure stability during inflation and the implications of (p)reheating for such models.