DEPARTMENT OF PHYSICS / HIP JOINT COLLOQUIA / SEMINARS 2018
- Thursday 18 January 2018 at 10.15 in A315: Aleksi Kurkela (CERN/Stavanger)
Gravitational-wave constraints on the QCD Equation of State
Abstract: The LIGO/Virgo detection of gravitational waves originating from a neutron-star merger, GW170817, has recently provided new stringent limits on the tidal deformabilities of the stars involved in the collision. I discuss how these measurements affect our understanding of the equation of state (EoS) of dense and cold nuclear matter. In particular, I generate the most generic family of neutron-star-matter EoSs that are consistent with firm state-of-the-art theoretical results at low and high baryon density, and further constrain the set of allowed EoSs by imposing robust observational astrophysical constraints. The gravitational wave observations have a dramatic impact on the set of allowed EoS and upon their inclusion we empirically determine the EoS to an unprecedented accuracy.
- Tuesday 23 January 2018 at 10.15 in A315: Timo Kärkkäinen (Helsinki)
Neutrinos beyond the standard model
Abstract: Neutrino oscillations, which were experimentally discovered during the turn of the millennium, are consistent with the rather unsurprising three-neutrino framework. In many extensions of the Standard Model, a larger neutrino sector is proposed and nonstandard oscillation effects will arise. I will discuss about the standard seesaw mechanisms, and impacts on neutrino oscillation phenomenology of those theories.
- Tuesday 30 January 2018 at 10.15 in A315: Jarno Rantaharju (Swansea)
A lattice realization of Ideal Walking
Abstract: I present recent results of the adjoint SU(2) gauged NJL model with 2 flavors of fermions in the adjoint representation, a simple realization of an Ideal Walking model. The adjoint SU(2) model is infrared conformal and the NJL model exhibits spontaneous chiral symmetry breaking. The interaction between the two forces creates an interesting dynamic, where a transition between an infrared conformal and a chirally broken model is found at a finite coupling and a large mass anomalous dimension is produced naturally. I study the phase diagram of the model with special interest on the order of the chiral symmetry breaking transition and the measure the mass anomalous dimension.
- Tuesday 6 March 2018 at 10.15 in A315: Kenneth Österberg (Helsinki)
Recent TOTEM results – probing the existence of a colourless 3-gluon bound state
Abstract: High energy elastic pp scattering has up to now conveniently been described by the t-channel exchange of a pair of gluons (or gluon ladder), the so-called “Pomeron”, or photon-exchange at very low |t|. The recent most precise ever determination of the rho parameter by TOTEM at 13 TeV center-of-mass energy in conjunction with the total pp scattering cross-section measurement suggests that Pomeron- and photon-exchange are not sufficient to describe the data. In fact, adding the exchange of a 3-gluon bound state, the so-called “Odderon”, lead to a significantly better description of the TOTEM measurements. In the seminar, I will describe the TOTEM measurements, show predictions with and without 3-gluon exchange and finally discuss other ways and processes to verify the existence of a colourless 3-gluon bound state.
- Tuesday 13 March 2018 at 10.15 in A315: Joosep Pata (ETH Zürich)
Searching for the direct top-Higgs coupling at CMS using the matrix element method
Abstract: I will describe why a direct determination of the coupling between the top quark and the Higgs boson is a particularly interesting measurement in Run 2 of the LHC and give an impression into how this coupling can be determined by searching for the production of top-quark pair associated Higgs production (ttH). I will describe the matrix element method, used in the upcoming CMS ttH(bb) analysis, as it applies to the analysis of multi-particle hadronic final states. Finally, I will discuss possible extensions of the method and how complex analyses in general can benefit from recent activity in machine learning.
- Tuesday 20 March 2018 at 10.15 in A315: Markus Seidel (CERN)
Top mass and subtle QCD effects
Abstract: I give an overview of the most precise top mass measurements at CMS and discuss their theoretical interpretation. Future improvements require measurements of radiation and non-perturbative effects for a better modeling of ttbar events. I will present a new measurement of jet substructure that can lead to a more precise determination of the effective alpha_s in final-state radiation for different jet flavors.
- Thursday 22 March 2018 at 10.15 in A315: Bogdan Stefanski (CU London)
The protected closed string spectrum of AdS3/CFT2 from integrability
Abstract: I will review the recent progress in computing the exact spectrum of closed strings in AdS3/CFT2 using integrability. The spectrum is determined through a set of all-loop Bethe Equations, from which one can find, for example, the protected closed string states and compare with supergravity results. Exact agreement is found in the case of AdS3xS3xT4. For AdS3xS3xS3xS1 past supergravity calculations predicted too many BPS states, many of which are not protected in string theory. I will discuss the current status of these states.
- Tuesday 27 March 2018 at 11.00 in A315: K. Kajantie (Helsinki) Note start delayed by 45 min!
Memory effect, supertranslations and symmetries at null infinity
Abstract: First I compute the memory effect, permanent displacement of relative positions of two detectors caused by a passage of a burst of gravitational radiation from a coalescing binary. Particular attention is focussed on null memory, that sourced by the gravitational radiation from the binary in the first place. The analogous physical effect can be studied in electrodynamics with its U(1) gauge invariance both in a gauge covariant way or fixing the gauge. In the context of gravity the relevant symmetry group of null infinity contains the Lorentz group but also direction dependent time translations, supertranslations. They correspond to U(1) gauge transformations. I discuss how the magnitude of these supertranslations can be related to the memory effect. Finally I summarize attempts to supertranslate a configuration with a black hole, dress the horizon with soft hair.
- Thursday 5 April 2018 at 10.15 in A315: Marco Marquard (CERN/ALICE)
Two ways to study heavy-ion collisions
Abstract: Ultrarelativistic heavy-ion collisions are used to study the quark-gluon plasma (QGP), a state of matter where quarks and gluons exist in a deconfined phase. After an introduction into the QGP and heavy-ion collisions, different techniques and probes to study heavy-ion collisions and possible signatures of a QGP will be discussed. This is followed by a deeper look at two measurements representing different approaches to study heavy-ion collisions, as they originate from different physical processes. While isolated photons as a probe are produced in initial hard scattering processes, the average transverse momentum of charged particles is dominated by the soft bulk production of particles. For each each measurement the analysis technique, results as well as an outlook is presented.
- Tuesday 10 April 2018 at 10.15 in A315: Maximilian Attems (Barcelona)
Non-conformal holographic fluid relaxation
Abstract: Ever since fast hydrodynamization has been observed in heavy ion collisions the understanding of the very early non-equilibrium stage of such collisions has been a topic of intense research. We use the gauge/string duality to model the creation of a strongly coupled Quark-Gluon plasma in a non-conformal gauge theory. In the dual gauge theory the Gregory-Laflamme instability corresponds to the spinodal instability. We uncover a new surprising example of the applicability of hydrodynamics to systems with large gradients. Moreover we explore collision of ultra-relativistic lumps of energy in the vicinity of a critical point.
- Thursday 12 April 2018 at 10.15 in A315: Alessandro Calandri (Marseille)
Search for the Standard Model Higgs boson produced in association with top quarks in the H->bb final state – b-jet idenfication and reconstruction in ATLAS
Abstract: The measurement of the top-quark Yukawa coupling is possible using the Higgs production in association with a pair of top quarks (ttH). The bb final state features the largest branching ratio among the various ttH decay modes, however its understanding is very challenging in light of the overwhelming non-resonant ttbb background. ATLAS results in the H->bb final state  will be presented in this seminar with a particular focus on the flavour-tagging algorithm developments and optimisations as well as the typical b-jet reconstruction and identification performance achieved.
- Tuesday 17 April 2018 at 10.15 in A315: Paul Hoyer (Helsinki)
Bound states and QCD
Abstract: Hadrons are bound states of QCD. The strong binding, color confinement and chiral symmetry breaking make hadrons appear different from QED atoms. Yet there are tantalizing similarities as well, including quantum numbers and the heavy quarkonium spectrum.I first discuss some principles for describing bound states in field theory. Atomic wave functions are non-polynomial in α and cannot be derived from Feynman diagrams. The Schrödinger equation is the contribution of lowest order in ℏ, with the potential determined by the classical photon field. Analogously, QCD allows a classical gluon field which implies confinement and chiral symmetric breaking. I show some explicit solutions.
- Friday 27 April 2018 at 10.15 in C310: Tatyana Arsenovich (Helsinki) Note place!
Reliability and quality assurance methods for the development of radiation hard particle detectors
Abstract: Silicon detectors for high energy physics applications should provide reliable data. Performance of the detectors should be stable in harsh radiation environment as their maintenance is extremely difficult, in some cases even impossible during the long operational time. To achieve the required reliability, the detectors should be extensively studied. The reliability of the quality assurance methods is a key element in the development of novel silicon detectors. In this seminar I am going to discuss the assessment of the silicon detector reliability and to review the main quality assurance methods and their impact on the development of the detectors.
- Tuesday 8 May 2018 at 10.15 in A315: Tommi Markkanen (Imperial College, London)
Evaporation of de Sitter space
Abstract: The exponentially expanding de Sitter solution is frequently encountered in cosmology due to its significance for the late and early Universe. However, its stability in a quantised theory has for a long time been the source of debate. In this talk we discuss this issue in the framework of semi-classical gravity. Based on a first principle calculation, I argue that when one considers the experiences of a local observer, the quantum back reaction destabilizes de Sitter space leading to a gradual continuous increase of the dS horizon. This implies that the cosmological ‘constant’ decays over time, with flat space as the asymptotic late time solution.
- Tuesday 8 May 2018 at 15.00 in Chemicum A110: John Ellis (King’s College, London) Special colloquium, note time and place!
What are we? Where do we come from? Where are we going?
Abstract: Particle physics addresses these fundamental questions by studying the fundamental structure of matter and using the knowledge gained to understand the evolution of the Universe, from the Big Bang to the distant future. In addition to our current understanding, this talk will also discuss some of the big open questions, such as the stability of space itself and the nature of the dark matter that holds galaxies together.
- Wednesday 9 May 2018 at 10.15 in A315: John Ellis (King’s College, London)
Global Standard Model Effective Field Theory Fit to LHC and Electroweak Data
Abstract: We have performed an updated global fit to precision electroweak data, W +W measurements at LEP, and Higgs and diboson data from Runs 1 and 2 of the LHC in the framework of the Standard Model Effective Field Theory (SMEFT). We exhibit the improvement in the constraints on operator coefficients provided by the LHC Run 2 data, and discuss the correlations between them. We also explore the constraints our fit results impose on several models of physics beyond the Standard Model, including models that contribute to the operator coefficients at the tree level and stops in the MSSM that contribute via loops.
- Tuesday 15 May 2018 at 10.15 in A315: Iason Baldes (DESY)
Residual Annihilations and Self-interactions of Asymmetric Dark Matter
Abstract: Dark matter coupled to light mediators has been invoked to resolve the putative discrepancies between collisionless cold DM and galactic structure observations. However, gamma-ray searches and the CMB strongly constrain such scenarios. To ease the tension, we consider asymmetric DM. We show that, contrary to the common lore, detectable annihilations occur even for large asymmetries, and derive bounds from the CMB, gamma-ray, neutrino and antiproton searches. We then identify the viable space for self-interacting DM. Direct detection does not exclude this scenario, but provides a way to test it.
- Thursday 17 May 2018 at 15.15 in A315: Mariana Frank (Montreal) Note special time!
E6 inspired U(1)- Extended MSSM: from Dark Matter to LHC
Abstract: I review briefly the motivation for supersymmetry, and for extending the gauge symmetry by an extra U(1), consistent with symmetry breaking from E6 SUSY GUT. Imposing universality conditions from the GUT scale, and using experimental constraints, I perform a scan of the parameters of the model. Both the right-handed sneutrino and the lightest neutralino can serve as DM candidates. Constraints from cosmic abundance and direct detection restrict the parameter space in each case. Finally, I discuss the possibility of observing signals of such models at the LHC. In particular, chargino pair production leading to 2 leptons and missing energy can yield significant signal to background enhancements.
- Tuesday 22 May 2018 at 14.15 in A315: Javier Tarrio (Brussels) Note special time!
Holography, cold dense matter and color superconductivity
Abstract: I will describe a model of a strongly interacting plasma with fundamental matter at finite density that arises in string theory. In a recent work the simplest phase of this system was studied, and instabilities towards more complicated phases were found. I will discuss in some more detail the instability towards the breaking of the gauge group, which gives rise to color superconductivity.
- Special seminar: Wednesday 23 May 2018 at 14 at Aalto university: Frank Wilczek (MIT, Stockholm)
Emergent Axions, and the Challenging Search for Real Ones
Abstract: The effective theory of axion electrodynamics governs interesting transport phenomena in real materials (topological insulators). I’ll discuss how the theory emerges from very basic considerations, and also review some confirming experiments. Then I’ll discuss recent proposals for experiments to detect the cosmic axion background, which push interesting frontiers of detector technology.
- Special colloquium: Thursday 24 May 2018 at 17 at Helsinki university, Great hall (juhlasali): Frank Wilczek (MIT, Stockholm)
The Strange, Unfinished Story of Time Reversal
Abstract: Few aspects of experience are as striking as the difference between past and future. Yet the fundamental equations of physics make no such distinction. Why is that? And how can the world look so different from the equations? Physicists have wrestled with those questions for centuries, yet they remain alive as frontiers of research.
- Tuesday 5 June 2018 at 10.15 in A315: Kirill Boguslavski (Jyväskylä)
Spectral function from real-time lattice gauge simulations
Abstract: We study the spectral properties of a highly occupied non-Abelian non-equilibrium plasma appearing ubiquitously in weak coupling descriptions of QCD matter. The spectral function of this far-from-equilibrium plasma is measured by employing linear response theory in classical-statistical real-time lattice Yang-Mills simulations. We establish the existence of transversely and longitudinally polarized quasiparticles and obtain their dispersion relations, effective mass, plasmon frequency, damping rate and further structures in the spectral and statistical functions. Our results are consistent with hard thermal loop (HTL) effective theory but also indicate effects surpassing its leading order. The method can be employed beyond the range of validity of HTL.
- Thursday 7 June 2018 at 10.15 in A315: Laurent Forthomme (HIP)
Central exclusive processes in the LHC era
Abstract: The physics of central exclusive processes – such as two-vector boson and dilepton production – can be studied at unprecedented energy scales in LHC experiments. In this seminar, I will describe the phenomenology of photon-induced reactions, along with the story so far of major attempts to observe and tag such processes in LHC’s runs 1 and 2. In particular, the latest observation of two-photon production of lepton pairs at the electroweak scale with the Precision Proton Spectrometer, accomplished jointly by the CMS and TOTEM collaborations, is discussed and put into perspective. This will also allow me to discuss the discovery potential through some prospects for future measurements with this apparatus.
- Tuesday 12 June 2018 at 10.15 in A315: Kai Nordlund (Helsinki)
Using molecular dynamics to aid dark matter searches
Abstract: There are a number of attempts for direct detection of dark matter particles via their elastic interaction with detector nuclei. To date, the detectors developed could detect dark matter particles with masses > 10 GeV/c^2. In this work , we showed that potential dark matter particles in the mass range down to 200 MeV/c^2 could be detected by new kinds of single-electron resolution single crystal semiconductor detectors. The dark matter particles in this mass range, if they exist, could give the detector nuclei recoils in the energy range 1 — 100 eV. If this is the case, the detector response can be calibrated with molecular dynamics simulations of low-energy self-recoils in the material. We used classical and time-dependent density functional theory molecular dynamics to calculate the response of the semiconductor detectors to dark matter recoils as a function of crystal direction, and using an analytical model translated this into a dependence of the signal on the time of the day. The diurnal variation could be a major benefit for distinguishing a dark matter particle signal from that of conventional standard model particles. F. Kadribasic, N. Mirabolfathi, K. Nordlund, A. E. Sand, E. Holmström, and F. Djurabekova, Directional Sensitivity In Light-Mass Dark Matter Searches With Single-Electron Resolution Ionization Detectors, Phys. Rev. Lett 120, 111301 (2018)
- Tuesday 7 August 2018 at 10.15 in A315: Mikko Laine (Bern)
On the quantum statistical physics of dark matter freeze-out
Abstract: The non-observation of dark matter at the LHC and other searches poses a challenge both for model building and for the theoretical tools with which any given model is addressed. In this talk issues related to the latter challenge are discussed, within the context of the classic WIMP paradigm. As a concrete example, we illustrate the recently fashionable idea that bound states could appear in the dark sector and significantly affect the freeze-out dynamics.
- Tuesday 14 August 2018 at 10.15 in A315: Anthony Zee (Santa Barbara)
Some speculations on the cosmological constant paradox
Abstract: We discuss some wildly speculative thoughts about the vexing unsolved problem about the cosmological constant paradox.
- Wednesday 15 August 2018 at 10.15 in A315: Jarkko Järvelä (Helsinki) Note special time!
On the capacity of entanglement
Abstract: Quantum entanglement is important for many physical phenomena. Quantitatively, it is most commonly characterized by entanglement entropy. In this talk we focus on another concept called the capacity of entanglement. We find that it is the quantum information theoretic counterpart of the thermal heat capacity. In many aspects, it is similar to entanglement entropy but there are some key differences. We discuss these points in context of qubit systems, quantum field theories and holography.
- Wednesday 22 August 2018 at 10.15 in A315: Wolfram Weise (TU München) Note special time!
Chiral EFT Approach to Nuclear Many-Body Systems – with implications for neutron stars
Abstract: Recent developments of Chiral Effective Field Theory applications to nuclear and neutron matter are summarized, with special emphasis on a (non-perturbative) approach using functional renormalization group methods. Topics include: nuclear thermodynamics, extrapolations to dense baryonic matter, and constraints from neutron star observables. An outlook is also given on hyperon-nuclear interactions and their possible role in the equation-of-state of neutron star matter.
- Monday 3 September 2018 at 14.15 in A315: Martijn Mulders (CERN) Note special time!
Top quark mass — the road toward ultimate precision?
Abstract: The top quark mass is a fundamental parameter of the Standard Model and its precise measurement will be one of the key legacy results of the Large Hadron Collider. Profiting from ever increasing data sets, improvements in calibration methods and refinements in analysis techniques the experimental determination of the top quark mass has reached a quoted precision of about 0.5 GeV or 0.3%. How much further improvement can we expect at the LHC in the coming years? In this seminar I plan to touch on various questions that exist regarding theoretical and experimental aspects of the current measurements, and to discuss possible ideas and approaches to tackle them, aiming for the ultimate precision.
- Tuesday 4 September 2018 at 10.15 in A315: Camille Bélanger-Champagne (Helsinki)
Nuclear fuel safeguards – the Finnish deep geological repository
Abstract: Nuclear safeguards programs are an important part of the implementation of international non-proliferation agreements. New safeguards protocols, and the technology to support them are needed, as countries such as Finland have begun construction of their final disposal facilities for spent nuclear fuel, with operations to begin within the next 10 years. A multipurpose, multitechnology instrument, with passive gamma emission tomography (PGET) and passive neutron albedo reactivity (PNAR) as the core technologies, is as been designed for partial defect verification of spent nuclear fuel, in conjunction with final disposal. A PGET prototype instrument as been built, and preliminary results from recent data taking campaigns at the Loviisa and Olkiluoto nuclear power plants (Finland) will be presented. Simulation studies of the PNAR technology will also be discussed.
- Tuesday 18 September 2018 at 10.15 in A315: Takaaki Ishii (Utrecht)
Black resonators in AdS5
Abstract: Fast rotating black holes may exhibit a superradiant instability. In asymptotically AdS spacetime, the gravitational waves emitted from such black holes are reflected by the AdS boundary and backreact to form new gravitational solutions called black resonators, whose zero-size limit is geons. In this talk, I will construct a class of geons and black resonators in five-dimensional AdS spacetime and study their properties including thermodynamics.
- Tuesday 2 October 2018 at 10.15 in A315: Kazuo Fujikawa (RIKEN)
Chiral anomaly and Berry’s phase
Abstract: Recently, chiral anomaly and Berry’s phase are often used in the study of chiral properties of condensed matter and nuclear physics. In my talk I first suggest to define adiabatic Berry’s phase precisely following the original ideas of Berry and Simon such that its topology arises from the singularity associated with the level crossing phenomenon. This definition covers most of the popular examples of Berry’s phase such as Stone’s model and the model of Xiao,Shi and Niu, but their validity domains are severely limited. Part of the freedom of the “monopole” associated with Berry’s adiabatic phase is frozen compared to the conventional monopole, and we suggest the term “adiabatic monopole”. A well-defined monopole is not derived from an adiabatic monopole. This limitation implies that the derivation of anomalous commutators of spatial coordinates from an adiabatic monopole associated with Berry’s phase is not justified. As a result, the derivation of anomalous charge non-conservation from the anomalous commutators of spatial coordinates in the literature is not valid, besides the covariant gauge anomaly thus derived does not satisfy the “anomaly matching condition”.
- Tuesday 9 October 2018 at 10.15 in A315: Shinsuke Kawai (Suwon, Korea)
Gauss-Bonnet Chern-Simons gravitational wave leptogenesis
Abstract: The gravitational Chern-Simons term coupled to an evolving axion is known to generate lepton number through the gravitational anomaly. We examine this leptogenesis scenario in the presence of the Gauss-Bonnet term over and above the gravitational Chern-Simons term. We find that the lepton production can be exponentially enhanced. The Gauss-Bonnet term creates CP-violating instability of gravitational waves that may appear transiently after inflation, and during the period of instability elliptically polarized gravitational waves are exponentially amplified at sub-horizon scales. This instability does not affect the spectrum of the cosmic microwave background as it occurs at much shorter length scales. In a typical scenario based on natural inflation, the observed baryon asymmetry of the Universe corresponds to the UV cutoff scale at 10^14−16 GeV.
- Tuesday 30 October 2018 at 10.15 in A315: Djuna Croon (TRIUMF)
Gravitational Waves signatures of Dark Matter
Abstract: In anticipation of data from the next generation of gravitational wave experiments and pulsar timing arrays, I will discuss the opportunities for phenomenological studies of particle physics beyond the Standard Model. I will focus on hidden gauge sectors, and discuss various astrophysical and cosmological sources of gravitational waves, including modified BNS/BBH binary mergers, exotic compact objects, and cosmic phase transitions. I will also comment on the dark matter relic abundance and complementarity with other experimental dark sector probes.
- Tuesday 6 November 2018 at 10.15 in A315: Aleksi Kurkela (CERN, Stavanger)
Emerging collectivity in pp, p-Pb, and Pb-Pb collisions at the LHC
Abstract: Standard monte-carlo event generators used to describe proton-proton collisions are based on an assumption that hadronic collisions can be treated as independent superpositions of partonic collisions. The recent observations of emerging collective behavior in high multiplicity proton-proton and proton-nucleus collisions challenges this picture. In nuclear collisions, the collective behavior is attributed to the formation of a droplet of thermalized plasma. I discuss the non-equilibrium evolution that leads to emergence of thermalized plasma in nuclear collisions using weak coupling techniques and discuss its implications to collectivity in small systems.
- Thursday 8 November 2018 at 10.15 in A315: Ulf Danielsson (Uppsala)
Reflections on the dS swampland
Abstract: A review of recent claims that there are no de Sitter vacua in string theory. What are the consequences for dark energy and the multiverse?
- Tuesday 13 November 2018 at 10.15 in A315: Michael Ramsey-Musolf (UMass Amherst)
TeV Scale Lepton Number Violation: Neutrinoless Double Beta Decay and the LHC
Abstract: Determining the origin of neutrino masses remains a compelling challenge at the interface of nuclear and high energy physics. The standard see-saw neutrino mass mechanism postulates the existence of new lepton number violating (LNV) interactions at very high energy scales. In this talk, I consider the possibility that LNV interactions responsible for neutrino mass may exist at the TeV scale. I discuss how the interplay of searches for neutrinoless double beta decay and LHC searches for LNV processes may probe this possibility. I also discuss several theoretical issues pertaining to these searches for TeV scale LNV.
- Tuesday 20 November 2018 at 10.15 in A315: Jonathan Braden (University College London)
A New Real-Time Picture of Vacuum Decay
Abstract: Quantum decay of false vacuum states via the nucleation of bubbles may have played an important role in the early history of our Universe. For example, in multiverse models that utilize false vacuum eternal inflation, the Big Bang of our observable Universe corresponds to one of these bubble nucleation events. Further, our observable Universe may have undergone a series of symmetry-breaking first-order phase transitions as it cooled, which may have produced a remnant background of gravitational waves.
- Thursday 22 November 2018 at 14.00-14.30 in Exactum B123: Ville Keränen (OP Corporate Bank)
What does a theoretical physicist do in a bank?
Abstract: At first sight banking doesn’t seem like it would have much to do with theoretical physics. In this talk I will describe an example problem one faces in a bank (modelling stock prices to price derivatives) and will try to explain how it connects to theoretical physics, such as quantum field theory in curved spacetime.
- Tuesday 27 November 2018 at 10.15 in A315: José Manuel Penín Ascariz (Santiago de Compostela)
Anisotropic D3-D5 black holes with unquenched flavors
Abstract: We construct a black hole geometry generated by the intersection of Ncc color D3- branes and Nff flavor D5-branes along a 2+1 dimensional subspace. Working in the Veneziano limit in which Nff is large and distributing homogeneously the D5-branes in the internal space, we calculate the solution of the equations of motion of supergravity plus sources which includes the backreaction of the flavor branes. The solution is analytic and dual to a 2+1 dimensional defect in a 3+1 dimensional gauge theory, with Nff massless hypermultiplets living in the defect. The smeared background we obtain can be regarded as the holographic realization of a multilayered system. We study the thermodynamics of the resulting spatially anisotropic geometry.
Fermion Bags in Lattice Field Theory
Abstract: I introduce the fermion bag representation and two of its applications in the numerical study of quantum field theories. Using a simple dual representation of fermionic terms in the action, it enables an efficient simulation algorithm and avoids sign problems introduced by the standard auxiliary field representation. I present two applications of the method: the 2 dimensional lattice Thirring Model, a theory with critical scaling behaviour and a common case study of the sign problem, and a 4 dimensional model SU(4) symmetric four fermion model with a potentially interesting phase structure.