Seminars 2015 – Seminars

DEPARTMENT OF PHYSICS / HIP JOINT COLLOQUIA / SEMINARS 2015

Tuesday 20 January 2015 at 10.15 in A315: Alfonso Ramallo (Santiago de Compostela)
Cold holographic matter
Abstract: After a brief review of the Landau Fermi liquid theory, we will discuss a holographic modeling of cold matter in terms of D-brane intersections. We will analyze the different regimes of these systems as a function of the temperature and, in particular, their zero-sound and diffusion modes.
Tuesday 3 February 2015 at 10.15 in A315: Sven Heinemeyer (Santander)
Higgs and Supersymmetry
Abstract: The particle discovered in the Higgs boson searches at the LHC in 2012 can be interpreted as the lightest Higgs boson of the Minimal Supersymmetric Standard Model (MSSM), in perfect agreement with predictions {\em before} the discovery. We briefly review the relevant phenomenology of the Higgs sector of the MSSM and the implication of the Higgs discovery for the model. We discuss possibilities for searches for the manifestation of Supersymmetry in the Higgs sector, including deviations from the Standard Model predictions as well as the search for additional Higgs bosons.
Wednesday 4 February 2015 at 10.15 in A315: Katherine Freese (Nordita, Stockholm)
The dark side of the Universe
Abstract: What is the Universe made of? This question is the longest outstanding problem in all of modern physics, and it is the most important research topic in cosmology and particle physics today. The reason for the excitement is clear: the bulk of the mass in the Universe consists of a new kind of dark matter particle, and most of us believe its discovery is imminent. I’ll start by discussing the evidence for the existence of dark matter in galaxies, and then show how it fits into a big picture of the Universe containing 5% atoms, 25% dark matter, and 70% dark energy. Probably the best dark matter candidates are WIMPs (Weakly Interacting Massive Particles). There are three approaches to experimental searches for WIMPS: at the Large Hadron Collider at CERN in Geneva; in underground laboratory experiments; and with astrophysical searches for dark matter annihilation products. Currently there are claimed detections in multiple experiments — but they cannot possibly all be right. Excitement is building but the answer is still unclear. At the end of the talk I’ll turn to dark energy and its effect on the fate of the Universe.
Thursday 5 February 2015 at 10.15 in A315: James Pinfold (Edmonton)
The MoEDAL Experiment at the LHC – a New Light on the High Energy Frontier
Abstract: In 2010 the MoEDAL experiment at the Large Hadron Collider (LHC) was unanimously approved by CERN’s Research Board to start data taking in 2015. MoEDAL is a pioneering experiment designed to search for highly ionizing avatars of new physics such as magnetic monopoles or massive (pseudo-)stable charged particles. Its groundbreaking physics program defines over 30 scenarios that yield potentially revolutionary insights into such foundational questions as: are there extra dimensions or new symmetries; what is the mechanism for the generation of mass; does magnetic charge exist; what is the nature of dark matter; and, how did the big-bang develop. MoEDAL’s purpose is to meet such far-reaching challenges at the frontier of the field.The innovative MoEDAL detector employs unconventional methodologies tuned to the prospect of discovery physics. The largely passive MoEDAL detector, deployed at Point 8 on the LHC ring, has a dual nature. First, it acts like a giant camera, comprised of nuclear track detectors – analyzed offline by ultra fast scanning microscopes – sensitive only to new physics. Second, it is uniquely able to trap the particle messengers of physics beyond the Standard Model for further study. MoEDAL’s radiation environment is monitored by a state-of-the-art real-time TimePix pixel detector array. I shall also briefly discuss a new proposal to include a new active MoEDAL sub-detector to search for millicharged particles.
Tuesday 10 February 2015 at 10.15 in A315: K. Kajantie (Helsinki)
Phases and phase transitions of hot QCD with lots of massless quarks
Abstract: For this talk QCD has Nc=3 colors and we want to study what happens when the number of quarks, assumed to be massless, grows, Nf=0,3,6,… We pretend that these numbers are so big that we can use holography, solve the equation of state from a 5-dimensional gravity model. The chirally symmetric quark-gluon plasma phase then is straightforward: temperature and entropy are those of a classical gravity black hole solution. However, at low T there are hadrons, but there is no classical solution giving their hadron gas thermodynamics – there is a T=0 solution from which masses of low-lying states can be computed. So we approach the problem phenomenologically and put in an ansatz for the hadron spectrum. Because of chiral symmetry breaking there at low T are at least Nf^2 massless Goldstone bosons, further there is a partly calculable Hagedorn spectrum of massive states. We try to see how the properties of the chiral phase transition constrain the hadron gas model and show explicitly how the equation of state looks like for a third order phase transition. These phenomenological constructions can be interpreted as 1-loop or even stringy corrections to the classical gravity dual. The final word on phase transition properties lies with lattice Monte Carlo, but imposing zero quark masses is very difficult on the lattice.
Tuesday 17 February 2015 at 10.15 in A315: Jürgen Reuter (Desy)
Electroweak Vector Boson Scattering at the LHC after the Higgs discovery
Abstract: The Large Hadron Collider (LHC) has greatly enlarged our understanding of electroweak symmetry breaking by the discovery of a Higgs boson compatible with the Standard Model (SM) of Particle Physics. The LHC was guaranteed to contribute to this understanding before it was switched on because the process of scattering of the longitudinal modes of the electroweak gauge bosons would have entered a strong interaction regime in the LHC energy reach without the presence of a light Higgs particle. There was for the first time evidence of this scattering process in the 2012 LHC data. Delicate cancellations in its otherwise rising cross section makes this process an ideal telescope for searches of physics beyond the SM (BSM). Some prime examples will be shown as well as methods to theoretically consistently describe these searches in a model-independent way.
Wednesday 18 February 2015 at 10.15 in A315: Timo Alho (Reykjavik)
Finite temperature monopole correlations in holographically flavored liquids
Abstract: We study the phase structure of a (2 + 1) -dimensional many-body system with a global U(1) -current via top-down holography, at finite temperature. The non-perturbative infrared behaviour of such a system can be probed by inserting a monopole operator coupled to the U(1) -current to the field theory. Holographically, the operator is dual to a bulk magnetic monopole. The specific model is obtained by adding a probe D3 brane to the D3D5 intersection, such that the probe D3 ends on the D5, sourcing a magnetic charge. At finite temperature we find a series of transitions between various stable and metastable phases.
Wednesday 4 March 2015 at 16.00 (note time!) in A315: Matti Kalliokoski (CERN)
Beam Loss Monitoring and Machine Protection of the LHC for Run 2
Abstract: During Long Shutdown 1 (LS1) a series of modifications and updates to the LHC was made. These were done to allow the accelerator to reach 7 TeV and to improve the machine safety. One main part of the machine protection of the LHC is the Beam Loss Monitoring system (BLM). It consists of about 4000 monitors that have the task to prevent the superconducting magnets from quenching and protect the machine components from damage, as a result of critical beam losses. In this talk, modifications to the LHC Beam Instrumentation during the LS1, especially to the BLM system, are discussed.
Tuesday 10 March 2015 at 10.15 in A315: Olli Taanila (Nikhef)
Analytical models of holographic thermalization
Abstract: AdS/CFT is one of the very few tools we have to study the out-of-equilibrium dynamics of strongly coupled systems. I present several different analytical models of gravitational collapse which are dual to the thermalization of a strongly coupled field theory. The time evolution of several different observables are computed in these backgrounds, such as two point functions and entaglement entropy.
Friday 20 March 2015 at 10.15 in A315: Miklos Långvik (Marseille)
Applications of conformal SU(2,2) transformations to spinfoams and spin-networks
Abstract: We attempt the construction of the cotangent bundle of SU(2,2) as a symplectic manifold using an analogy to previous approaches. However, the manifold ends up being a Lagrangian submanifold. We then study and discuss different applications of it to spinfoam models. Most notably, the concept of a particle in a Poincaré invariant spacetime is discussed and the geometrical interpretation of our construction for full SU(2,2) is clarified. The talk will include a brief introduction to spinfoam models and especially a short review of how fermions enter spinfoams.
Thursday 26 March 2015 at 10.15 in A315: Laszlo Jenkovszky (Bogolyubov Institute for Theoretical Physics, National Ac. Sc. of Ukraine)
Regge factorization and diffraction dissociation at the LHC
Abstract: At the LHC, for the first time the nearly forward elastic scattering amplitude is completely determined by vacuum (Pomeron) exchange in the t-channel, making possible the full use of Regge factorization. Based on a simple Regge (Pomeron) pole exchange, different diffractive processes, including single, double proton dissociation as well as central production are related and compared with the existing LHC measurements.
Tuesday 7 April 2015 at 10.15 in A315: A. Rebhan (Wien)
Top-down holographic glueballs and their decay patterns
Abstract: I report recent results on the spectrum and the decay patterns of scalar and tensor glueballs in the top-down holographic Witten-Sakai Sugimoto model. This model, which has only one free dimensionless parameter, gives semi-quantitative predictions for the vector meson spectrum, their decay widths, and also a gluon condensate in agreement with SVZ sum rules. The predictions for glueball decay are compared with experimental data for some of the widely discussed gluon candidates in the meson spectrum.
Thursday 16 April 2015 at 10.15 in A315: Giacomo Cacciapaglia (Lyon, IPN)
Unveiling the dynamics behind a composite Higgs
Abstract: I will present a novel approach to composite Higgs model building, based on a simple fundamental dynamics. It allows to describe in a unified way the Higgs as a pNGB and as a Technicolor-like bound state. The status after the LHC Run I will be discussed, together with the interplay with Lattice calculations and possible avenues for model building.
Thursday 23 April 2015 at 10.15 in A315: Jorma Louko (Nottingham)
Did the chicken survive the firewall?
Abstract: The forty-year debate about the final state of an evaporating black hole was recently reinvigorated by the suggestion that if unitarity is preserved, the black hole horizon develops a “firewall” which a) affects strongly any matter that crosses it and b) erases any information that such matter may carry about the outside world.

We present evidence that neither a) nor b) is true for a firewall within flat spacetime quantum field theory, arguing that the same holds for sufficiently young gravitational firewalls. A firewall’s prospective capability to resolve the information loss paradox must hinge on its detailed gravitational structure, presently poorly understood.
Tuesday 28 April 2015 at 10.15 in A315: Dorota Sokolowska (Warsaw)
Dark matter in multi-scalar extensions of the Standard Model with discrete symmetries
Abstract: Multi-scalar extensions of the Standard Model can accommodate a viable Dark Matter candidate and modification of Higgs decay rates, particularly into two photons. One of the simplest choices for the extended scalar sector is the Inert Doublet Model, i.e. the Standard Model with an additional inert scalar doublet. The IDM can be further extended by extra doublets or singlets, which may modify both DM- and collider phenomenology.
In this talk I will discuss the the interplay between the LHC results for the decay of the SM-like Higgs into two photons and the properties of Dark Matter from Planck measurements. Constraints for multi-scalar models obtained in this way are stronger or comparable to the constraints provided by direct and indirect detection experiments for low, medium and high Dark Matter mass regions.
Tuesday 12 May 2015 at 10.15 in A315: Hans-Peter Nilles (Bonn)
Unification of Fundamental Interactions
Abstract: Symmetries have played a crucial role in the development of the standard model of particle physics. Moreover, they are believed to provide the key ingredients for a unified description of all fundamental interactions. We review the arguments that favour the investigation of these mathematical structures and explain possible consequences for particle physics and cosmology.
Tuesday 19 May 2015 at 10.15 in A315: Yago Bea (Santiago de Compostela)
Massive study of magnetized unquenched ABJM
Abstract: We study the physics of a magnetized probe D6-brane in the ABJM theory with unquenched massive flavor. We analyze the effect of the mass of the background branes in the magnetic catalysis of chiral symmetry breaking, and also the effect of the magnetic field on the meson spectrum. Besides, we obtain a non-commutative version of the background via a TsT rotation, which has an NSNS B2 field turned on, as an intermediate step towards a fully backreacted solution. In addition, we include new analytical solutions, perturbative in flavor, for the background functions.
Tuesday 2 June 2015 at 10.15 in A315: Stefan Pokorski (Warsaw)
Looking for hidden supersymmetry
Abstract: After a brief review of the state of supersymmetry after RUN I of the LHC, it will be argued that the supersymmetric electroweak sector may play the leading role in its discovery. Experimental signatures of electroweakinos and the prospects for their discovery will be discussed.
Tuesday 9 June 2015 at 10.15 in A315: Harvey Meyer (Mainz)
Real-time phenomena in finite-temperature QCD
Abstract: I present two topics in finite-temperature QCD: one concerns the pion quasiparticle and its dispersion relation in the low-temperature phase; the second concerns non-static screening masses in the high-temperature phase, the corresponding perturbative predictions and the relation of these masses to transport properties and the dilepton rate.
Thursday 11 June 2015 at 10.15 in A315: Carlos Hoyos (Oviedo)
Ward identities and transport in 2+1 dimensions
Abstract: The Hall viscosity of chiral superfluids is determined by the angular momentum density. One can understand and generalize this relation using Ward identities of the energy-momentum tensor. Furthermore, the same identities connect viscosities and conductivities. A preliminary analysis in AdS/CFT reveals that the identities seem to be non-trivial in the sense that they cannot be derived simply from the asymptotic expansion of the solutions.
Tuesday 18 August 2015 at 13.15 in A315; Note time!: Jacob Bekenstein (Hebrew University of Jerusalem)
Playing with quantum gravity on the tabletop
Abstract: Many would class the quantum theory of gravity as the number-one open problem in theoretical physics. The subject is at least seventy years old, but all along it has been almost exclusively a theoretical undertaking. After describing some currently planned experiments, I will focus on the quantum foam idea, and delineate the idea for a relatively simple tabletop experiment to expose it. This experiment relies on instrumentation which is routine in quantum optics. I will also examine sources of noise and strategies for their control.
Tuesday 8 September 2015 at 10.15 in A315: Robert Fleischer (Nikhef, Amsterdam)
In Pursuit of New Physics with B Decays: Theoretical Status and Prospects
Abstract: The exploration of B-meson decays has reached an unprecedented level of sophistication, with a phase of even much higher precision ahead of us thanks to the next run of the LHC and the future era of Belle II and the LHCb upgrade. For many processes, the theoretical challenge in the quest to reveal possible footprints of physics beyond the Standard Model will be the control of uncertainties from strong interactions. After a brief discussion of the global picture emerging from the LHC data, I will focus on the theoretical prospects and challenges for benchmark B decays to search for new sources of CP violation, and highlight future opportunities to probe the Standard Model with strongly suppressed rare B decays.
Thursday 10 September 2015 at 10.15 in A315: Aleksi Kurkela (CERN)
Hydrodynamisation in high energy nuclear collisions from QCD Lagrangian?
Abstract: Thermalisation, isotropisation and hydrodynamisation in high energy collisions of large nuclei has been studied in numerous models. I present a computation which is as close as possible to a first principle one starting from the QCD Lagrangian.
Thursday 10 September 2015 at 14.15 in E206: Yen Chin Ong (Nordita, Stockholm) Note place and time!
Hawking evaporation time scale of black holes in Anti-de Sitter spacetime
Abstract: If an absorbing boundary condition is imposed at infinity, an asymptotically Anti-de Sitter Schwarzschild black hole with a spherical horizon takes only a finite amount of time to evaporate away even if its initial mass is arbitrarily large. In fact this is a rather generic property for an asymptotically locally AdS spacetime: regardless of their horizon topologies, neutral AdS black holes in general relativity take about the same amount of time to evaporate down to the same size. We explain this surprising property in this talk.
Tuesday 29 September 2015 at 10.15 in A315: Jose Miguel No (Sussex)
Probing the Electroweak Phase Transition at LHC and Beyond
Abstract: Uncovering the nature of the electroweak (EW) phase transition in the early Universe would be key to shed light on the possible origin of the cosmic matter-antimatter asymmetry. We discuss various ways in which searches for new physics beyond the Standard model (SM) at LHC can be used to probe the nature of the EW phase transition, and their implications for the generation of the baryon asymmetry of the Universe at the EW scale.
Tuesday 6 October 2015 at 10.15 in A315: Jarno Rantaharju (Odense)
Lattice Four-Fermion Interactions for Beyond Standard Model Physics
Abstract: We present a study of a lattice model of chirally symmetric four-fermion interactions, the Nambu Jona-Lasinio model, with Wilson fermions. Four fermion operators are a necessary part of many models of beyond Standard Model physics. In particular we are interested in technicolor models, where effective four-fermion operators are used to generate the standard model fermion masses. In the ideal walking scenario, the same interaction is responsible for breaking the chiral symmetry in an otherwise conformal model. As a first step, we study the restoration and spontaneous breaking of chiral symmetry in the lattice NJL model before adding a gauge interaction. We map the phase structure of the model and establish chiral symmetry breaking.
Tuesday 13 October 2015 at 10.15 in A315: Alejandro Cabo (La Habana, Cuba)
Is a generalized NJL model the effective action of massless QCD?
Abstract: A local and gauge invariant alternative version of QCD for massive fermions introduced in previous works, is considered here to
propose a model which includes Nambu-Jona-Lasinio (NJL) terms in the action. The Lagrangian includes new vertices which at first sight look as breaking power counting renormalizability. However, these terms also modify the quark propagators, to become more convergent at large momenta, thus indicating that the theory is renormalizable. Therefore, it follows the surprising conclusion that the added NJL four fermion terms do not break renormalizability. The approach can also be interpreted as a slightly generalized renormalization procedure for massless QCD, which seems able to incorporate the mass generating properties for the quarks of the NJL model, in a renormalizable way. It also seems to have opportunity to implement Fritzsch’s Democratic Symmetry description of the quark mass hierarchy.
Thursday 15 October 2015 at 10.15 in A315: Tommi Alanne (CP3-Origins, Odense)
Elementary Goldstone Higgs and raising the fundamental scale
Abstract: We study an extension of the scalar sector of the Standard Model (SM) where the observed Higgs is a pseudo-Goldstone boson (pGB) associated with the global symmetry breaking pattern SU(4) to Sp(4). This particular breaking pattern is interesting, because depending on the embedding of the electroweak (EW) symmetry, the breaking of the global symmetry can either leave the full EW sector intact, break the EW completely to electromagnetism, or more interestingly lead to something between these two extreme cases. In the unbroken case, the entire Higgs doublet can be identified with four of the five Goldstone bosons of the global symmetry breaking.All of the different alignments of the EW symmetry are equivalent at the tree-level, but since the gauging of the electroweak sector and introducing Yukawa terms for the SM fermions break the global symmetry of the scalar sector, quantum effects determine a preferred vacuum alignment.

In this talk, I will present the main results of our study and show that very slightly broken EW symmetry is preferred. Therefore, the observed Higgs boson is dominantly a pGB, and interestingly the electroweak scale emerges due to the alignment of the EW sector in the global symmetry, whereas the fundamental scale of the spontaneous symmetry breaking is significantly higher.
Tuesday 20 October 2015 at 10.15 in A315: Timo Alho (Reykjavik)
Geometric Algebra: a coordinate free formalism for inner product spaces
Abstract: Geometric Algebra (GA) is a mathematical system defined by imbuing the vectors of an inner product space directly with the Clifford algebra generated by the inner product, without considering a separate representation of the algebra operating on the vectors. This simple change in point of view gives a system which generalizes exterior algebra, quaternions, spinors, and many other algebras used in theoretical physics, while simplifying both concepts and calculations. This talk will open a brief course on the algebra and its extension to geometric calculus. During the talk we will primarily give elementary details of the formalism, with more advanced topics to be handled later during the course. Some applications are pointed out for motivation.
Thursday 22 October 2015 at 10.15 in A315: Timo Alho (Reykjavik)
Geometric Algebra: a coordinate free formalism for inner product spaces
Abstract: Continuation of the lecture on Tuesday.
Tuesday 27 October 2015 at 10.15 in A315: Alexander Merle (MPI, Munich)
Sterile Neutrino Dark Matter: From Particle to Astrophysics and back
Abstract: In the absence of a clear WIMP signal, we should think about alternative candidates for Dark Matter. A very well motivated example is a (up to now hypothetical) sterile neutrino with a mass of a few keV. In this talk, I will give an overview over the topic of keV sterile neutrino Dark Matter, thereby exploring all corners from Dark Matter production in the early Universe over astrophysical bounds and neutrino phenomenology to particle physics model building aspects. While WIMPs are not dead yet, they have to learn how to live in the neighbourhood of serious competitors.
Tuesday 3 November 2015 at 10.15 in A315: Lene Bryngemark (Lund)
Search for physics beyong the Standard Model using dijet distributions in ATLAS
Abstract: The LHC gives us access to the highest collider energies, at the highest intensities, providing a unique opportunity to thoroughly examine the constituents of matter and their interactions at ever smaller distances and higher mass scales. Produced in the strong — or a new, previously unseen — interaction, jets probe the very energy frontier. With the recent increase in LHC beam energy, ATLAS makes use of this sensitivity to make its first statements of what physics looks like in a new energy regime. In this presentation I show the results from both the 8 and the more recent 13 TeV analysis of dijet mass and angular distributions.
Thursday 5 November 2015 at 10.15 in A315: David Daverio (Geneva)
Large scale structure formation within a general relativistic framework
Abstract: One century after the conception of General Relativity (GR), there is still a large pool of predictions we still have difficulties to get. Indeed, to give only one example, large scale structure formation is still simulated within a Newtonian framework. This framework, even well suited for cosmology as it can be understood as a week field quasi static approximation of GR, does not take into account the propagating degree of freedom of GR and is not well suited to include relativistic sources such as neutrinos. Recently, the first code aiming to simulate large scale structure within a general relativistic framework has been developed. This code, gevolution, solves GR in the weak field limit using the approximation scheme proposed in Adamek et al. 2014 and is constructed on top of the framework LATfield2 which manages the particles and provides a scalable parallelisation allowing to run with lattice of 4096^3 cells with one particle per cell on 16k processes. In this talk we will discuss the method used to develop this code and first results of cold dark matter simulation will be presented.
Tuesday 10 November 2015 at 10.15 in A315: David Salek (Amsterdam)
Dark matter (and dark mediators) at the LHC
Abstract: The LHC results on dark matter from Run-1 were mostly interpreted in the framework of effective field theories. Simplified models involve new mediators between the Standard Model and the Dark Sector and allow for richer phenomenology and more complex interpretations. Possible dark matter search strategies at the LHC in Run-2 will be discussed.
Thursday 12 November 2015 at 14.15 in E207 (note place): Jaeyoung Park (Energy Matter Conversion Corporation, San Diego)
Polywell Fusion – Electric Fusion in a Magnetic Cusp
Abstract: Nuclear fusion power is considered the ultimate energy source because of its nearly inexhaustible supply of cheap fuels,
intrinsic safety, zero carbon emissions and lack of long-lived radioactive waste. In this talk, I will introduce the Polywell fusion concept that may offer a low cost and rapid development path to power the world economically and sustainably. As conceived by Dr. Robert Bussard at Energy Matter Conversion Corporation (EMC2) in 1985, the Polywell fusion concept combines electric fusion with magnetic cusp confinement. This allows the Polywell reactor to be small, stable, and highly efficient. Recently, EMC2 carried out an experiment that demonstrated dramatically improved high-energy electron confinement in a magnetic cusp system operating at beta (=plasma pressure/magnetic field pressure) near 1. This result has significant implications for cusp related schemes for producing controlled nuclear fusion power.
Tuesday 17 November 2015 at 10.15 in A315: Georgios Itsios (Santiago de Compostela)
Exploring cold holographic matter
Abstract: In this talk we discuss aspects of cold matter using holographic techniques. Our holographic description is realized through a top-down approach, in which we consider D-brane intersections of different dimensionalities. We will analyze several properties of these systems such as the speed of first sound, the diffusion constant and the speed of zero sound. We also discuss the specific case of the D3-D5 intersection with a non-zero flux across the internal part of its worldvolume.
Thursday 19 November 2015 at 10.15 in A315: Joonas Nättilä (Tuorla, Turku)
Equation of state for the dense matter inside neutron stars using thermonuclear explosions
Abstract: In my talk I will describe how observations of thermonuclear explosions on top of neutron stars ends up constraining the size of these ultra-compact objects. I will also show how we can model these explosions and how the atmosphere of the star modifies the emerging spectrum. As it turns out, good understanding of the physics behind these powerful bursts is also crucial for accurate mass and radius measurements. From the size measurements we can then obtain a parametrized equation of state of the cold dense matter by using Bayesian methods. This allows us to set limits on some nuclear parameters and to constrain an empirical pressure-density relation for the dense neutron matter.
Tuesday 24 November 2015 at 10.15 in A315: Jacopo Ghiglieri (Bern)
Gravitational wave background from Standard Model physics
Abstract: Any plasma in thermal equilibrium emits gravitational waves, caused by physical processes such as macroscopic hydrodynamic fluctuations and microscopic particle collisions. We will show that, for the largest wavelengths, the emission rate is due to the former process and is proportional to the shear viscosity of the plasma. In the Standard Model at T > 160 GeV, the shear viscosity is dominated by the most weakly interacting particles, right-handed leptons, and is relatively large. We estimate the order of magnitude of the corresponding spectrum of gravitational waves. At smaller wavelengths the leading contribution is given by particle collisions, which we also estimate at leading logarithmic order. Even though at small frequencies (corresponding to the sub-Hz range relevant for planned observatories such as eLISA) this SM background is tiny compared with that from non-equilibrium sources, we conclude that the total energy carried by the high-frequency part of the spectrum is non-negligible if the production continues for a long time. Finally, we suggest that this may constrain (weakly) the highest temperature of the radiation epoch. Observing the high-frequency part directly sets a very ambitious goal for future generations of GHz-range detectors.
Thursday 26 November 2015 at 14.15 in E207 (note place!): Albert de Roeck (CERN)
The Large Hadron Collider: The Present and the Future.
Tuesday 1 December 2015 at 10.15 in A315: Heribert Weigert (Cape Town)
QCD at small high energies: Wilson line correlators in the Color Glass Condensate and beyond
Abstract: Modern collider experiments use ever higher energies for many reasons, be it to study the QCD phase transition, to study the newest confirmed addition to the Standard Model or to search for physics beyond the standard model. In all of his QCD plays a central role, be it the immediate area of study (as with the quark gluon plasma) or as the main limiting factor on precision (as with standard model particle physics). Over the last decade it has been established that at small x the machinery and phenomenology of the Color Glass Condensate provide powerful tools to study the energy dependence of cross sections for a wide range of observables. Its evolution equation, the JIMWLK equation has a structural analogue in jet evolution equations (the BMS equation and its finite Nc generalizations) with a conformal map establishing the connection. The key ingredient that drives cross sections in all these cases are Wilson line correlators which also appear in GPDs and in energy loss calculations aiming at studying the QCD as a medium. This is clearly too big a canvas to fill with paint completely with one talk, instead, I will content myself with the first steps needed to expose these connections, starting from JIMWLK and the CGC, and show some ideas of how to study and analyze the underlying structures.
Thursday 10 December 2015 at 14.15 in E206 (note place!): David Milstead (Stockholm)
A new high precision search for neutron-antineutron oscillations at the ESS
Abstract: In this talk I shall discuss how a search for neutron-antineutron oscillations can be carried out at the European Spallation Source. It will be shown how such oscillations can provide a unique probe of some of the central questions in particle physics and cosmology: the energy scale and mechanism for baryon number violation, the origin of the baryon-antibaryon asymmetry of the universe, and the mechanism for neutrino mass generation. An overview of the proposed experiment and its capability to a sensitivity to the oscillation probability, which is three orders of magnitude greater than previously obtained, will be given. The international collaboration which has been formed to carry out the proposed work will also be described.
Thursday 17 December 2015 at 10.15 in A315: Martin Krššák (Sao Paulo)
Teleparallel gravity and the role of inertia in theories of gravity
Abstract: The central role in general relativity is played by the principle of equivalence, which suggests that gravity and inertia are locally indistinguishable, and it is hardcoded into general relativity through the use of the Levi-Civita geometry. In this talk, I will present an interesting work-around to this problem known as teleparallel gravity. It can be understood as a dual theory to general relativity, where gravity is attributed to torsion of spacetime, rather than curvature. As it turns out, in this theory it is possible to separate (non-locally) the problematic inertial contributions from gravity, and define the finite, purely gravitational, action. I will show that this subtraction of the inertial effects closely resembles holographic renormalization, and discuss its applications in holography and modified gravity.
Friday 18 December 2015 at 10.15 in A315: Ville Keränen (Oxford, Note day!)
Thermalization in the AdS/CFT duality
Abstract: We study examples of out of equilibrium systems in the context of the AdS/CFT duality. We attempt to draw general conclusions from these studies and in particular will highlight the role of black hole quasinormal frequencies in determining the rate at which these systems approach thermal equilibrium.