text:
# DEPARTMENT OF PHYSICS / HIP JOINT COLLOQUIA / SEMINARS 2010

• Tuesday 19 January 2010 at 10.15 in E204: Luigi Del Debbio (Edinburgh University)
Strongly interacting theories beyond the Standard Model
Abstract: Novel technicolor theories have been proposed, that could be viable candidates to describe physics beyond the standard Model, to be unveiled at the LHC. Lattice simulations are a privileged tool to investigate the nonperturbative behaviour of these theories. I present results from recent lattice simulations, and discuss their implications for phenomenology.
• Tuesday 26 January 2010 at 10.15 in E204: M. Vepsäläinen (Helsinki University)
Dimensionally regularized Polyakov loop correlators in hot QCD
Abstract: The static potential between a heavy quark and an antiquark is modified when they a subjected to thermal environment. In particular, in the deconfined phase of QCD the free color charges screen the potential, leading eventually to the dissociation of heavy quark bound states. At finite temperature the potential is usually computed on lattice by correlating loops around (periodic) time direction. I will review our recent perturbative results on these correlators and discuss the theoretical shortcomings in using them to define the potential. Finally, I will point out a recent suggestion on how to non-perturbatively define a gauge invariant quark-antiquark static potential. (arxiv: 0911.3480)
• Tuesday 2 February 2010 at 10.15 in E204: Sean Nowling (University of Helsinki)
Solitons in Holographic Superfluids
Abstract: The gauge/gravity duality provides a new set of tools for exploring the physics near 2+1 dimensional quantum critical points. In many highly quantum states of matter, soliton configurations yield clues about the physics of both large and small length scales. I will review a holographic model for a relativistic superfluid. I will then discuss dark soliton and vortex solutions supported by this superfluid. (arxiv:0911.1866 and 0912.4280)
• Tuesday 9 February 2010 at 10.15 in E204: Jyrki Piilo (University of Turku)
Open systems with memory
Abstract: The theory of open quantum systems describes the dynamics of a system of interest interacting with its environment. When the environment has nontrivial structure, the system dynamics exhibits non-Markovian memory effects. We have recently developed a non-Markovian quantum jump description for such systems. The basic idea and insight is that the negative rates associated to non-Markovian quantum processes allow the system undo an event which happened earlier. In the more general stochastic process framework, this leads to the manifestation of memory as certain correlations between the realizations of the stochastic process. We conclude by discussing how one can define a measure for memory based on quantifying the information flow between the system and its environment. Essentially, in non-Markovian systems the information flow between the system and the environment gets temporarily reversed, and the system regains part of the information that it earlier leaked to the environment. In other words, in Markovian systems the distinguishability between any pair of states always decreases with time while in non-Markovian systems the distinguishability temporarily increases due to the memory. (See http://physics.aps.org/synopsis-for/10.1103/PhysRevLett.103.210401).
• Thursday 11 February 2010 at 10.15 in A315: W. Horowitz (Ohio State University)
Jet quenching, perturbative QCD and AdS/CFT
Abstract: The basic theoretical and experimental tools of heavy ion phenomenology are reviewed, including the recent application of AdS/CFT to bulk QCD physics. Jet suppression is argued to be a unique tool for studying collective degrees of freedom for the problem. Paying special attention to high momentum probes, we discuss the qualitative successes of both perturbative QCD and AdS/CFT and propose novel experimental observables for falsifying one or both sets of calculations. The extension of AdS heavy quark drag to both hot and cold nuclear matter, giving greater confidence in the universality of those results, is presented. Time permitting, the assumptions underpinning the pQCD derivations will be discussed leading to quantitative estimates of a systematic theoretical uncertainty for perturbative predictions in jet quenching.
• Tuesday 16 February 2010 at 10.15 in E204: Marco Panero (ETH Zürich)
Hot, colorful and strongly interacting
Abstract: The gauge/gravity correspondence developed in String Theory provides powerful analytical techniques to study strongly interacting systems, and is hoped to eventually lead to a theoretical description of the nearly inviscid, strongly coupled fluid produced in heavy ion collision experiments. However, most of the predictions that have been worked out in this approach rely on the mathematical simplifications taking place when the rank of the gauge group is infinite, and it is not obvious whether they can also be accurate for the physical case of a quark-gluon plasma with N = 3 colors. In this talk, I present lattice simulations of SU(N) gauge theories with 3, 4, 5, 6, and 8 colors, and their extrapolation to the large-N limit. The results reveal that the equation of state is only mildly dependent on N, and that the equilibrium properties of the strongly interacting plasma can be successfully described by gauge/gravity models. Furthermore, for all gauge groups investigated, the trace anomaly appears to exhibit a characteristic dependence on the temperature, perhaps induced by contributions of non-perturbative origin. The implications of these results, as well as some future research lines, are pointed out. (arXiv:0907.3719)
• Tuesday 9 March 2010 at 10.15 in E204: Janne Alanen (University of Helsinki)
Thermodynamics of infrared fixed point and walking technicolor field theories from gauge/gravity duality
Abstract: I discuss applications of gauge/gravity duality to derive the thermodynamics of a field theory with asymptotic freedom in the ultraviolet and a fixed point in the infrared. One finds that the theory has a high temperature quark-gluon phase and a low $T$ conformal unparticle phase. The phase transition between the phases is of first order or continuous, depending on the ratio of the radii of asymptotic AdS$_5$ spaces at $T=0$ and $T=\infty$. The method also applies to theories of walking technicolor type with a nearly conformal beta function at some intermediate value of the coupling. Then one finds three phases with phase transitions in between. The results are predictions from a model of gauge/gravity duality. (arXiv:0912.4128)
• Tuesday 23 March 2010 at 10.15 in E204: Valery Nesvizhevsky (Institute Laue-Langevin, Grenoble)
Gravitational and centrifugal quantum states of neutrons and fundamental short-range interactions
Abstract: The “whispering gallery” effect is known since ancient times for sound waves in air, later in water, more recently for electromagnetic waves of a broad range: radio, optics, Roentgen etc. It consists of wave localization near a curved reflecting surface. It is expected for waves of various nature, for instance, for atoms and neutrons. For matter waves it would include a new feature: a massive particle would be settled in quantum states, with parameters depending on its mass. Here, we present for the first time the quantum whispering gallery effect for cold neutrons. Deeply bound whispering gallery states are long-living and weakly-sensitive to surface potential; highly excited states are short-living and very sensitive to the wall potential shape.
This phenomenon provides an example of an exactly solvable problem analogous to the “quantum bouncer”. It is complementary to the recently discovered gravitationally bound quantum states of neutrons. In relation to this analogy we present also the GRANIT project aiming at improvement of accuracy of measurement of the quantum states parameters by several orders of magnitude, taking advantage of long storage of ultracold neutrons at specular trajectories and resonance transitions between the gravitationally bound quantum states of neutrons.
These two experiments are motivated by searches for short-range interactions (spin-independent and spin-dependent ones), by studying the interaction of a quantum system with a gravitational field, by searches for extensions of the Standard model, by the unique possibility to check the equivalence principle for an object in a quantum state and by studying various quantum optics effects. These two phenomena provide the first direct demonstration of the weak equivalence principle for a massive particle in a pure quantum state.
• Tuesday 30 March 2010 at 10.15 in E204: David Weir (Imperial College, London)
The quantum mechanics of topological defects
Abstract: Topological solitons are a ubiquitous feature of high energy physics, cosmology and also condensed matter physics due to their formation in symmetry breaking phase transitions. Unfortunately, perturbative results are limited and so many calculations are performed classically or in supersymmetric theories. In this seminar lattice Monte Carlo simulations are proposed as a nonperturbative method of studying topological solitons, their excitations and interaction form factors in the full quantum theory. Using the scalar kink and the ‘t Hooft-Polyakov monopole as prototypes, the use of correlation functions in sectors of fixed topological charge is demonstrated.
• Tuesday 13 April 2010 at 10.15 in E204: Sabrina Maniscalco (University of Turku)
Long life to quantum correlations!
Abstract: The interaction between a quantum system and its environment causes the rapid destruction of crucial quantum properties, such as the existence of quantum superpositions and of quantum correlations in composite systems. Decoherence and dissipation caused by the environment are responsible for the extreme fragility of quantum states and explain why quantum phenomena appear so weird to our eyes and our mind, used to deal with everyday classical objects. Moreover, decoherence is the major enemy of quantum technologies such as quantum computers and quantum communication devices. Is there any environment-resistant quantum property? Is there any physical system in which quantum correlations can survive, completely unaffected by the environment? After reviewing the main results on the quantum to classical transition, I will present the first evidence of the existence of a positive answer to these questions. The discovery of environment-resistant quantum correlations unveils a new feature of one of the most fundamental and fascinating aspects of quantum theory and may be a key breakthrough on quantum technologies. (arxiv:1001.5441)
• Tuesday 20 April 2010 at 10.15 in A315: William M. Morse (Omega group, Brookhaven National Laboratory)
g-2 of the muon, and electric dipole moment of the muon, proton, and deuteron
Abstract: After we finished the muon g-2 experiment at Brookhaven we began thinking about a dedicated experiment to measure the edm of the muon. This led to new ideas to measure the edm of the proton and the deuteron at the level of 10-29 ecm, 10^3 times better than the present limit on the edm of the neutron. The experimental challenges will be discussed.
• Wednesday 21 April 2010 at 14.15 in D101: Stuart Kauffman (Tampere University of Technology, University of Calgary and the Santa Fe Institute), joint HIP/Mathematics seminar, note time!
Mind, brain, consciousness, and the quantum observer: A speculative lecture
Abstract:The talk is a very speculative attempt to point out a new “poised realm” between quantum and classical behavior where long lived partial decoherence can persist. This opens lots of possibilities for potential new physics, answers to old philosophy of mind problems we’ve had since Descartes, and maybe maybe even how a conscious human observer could be, as Bohr said, “constitutive of the world”.
• Tuesday 27 April 2010 at 10.15 in E204: Shahin Sheikh-Jabbari (IPM, Tehran)
M-flation: Inflation From Matrix Valued Scalar Fields
Abstract: We study an inflationary setup in which the inflaton fields are matrix valued scalar fields with a generic quartic potential, M-flation. We analyze the rich landscape of multi-field inflationary models which arise from M-flation. As examples we study the single field and two field inflationary models in the M-flation landscape. Within our setting we find a natural solution to the generic problems of chaotic inflationary models, the super-Planckian field values and unnaturally small couplings, while still producing considerable amount of gravity waves that can be probed by future CMB polarization experiments such as PLANCK, QUIET and CMBPOL.
• Tuesday 4 May 2010 at 10.15 in E204: Joaquin Drut (Ohio State University)
From lattice QCD to cold atoms and graphene: new methods for strongly interacting fermions.
Abstract: Sophisticated algorithms and hardware advances, recent and not-so-recent, have propelled the field of lattice QCD to the forefront of large-scale high-performance computing. Are condensed matter theorists reaping the benefits of these developments? In this talk I will discuss two cases in which lattice QCD methods are directly applicable to condensed matter systems: graphene and cold atoms in the BEC-BCS crossover.
In the case of graphene, those methods have allowed us to study the onset of spontaneous chiral symmetry breaking in the non-perturbative regime of strong Coulomb coupling. We have found that this phenomenon is likely to occur in suspended graphene samples as a second order phase transition.
The same advanced algorithms are making it possible to perform large-scale simulations of cold atoms in the BEC-BCS crossover, surpassing the limitations of determinantal Monte Carlo and allowing us to get closer to the thermodynamic limit. I will give an overview of the current status of the field focusing on the unitary limit, where numerical simulations are essential as the system is maximally strongly coupled.
• Tuesday 11 May 2010 at 10.15 in A315: Larus Thorlacius (Nordita)
Non-Fermi-liquid behavior via gravity
Abstract: Gravity models realizing anisotropic scaling symmetry provide a holographic rendition of strongly coupled quantum critical points, with finite temperature effects encoded in the spacetime geometry of black holes. Relatively simple holographic models of this type reproduce, at a qualitative level, several aspects of non-Fermi-liquid behavior observed in strongly correlated electron systems in two and three spatial dimensions.
• Tuesday 25 May 2010 at 10.15 in A315: Murat Günaydin (Penn State University)
Minimal unitary representations, AdS/CFT dualities and supersymmetry
Abstract: Noncompact groups enter theoretical physics in three major ways, namely as spacetime symmetry groups, as internal symmetry groups such as U-duality groups in supergravity and as spectrum generating symmetry groups. Some of these noncompact groups admit supersymmetric extensions to supergroups. I will review a unified approach to the construction of minimal unitary representations of noncompact groups and supergroups and discuss their fundamental importance to AdS/CFT dualities and to spectrum generating extensions of U-duality groups. (blackboard talk)
• Tuesday 1 June 2010 at 10.15 in A315: Jose Gracia-Bondia (University of Zaragoza)
Quantum gauge models without classical Higgs mechanism
Abstract: Current orthodox accounts in particle physics about the scalar sector of the Standard Model and GUTs seem to be of two kinds. On the one hand, one finds the assertion that the Higgs(–Englert–Brout–Guralnik–Hagen–Kibble) mechanism is necessary to give particles their mass. On the other hand, the Higgs sector itself is often seen almost as a blemish, completely ad-hoc, unmotivated and not part of a gauge theory. We re-examine the status of massive gauge theories, from a viewpoint in which massive vector bosons are taken as fundamental particles, and BRS invariance as the fundamental symmetry of gauge theory. This framework explains the presence of physical Higgs particles, which become thus part and parcel of quantum gauge theory. The phenomenological Lagrangians stemming from spontaneous symmetry breakdown appear under a new light.
• Tuesday 15 June 2010 at 10.15 in A315: Carl M. Bender (Washington University St. Louis)
Making sense of non-Hermitian Hamiltonians
Abstract: The average quantum physicist on the street believes that a quantum-mechanical Hamiltonian must be Dirac Hermitian (invariant under combined matrix transposition and complex conjugation) in order to guarantee that the energy eigenvalues are real and that time evolution is unitary. However, the Hamiltonian H=p^2+ix^3, which is obviously not Dirac Hermitian, has a real positive discrete spectrum and generates unitary time evolution, and thus it defines a fully consistent and physical quantum theory. Evidently, the axiom of Dirac Hermiticity is too restrictive. While H=p^2+ix^3 is not Dirac Hermitian, it is PT symmetric; that is, invariant under combined space reflection P and time reversal T. The quantum mechanics defined by a PT-symmetric Hamiltonian is a complex generalization of ordinary quantum mechanics. When quantum mechanics is extended into the complex domain, new kinds of theories having strange and remarkable properties emerge. Some of these properties have recently been verified in laboratory experiments. If one generalizes classical mechanics into the complex domain, the resulting theories have equally remarkable properties. [This talk will be presented at an elementary colloquium-style level and will be easy to understand and broadly accessible.]
• Tuesday 22 June 2010 at 10.15 in A315: Priyotosh Bandyopadhyay (KIAS, Seoul, Korea)
Displaced Higgs production in type III seesaw at the LHC
Abstract: I will talk about supersymmetric type III seesaw model. Here the scalar partners of the triplet fermions could include the lightest supersymmetric particle and so a dark matter candidate. I will discuss the case with a bino like NLSP and one of these scalar partners of triplet fermions as LSP candidate, especially I’ll consider the three body and two body decay widths. The three body decay can give rise to displaced Higgs production and can be a signature of this model.
• Monday 28 June 2010 at 10.15 in A315: Antonio Pich (Valencia)
Flavour phenomenology on the “aligned” two-Higgs-doublet model
Abstract: TBA
• Tuesday 3 August 2010 at 10.15 in A315: Alexander Dolgov (University of Ferrara, Italy)
Condensation of electrically charged bosons in solid state and cosmology
Abstract: Screening of impurities in plasma in presence of Bose condensed electrically charged fields is considered. It is shown that the condensate drastically changes the asymptotic behavior of the screened potential. In particular, the exponential Debye screening is transformed into a power law one. Moreover, the screened potential oscillates similar to the Friedel oscillations found for fermions in the middle of the previous century. The Bose condensate of charged vector bosons is also considered. The condensate may be in two possible states: ferromagnetic or antiferromagnetic. It is shown that in the minimal electroweak model W-bosons condense in ferromagnetic state. This could lead to spontaneous magnetization of the primeval plasma and generate seed fields necessary for creation of large scale cosmological magnetic fields.
• Thursday 5 August 2010 at 10.15 in A315: Eliezer Rabinovici (Hebrew University, Jerusalem)
Abstract: I will discuss work with J. Barbon on the holographic duals of the bubbles causing vacuum decay in AdS spaces. Lessons on the fate of big crunch singularities and their resolution will be drawn.
• Tuesday 17 August 2010 at 10.15 in A315: Francois Englert (Universite Libre de Bruxelles, Belgium)
The hidden horizon and black hole unitarity
Abstract: Since the theoretical discovery of black hole evaporation through Hawking radiation the question of the unitarity of its evolution has been a major challenge for our understanding of black hole physics and of quantum physics in general. Conventionally, one seems to be faced with an alternative: either there is, as in the original Hawking derivation, no information in the thermal state and unitarity is violated, or the information is contained in the radiation and unitarity is preserved, but then the Hawking derivation appears to be essentially incorrect. Violating unitarity is difficult to believe, in particular in view of some theoretical achievements of string theories and of the AdS-CFT correspondence. On the other hand, the simplicity of the Hawking derivation and the consistency of its conclusions with the Bekenstein entropy makes one reluctant to disregard it.
Our basic ingredient to cope with the unitarity issue and transcend the alternative is the following. In conventional relativistic field theory, the S-matrix describing elementary particle interactions is evaluated in a flat background. If coupling to gravity is included, distinct S-matrix elements may, in principle, require distinct backgrounds. We shall argue that this effect indeed dramatically affects the black hole S-matrix.
More precisely we propose a scheme in which the semi-classical approximation of a unitary black hole S-matrix in a space-time without horizon leads to the conventional approach in a space-time endowed with a classical event horizon. The latter follows from saddle point contribution to inclusive S-matrix amplitudes, while unitarity is borne out by the more detailed exclusive S-matrix amplitudes. Although the computations of unitary amplitudes would require a detailed theory of quantum gravity, the proposed scheme itself, which appeals to the metric description of gravity only in the vicinity of stationary points, does not.
• Wednesday 18 August 2010 at 14.15 in A315: Francois Englert (Universite Libre de Bruxelles, Belgium)
Broken symmetries
Abstract: – Physics, as we know it, is an attempt to interpret the diverse phenomena as particular manifestations of general testable laws. This vision of a world ruled by general testable laws is relatively recent. Essentially it started at the Renaissance and experienced a rapid development. The crucial ingredient was the inertial principle, initiated by Galileo (1564-1642), which essentially states that the uniform motion of a system does not affect the physics within the system and hence cannot be detected by an experiment performed within the system. This is a profound idea: the very fact that we do not feel such a motion confirms the universality of the Galilean physics approach to the understanding of nature in the sense that we ourselves may be viewed as a physical system.
– Starting from the inertial principle, Newton formulated at the end of the 17th Century the celebrated universal law of gravitation. He envisaged the world as composed of small interacting entities, which we now call elementary particles. In the 19th century, Maxwell established the general laws of electromagnetism explaining electric and magnetic phenomena as well as the propagation of light. These laws were expressed in terms of a field, that is an object filling an extended region of space, propagating like a wave with the velocity of light and transmitting electric and magnetic interactions. The notions of particles and waves were unified in a subtle manner during the first decades of the 20th Century in Quantum Mechanics and the inertial principle was extended by Einstein to electromagnetism in the theory of Relativity. On the other hand the Newtonian law of gravitation was generalized by Einstein in 1915. The new theory of gravity, called General Relativity, opened to scientific investigation the cosmological expansion of the universe. These impressive developments in the first half of the 20th Century made it conceivable that all phenomena, from the atomic level to the edge of the visible universe, be governed solely by the known laws of classical general relativity and quantum electrodynamics, the quantum version of Maxwell.s electromagnetic theory.
– Gravitational and electromagnetic interactions are long range interactions, meaning they are felt by objects, no matter how far they are separated from each other. But the discovery of subatomic structures revealed the existence of other fundamental interactions that are short range, being negligible at larger distance scales. In the beginning of the 60s, the theoretical interpretation of short range fundamental interactions seemed to pose insuperable obstacles.
– The breakthrough came from the notion of spontaneous symmetry breaking introduced in field theory by Nambu in 1960. In 1964 Brout and Englert, and then independently Higgs, discovered a mechanism based on spontaneous symmetry breaking by which short range interactions are generated from long range ones. The mechanism of Brout, Englert and Higgs, allowed the theoretical analysis of short range forces by unifying in the same theoretical framework the two type of forces. This discovery, which will be explained in detail in this talk, permitted to extend laws known at the macroscopic level to the nuclear and the subnuclear levels and opened the way to a modern view of unified laws of nature
• Tuesday 7 September 2010 at 10.15 in E204: Saurabh Rindani (Physics Research Lab, Ahmedabad)
TBA
Abstract: TBA
• Tuesday 31 August 2010 at 10.15 in A315: Carl E. Carlson (College of William and Mary, Williamsburg, USA)
Connecting dark matter to electrons and positrons: low energy terrestrial experiments and the galactic center 511-keV line
Abstract: A number of astrophysical observations have motivated speculative explanations involving dark matter. This talk will review the dark matter scenario underlying the speculation; explain how experiments at terrestrial electron accelerator laboratories, like JLab or MAMI, can test the scenario; and, returning to some of the original observations, discuss how the observed angular profile of our galactic center 511-keV photon excess can allow us to select among combinations of particular dark matter (and other) positron production mechanisms and particular models for the dark matter distribution.
• Tuesday 14 September 2010 at 10.15 in E204: S. D. Odintsov (Space Research Institute (ICE) CSIC and ICREA, Barcelona)
Modified gravity as unification of inflation with dark energy: from conventional theory to Horava-Lifshitz gravity
Abstract: We give a general review of several 4-dimensional models of modified gravity: F(R) theory, Gauss-Bonnet gravity, non-local gravity and Horava-Lifshitz F(R) theory. Qualitatively, the possibility to unify the inflation with dark energy in such an approach, through cosmological reconstruction procedure, is demonstrated. The models may pass the local and cosmological tests and have a very rich cosmological structure.
• Tuesday 21 September 2010 at 10.15 in E204: Saurabh Rindani (Physics Research Lab, Ahmedabad)
Probing new physics at and e+e- collider with polarized beams
Abstract: A future linear e+e- collider operating at a centre-of-mass energy of a few hundred GeV would provide detailed information on properties of standard model particles, as well as probe new physics. It is expected that the electron as well as positron beams at such a collider would be polarized. Both longitudinal and transverse polarizations would be feasible. The talk will first describe how certain model-independent features of physics beyond the standard model may be deduced from a study of the kinematics of processes with polarized beams. Special emphasis will be placed on CP properties of new interactions. Next, a detailed discussion on the advantages of beam polarization in the simultaneous independent determination of trilinear anomalous couplings of a Higgs particle to two gauge bosons (ZZ or gamma Z) will be presented.
• Thursday 23 September 2010 at 14.15 in CK112 (Exactum): Special lecture in Finnish:
HIPin CMS-ohjelman johtaja Jorma Tuominiemi jää eläkkeelle 1.10.2010 alkaen ja pitää luennon

Puoli vuosisataa kokeellista hiukkasfysiikkaa
Esitelmän jälkeen on kahvitarjoilu.
• Tuesday 28 September 2010 at 10.15 in E204: Paula Eerola (Department of Physics and HIP)
New results from CMS
Abstract: TBA
• Tuesday 5 October 2010 at 10.15 in E204: Hannu Holopainen (Jyväskylä)
Event-by-event hydrodynamics and elliptic flow from fluctuating initial state
Abstract: We develop a framework for event-by-event ideal hydrodynamics to study the differential elliptic flow which is measured at different centralities in Au+Au collisions at Relativistic Heavy Ion Collider (RHIC). Fluctuating initial energy density profiles which here are the event-by-event analogues of the eWN profiles, are created using a Monte Carlo Glauber model. Using the same event plane method for obtaining v_2 as in the data analysis, we can reproduce both the measured centrality dependence and the p_T shape of charged-particle elliptic flow up to p_T\sim2~GeV. We also consider the relation of elliptic flow to the initial state eccentricity using different reference planes, and discuss the correlation between the physical event plane and the initial participant plane. Our results demonstrate that event-by-event hydrodynamics with initial state fluctuations must be accounted for before a meaningful lower limit for viscosity can be obtained from elliptic flow data. (based on: Hannu Holopainen, Harri Niemi, Kari J. Eskola, e-Print: arXiv:1007.0368 [hep-ph])
• Tuesday 19 October 2010 at 10.15 in E204: Antti Kupiainen (Department of Mathematics)
Did the Fields Medals go to Physics?
Abstract: The International Congress of Mathematicians awarded four Fields medals (“Nobel prizes of mathematics”) in August 2010. Two of these prizes were given for work in mathematical physics and a third one also was related to it. I will briefly discuss these works and try to explain why mathematical work has also brought new physical insight to these problems.
• Monday 25 – Friday 29 October 2010 lectures of the International Graduate School Bielefeld-Paris-Helsinki:
Paula Eerola (University of Helsinki, HIP): Physics at the LHC
Keijo Kajantie (University of Helsinki, HIP): AdS/QCD
Marco Panero (University of Helsinki, HIP): Introduction to lattice
Mikko Sainio (University of Helsinki, HIP): Chiral symmetry
Kim Splittorff (NBI, Copenhagen): Random matrix models
Anders Tranberg (NBI, Copenhagen): Field theory simulations in cosmology
Kimmo Tuominen (Jyväskylä): Technicolor
• Friday 19 November 2010 at 10.15 in E207 (note place!): Walter Wuensch (CERN, Geneva)
Introduction to CLIC and the quest for high-gradients
Abstract: An international collaboration lead by CERN is developing a multi-TeV electron positron linear collider, CLIC (Compact Linear Collider). One of the most challenging performance advances beyond what is found in the current generation of accelerators is the 100 MV/m accelerating gradient ? such a high value shortens and consequently reduces the cost of the facility. I will present an overview of the CLIC machine and then describe the experimental and theoretical efforts underway to develop the high-gradient accelerating structures.
• Tuesday 23 November 2010 at 10.15 in E204: Yuya Sasai (HIP and Department of Physics, Helsinki)
Shear viscosity of a highly excited string and black hole membrane paradigm
Abstract: The black hole membrane paradigm states that a certain viscous membrane seems to be sitting on a stretched horizon of a black hole from the viewpoint of a distant observer. However, the microscopic interpretation of the membrane is not still clear. We have obtained the shear viscosity of a higly excited string and shown that the shear viscosity of the fictitious membrane can be reproduced by the highly excited string covering the stretched horizon except for a numerical coefficient.
• Tuesday 30 November 2010 at 10.15 in E204: Sami Räsänen (HIP and Department of Physics, Jyväskylä)
First LHC results on the charged particle multiplicity and elliptic flow in Pb+Pb collisions at 2.76 TeV
Abstract: ALICE (A Large Ion Collider Experiment) at CERN LHC is designed based on needs of relativistic heavy ion collisions. First stable lead ion beams were reached on 8 November 2010 and eagerly awaited measurements at the collision energy of 2.76 TeV started, meaning over a factor of 10 increase from RHIC at Brookhaven. I will discuss the first results published by ALICE on 17 November, the charged multiplicity and elliptic flow. These basic measurements have a clear significance in heavy ion community which is reflected by the fact that the expectations for multiplicity in central rapidity region has varied over the years in between 1000 to 8000, and even the final model predictions just before the measurements had a factor of two spread in results.
• Thursday 2 December 2010 at 10.15 in A315: Irina Dymnikova (University of Warmia and Mazury, Poland and A.F. Ioffe Physico-Technical Institute, St. Petersburg, Russia)
Possibilities and surprises of vacuum dark fluid
Abstract: I review models for unified description of dark energy and dark matter and outline in detail vacuum dark fluid which provides DE-DM unification based on space-time symmetry and implied by the Einstein equations. A vacuum dark energy is described by a time-evolving and spatially inhomogeneous cosmological term. Dark matter is presented by compact objects generically related to vacuum dark energy: regular black holes, their remnants and gravitational solitons. In nonlinear electrodynamics coupled to gravity, field equations predict the existence of electrovacuum solitons asymptotically Kerr-Newman, for a distant observer, with the gyromagnetic ratio g=2.
• Tuesday 7 December 2010 at 10.15 in E204: Matts Roos (Department of Physics, Helsinki)
Dark matter in galaxies
Abstract: The distribution of matter in galaxies of different luminosities and Hubble types, as inferred from observations, plays an important role in cosmology, extragalactic astrophysics, astroparticle physics, as well as in a number of issues in high-energy astrophysics, galactic astronomy, star formation and evolution and general relativity.
Notwithstanding the general successes of the LCDM scenario in explaining the structure and evolution of the universe, there is a growing conviction that the structural properties of the dark and luminous components in galaxies hold important clues about the nature of dark matter and the processes that are responsible for galaxy formation.
This initiative aims to communicate results on the phenomenology of the mass discrepancy problem in galaxies to those scientists engaged with the dark matter problem in astrophysics, astroparticle physics and cosmology
Talk in connection with the Dark Matter Awareness Week, see http://people.sissa.it/~salucci/DMAW2010/DMAW2010.pdf.
• Thursday 9 December 2010 at 10.15 in A315: Dietrich Bödeker (Department of Physics, University of Bielefeld)
Thermal production of Majorana neutrinos
Abstract: The production of Majorana neutrinos is relevant for models of thermal leptogenesis in the very early Universe. We focus on the high-temperature limit where all masses, including the mass of the lightest Majorana neutrino are small. The production can proceed via 1<-> 2 decays and recombination processes. We consider new collinear production mechanisms like Bremsstrahlung and pair annihilation, mediated by multiple soft gauge interactions, which also contribute at leading order. We find that they enhance the rate by at least a factor 3 compared to the 1 <-> 2 decays.
• Thursday 16 December 2010 at 10.15 in A315: Daniel Figueroa (HIP, Helsinki)
Note time and place

Gravitational Waves from Reheating and Phase Transitions after Inflation
Abstract: Between the end of Inflation and primordial nucleosynthesis, the Universe goes through non-linear, non-perturbative and out-of-equilibrium stages, like Reheating or Phase Transitions (PhT). In particular, the spatial distribution of the fields develops inhomogeneities during these complicated periods, producing Gravitational Waves (GW) copiously. This seminar will thus be devoted to the details of the generation of such primordial GW backgrounds, studying global and gauge scenarios of Reheating and PhT’s, and considering both sub- and super-horizon scales. GW decouple upon production and propagate unimpeded carrying invaluable information about the high energy process that generated them. Therefore, the detection of this gravitational radiation would open a new observational window into the very early Universe. Moreover, these GW backgrounds may easily have a much greater amplitude than the GW background expected from Inflation (and might even mimic the spectrum of the latter), so a correct understanding of them seems timely.
References:
Dufaux, Figueroa, Garcia-Bellido, Phys.Rev.D82:083518,2010, arXiv:1006.0217; Fenu, Figueroa, Durrer, Garcia-Bellido, JCAP 0910:005,2009, arXiv:0908.0425; Figueroa, Garcia-Bellido, Phys.Rev.D77:043517,2008, arXiv:0707.0839; Figueroa, Garcia-Bellido, Phys.Rev.Lett.98:061302,2007, arXiv:astro-ph/0701014
• Friday 17 December 2010 at 14.15 in A315: Niko Jokela (Technion, Haifa)
Holographic quantum Hall fluid
Abstract: We consider a system of fermions in 2+1 dimensions based on D7-brane probes in AdS_5 X S^5. The system is stabilized by turning on appropriate fluxes. We analyze the system in the presence of a chemical potential and a magnetic field. We show that at low temperature the system is in a fractional quantum Hall state whose filling fraction is naturally quantized and depends on a single parameter. We also discuss the transport properties and the phase diagram of this system. Time permitting, we will also discuss the neutral bosonic excitation spectrum, closely resembling that of a quantum Hall fluid, including a magneto-roton excitation.
• Tuesday 21 December 2010 at 10.15 in E204: Mikko Voutilainen (CERN and University of Helsinki)
Jet quenching in heavy ion collisions, new results from CMS
Abstract: The LHC Experiments ALICE, ATLAS and CMS have recorded and analysed heavy ion (Pb-Pb) collisions at over ten times higher energy than ever before. Earlier experiments at RHIC established the formation of Quark Gluon Plasma in the form an ideal liquid, and produced preliminary results of possible “jet quenching”, i.e. the attenuation or disappearance of the spray of hadrons from hard scattered partons. The LHC experiments, with first announcement from ATLAS, have now found solid evidence for jet quenching, with its magnitude exceeding many expectations. This seminar will discuss these findings, new CMS results and their interpretation (arXiv:1011.6182).


text:
# Estimating change in RMS of noise given FIR filter coefficients

Filtering noise leads to a change in the overall RMS of the noise as demonstrated by the following code-block. which uses scipy's firwin2 to calculate the taps. The first set of taps (taps1) generates a large notch from 1 to 40 kHz whereas the second set of taps (taps2) generates a small notch from 4 to 7 kHz.

import matplotlib.pyplot as plt
import numpy as np
from scipy import signal

def rms_db(x):
rms = np.sqrt(np.mean(x ** 2))
return 20 * np.log10(rms)

ntaps = 10001

freq1 = [0,  1e3, 2e3,  40e3, 41e3, 50e3]
gain1 = [1,  1,   1e-2, 1e-2, 1,    1   ]
taps1 = signal.firwin2(ntaps, freq1, gain1, fs=100e3)

freq2 = [0,  4e3, 5e3,  6e3,  7e3,  50e3]
gain2 = [1,  1,   1e-3, 1e-3, 1,    1   ]
taps2 = signal.firwin2(ntaps, freq2, gain2, fs=100e3)

# Generating uniform noise from -sqrt(3) to sqrt(3) results in RMS value of 1
noise = np.random.uniform(-np.sqrt(3), np.sqrt(3), size=100000)

# Trim off the first ntaps to eliminate boundary conditions
noise1 = signal.lfilter(taps1, 1, noise)[ntaps:]
noise2 = signal.lfilter(taps2, 1, noise)[ntaps:]
noise = noise[ntaps:]

print('Unfiltered noise RMS (dB re 1Vrms): {:.2f}'.format(rms_db(noise)))
print('Filtered noise1 RMS (dB re 1Vrms): {:.2f}'.format(rms_db(noise1)))
print('Filtered noise2 RMS (dB re 1Vrms): {:.2f}'.format(rms_db(noise2)))

As expected, filtering the noise leads to a reduction in RMS of approx. -6.65 dB for the large notch filter and approx. -0.19 dB for the small notch filter. Running the code gives us the following values.

Unfiltered noise RMS (dB re 1Vrms): 0.01
Filtered noise1 RMS (dB re 1Vrms): -6.65
Filtered noise2 RMS (dB re 1Vrms): -0.19

Since noise is inherently random, the actual reduction, in dB, of the noise will vary each time I run the code. I'd like to estimate the theoretical reduction in RMS that results from a particular when it's applied to a broadband signal (i.e., a signal containing equal power at all frequencies).

I thought I might be able to use freqz to estimate this:

w, h1 = signal.freqz(taps1, fs=fs)
h1 = np.abs(h1)

w, h2 = signal.freqz(taps2, fs=fs)
h2 = np.abs(h2)

plt.plot(w, 20 * np.log10(h1))
plt.plot(w, 20 * np.log10(h2))
plt.xlabel('Frequency (Hz)')
plt.ylabel('Gain (dB)')

average_db1 = 20 * np.log10(h1.mean())
average_db2 = 20 * np.log10(h2.mean())

print('Expected change in RMS for filter 1 (dB): {:.2f}'.format(average_db1))
print('Expected change in RMS for filter 2 (dB): {:.2f}'.format(average_db2))

However, this gives me an expected change in RMS that does not match the empirically-calculated change in RMS above.

Expected change in RMS for filter 1: -12.85
Expected change in RMS for filter 2: -0.35

Here is a plot of the frequency response of each filter.

# Update

Per @Hilmar, I was doing the averaging incorrectly. I needed to average power, not amplitude. The correct calculation:

average_db1 = 20 * np.log10(np.sqrt(np.square(h1).mean()))
average_db2 = 20 * np.log10(np.sqrt(np.square(h2).mean()))

• Re your final update, just simply do average_db1 = 10 * np.log10(np.square(h1).mean()) . No need to sqrt and then multiply by 20. (minor but it jumps out at me like saying 4 is the square of the square root of 4 :) ). ( @TimWescott you were searching for examples where you would use 10log) Jan 6 at 5:48
• Thanks! A very valid point @DanBoschen.
Jan 6 at 18:28
• I hope I didn't come across as being nit-picky! Jan 6 at 20:00
• No. It's a good reminder about the difference between power and amplitude. Thanks!

format: plain