DEPARTMENT OF PHYSICS / HIP JOINT COLLOQUIA / SEMINARS 2014
Tuesday 21 January 2014 at 10.15 in A315: Blaise Goutéraux (Nordita, Stockholm) Holographic metals and insulators Abstract: In this talk, we’ll comment on generic scaling properties of holographic metals and insulators, in particular through the low-temperature, low-frequency behaviour of their transport coefficients such as the optical conductivity.
Tuesday 4 February 2014 at 10.15 in A315:Yann Mambrini (Orsay) Phenomenological aspects of Dark Matter in the light of recent experimental results Abstract: In 2013, several results have been released from different experimental groups looking for dark matter in our galaxy, from the direct detection constraints obtained by XENON and LUX to possible smoking gun signals suggested by the FERMI data or to missing energy searches at LHC. I will review the simplest yet motivated extensions of the standard model and explain why they begin to be severely constrained (if not excluded) by a combination of these sets of new data.
Thursday 6 February 2014 at 10.15 in A315: Aleksi Kurkela (CERN) Thermalization in weakly coupled nonabelian plasmas Abstract: Nonabelian plasmas far from equilibrium are a generic feature of early universe cosmology and appear in the early stages of heavy ion collisions. In my talk, I will discuss how such systems relax towards equilibrium, and the physical processes that drive the thermalization in the weak coupling limit. In particular, I will discuss the role of screening, collinear splitting and plasma instabilities out of equilibrium.
Tuesday 18 February 2014 at 10.15 in A315: Jörn Kersten (Hamburg) New Physics in the Late Early Universe Abstract: The measurements of the cosmic microwave background by the Planck satellite seem to confirm the standard LambdaCDM cosmological scenario. However, a closer look reveals some tension in this simple picture. There are hints for a larger radiation density than expected in the standard model (“dark radiation”). Planck results for some cosmological parameters do not agree completely with local measurements of these parameters at low redshift, which points to a hot dark matter component. Finally, the observed structures at relatively small scales do not quite agree with the predictions by simulations of structure formation. While all these problems might eventually be solved by astrophysics, they could also point to new physics beyond the standard models of particle physics and cosmology. I will discuss two scenarios for the latter, the production of dark radiation in late particle decays, and a model where the cold dark matter has self-interactions as well as interactions with sterile neutrinos.
Tuesday 25 February 2014 at 10.15 in A315: Alessandro Amato (Swansea) Transport coefficients of quark-gluon plasma Abstract: A lattice calculation is presented for the electrical conductivity of the QCD plasma at finite temperature, using a tadpole improved clover action with 2+1 dynamical flavours and conserved currents. The behaviour of this transport coefficient is shown over a wide range of temperatures, across the deconfining transition. The spectral functions relevant for the analysis are extracted using the MEM algorithm, with a detailed investigation of its systematics.
Tuesday 25 February 2014 at 14.15 in E206: Dirk Rischke (Frankfurt) Note time and place! Inhomogeneous phases in dense strongly interacting matter – a generic phenomenon? Abstract: Calculations within QCD-inspired models as well within QCD in the large-N_c limit show that dense quark matter features inhomogeneous phases. The order parameter for chiral symmetry breaking varies periodically, in the form of a chiral density wave (“chiral spiral”) or in the functional form of a Jacobi elliptic function. In this talk, I will demonstrate that this phenomenon also occurs in an effective chiral model with purely hadronic degrees of freedom. The parameters of the model are adjusted to give a reasonable fit of hadron vacuum properties. The model is also able to reproduce nuclear matter saturation properties. We find that, above a density of about 2.4 times the nuclear matter ground state density, an inhomogeneous phase sets in, where the chiral order parameter varies in the form of a chiral density wave. Thus, inhomogeneous phases seem to be a generic feature of high-density strongly interacting matter.
Tuesday 4 March 2014 at 10.15 in A315: Laura Covi (Göttingen) SuperWIMPs at the LHC Abstract: We will review the status of SuperWIMP Dark Matter and then discuss recent bounds and prospects at the LHC especially in the case of stop NLSP. We will then discuss an intriguing idea of connecting SuperWIMP gravitino DM with baryogenesis at the weak scale through R-parity breaking.
Monday 10 March 2014 at 10.15 in E206: Miklos Långvik (Marseille) Note place and time! Aspects of Locally Conformal Spinnetworks Abstract: Spinnetworks are a 3d geometry employed as the kinematical states of Loop Quantum Gravity (LQG) and Spin Foam (SF) models, the covariant counterpart to the Hamiltonian formulation of LQG. In this talk we explore a particular representation (all 3 Casimirs proportional) of the cotangent bundle of the double cover of the conformal group T*SU(2,2) that sits inside T*SL(2, C). We find that the generator of dilatations changes the extrinsic curvature of the triangulation, something we interpret as curving the edges of the tetrahedra of the triangulation. This has previously been suggested to account for the cosmological constant in the SF-models, which is currently described by the quantum group T*SL_q(2, C). We also discuss a possible extension of the construction to locally conformal spinnetworks that take into account all possible values of the 3 Casimirs of the conformal group. This talk will be preceded by a relatively lengthy introduction to both LQG and SF-models to highlight the main ideas behind the quantization of geometry and the particular constructions.
Tuesday 11 March 2014 at 10.15 in A315: Germano Nardini (Desy) Higgs sector and collider signatures in the triplet extension of the MSSM Abstract: The MSSM can accommodate the observed Higgs mass m_h ~ 126 GeV at the price of some unpleasant amount of tuning. This problem can be alleviated in scenarios with an enlarged field content. By requiring minimality, only two options are allowed to extend the MSSM: either a singlet or a SU(2)_L triplet can be added. This talk focuses on the latter possibility. In particular, we will discuss its Higgs sector and signatures at collider. Comments on loop-induced Higgs decays, as well as on constraints coming from dark matter analyses, will be also provided.
Tuesday 18 March 2014 at 10.15 in A315: Mohammad Mirkazemi (MPI, Garching) Brightest X-ray clusters of galaxies in the CFHTLS wide fields: Red sequence finder, optical mass estimator, and stellar mass estimation Abstract: Red sequence technique is one of the robust tool to identify galaxy clusters. This talk will introduce a new multi-color red sequence method. Using a spectroscopic sample of early-type galaxies and different stellar population models, I determined red sequence configuration parameters such as color model and a characteristic magnitude. I will show that our red sequence finder is a robust tool for determining the clusters redshift. Moreover, the correlation between z-band luminosity and total mass of clusters (derived from the X-ray luminosity) will be discussed. At the end, I will also present my recent work on the stellar mass estimation in CFHTLS and dependence of galaxy stellar mass function on the environment.
Tuesday 25 March 2014 at 10.15 in A315: Mikko Möttönen (Aalto University) Observation of Dirac monopoles in a synthetic magnetic field Abstract: Magnetic monopoles–particles that behave as isolated north or south magnetic poles–have been the subject of speculation since the first detailed observations of magnetism several hundred years ago. Numerous theoretical investigations and hitherto unsuccessful experimental searches have followed Dirac’s 1931 development of a theory of monopoles consistent with both quantum mechanics and the gauge invariance of the electromagnetic field. The existence of even a single Dirac magnetic monopole would have far-reaching physical consequences, most famously explaining the quantization of electric charge. Although analogues of magnetic monopoles have been found in exotic spin ices and other systems there has been no direct experimental observation of Dirac monopoles within a medium described by a quantum field, such as superfluid helium-3. Here we demonstrate the controlled creation of Dirac monopoles in the synthetic magnetic field produced by a spinor Bose-Einstein condensate. Monopoles are identified, in both experiments and matching numerical simulations, at the termini of vortex lines within the condensate. By directly imaging such a vortex line, the presence of a monopole may be discerned from the experimental data alone. These real-space images provide conclusive and long-awaited experimental evidence of the existence of Dirac monopoles. Our result provides an unprecedented opportunity to observe and manipulate these quantum mechanical entities in a controlled environment.
Tuesday 1 April 2014 at 10.15 in A315: Venus Keus (Southampton) Multi Higgs doublet models Abstract: Multi Higgs-doublet models (NHDMs) are amongst the simplest extensions of the Standard Model, motivated for instance by Supersymmetric scenarios. I will discuss NHDMs with various symmetry groups which contain viable dark matter candidates, preserved by the remnant of the symmetry after EWSB. I will describe the dark matter phenomenology of these models and look into new Higgs decay channels offered by the extra doublets and their effect on the Standard Model Higgs couplings.
Tuesday 8 April 2014 at 10.15 in A315: Maxime Gouzevitch (Universite Claude Bernard-Lyon I, France) Standard Model Physics at the LHC Abstract: The LHC has collected a wealth of data, which strongly supports the Standard Model of particle physics, and has so far lent little evidence for new physics beyond it. We give an overview of the Standard Model Physics program and recent results at the CMS experiment, with highlights such as the measurement of alpha_s in the TeV scale.
Tuesday 15 April 2014 at 10.15 in A315: Tomas Lindén (HIP) Compact fusion reactors Abstract: Fusion research is currently to a large extent focused on tokamak (ITER) and inertial confinement (NIF) research. In addition to these large international or national efforts there are private companies performing fusion research using much smaller devices than ITER or NIF. The attempt to achieve fusion energy production through relatively small and compact devices compared to tokamaks decreases the costs and building time of the reactors and this has allowed some private companies to enter the field, like General Fusion and Lawrenceville Plasma Physics. Some of these companies are trying to demonstrate net energy production within the next few years. If they are successful their next step is to attempt to commercialize their technology. In this presentation an overview of compact fusion reactor concepts is given.
Tuesday 22 April 2014 at 10.15 in A315: Risto Paatelainen (Jyväskylä) Modeling the space-time evolution of ultrarelativistic heavy-ion collisions Abstract: Understanding the different stages of ultrarelativistic heavy-ion collisions is essential in extracting the properties of the quark-gluon plasma. In this seminar talk I will review our perturbative QCD based model for the initial production of matter which is combined with a hydrodynamical framework for the subsequent space-time evolution. Finally, I will compare the results from the model with experimental data from RHIC and LHC based on which we can constrain the shear viscosity of the QCD matter.
Thursday 24 April 2014 at 10.15 in A315: Andreas Schmitt (Wien) Sound modes and two-stream instability in a relativistic superfluid Abstract: Relativistic superfluids are most likely present in the interior of compact stars, in nuclear matter and/or quark matter. I will discuss a field-theoretical approach to superfluidity and how it is connected to the usual two-fluid picture developed by Landau for superfluid helium. I will then show some applications of this approach, most notably the two sound modes for all temperatures and the so-called two-stream instability that is known from plasma physics and that may be relevant for compact star phenomenology.
Tuesday 6 May 2014 at 10.15 in A315: Michał Heller (Amsterdam/Warsaw) Gauge fields out of equilibrium – a holographic approach Abstract: Ultra-relativistic heavy ion collision programs at RHIC and LHC probe the properties of matter under extreme conditions in which quarks and gluons are liberated from hadrons and form the quark-gluon plasma. I will discuss the progress on theoretical understanding of the formation of the quark-gluon plasma in heavy ion collisions, and related questions, coming from the first principle calculations in the models of strong interactions solvable using holography. This leads to a fascinating connection with gravitational physics, in particular black hole formation and dynamics, which I will discuss in detail.During the week Michał Heller will further give several lectures on numerical methods in holography, the schedule is here,
Thursday 8 May 2014 at 10.15 in A315: Nick Evans (Southampton) Dynamic AdS/QCD & the Conformal Window Abstract: I introduce a simple holographic description of SU(Nc) gauge theory with Nf quark flavours. The dynamics of the gauge theory is input through the running of the anomalous dimension of the quark mass, gamma. The model predicts the on-set of chiral symmetry breaking when gamma=1. It then describes the hyperscaling relations in the conformal Window, a Miransky type phase transition, walking dynamics including a light sigma particle, and QCD-like behaviour at small Nf.
Tuesday 13 May 2014 at 10.15 in A315: Marco Panero (Madrid) Real-time dynamics from a Euclidean lattice: The physics of jet quenching in high-temperature QCD Abstract: When the “fireball” of deconfined quark-gluon plasma (QGP) created in a heavy-ion collision expands and cools down, it produces hadronic jets with very striking features, including the suppression of large transverse momenta and of correlations between back-to-back particles. These effects are generically referred to as “jet quenching”, and give important information about the QGP: they indicate that, when a hard parton propagates through the deconfined medium, it undergoes multiple interactions with the plasma constituents, which lead to energy loss and momentum broadening. A theoretical study of this process is particularly difficult, because it involves both perturbative and non-perturbative physics. In addition, the dynamical, real-time nature of the phenomenon hinders a direct approach based on numerical simulation on a lattice. In this talk, however, it will be shown how one can tackle the problem, combining the lattice approach with ideas related to dimensional reduction in high-temperature QCD.
Wednesday 14 May 2014 at 10.15 in A315: Peter Dendooven (Groningen) Proton therapy research at KVI-Center for Advanced Radiation Technology Abstract: In cancer treatment, proton beam radiotherapy exploits the highly localized dose deposition of protons to minimize the dose delivered to healthy tissue surrounding a tumor. As a result, collateral damage to healthy tissue is less compared to photon radiotherapy: complications are reduced and the patient’s quality of life after treatment is improved. However, the more precise irradiation possible with protons means an irradiation with protons is less forgiving with respect to dose delivery errors such as proton range uncertainties, patient mispositioning and anatomical changes in the patient during the course of treatment. At KVI Center for Advanced Radiation Technology of the University of Groningen, we investigate several issues aiming at improved proton radiotherapy. Better knowledge of the patient in terms of proton stopping power by making use of dual-energy CT images and proton radiography is investigated. The clinical implementation of in-vivo dose delivery verification by imaging secondary radiation produced by the proton beam as part of quality assurance is being studied. Also, a better primary proton dose standard in terms of heat deposit in water is investigated. An overview of our proton-therapy related research, with some emphasis on in-vivo dose delivery verification will be presented.
Tuesday 20 May 2014 at 10.15 in A315: Biswarup Mukhopadhyaya (Allahabad) The Higgs Boson as the Gateway to New Physics Abstract: The recent experimental results on the Higgs boson, while coming as confirmation of the standard electroweak theory, also encounter us with the potential of indicating new physics at the fundamental level hidden therein. Some recent efforts in this direction will be discussed in this talk, both emphasizing a model-independent approach and in the context of a specific scenario.
Tuesday 27 May 2014 at 10.15 in A315: Jacek Dobaczewski (Fidipro professor, Jyväskylä) Nuclear density functional theory Abstract: In the condensed-matter, atomic, and molecular physics, density functional theory (DFT) is a universal approach to compute ground state and excited configurations of many-electron systems. At present, the DFT strategy is also intensely studied and applied in the area of nuclear structure. The nuclear energy density functional (EDF) – a natural extension of the self-consistent mean-field theory – is a tool of choice for computations of ground-state properties and low-lying excitations of medium-mass and heavy nuclei. Over the past thirty-odd years, a lot of experience was accumulated in implementing, adjusting, and using the EDF methods in nuclei, and this research direction is still actively pursued. In particular, current developments concentrate on (i) attempts to improve the performance and precision delivered by the nuclear EDF methods, (ii) derivations of density functionals from first principles rooted in the low-energy chromodynamics and effective theories, and (iii) including effects of low-energy correlations and symmetry restoration. The seminar will give an overview of foundations and recent achievements gained within the nuclear EDF methods.
Wednesday 28 May 2014 at 10.15 in A315: Mariana Frank (Montreal) Charginos and neutralinos beyond MSSM Abstract: After the discovery of the Higgs Boson, the LHC is poised to reopen, operating at centre of mass energy of 13 TeV, and to look for signals of physics beyond the Standard Model. Supersymmetry remains the favourite scenario, and if valid, it is likely to manifest itself in observations of signals coming from the production and decays of charginos and neutralinos. I analyse these in two models beyond the minimal scenario, one with extra higgsinos (fermionic partners of Higgs bosons), and one with extra gauginos (fermionic partners of gauge bosons), and show that the production is likely to be enhanced, and the decay modes altered. Investigating the final signal (into one, two, and three or more leptons) is likely to yield distinguishing signals for the models and offer indications of the extended gauge structure.
Tuesday 3 June 2014 at 10.15 in A315: Matti Järvinen (Heraklion) New results from holographic V-QCD Abstract: I discuss latest developments in holographic bottom-up models for QCD in the Veneziano limit (V-QCD) at finite quark mass. Masses, the S-parameter, and condensates have expected mass dependence for all values of x=Nf/Nc, and the axial anomaly of QCD is correctly implemented by a string-motivated CP-odd sector of the V-QCD action. Consequently, the pion and eta prime masses satisfy the Gell-Mann-Oakes-Renner and Witten-Veneziano relations. I also discuss how double trace deformations can be studied.
Thursday 5 June 2014 at 10.15 in A315: Santosh Kumar Rai (Allahabad) Some Higgs studies after the “Higgs” discovery Abstract: After giving a flavour of some basic extensions of the Higgs sector beyond the Standard Model, I will discuss two different Higgs physics scenarios where the extensions to the Higgs sector are inherently chromophobic by construction and their implications in the context of LHC studies.
Friday 6 June 2014 at 10.15 in Exactum/CK112: Charles Bennett (Baltimore, Principal Investigator, WMAP) Note change of lecture hall! Cosmology and the Cosmic Microwave Background Abstract: Studies of the Cosmic Microwave Background (CMB) have led to major advances in cosmology. In this talk I will summarize recent CMB results and their implications for cosmology. I will compare and contrast select WMAP and Planck cosmological results. I will also discuss other some cosmological measurements, both past and future, that do not involve the CMB. I will focus on how these measurements help to test cosmological models and narrow the range off their associated parameters. Specific topics will include constraints on the Hubble constant and inflation models.
Monday 9 June 2014 at 14.15 in A315: Ioan Ghisoiu (Bern) Three-loop Debye mass and effective coupling in thermal QCD Abstract: QCD at finite temperature is afflicted with infrared divergences that can be cured in part in the framework of a dimensionally reduced effective theory, Electrostatic QCD. We determine the three-loop effective parameters of this theory as matching coefficients to full QCD.
Tuesday 10 June 2014 at 10.15 in A315: Aleksi Kurkela (CERN) Bottom-up thermalization in heavy-ion collisions Abstract: It is a commonly held belief that weak coupling dynamics are in contradiction with the apparently fast thermalization observed in heavy-ion collisions at RHIC and at the LHC. This belief is based on solely parametric estimates and naturalness arguments in the “Bottom-up?? picture of thermalization of Baier, Mueller, Schiff, and Son. In my talk, I will discuss elevating this parametric picture into a numerical one through simulations in an effective kinetic theory. I discus how the numerical factors play an important role and show that the Bottom-Up scenario results in rapid thermalization at realistic couplings.
Thursday 14 August 2014 at 10.15 in A315: Timo Alho (Jyväskylä) Thermodynamics of holographic models for QCD in the Veneziano limit Abstract: We have studied the thermodynamics of a class of holographic bottom-up models for QCD in the limit where both Nc and Nf go to infinity such that their ratio is finite. These Veneziano QCD -models incorporate a gravity-dilaton system to model the glue dynamics and a scalar tachyon for the fermion degrees of freedom. We have solved the system with full backreaction at finite temperature and finite chemical potential, allowing a determination of the chiral and deconfining transitions. I will also discuss ongoing work in modeling the low-temperature hadron gas phase.
Thursday 14 August 2014 at 14.15 in A315: Matthias Ihl (Porto) Holographic Bilayer/Monolayer Phase Transitions Abstract: In the present talk, I will discuss the phase structure of bilayer and monolayer phases in the (2+1)-dimensional defect field theory whose gravity dual is obtained by embedding D5/anti-D5 probe flavour branes in the singular conifold. We study in detail the embedding equations and compare the free energies of the resulting configurations at non-zero temperature and external magnetic field perpendicular to the defects. Moreover, we analyse the meson spectrum and confirm the stability of the single bilayer solution.
Tuesday 19 August 2014 at 10.15 in A315: Tommi Markkanen (Helsinki) Spacetime curvature and the Higgs stability during inflation Abstract: It is currently widely accepted that for a high scale of inflation the EW Higgs vacuum is unstable due to large fluctuations of order H. However, this conclusion is reached by neglecting potentially significant effects induced by the spacetime curvature. In this talk I review the derivation of a one-loop SM Higgs effective potential in curved space and discuss its implications. In particular I will show that generally a large curvature mass is generated which can stabilize the potential against fluctuations induced by inflation.
Tuesday 26 August 2014 at 10.15 in A315: Mikko Laine (Bern) Towards first principles in particle cosmology Abstract: Some of the important issues in particle cosmology (such as the existence of a matter-antimatter asymmetry) can be faithfully addressed in terms of interactions probed at terrestrial experiments, only if we know how to compute reliably with relativistic thermal quantum field theories. After outlining a few of the conceptual and technical challenges involved, I illustrate the status of the field with the example of the right-handed neutrino production rate in a very early universe. The role that this quantity plays in practical matter-antimatter asymmetry computations is briefly sketched.
Tuesday 2 September 2014 at 10.15 in A315: Gero von Gersdorff (Sao Paulo) New Physics Effects in Anomalous Gauge Boson Vertices Abstract: Indirect bounds on New Physics from precision measurements of the Standard Model properties have proven to be a valuable and powerful tool to constrain theories beyond the Standard Model (BSM). Parallel to direct searches, the LHC will also be able to improve on these indirect limits, and open a few new avenues not explored so far. One of them concerns the quartic gauge-boson self-interactions. In this talk we explain how the latter can be used to consider various BSM scenarios. We will in particular focus on processes involving four photons which could be measured at the LHC with the aid of forward detectors, and which gives a unique probe of New Physics. As an example, we will consider Warped Extra Dimensions, and explore the complementarity of the various precision measurements.
Tuesday 9 September 2014 at 10.15 in A315: Bhupal Dev (Univ. of Manchester) Naturally Aligned Two Higgs Doublet Model and its Collider Signatures Abstract: We show that the lightest Higgs sector resulting from a Maximally Symmetric Two Higgs Doublet Model (MS-2HDM) based on the SO(5)-symmetry becomes naturally aligned with that of the Standard Model (SM), independently of the charged Higgs boson mass and \tan\beta. Nevertheless, renormalization group effects due to the hypercharge gauge coupling and third-generation Yukawa couplings may break sizably this SM alignment, along with the custodial symmetry inherited by the SO(5) group. Using the current Higgs signal strength data from the LHC, which disfavor large deviations from the SM alignment limit, we derive lower mass bounds on the heavy Higgs sector as a function of \tan\beta, which can be stronger than the existing limits for a wide range of parameters. Finally, we propose new collider signals involving third-generation quarks to directly probe the heavy Higgs sector of the MS-2HDM during the run-II phase of the LHC.
Tuesday 30 September 2014 at 10.15 in A315: Shahin Sheikh-Jabbari (IPM, Tehran, Iran) The Quest for Quantum Gravity, the necessity and viewpoints Abstract: Gravity is the only interaction which appears among all existing objects and in our current physics is formulated through Einstein theory of General Relativity (GR). Although it has many theoretical appealing features and successes with the current experiments and observations, GR suffers from theoretical shortcomings. The most common way to remedy these shortcomings comes through quantization of the theory. Despite of many efforts and trying various approaches, a consistently quantized gravity has remained elusive. In this colloquium talk I will review these shortcomings and some of the main approaches taken to formulate Quantum Gravity.
Tuesday 30 September 2014 at 14.15 in A315: Tuomas Hapola (Durham) Higgs Plus Multiple Jets with HEJ Abstract: The High Energy Jets (HEJ) framework provides an approximation to the all-order perturbative calculation of observables in processes with multiple hard jets. In this talk I will first introduce the framework, and discuss recent comparisons to the data from the LHC and Tevatron. Then I will discuss predictions for the production of Higgs boson with multiple jets using HEJ.
Thursday 2 October 2014 at 10.15 in A315: Arttu Rajantie (Imperial College) Quantum field theory of elementary magnetic monopoles Abstract: Ever since Dirac’s discovery that quantum mechanics allows magnetic monopoles, there have been attempts to add them to quantum electrodynamics as dynamical degrees of freedom rather than as a static classical background as in Dirac’s calculation. However, the proposed formulations have been impractical due to issues like lack of manifest Lorentz invariance or locality. When ‘t Hooft and Polyakov discovered topological monopole solutions in GUT-like non-Abelian theories, the attention shifted to them. However, there is no physical reason to rule out the possibility of elementary monopoles, and some of their key properties can be different from ‘t Hooft-Polyakov monopoles. In particular, their mass is a free parameter and can therefore be light. I present a lattice formulation of QED with light elementary magnetic monopoles and show simulation results which demonstrate that they behave as expected. This shows that magnetic monopoles do not have to be related to grand unification, and that they can be light enough to be produced at the LHC and detected at the new MoEDAL experiment.
Tuesday 7 October 2014 at 10.15 in A315: Sourov Roy (Indian Association for the Cultivation of Science, Kolkata) Phenomenology of U(1)_R -lepton number model Abstract: In this talk I shall discuss light neutrino masses and mixing, phenomenology of a keV sterile neutrino dark matter and the Higgs boson signal rate in the di-photon channel at the LHC, in the framework of U(1)_R-lepton number model augmented by a right handed neutrino superfield. The lepton number of the standard model fermions are identified with the negative of their R-charges. As a result, a subset of leptonic R-parity violating operators can be present and are consistent with the U(1)_R symmetry. One of the sneutrinos might acquire a substantial vacuum expectation value leading to interesting phenomenological consequences. This model not only provides a small tree level mass to one of the active neutrinos but also renders a suitable warm dark matter candidate in the form of a sterile neutrino with negligible active-sterile mixing. This can explain the recent observation of an X-ray line signal at around 3.5 keV. In order to fit the experimental results involving light neutrino masses and mixing angles we introduce a small breaking of U(1)_R symmetry. The lightest Higgs boson mass receives an additional tree level contribution proportional to the square of the neutrino Yukawa coupling f. This allows for a 125 GeV Higgs boson at the tree level for an order one f and still having a small tree level mass for the active neutrino.
Thursday 9 October 2014 at 10.15 in A315: Lauri Wendland (Helsinki) New results on charged Higgs boson searches Abstract: A scalar boson at mH = 125 GeV has been discovered, but is it the only one? The existence of further scalar bosons would represent unambiguous evidence for physics beyond the SM. In this seminar, the new preliminary CMS results on charged Higgs boson searches are discussed and compared with ATLAS results. Model-independent limits will be shown and an interpretation of them is given in the MSSM benchmark scenarios.
Tuesday 14 October 2014 at 10.15 in A315: Adam Falkowski (Orsay) Higgs and electroweak precision data Abstract: I will discuss interpretation of the LHC Higgs data in the framework of effective field theories. Assuming there’s no new light particles beyond those of the SM, this framework allows one to describe the data in a completely model-independent way. At the technical level, this involves extending the SM Lagrangian by higher-dimensional operators constructed out of the SM fields. These operators encode the possible effects of new heavy particles in a systematic expansion in operator dimensions, with the leading effects expected from dimension-6 operators. In the talk I will describe the connection of the effective Lagrangian to Higgs observables. I will put a special focus on the synergy between the Higgs data and electroweak precision observables.
Thursday 16 October 2014 at 10.15 in E206 (Note place!): Matthew Lippert (Amsterdam) Holographic Anyonic Superfluidity Abstract: This talk will be about an unusual type of superfluid, one made up of anyons. I will discuss anyons, their relation to the quantum Hall effect, and how an anyonic superfluid is unlike a typical superfluid. Then I will describe a holographic model of a strongly-coupled anyonic superfluid and the stability of its supercurrents.
Tuesday 28 October 2014 at 10.15 in A315: Tobias Zingg (Helsinki) A holographic Model for strongly correlated Fermions Abstract: I will give a brief outline of the concept of gauge/gravity duality and how it is used to study novel phases of metals, where a physical description via Fermi liquid theory and other prevalent methods breaks down. The main focus will be on my current and recent work on ‘electron star’ models and their potential to capture features of systems with strongly correlated fermions.
Tuesday 4 November 2014 at 10.15 in A315: Per Osland (Bergen) CP violation in the Higgs sector and LHC constraints Abstract: I will describe CP violation in the Two-Higgs-Doublet model, and how it can be identified experimentally. Also, I will show that in spite of having a Standard-Model-like Higgs particle at the LHC, there could still be room for CP violation. One manifestation is a triple-Z vertex. In this model, this would however be accompanied by some flavour-changing interactions.
Tuesday 11 November 2014 at 10.15 in A315: Diego Aristizabal (University of Liege, Belgium) From neutrino masses to dark matter Abstract: Neutrino masses provide an unquestionable prove that at certain unknown but probably “high” energy scale new physical degrees of freedom are at work. The conventional approach, based on standard seesaws, although being compelling due to their simplicity and theoretical motivation lack experimental testability. In contrast, other “incarnations” of the effective Weinberg operator allow TeV-ish dof, so offering, in principle, testable pathways to neutrino masses. In this talk, after discussing some generalities of neutrino mass generation, I will then show that a program aiming at a fairly model-independent classification of radiative neutrino mass generation is possible. Finally, I will briefly comment on possible links between radiative neutrino mass generation and the origin of dark matter.
Thursday 13 November 2014 at 10.15 in A315: Tomas Brauner (Wien) Applications of Galilei invariance in condensed matter physics Abstract: I will discuss two directions of my recent work, connected by the notion of Galilei invariance and both motivated by condensed matter physics phenomena. In the first half of the talk, I will give an introduction to nonrelativistic general coordinate invariance, a concept that appeared in the context of effective field theories for quantum Hall systems. I will explain in detail how a given (not necessarily Galilei-invariant) nonrelativistic field theory can be coupled to background spacetime geometry, and mention possible use of such a construction. The second half of the talk will be devoted to magneto-optical properties of the topological insulator Bi2Se3. Upon a brief introduction to the subject, I will discuss a recent experiment which suggests that, despite being described at low energies by the Dirac equation similarly to graphene, this system features an emergent Galilei symmetry. Only basic knowledge of field theory and differential geometry will be required, and ignorance of condensed matter physics desired.
Tuesday 25 November 2014 at 10.15 in A315: Ushoshi Maitra (HRI, India) Status of additional scalar states at the LHC Abstract: In this talk I’m going to explore a scenario where along with the observed scalar at 125 GeV we can still accommodate an additional scalar. I’ll be focusing on the scalar called radion, which is an artifact of stabilizing the moduli of Randall Sundrum model. I’ll also consider the mixing of radion with Higgs. I’ll show that this observed scalar cannot be an unmixed radion however, it can still be a mixed Higgs with mixed radion nearby. I’ll also discuss a search strategy that can be used to discover a very light radion at the LHC (1410.0396) .
Tuesday 9 December 2014 at 10.15 in A315: Christian Gross (Helsinki) SUSY GUT models with non-Abelian flavour symmetry Abstract: I will discuss supersymmetric SU(5) GUTs with a non-Abelian flavor symmetry group A_4. After spontaneous flavor symmetry breaking the models give rise to the observed fermion masses, mixing angles and the quark CP phase. In addition one obtains various interesting predictions, in particular for the neutrino sector. I will also comment on the SUSY flavor and CP problems in these models.
Tuesday 16 December 2014 at 10.15 in A315: Niko Jokela (Helsinki) Hall states in partially quenched Chern-Simons matter theories Abstract: In this talk I will show how to systematically construct holographic duals to quantum Hall states in Chern-Simons matter theories with dynamical flavors. The construction involves parity breaking quantized internal flux in the flavored ABJM background. The effects of the sea quarks are captured in the anomalous mass dimension of the quenched flavors as well as in contributing to the filling fraction of the Hall state in terms of intrinsic disorder.