DEPARTMENT OF PHYSICS / HIP JOINT COLLOQUIA / SEMINARS 2019
- Thursday 7 February 2019 at 10.15 in A315: Lars Bergström (Stockholm)
Primordial Black Holes as Dark Matter?
- Tuesday 12 February 2019 at 10.15 in A315: Ulf Gran (Gothenburg)
Dynamical symmetry enhancement near black hole horizons
Abstract: In this talk I will sketch a general proof of the (super)symmetry enhancement occurring near black hole horizons, a phenomenon previously observed only on a case by case basis. I will also show that the symmetry algebra for all supersymmetric black hole horizons with non-trivial fluxes includes an sl(2,R) subalgebra.
- Thursday 14 February 2019 at 10.15 in A315: Jugoslav Stahov (Tuzla)
The single energy partial wave analysis of scattering data with analyticity constraints
Abstract: The use of the analytic properties of invariant scattering amplitudes as constraints in PWA (partial wave analysis) of scattering data, makes it possible to obtain a unique partial wave solution in a model independent way. The idea is applied in KH80 PWA of πN scattering data using so called Pietarinen’s expansion method. We give an overview of efforts in implementation of this method in analysis of meson photoproduction and πN scattering data.
- Tuesday 12 March 2019 at 10.15 in A315: Matteo Baggioli (Madrid)
Holographic viscoelastic phases of matter: from fluids to solids and more
Abstract: Holographic techniques have been widely and successfully used to describe strongly coupled fluids. In this talk I will review how bottom-up holographic models can be extended to include also solid and especially viscoelastic phases of matter. I will show how to formalize the (visco)-elastic response and I will discuss in details the vibrational phononic degrees of freedom from an holographic perspective. Finally I will apply the formalism to several condensed matter open questions. If time permits:
1) I will show the connections to the effective field theory (EFT) methods
2) I will discuss also how these ideas have triggered relevant developments in soft matter theory and experiments dealing with the glassy anomalies and the low frequency elastic response in liquids.
No detailed knowledge of AdS-CMT methods is required and lot of low energy condensed matter will be present.
- Tuesday 19 March 2019 at 10.15 in A315: Chitta Das (JINR)
Octant of θ23 in neutrino mixing and beyond the Standard Model
Abstract: The prospect for resolving the octant of the neutrino mixing angle θ23, that is, whether the atmospheric mixing angle is in higher octant (θ23 > 45°) or in lower octant (θ23 < 45°), in future long baseline neutrino experiments, will be explained in this talk. We found out, long baseline experiments measuring the νμ→νe transition probability are capable of resolving this degeneracy, also we present the importance of the matter effects with baseline length in the determination of the octant with the GLoBES software. We have shown how runtime ratio in neutrino and anti-neutrino modes contribute to the octant determination. The sensitivity to θ23 octant is shown as contour plots on the (θ23−45°, δ)-plane, where δ is the CP phase in the neutrino mixing matrix. We demonstrate the true values of θ23 for which the octant can be experimentally determined with a 5σ certainty level and the interference on the octant determination that arises from the unconstrained CP violation angle δ. In our results, we establish a connection between the beam sharing and mass hierarchy, in particular, we numerically derived the sensitivity limits of the possible non-unitarity of neutrino mixing on the experimental determination of θ23.
- Thursday 25 April 2019 at 10.15 in A315: Ville Vaskonen (King’s College)
Primordial black holes in the light of LIGO observations
Abstract: The observation of gravitational waves from black hole mergers by LIGO has revived the interest in the possibility of primordial black hole (PBH) dark matter. In this talk I will, after a short introduction to PBH formation and constraints, describe how PBH binaries are formed in the early universe and discuss their evolution. Finally, I will use the merger rate estimates and the LIGO observations to put constraints on the PBH abundance, and show that the observed merger rate can be explained by PBHs forming O(0.1%) of dark matter with a narrow mass distribution around 20 solar masses.
- Tuesday 30 April 2019 at 10.15 in A315: Carlos Hoyos (Oviedo)
Effective long distance q-qbar potential in holographic RG flows
Abstract: We study the q -qbar potential in strongly coupled non-conformal field theories with a non-trivial renormalization group flow via holography. We focus on the properties of this potential at an inter-quark separation L large compared to the characteristic scale of the field theory. These are determined by the leading order IR physics plus a series of corrections, sensitive to the properties of the RG flow. To determine those corrections, we propose a general method applying holographic Wilsonian renormalization to a dual string. We apply this method to examine in detail two sets of examples, 3+1-dimensional theories with an RG flow from an IR fixed point driven by an irrelevant deformation; and theories that are confining in the IR. We discuss the physical interpretation of these results and how could they be used to check our understanding of confinement in gauge/gravity duals using lattice QCD.
- Tuesday 7 May 2019 at 10.15 in A315: Toni Mäkelä (HIP, Helsinki)
Flavour-dependent jet energy corrections and top quark mass
Abstract:The most accurate single measurements of the top quark mass performed at the LHC differ from the measurement of Tevatron’s D0 experiment by about 2.5 GeV. This amounts to almost 3 standard deviations. Since D0 claims similar precision to the LHC experiments, this inconsistency has been a long-standing issue. As the moratorium for the internal notes of D0 finally expired in 2018, we have been able to perform a first-ever accurate reproduction of the D0 methods using standalone simulations. In particular we investigate the b-jet energy scale corrections which are crucial to top mass measurements. We investigate the sensitivity of the b-jet correction to various assumptions and suggest refinements to the analysis, bringing the results closer to the modern LHC experiments.
- Tuesday 14 May 2019 at 10.15 in A315: Pierre Auclair (Paris)
The stochastic background of gravitational waves from cosmic strings
Abstract: The advent of gravitational wave astronomy offers a new way to probe our Universe, from astrophysical sources, such as mergers of compact objects, to cosmological sources. One expected source of gravitational waves of cosmological origin are cosmic strings. These one-dimensional objects are predicted to be produced in the early universe during phase transitions. To this day, cosmic strings have not yet been discovered but their presence should produce a wide range of signatures due to their gravitational and non-gravitational effects.
- Friday 24 May 2019 at 13.15 in D101: Frank Wilczek (MIT and Stockholm)
Axion plasmon converter
Abstract: Axions are hypothetical particles whose existence would solve an important problem in fundamental physics and supply the dark matter of the universe. I will briefly review the motivations for axions and the status of experimental searches, and then describe a new approach which appears quite promising.
Frank Wilczek will in Helsinki also attend this event on Saturday.
- Thursday 13 June 2019 at 10.15 in A315: Sebastian Schuster (Wellington Univ)
Sparsity – Quantifying the Difference Between Hawking Radiation and Black Body Radiation
Abstract: In the mid-1970s, Stephen Hawking discovered the evaporation of black holes. Since then it has not just become a hallmark of quantum field theory in curved space-time, but also one of the most important clues towards a quantum theory of gravity. The subsequent decades have seen advances of formal, numerical, and pedagogical nature; yet just as much formation of folklore. Core and center to both folklore and advances is the comparison of black hole radiation to black body radiation. In this talk we shall present a heuristic quantity, “sparsity”, for quickly performing this comparison. This quantity is simple to explain, easy to calculate, and helps illustrate the differences and commonalities of the two types of radiation. Beyond this, it is also possible to extend results from the original, 3+1-dimensional contexts to higher dimensions. We can reproduce some results regarding the different emission characteristics of different particle species in higher dimension known from previous numerical studies in the literature.
- Tuesday 25 June 2019 at 10.15 in A315: Niko Koivunen (Helsinki)
Froggatt-Nielsen mechanism in 331-models
Abstract: The models with the gauge group $SU(3)_c\times SU(3)_L\times U(1)_X$ (331-models) have been advocated to explain why there are three fermion generations in Nature. As such they provide partial understanding of the flavour sector. The hierarchy of fermion masses in the Standard Model is another puzzle which remains without compelling explanation. In this talk I present a model that incorporates Froggatt-Nielsen mechanism into a 331-model in order to explain both fundamental problems. It turns out that no new additional scalar representations are needed to take care of this. The 331-models thus naturally include explanations to both the number of fermion generations and their mass hierarchy. This talk is based on arXiv:1706.09463[hep-ph] and arXiv:1905.05278[hep-ph].
- Thursday 27 June 2019 at 10.15 in A315: Suvankar Dutta (IISER Bhopal India)
Towards Phase Space Description of Chern-Simons matter theories on generic three manifolds
Abstract: We shall start with a generic discussion on phase space description of unitary matrix model. It is well known that eigenvalues of unitary matrices are like positions of free fermions. Writing the partition function in terms of representations of unitary group, it is possible to show that number of boxes in Young diagram plays the role of momentum of those fermions. A relation between eigenvalues and number of boxes allows one to provide a phase space description for different large N phases of the theory. We shall consider Chern-Simons matter theory on Seifert manifolds and show how to write down the partition function of such theories in terms of unitary matrix models using the connection between CS theory and WZW model. We discuss large N phase structure and level rank dualities of such theories.
- Thursday 27 June 2019 at 14.15 in A315: Florian Reindl (HEPHY and TU Vienna)
The COSINUS experiment – Cryogenic NaI detectors for direct dark matter search
Abstract:Today, the situation in direct dark matter detection is controversial: The DAMA/LIBRA experiment observes an annual modulation signal at high confidence. Furthermore, this signal is perfectly compatible in terms of period and phase with the expectation for a galactic halo of dark matter particles which interact in their NaI target crystals. However, in the so-called standard scenario on dark matter halo and dark matter interaction properties, the DAMA/LIBRA signal contradicts null-results of numerous other experiments.
The new experiment COSINUS aims for a model-independent cross-check of the DAMA/LIBRA signal. Such a cross-check is absent up to now and necessarily requires the use of the same target material (NaI). While several experimental efforts are planned or already ongoing, COSINUS is the only experiment operating NaI as cryogenic detector which yields several distinctive advantages: Discrimination between electronic interactions and nuclear recoils off sodium and iodine on event-by-event basis, a lower nuclear recoil energy threshold and a better energy resolution. In this contribution we will review the prototype measurements performed so far, present the plans for the new underground facility foreseen to be installed at LNGS and give an outlook on the COSINUS timescale.
- Friday 28 June 2019 at 10.15 in A315: Emidio Gabrielli (Trieste)
Searching for the Dark sector
Abstract: A prediction of recent models possibly explaining the fermion-mass hierarchy is the existence of a massless dark photon. Its interaction is restricted to a hidden sector made up of massive dark fermions (which are promising dark-matter candidates), and heavier scalar messengers connecting the SM with the dark fields. A new intriguing phenomenology is predicted that can show up at present and future colliders. The main phenomenological aspects of this scenario are presented, by stressing its astrophysical and cosmological implications.
- Tuesday 30 July 2019 at 10.15 in A315: Stan Brodsky (SLAC)
Meson/Baryon/Tetraquark Supersymmetry from Superconformal Algebra and Light-Front Holography
Abstract: Superconformal algebra leads to remarkable connections between the masses of mesons and baryons of the same parity — supersymmetric relations between the bosonic and fermionic bound states of QCD. Supercharges connect the mesonic eigenstates to their baryonic superpartners, where the mesons have internal angular momentum one unit higher than the baryons. We also predict the existence of tetraquarks which are degenerate in mass with baryons with the same angular momentum. An effective supersymmetric light-front Hamiltonian for hadrons composed of light quarks can be constructed by embedding superconformal quantum mechanics into AdS space. The breaking of conformal symmetry determines a unique quark-confining light-front potential for light hadrons including spin-spin interactions in agreement with the soft-wall AdS/QCD approach and light-front holography. The mass-squared of the light hadrons can be expressed as a frame-independent decomposition of contributions from the constituent kinetic energy, the confinement potential, and spin-spin contributions. The mass of the pion eigenstate vanishes in the chiral limit. Only one mass parameter appears; it sets the confinement mass scale, a universal value for the slope of all Regge trajectories, the nonzero mass of the proton and other hadrons in the chiral limit, as well as the mass parameter of the pQCD running coupling. The result is an effective coupling defined at all momenta. The matching of the high and low momentum-transfer regimes determines a scale Q_0 which sets the interface between perturbative and nonperturbative hadron dynamics. as well as the factorization scale for structure functions and distribution amplitudes. This procedure, in combination with the scheme-independent PMC procedure for setting renormalization scales, can greatly improve the precision of QCD predictions.
- Tuesday 6 August 2019 at 10.15 in A315: Jacob Sonnenschein (Tel Aviv)
Recent result of the HISH ( Holography inspired stringy hadron) model
Abstract: Holography inspired stringy hadron (HISH) is a model that describes hadrons as strings in four dimensional flat space-time. For mesons, baryons and exotics- open strings with endpoint (massive) particles, and for glueballs- closed strings. In the first part of the talk I will summarize the derivation and the results of the model. In particular the spectra and decay width of hadrons including possible identification of glue-balls and exotic hadrons. I will compare these results with the PDG experimental data. In the second part of the talk I will describe the quantization of a string with massive endpoints. This will include the classical solutions of rotating strings and the transverse and planar quantum fluctuations in the quadratic approximation. I will introduce an alterna-
tive method of renormalizing the system and computing the intercept. Next I will discuss the modification due to the non-criticality of the string and present the HISH Regge-like trajectories. In the third part I will describe the derivation of the scattering amplitude of strings with charges on their endpoints in constant electro-magnetic fields. I will determine the corresponding OPEs and derive the modification of the Veneziano amplitude. This will include a change of the target space metric and phases due to the underlying non-commutative geometry
- Tuesday 13 August 2019 at 10.15 in A315: Philipp Schicho (Bern)
3-Loop Gauge Coupling in Hot QCD
Abstract: Dimensionally reduced effective theories have been very successful for studying the thermodynamics of non-Abelian gauge theories. In the context of the dimensionally reduced effective theory for thermal QCD (“EQCD”), I will go through its construction and the relevant scales of hot QCD including the coupling renormalisation of “magnetostatic” QCD (“MQCD”). A recent computation of the latter shows a leftover logarithmic divergence originating from 3-loop effects from non-zero Matsubara modes. Therefore, I will demonstrate, through 1-loop and 2-loop computations that it is vital to include dimension-six vertices and that their effects are in general of the same order or larger than the hard-mode contribution.
- Tuesday 20 August 2019 at 10.15 in A315: Hamid Mehdipour (Islamic Azan University, Lahijan branch)
Noncommutative Hayward Black holes
Abstract: The final stages of the black hole evaporation for Hayward solutions are studied. The results show that the behavior of Hawking’s radiation changes considerably at the small radii regime such that the black hole does not evaporate completely and a stable remnant is left. We show that stability conditions hold for the Hayward solutions found in the Einstein gravity coupled with nonlinear electrodynamics. We analyze the effect that an inspired model of the noncommutativity of spacetime can have on the thermodynamics of Hayward spacetimes. This has been done by applying the noncommutative effects to the non-rotating and rotating Hayward black holes. In this setup, all point structures get replaced by smeared distributions owing to this inspired approach. The noncommutative effects result in a colder black hole in the small radii regime as Hayward’s free parameter increases. As well as the effects of noncommutativity and the rotation factor, the configuration of the remnant can be substantially affected by the parameter g. However, in the rotating solution it is not so sensitive to g with respect to the non-rotating case. As a consequence, Hayward’s parameter, the noncommutativity and the rotation may raise the minimum value of energy for the possible formation of black holes in TeV-scale collisions. This observation can be used as a potential explanation for the absence of black holes in the current energy scales produced at particle colliders. However, it is also found that if extra dimensions do exist, then the possibility of the black hole production at energy scales accessible at the LHC for large numbers of extra dimensions will be larger.
- Tuesday 27 August 2019 at 10.15 in A315: Tommi Tenkanen (Johns Hopkins University)
Spectator Dark Matter
Abstract: The observed dark matter abundance in the Universe can be fully accounted for by a minimally coupled spectator scalar field that was light during inflation and has sufficiently strong self-coupling. In this scenario, dark matter was produced during inflation by amplification of quantum fluctuations of the spectator field. The self-interaction of the field suppresses its fluctuations on large scales, and therefore avoids isocurvature constraints. The scenario does not require any fine-tuning of parameters. I will also discuss ways to test the scenario.
- Tuesday 27 August 2019 at 14.15 in A315: Tiina Naaranoja (University of Helsinki)
Diamond Time-of-Flight Detectors and their Radiation Tolerance
Abstract: Diamond is used as a time-of-flight detector in the Precision Proton Spectrometer at the CERN LHC. A single layer of single diamond detectors can reach 80 ps time resolution, whereas a single layer of double diamond can reach under 50 ps time resolution. The radiation tolerance of these detectors is studied to determine their lifetime in the experiment and the evolution of the performance of the detectors. Important metrics are charge collection efficiency, which translates into particle detection efficiency, and time resolution. Phenomena, such as space charge polarization, which are caused by the radiation induced defects, are also discussed.
- Tuesday 10 September 2019 at 10.15 in A315: Javier Subils (Barcelona)
Mass gap without confinement
Abstract: I will describe a one-parameter family of three-dimensional gauge theories with known supergravity holographic duals which display interesting infrared behaviours. Namely, these theories exhibit a mass gap but no confinement. Moreover, they interpolate between a theory with an infrared fixed point and a confining theory. We will examine the existence of a light pseudo-dilaton in the spectrum near the fixed point and discuss the phase diagram of these theories.
- Tuesday 1 October 2019 at 10.15 in A315: Graham White (Triumf, Canada)
Electroweak baryogenesis, experimental status, progress and extensions
Abstract: Electroweak baryogenesis is a minimal and compelling explanation for why we are here. It also has the advantage of being testable due to its connection to the weak scale. I outline these experimental tests and highlight theoretical uncertainties that blur the conversation between theory and experiment. I then present the status of some of the simplest baryogenesis models before show extensions to the paradigm itself.
- Thursday 17 October 2019 at 14.15 in Exactum B120: Bill Murray (Warwick, CERN) Note time and place!
Probing the Origin and Future of the Universe
Abstract: The Higgs boson discovered at LHC in 2012 demonstrates the existence of the BEH field, which arises from the unique equation of state of Higgs bosons. Taken literally, the equations say this field could cause the Universe to collapse at any moment. But modify the potential and it might explain the observed matter-antimatter asymmetry. The high-luminosity LHC is designed to increase the dataset by a factor ten, which should allow our first glimpses of the Higgs boson self-interaction, and could help us understand either of these facets.
The upgrade work for the accelerator and the ATLAS detector will be outlined, along with a review of the physics programme focussing on the Higgs physics measurements and searches.
- Tuesday 22 October 2019 at 10.15 in A315: Santosh Rai (Harish-Chandra Research Institute)
Some non-standard signals for vector-like quarks at LHC
Abstract: Most of the existing experimental searches for vector-like quarks(VLQ) at the LHC have been carried out under the assumption that the vector-like quarks decay to one of the following final states (Wb, Zt, Ht) for charge 2/3 and (Wt, Zb, Hb) for charge -1/3 . This may not be the case in many BSM models with VLQs. For different gauge extended models I will discuss scenarios where after the production the vector-like quarks decay via non-standard modes to give final states that are different from the above searched ones and discuss their possible signals at the LHC.
- Thursday 24 October 2019 at 10.15 in A315: Juan F. Pedraza (London)
Constraining higher order gravities with subregion duality
Abstract: In higher derivative theories, gravity can travel slower or faster than light. With this feature in mind, I will revisit the construction of the causal and entanglement wedges in this type of theories, and argue that they must be constructed using the fastest mode instead of null rays. I will explain how the property of causal wedge inclusion, i.e., the fact that the causal wedge must be contained in the entanglement wedge, can be used to obtain strong constraints on the higher derivative gravity couplings. The results are similar to the bounds previously obtained by Camanho et. al. based on high energy graviton scattering. I will present a systematic analysis in Gauss-Bonnet gravity to illustrate our findings.
- Tuesday 29 October 2019 at 10.15 in A315: Kristjan Kannike (Tartu)
Scalar Singlet Dark Matter With and Without Z3 Symmetry
Abstract: Besides Z2, the Z3 group is the next simplest discrete symmetry that can stabilise dark matter. In addition to the Standard Model Higgs boson, our model contains a complex scalar singlet S. If dark matter lives in the unbroken Z3 phase, then S is the dark matter candidate. The presence of the cubic term allows semi-annihilation processes to dominate the determination of the relic density and suppress the dark matter direct detection cross section. Even when Z3 is broken, the imaginary part of S is a pseudo-Goldstone candidate of dark matter. In this case, the direct detection cross section is still suppressed, but a first order cosmic phase transition can produce a stochastic gravitational wave background potentially detectable in future satellite experiments such as LISA or BBO.
- Wednesday 6 November 2019 at 10.15 in HIP meeting room: Valentina Puletti (Reykjavik)
Entanglement measures in generalised quantum Lifshitz models
Abstract: The talk focusses on the computation and analysis of entanglement measures in generalised quantum Lifshitz models. These are free field theories with Lifshitz scaling symmetry which extend the (2+1)-dimensional quantum Lifshitz model to higher dimension, and provide us with simple models for non-relativistic critical theories. I will introduce various entanglement measures, such as entanglement entropy and logarithmic negativity (suitable to characterising quantum entanglement for pure and mixed states respectively), outline their computation in generalised quantum Lifshitz theories, and discuss the results.
- Tuesday 12 November 2019 at 10.15 in A315: Oscar Henriksson (Helsinki)
Finite density gauge theories and brane instabilities
Abstract: At finite density, gauge theories such as QCD can display interesting phases such as color superconductivity. Through gauge/gravity duality, finite density gauge theories can have a geometric realization as spinning or charged branes in a higher-dimensional spacetime. I will review some relevant aspects of gauge/gravity duality, and then discuss how it can be used to describe strongly coupled versions of some gauge theory phases.
- Wednesday 13 November 2019 at 10.15 in A315: Heerak Banerjee (Kolkata)
Nondecoupling supersymmetry and an Lμ−Lτ gauge boson at Belle-II
Abstract: We find that the radiative contribution of charged sleptons to the γ−Z ′kinetic mixing is nondecoupling in the presence of a gauged U(1)Lμ−Lτ symmetry, depending logarithmically on the ratio (r) of stau to smuon masses. The signal process, e+e−→γZ′→γ+E/ at Belle-II arises through kinetic mixing in this case. Considering the constraints on gauged U(1)Lμ−Lτ models, we show that any significant excess in all but the highest photon energy bin would be a smoking gun for such heavy scalar fields in SUSY coupling to Z′. This process can probe large swathes of the r vs gX parameter space as well as the MZ′−gX parameter space still allowed in gauged U(1)Lμ−Lτ models for superheavy sparticles.
- Tuesday 19 November 2019 at 10.15 in A315: Viljami Leino (Munich)
Lattice constraints to heavy quark diffusion coefficent
Abstract: The matter produced in heavy ion collisions at ALICE and RHIC can be characterized as a strongly couplend quark gluon plasma. Within this plasma, the heavy quarks can be seen to behave with Langevin dynamics, with the diffusion expressed with heavy quark momentum diffusion coefficient. We measure the diffusion coefficient non-perturbatively using lattice field theory simulations. We present the results in very wide temperature range allowing us to connect to perturbation theory and observe the temperature dependence of this quantity.
- Thursday 21 November 2019 at 10.15 in A315: Varun Sethi (Delhi U) CANCELLED due to travel difficulties!!
Brane configurations and tachyons at finite temperature in dense holographic QCD
Abstract: Starting with arXiv:1104.2843 [hep-th], which presents a top-down approach to holographic superconductor using an intersecting brane configuration in Witten-Sakai-Sugimoto model at finite density, we consider a toy configuration of intersecting D3-branes to model the above brane configuration and analyse its thermal stability in Yang-Mills approximation. We further extend the calculation to consider intersecting stacks of D-branes at finite temperature. A different brane configuration is then proposed, that could arise in the context of arXiv:1104.2843 [hep-th]. We then study and compare various phases of the holographic QCD model at finite baryon number and isospin chemical potential.
- Tuesday 26 November 2019 at 10.15 in A315: Karapet Mkrtchyan (Pisa)
The problem of interacting Lagrangian for higher-spin gravity and the progress in three dimensions
Abstract: I shall review the general problem of constructing action for higher-spin gravity ( a massless with spin bigger or equal to 2 fields, in addition to the metric graviton and lower spin fields) theories in arbitrary space-time dimensions, and comment in detail on the recent progress in constructing Lagrangian interactions for massless bosonic fields of arbitrary spin in three dimensions. Relevant publications:
- Thursday 28 November 2019 at 10.15 in A315: Jorinde van de Vis (DESY)
Reheating after multifield inflation with nonminimal couplings
Abstract: Multiple scalar fields with nonminimal couplings to gravity form a well-motivated class of models that can describe inflation in accordance with cosmological observations. As a result of the nonminimal couplings, the field space is curved, leading to very efficient particle production when inflation ends. After introducing a framework to study particle production in these models, I will focus on two topics:
I Particle production after Higgs inflation. In a linearized treatment of reheating, I will show how the curved field space leads to very efficient production of gauge fields/Goldstone bosons, possibly resulting in instantaneous reheating.
II A lattice study of reheating after inflation with two fields. I introduce several time scales to quantify the efficiency of reheating. I will show that, even in the case where isocurvature modes are produced in copious amounts, the model is still consistent with CMB-observables.
- Tuesday 3 December 2019 at 10.15 in A315: Alberto Roper-Pol (Colorado)
Gravitational wave production from MHD turbulence in the early-universe
Abstract: Possible future detections of gravitational waves with LISA open a new window on gravitational astronomy, which might allow us to obtain direct evidence of the very early universe physics. In the case of a first-order phase transition, the generation of false vacuum bubbles is expected, and this process could lead to turbulent motions in the primordial plasma. At the same time, cosmological phase transitions could reproduce the required conditions for primordial magnetogenesis. I will present the results of direct numerical MHD simulations of primordial magnetic fields and turbulent motions, and the production of gravitational wave radiation due to MHD turbulence. We conclude that the gravitational waves produced during a first-order electroweak phase transition could be detected by LISA if at least 1% of the total energy density of the universe is transformed into magnetic and/or kinetic energ
- Thursday 5 December 2019 at 10.15 in A315: Andreas Schmitt (Southampton)
Dense quark and nuclear matter from holography
Abstract: Neutron stars host the densest matter in the universe and possibly contain a core of deconfined quark matter. Therefore, a theoretical understanding of these ultra-dense objects requires an approach that accounts for both nuclear and quark matter on the same footing and for a possible transition between them. I will present a holographic calculation where nucleons are described by interacting instantons and will show how nuclear matter can be continuously connected with deconfined quark matter.
- Thursday 12 December 2019 at 10.15 in A315: Javier Mas (Santiago de Compostela)
Periodically Driven AdS/CFT
Abstract: Quantum systems interacting with a periodic agent go by the name of Floquet systems. They have show to exhibit unexpected features, prominently, the strong resilience against decoherence, as well as the appearance of topologically protected transport properties. We have performed numerical simulations in Global AdS in various models. Remarkably the external agent act similarly to a bath, and the both ways exchange of energy can lead to stable evolutions that don’t collapse. We map out the boundary of the regions of stability. Beyond that, unstable solutions typically decay into a black hole. However we also find end points of the instability that avoid decoherence. Finally we perform various numerical experiments to study the adiabaticity of slow modulations in the driving. In particular, we device a protocol that allows to create a boson star out of Anti de Sitter vacuum, and speculate about the analogy with a Time Crystal.
- Thursday 19 December 2019 at 10.15 in A315: Wilke van der Schee (CERN)
Gravitational Waves from Holographic Neutron Star Mergers
Abstract: In this talk I will first give some overview on the current status of neutron star mergers, in particular focusing on the equation of state. In the strongly coupled regime the equation of state is hard to compute from first principles, which is why I will then introduce a holographic model. Interestingly this equation of state is rather stiff (high speed of sound), and can give rise to neutron stars compatible with astrophysical bounds. In the last part I will present our full numerical simulations of neutron star mergers, together with the gravitational wave power spectrum.