Central European Institute for Cosmology and Fundamental Physics

Past seminars

7 May 2018, 14:00    Diego Blas,  Probing dark matter properties with pulsar timing


4 May 2018, 14:00    Peter Tinyakov,  Compact stars as dark matter probes


3 May 2018, 14:00    Jan Novák,  Scalar perturbations of Galileon cosmologies in the mechanical approach in the late Universe


12 Apr 2018, 14:00    Tomi Koivisto,  Symmetric Teleparallelism


10 Apr 2018, 14:00    Luca Marzola,  The 21-cm Line


27 Mar 2018, 14:00    Julian Adamek,  Evolving The Metric - N-body simulations for relativistic cosmology

20 Mar 2018 14:00     Patrick Stengel,  The Higgs boson can delay Reheating after Inflation

15 Mar 2018 14:00    Ilidio Lopes,  Impact of dark matter in stellar oscillations

20 Feb 2018 14:00     Eric Bergshoeff,  Gravity and the spin-2 planar Schroedinger equation

1 Feb 2018 16:00     Luca Visinelli,  Axions in cosmology and astrophysics

12 Feb 2018 14:00     Roberto Oliveri,  Gravitational multipole moments from Noether charges

30 Jan 2018 14:00     Eleonora Villa,  Theoretical systematics in galaxy clustering in LCDM and beyond

23 Jan 2018 14:00     Petr Satunin,  Constraints on violation of Lorentz invariance from atmospheric showers initiated by multi-TeV photons

12 Dec 2017 14:00     David Svoboda,  Twisted brackets, fluxes, and deformations of para-Kahler manifolds

11 Dec 2017 16:00     Martin Roček,  WZW models and generalized geometry

05 Dec 2017 14:00     Dimitris Skliros,   Coherent states in String Theory

04 Dec 2017 14:00     Ed Copeland,  Screening mechanisms and testing for them in cosmology and the laboratory

30 Nov 2017 14:00     Marc Gillioz,  Sum Rules for the "c" Anomaly in 4 Dimensions

28 Nov 2017 14:00     Sugumi Kanno,  Decoherence of Bubble Universes

27 Nov 2017 14:00     Rachel Houtz,   Little Conformal Symmetry and Neutral Naturalness

08 Nov 2017 14:00     Pierre Fleury,  Weak lensing with finite beams

07 Nov 2017 14:00     Frederik Lauf,  Classification of three-dimensional Chern-Simons-matter theories

06 Nov 2017 14:00     Andrei Gruzinov,  Particle production by real (astrophysical) black holes

23 Oct 2017 14:00     George Pappas,   Neutron stars as matter and gravity laboratories

16 Oct 2017 14:00     Tessa Baker,   Tests of Beyond-Einstein Gravity

02 Oct 2017 14:00    Piotr Surowka  New developments in hydrodynamics
08 Sep 2017 14:00   Dani Figueroa, Higgs Cosmology: implications of the Higgs for the early Universe
06 Sep 2017 14:00   Sergey Ketov, Starobinsky inflation in supergravity
06 Sep 2017 11:00   Dalimil Mazáč, Analytic conformal bootstrap and QFT in AdS2
29 Jun 2017 14:00   Bruce Bassett, Rise of the Machine: AI and Fundamental Science
28 Jun 2017  14:00   Dmitri Semikoz, Signatures of a two million year old nearby supernova in antimatter data
2 Jun 2017  14:00   David Alonso, Science with future ground-based CMB experiments
22 May 2017  14:00   Mathieu Langer, Magnetizing the intergalactic medium during reionization
16 May 2017  16:00   Sergey Sibiryakov Counts-in-cells statistics of cosmic structure
25 Apr 2017  14:00    Ippocratis Saltas, What can unimodular gravity teach us about the cosmological constant?
12 Apr 2017  14:00    Andrei Nomerotski, Status and Plans for Large Synoptic Survey Telescope
  6 Apr 2017  14:00    Alex Vikman, The Phantom of the Cosmological Time-Crystals
  3 Apr 2017  14:00    Jnan Maharana, Scattering of Stringy States and T-duality
27 Mar 2017  14:00   Michal Bilek Galaxy interactions in MOdified Newtonian Dynamics (MOND)
27 Feb 2017  16:00   Misao Sasaki, Signatures from inflationary massive gravity
23 Feb 2017  14:00   Misao Sasaki, Inflation and Beyond
14 Dec 2016  14:00   Giovanni Acquaviva, Dark matter perturbations with causal bulk viscosity
  9 Dec 2016  14:00   David Pirtskhalava, Relaxing the Cosmological Constant
14 Nov 2016  14:00   Glenn Barnich, Finite BMS transformations
18 Oct 2016   14:00   Eugeny Babichev, Gravitational origin of dark matter





07/05/2018 -- Diego Blas (King's College London)

Time:  14:00

Place: 226

The high quality of the data from pulsar timing makes of it a fantastic resource to understand gravitational phenomena. Traditionally this has been used to test general relativity. In this talk I will describe a less explored possibility: using pulsar timing to understand dark matter properties. I will focus on (possibly) detectable modifications of binary orbits due to the interaction with dark matter in different scenarios.

04/05/2018 -- Peter Tinyakov (University Of Brussels)

Time:  14:00

Place: 226

Compact stars - neutron stars and white dwarfs - can capture and accumulate dark matter. Even though only a tiny fraction of the star mass can be accumulated in realistic conditions, this may lead to dramatic consequences such as the star collapse into a black hole. Thus, mere existence of neutron stars and white dwarfs sets constraints on DM models where this phenomenon occurs. Alternatively, if only a fraction of NS is converted into black holes, these may be identified with the gravitational wave detectors: the masses of such BH are around one solar mass, while stellar evolution does not lead to BH lighter than ~2 solar masses. We will discuss in detail two examples: the DM composed of primordial black holes, and asymmetric DM with self-interactions.



03/05/2018 -- Jan Novák (Technical University of Liberec)

Time:  14:00

Place: 226

We investigate the Universe at the late stage of its evolution and inside the cell of uniformity 150 - 370 MPc. We consider the Universe to be filled at these scales with dust like matter, a minimally coupled Galileon field and radiation as matter sources. We will use the mechanical approach and therefore the peculiar velocities of the inhomogeneities as well as fluctuations of other perfect fluids are nonrelativistic. Such fluids are said to be coupled, because they are concentrated around inhomogeneities. We investigate the conditions under which the Galileon field can become coupled. We know from previous work that at background level coupled scalar field behave as a two-component perfect fluid: a network of frustrated cosmic string and cosmological constant. We found a correction for the Galileon field, which behaves like matter. We investigate a similar task for K-essence models and we try to find the conditions under which the K-essence scalar field with the most general form for its action can become coupled. We investigate at the background level three particular examples of the K-essence models: (1) the pure kinetic K-essence field, (2) a K-essence with a constant speed of sound and (3) the K-essence model with the Lagrangian bX+cX2−V (φ). We demonstrate that if the K-essence is coupled, all these K-essence models take the form of multicomponent perfect fluids where one of the component is the cosmological constant. Therefore, they can provide the late-time cosmic acceleration and be simultaneously compatible with the mechanical approach.



10/04/2018 -- Luca Marzola (National Institute of Chemical Physics and Biophysics, Tallinn)

Time:  14:00

Place: 117

In this talk I review the origin of the 21-cm line and explain why the particle physics community is making such a big deal out of it. I will show two possible ways to use the new results of the EDGES experiment and try to convince you that, maybe, you should have a look into the matter too.

12/04/2018 -- Tomi Koivisto (NORDITA, Stockholm)

Time:  14:00

Place: 226

Teleparallel gravity is formulated in terms of a flat spacetime affine connection. In the symmetric teleparallelism, the affine connection is further torsion-free. These simplifications may improve the theory of gravity both technically (only first derivatives and no boundary term in the action) and conceptually (resolution of the gravitational energy, separation of the inertial effects). In the talk we will review these formulations and discuss some recent developments in the symmetric teleparallel geometry that were reported in the pre-print arXiv:1803.10185.

27/03/2018 -- Julian Adamek (Queen Mary University London)

Time:  14:00

Place: 117

I present a general (relativistic) framework for numerical simulations of cosmic large-scale structure in the context of generic metric theories of gravity. The full spacetime metric is evolved within a weak-field description, while cold dark matter is represented as an N-body ensemble that follows timelike geodesics. The framework allows one to study phenomena that lead to generic modifications of the metric perturbations, either by introducing new relativistic sources or by modifying the theory of gravity.


20/03/2018 -- Pat Stengel (University of Stockholm)

Time:  14:00

Place: 117

The Standard Model Higgs boson, which has previously been shown to develop an effective vacuum expectation value during inflation, can give rise to large particle masses during inflation and reheating, leading to temporary blocking of the reheating process and a lower reheat temperature after inflation. We study the effects on the multiple stages of reheating: resonant particle production (preheating) as well as perturbative decays from coherent oscillations of the inflaton field. Specifically, we study both the cases of the inflaton coupling to Standard Model fermions through Yukawa interactions as well as to Abelian gauge fields through a Chern-Simons term. We find that, in the case of perturbative inflaton decay to SM fermions, reheating can be delayed due to Higgs blocking and the reheat temperature can decrease by up to an order of magnitude. In the case of gauge-reheating, Higgs-generated masses of the gauge fields can suppress preheating even for large inflaton-gauge couplings. In extreme cases, preheating can be shut down completely and must be substituted by perturbative decay as the dominant reheating channel. Finally, we discuss the distribution of reheating temperatures in different Hubble patches, arising from the stochastic nature of the Higgs VEV during inflation and its implications for the generation of both adiabatic and isocurvature fluctuations.


15/03/2018 -- Ilidio Lopes (University of Lisbon)

Time:  14:00

Place: 226

For the past decade asteroseismology has opened a new window into studying the physics inside stars. Today, it is well known that more than ten thousand stars have been found to exhibit solar-like oscillations. This large amount of high-quality data for stars of different masses and sizes is having a profound impact in our understanding of the structure of stars in the main and the post-main sequence, on the formation and evolution of stellar clusters in our Galaxy. Moreover, it can be used to test new fundamental laws of nature including the existence of dark matter. While many particle candidates have been proposed as the main constituents of dark matter, the impact of such candidates in the evolution of stars has been sparsely addressed. In this talk, I will focus on the impact that dark matter has in the evolution of stars, and how stellar oscillations have been used to constrain the properties of dark matter. I will discuss the potential of the next generation of asteroseismic missions helping us to address this problem.

20/02/2018 -- Eric A. Bergshoeff (University of Groningen)

Time:  14:00

Place: 226

A Schroedinger equation proposed for the GMP gapped spin-2 mode of fractional Quantum Hall states is found from a novel non-relativistic limit, applicable only in 2+1 dimensions, of the massive spin-2 Fierz-Pauli field equations. It is also found from a novel null reduction of the linearized Einstein field equations in 3+1 dimensions, and in this context a uniform distribution of spin-2 particles implies, via a Brinkmann-wave solution of the non-linear Einstein equations, a confining harmonic oscillator potential for the individual particles.


11/12/2017 -- Martin Roček (SUNY, Stony Brook)

Time:  16:00

Place: auditorium

WZW models and generalized geometry

I'll review (2,2) superspace and explore how to describe the generalized kahler structure of (2,2) supersymmetric WZW models, presenting surprising new results for SU(3).


8/11/2017 -- Pierre Fleury (University of Geneva)

Time:  14:00

Place: 117

Weak lensing with finite beams

The standard theory of weak gravitational lensing relies on the infinitesimal light beam approximation. In this context, images are distorted by convergence and shear, the respective sources of which unphysically depend on the resolution of the distribution of matter—the so-called Ricci-Weyl problem. In this talk, I will discuss a strong-lensing-inspired formalism designed to deal with finite light beams. I will show that it solves the Ricci-Weyl problem. Furthermore, finite-size effects systematically enhance the beam’s distortions, which could affect the interpretation of cosmic shear data.


6/11/2017 -- Andrei Gruzinov (New York University)

Time:  14:00

Place: 226

Particle production by real (astrophysical) black holes

The rate of production of light bosons (if they exist) by astrophysical black holes is calculated. Observability of this effect is discussed.


23/10/2017 -- George Pappas (Lisbon Centre for Astrophysics)

Time:  14:00

Place: 226

Neutron stars as matter and gravity laboratories

Compact objects in general and neutron stars (NSs) in particular open a window to some of the most extreme physics we can find in nature. On the one hand in the interior of NSs we can find matter in very extreme densities, exceeding nuclear densities and anything we can probe in the laboratory, while on the other hand NSs are related to the strongest gravitational fields next only to those found in black holes. Therefore studying NSs gives us access to both supranuclear densities as well as strong gravity and can be used to get information and test our theories of matter (equation of state) and gravity. The relevant properties of the structure of NSs are encoded on the spacetime around them and by studying the astrophysical processes that take place around NSs we can map that spacetime and extract these properties (i.e., the multipole moments, the equation of state, etc). In this talk we will discuss these properties of NSs and how they are related to the properties of the spacetime around them both in GR and in one of the proposed alternative theories of gravity. We will also talk about the relation of these properties to astrophysical observables and how one could tell these theories apart.


16/10/2017 -- Tessa Baker (Oxford University)

Time:  14:00

Place: 226

Tests of Beyond-Einstein Gravity

Corrections to General Relativity on large distance scales are under consideration as an explanation of cosmic acceleration. However, studying extended gravity models on an individual basis is a labour-intensive way of testing these ideas. I will explain how instead EFT-inspired parameterised methods can be used as a powerful and efficient way of testing for deviations from GR. I will outline the theoretical foundations of these techniques, and describe the current status of their observational constraints.


8/9/2017 -- Dani Figueroa (CERN)

Time:  14:00

Place: 117

Higgs Cosmology: implications of the Higgs for the early Universe.

I will discuss some of the consequences arising when we take into account the existence, and hence the presence, of the Standard Model Higgs during Inflation. In particular, I will derive stringent constraints on the couplings of the Higgs to the inflationary and gravitational sectors. I will also discuss the circumstances under which the Higgs can be resposible for the origin of the Standard Model species required by the 'hot Big Bang' paradigm. If there is enough time, I will also discuss the implications of all this for primordial gravitational waves.


6/9/2017 -- Sergey Ketov (Tokyo Metropolitan University)

Time:  14:00

Place: 117

Starobinsky inflation in supergravity

I begin with an introduction to Starobinsky inflation based on (R+R^2) gravity, in light of Planck data about CMB. Next, I introduce the supergravity extensions of Starobinsky inflation, review their problems and possible solutions. I conclude with a discussion of reheating after Starobinsky inflation in the context of supergravity.

29/6/2017 -- Bruce Bassett (University of Cape Town)

Time:  14:00

Place: Room 117

Rise of the Machine: AI and Fundamental Science

With the recent spectacular advances in machine learning we are naturally confronted with the question of the limits of Artificial Intelligence (AI). Here we will review how AI is being used in astronomy, discuss the future role of AI in fundamental science and finally discuss whether AI will ever be able to undertake its own original research.

28/6/2017 -- Dmitry Semikoz (APC, Paris)

Time:  14:00

Place: Lecture hall

Signatures of a two million year old nearby supernova in antimatter data.

In this talk I will  show how one can explain multiple anomalies in the cosmic ray data by adding the effects of a 2 million year old nearby supernova to static model of galactic cosmic rays. In particular, this supernova can explain the excess of positrons and antiprotons above 20 GeV found by PAMELA and AMS-02, the discrepancy in the slopes of the spectra of cosmic ray protons and heavier nuclei in the TeV-PeV energy range and the plateau in cosmic ray dipole anisotropy in the 2-50 TeV energy range. Same supernova was responsible for Fe60 measured in ocean crust.

2/6/2017 -- David Alonso (University of Oxford)

Time:  14:00

Place: Room 117

Science with future ground-based CMB experiments.

After the findings of Planck, the immediate future of CMB observations lies with the next generation of ground-based experiments. In this talk I will first introduce the most compelling science objectives for these experiments in combination with future large-scale-structure surveys. Then I will describe a number of novel observational methods to tackle these objectives enabled by the enhanced angular resolution and reduced noise levels of Stage-3 and Stage-4 observatories, as well as the main challenges they will face.

22/5/2017 -- Mathieu Langer (Université Paris-Sud)

Time:  14:00

Place: Room 117

Magnetizing the intergalactic medium during reionization.

An increasing amount of evidence indicates that cosmological sheets, filaments and voids may be substantially magnetised. The origin of magnetic fields in the the Intergalactic Medium is currently uncertain. It seems now well known that non-standard extensions to the physics of the Standard Model are capable of providing mechanisms susceptible of magnetising the Universe at large. Much less well known is the fact that standard, classical physics of matter-radiation interactions possesses actually the same potential. After reviewing briefly our current knowledge about magnetic fields on the largest scales, I will discuss a magnetogenesis mechanism based on the exchange of momentum between hard photons and electrons in an inhomogeneous Intergalactic Medium. Operating in the neighbourhood of ionising sources during the Epoch of Reionization, this mechanism is capable of generating magnetic seeds of relevant strengths on scales comparable to the distance between ionising sources. In addition, summing up the contributions of all ionising sources and taking into account the distribution of gas inhomogeneities, I will show that this mechanism leaves the IGM, at the end of Reionization, with a level of magnetization that might account for the current magnetic fields strengths in the cosmic web.

--based on Durrive & Langer, MNRAS, 2015, and Durrive et al. MNRAS 2017 (submitted)--

16/5/2017 -- Sergey Sibiryakov (CERN, EPFL, INR RAS)

Time:  16:00

Place: Room 117

Counts-in-cells statistics of cosmic structure and non-perturbative methods of  quantum field theory

I will show how the probability distribution for matter over/under- densities in spherical patches of the universe can be derived from first principles using the instanton technique borrowed from quantum field theory. The spherical collapse solution plays the role of an instanton, whereas deviations from sphericity are consistently accounted for by a Gaussian integral over small perturbations around the instanton. The method is valid even for large — by a factor ten — deviations from the mean density and provides a way to probe the dynamics of dark matter and statistics of initial fluctuations in the regime where perturbative treatment does not apply.

25/4/2017 -- Ippocratis Saltas (University of Lisbon)

Time:  11:00

Place: Room 117

What can unimodular gravity teach us about the cosmological constant?

Unimodular gravity became very popular over the last years as a theory that could shed light on the cosmological—constant problem. In this talk, I will explain the idea behind unimodular gravity, and discuss its (in)ability to bring a new perspective to the problem of the cosmological vacuum.

12/4/2017 -- Andrei Nomerotski (Brookhaven National Lab, USA)


Time:  14:00

Place: Lecture Theatre

Status and Plans for Large Synoptic Survey Telescope

Investigation of Dark Energy remains one of the most compelling tasks for modern cosmology. It can be studied with several probes which are accessible through precise and deep surveys of the Universe. In the talk I will review the status and plans for Large Synoptic Survey Telescope, which will precisely measure the positions and shapes of billions of galaxies along with estimates of their distances, providing an order-of-magnitude improvement relative to current experiments. LSST Camera employs thick, fully depleted CCDs with extended infrared sensitivity. The talk will provide more detail on the camera design and will discuss limitations on the achievable precision coming from the instrumentation.

6/4/2017 -- Alex Vikman (CEICO, Institute of Physics)

Time:  14:00

Place: Lecture Theatre

The Phantom of the Cosmological Time-Crystals

I will discuss a recently proposed new cosmological phase where a scalar field moves exactly periodically in an expanding spatially-flat Friedmann universe. On average this phase has a vacuum or de Sitter equation of state and can be interesting to model Inflation and Dark Energy in a novel way. This phase corresponds to a limiting cycle of the equations of motion and can be considered as a cosmological realization of a general idea of a "time-crystal" introduced by Wilczek et. all in 2012. Recently we showed that this cosmological phase is only possible, provided the Null Energy Condition is violated and the so-called Phantom divide is crossed. Using methods from the dynamical systems, we proved that in a rather general class of single scalar field models called k-essence: i) this crossing causes infinite growth of quantum perturbations on short length-scales, and ii) exactly periodic solutions are only possible, provided the limiting cycle encircles a singularity in the phase plane. The configurations neighboring this singular curve in the phase space are linearly unstable on one side of the curve and superluminal on the other side. Moreover, the increment of the instability is infinitely growing for each mode by approaching the singularity, while for the configurations on the other side, the sound speed is growing without limit. We illustrated our general results by analytical and numerical studies of particular models proposed by Wilczek and collaborators. Finally I will briefly discuss systems where this idea of time-crystals may be realized.


 3/4/2017 -- Jnan Maharana (Institute of Physics, Sachivalaya Marg, India)


Time:  14:00

Place: Room 226.

Scattering of Stringy States and T-duality

First a brief overview of target space duality will be presented. Compactification of a closed bosonic string in its massless backgrounds wil be considered when it is compactified on a d-dimensional torus. The vertex operators associated with the moduli of the compactified closed string will be constructed. The Kawai-Llewellyn-Tye factorization technique will be utilized to show the T-duality transformation properties of S-matrix for the moduli.


27/3/2017 -- Michal Bilek (Astronomical Institute of the Czech Academy of Sciences)

Time: 14:00

Place: Room 117.

Galaxy interactions in MOdified Newtonian Dynamics (MOND)

MOdified Newtonian Dynamics (MOND) is a promising attempt to solve the missing mass problem by changing the standard laws of physics rather than by postulating the dark matter. MOND has been inspired by observations of isolated disk galaxies. It is thus important to test it also in other objects. First, I will give a short introduction to MOND and review the published simulations of interacting galaxies. I will then present my work on testing MOND in elliptical galaxies using remnants of accreted satellites and my simulation of the past close encounter of Milky Way and the Andromeda galaxy that MOND predicts. I will discuss observational evidence for this encounter.

27/2/2017 -- Misao Sasaki (Yukawa Institute for Theoretical Physics, Kyoto -- director)

Time: 16:00

Place: Room 117.

Signatures from inflationary massive gravity.

Inflation is a natural platform for modified gravity. In this talk, we consider
a theory that spontaneously violates the local SO(3) symmetry, which gives
rise to a preferred spatial frame during inflation.
As a result, the tensor modes become massive. We argue that this theory
leads to several interesting observational signatures.


23/2/2017 -- Misao Sasaki

Time: 14:00

Place: Lecture hall.

Colloquium: Inflation and Beyond.

There is strong observational evidence now that the Universe has
experienced an almost exponential expansion at its very early stage, called
inflation. In this talk I first review the inflationary universe and its observational
predictions. Then I discuss possible future directions beyond and behind theory
of inflation, and their observational signatures.


14/12/2016 -- Giovanni Acquaviva (Charles University, Prague)

Time: 14:00

Place: Room 226

Dark matter perturbations with causal bulk viscosity

We analyse the evolution of perturbations of cold dark matter endowed with bulk viscosity.  Focusing on structure formation well within the Hubble radius, the perturbative analysis is carried out in the Newtonian approximation while the bulk viscosity is described by Israel-Stewart's causal theory of dissipation.  Differently from previous analysis based on non-causal theories, we obtain a density contrast evolution governed by a third order equation.  This framework can be employed to address some of the current inconsistencies in the observed clustering of galaxies.

 9/12/2016 -- David Pirtskhalava (EPFL, Lausanne, Switzerland)
Time: 14:00
Place:Room 117.

Relaxing the Cosmological Constant

 14/11/2016 --Glenn Barnich (Université Libre de Bruxelles & International Solvay Institutes)
Time: 14:00
Place: Room 117

Finite BMS transformations

 18/10/2016 -- Eugeny Babichev (Laboratoire de Physique Théorique d'Orsay, Orsay, France)
Time: 14:00
Place: Room 117

Gravitational origin of dark matter