Theoretical Cosmology Meetings
To actively encourage the field of Theoretical Cosmology in the Netherlands and to set an informal stage for the exchange of ideas, the small but growing Dutch Theoretical Cosmology community organizes Friday afternoon meetings approximately 6 times a year --- usually on the first Friday of the month. The meetings start in the afternoon with a main speaker, followed by a short break to continue with a journal club discussion on some topic of current interest. We end the afternoon with drinks. The supporting institutes, Leiden, Amsterdam and Utrecht, each take turns in hosting the event.
For more details (personalia) about the landscape of Dutch Theoretical Cosmology, click the THC landscape button on the left menu. For a list of accomplishments and the latest THC news click here.
Schedule 2011-2012
Friday December 7, 2012 (University of Utrecht)
1400h: Minnaert building, room 401Speaker: Pedro Ferreira (Oxford)
Title: TBA
Abstract: TBA
Friday June 1, 2012 (Nikhef Institute)
1400h: Seminar room H331Speaker: Gianmassimo Tasinato (University of Portsmouth, UK)
Title: Non-linear interactions and exact solutions in massive gravity
Abstract: I will start discussing the basic features of a covariant massive gravity model, which is a candidate for a ghost-free non-linear extension of Fierz-Pauli. I will then analyze how strong coupling effects make the phenomenology of this model particularly interesting. First, I will show how non-linear interactions are able to screen the effects of additional degrees of freedom in this theory, leading to predictions compatible with general relativity. Then, I will discuss a general class of exact solutions of this theory, containing cosmological configurations able to describe present day acceleration of our universe with no need of a positive cosmological constant. I will conclude discussing the surprising properties of the dynamics of fluctuations around some of these configurations.
1530h: Journal club discussion
Speaker: Damien George (Nikhef)
Gorge will discuss : arXiv:.
Friday May 11, 2012 (Nikhef Institute, Amsterdam)
1400h: Nikhef Building (oppesite to the Science Park 904 building), H331Speaker: Sera Cremonini (DAMTP)
Title: A Critical Look at Effective Field Theory Violations During Inflation
Abstract: I will discuss the validity of effective field theory methods and the decoupling of heavy fields during inflation. In particular, I will consider inflationary models in which the inflaton is coupled to a heavy (super-Hubble) degree of freedom which is initially in its vacuum state. A temporary departure from inflation can lead to a period of non-adiabaticity, during which effective field theory methods are known to fail. However, the locality of the event and energy conservation lead to a tight bound on the size of the effects of the heavy field, and therefore on the resulting corrections to the power spectrum. These results further motivate the use of effective field theory methods to characterize inflationary dynamics, and focus the question of observability of additional degrees of freedom during inflation to near the Hubble scale or below.
1530h: Journal club discussion
Speaker: Ana Achucarro (U. of Leiden)
Ana will discuss her most recent paper on ``Heavy fields, reduced speeds of sound and decoupling during inflation'' : arXiv:1205.0710.
Friday April 13, 2012 (University of Utrecht)
1400h: Minnaert building, MG 211Speaker: Thomas Konstandin (CERN & DESY)
Title: Electroweak baryogenesis - a status report
Abstract: After a review of the mechanism of electroweak baryogenesis I discuss its viability in different models in the light of recent experimental results. In particular, I discuss the status in the MSSM and in a class of singlet extensions that serve as effective theories to composite Higgs models.
1530h: Journal club discussion
Speaker: Jan Weenink (U. of Utrecht)
Jan will give an overview of recent developments in inhomogeneous cosmologies. The discussion will be based on:
arXiv:1203.4567, "Cosmology when living near the Great Attractor" by Valkenburg & Bjaelde;
arXiv:1110.2587, "Topological quintessence" by Bueno Sanchez & Perivolaropoulos;
arXiv:1203.6776 , "Inhomogeneous vacuum energy" by Wands et al;
arXiv:1203.6776 , "Inhomogeneous non-Gaussianity" by Byrnes et al.
Friday March 2, 2012 (University of Leiden)
1400h: Seminar in Lorentz Seminar RoomSpeaker: Mikhail Shaposhnikov
Title: Scale-invariant alternatives to general relativity
Abstract: We study the general class of gravitational field theories constructed on the basis of scale invariance (and therefore absence of any mass parameters) and invariance under transverse diffeomorphisms (TDiff), which are the 4-volume conserving coordinate transformations. We show that these theories are equivalent to a specific type of scalar-tensor theories of gravity (invariant under all diffeomorphisms) with a number of properties, making them phenomenologically interesting. In particular, they lead to the evolution of the universe supported by present observations: inflation in the past, followed by the radiation and matter dominated stages and accelerated expansion at present. All mass scales in this type of theories come from one and the same source. The massless particle spectrum of these theories contains the graviton and a new particle -- dilaton, which has only derivative couplings and thus escapes the fifth force constraints.
1530h: Journal club discussion
Speaker: Dmytro akubovskyi will lead the discussionon on ``Cores in warm dark matter haloes: a Catch 22 problem'' by Andrea V. Maccio', Sinziana Paduroiu, Donnino Anderhalden, Aurel Schneider, Ben Moore, arXiv:1202.1282.
Friday February 3, 2012 (University of Leiden)
1400h: Seminar in Lorentz Seminar RoomSpeaker: Julien Lesgourges (CERN)
Title: The intriguing radiation content of the universe
Abstract: In the minimal cosmological model, during the radiation dominated stage, the energy of the universe is attributed to photons and to the three known families of active neutrinos, with standard properties. This assumption is still poorly constrained by the data, but in the last few years a number of cosmological and particle physics experiment raised some marginal preference for a radiation density excess. Within the next twelve months, cosmological experiments like Planck or BOSS will trigger some spectacular progress in understanding the abundance and properties of cosmological radiation. We will try to shed some light on these issues, first by clarifying the observable effects of extra light relics in cosmology, and second by summarizing the theoretical challenges for neutrino physics and cosmology that may result from a possible excess detection.
1530h: Journal club discussion
Speaker: Ted van der Aalst will lead the discussionon on two papers on conformal invariance in inflation: arXiv:1108.0874 (Creminelli), arXiv:1103.4164 (Antoniadis, Mazur, Mottola).
There will be another talk at Utrecht (MG 401) given by Chiara Caprini (CEA, Saclay) at 2pm on February 20, Monday. Everyone is welcome.
Title: Gravitational waves from first order phase transitions
Abstract: Gravitational waves can constitute a unique probe of the very early universe. This seminar concentrates on a particular source of a stochastic background of gravitational waves, namely a primordial first order phase transition. The gravitational wave signal is generated by the collision of the broken phase bubbles and by the magnetohydrodynamic turbulence in the primordial plasma stirred by the bubble collision. It will be shown how the main features of the gravitational wave spectrum can be predicted by simple, general arguments based on the source properties, such as its time evolution and space structure. Detection prospects will be discussed in particular for the electroweak phase transition, in connection with the new NGO/eLISA mission of ESA.
Friday December 2, 2011 (University of Leiden)
Special Note: Avi Loeb will be delivering the Sackler Lectures in Leiden Nov 21-25. These will include an introduction to 21 cm cosmology, which will be the topic of Pritchard's talk on December 2. Everyone is welcome to attend both events.1400h: Seminar in Lorentz Seminar Room
Speaker: Jonathan Pritchard (Imperial)
Title: Exploring the dawn of cosmic structure with the 21 cm line and CO mapping
Abstract: The first billion years after the
Big Bang is the period where the first stars and galaxies form yet this
period remains one at the frontier of observations. In this talk,
I will discuss new techniques that promise the possibility of
transforming our understanding of this period. First, I will
discuss applications of radio observations of the redshifted 21 cm
line. Observations of the sky averaged global signal with single dipole
experiments and measurements of fluctuations with interferometers could
offer new insights into reionization and early X-ray and UV emission of
the first galaxies. I will also discuss the possibility for
"intensity mapping" in atomic and molecular lines as an alternative to
traditional galaxy surveys. Focussing on CO intensity mapping
during the epoch of reionization, I will explore how such measurements
could provide a large scale context for our understanding of how
galaxies form and produce metals.
1530h: Journal club discussion
Speaker: Sander Mooij will lead the discussion about the article "The principle of relative locality," by Giovanni Amelino-Camelia, Laurent Freidel, Jerzy Kowalski-Glikman and Lee Smolin, arXiv:1101.0931.
November, 2011
There will be three Amsterdam-area cosmology events in November:
1) APP at the University of Leiden, November 3
2) Special THC Seminar at the University of Amsterdam, Friday November 4
1400h in room C4.174 (right across the elevator on the 4th floor)
Speaker: Thomas Hartman (Princeton)
Title: Holography in de Sitter Space with a Free CFT
Because de Sitter space shares some
features with anti-de Sitter, it is tempting to apply holography and
the AdS/CFT correspondence to cosmology, but specific theories are
difficult to construct. I will describe a proposal for an explicit
holographic duality in four-dimensional de Sitter space, based on
higher spin gravity. The boundary CFT is free and therefore provides an
exactly solveable toy model for quantum gravity in de Sitter space.
3) Strong Coupling and Holography in Cosmology Workshop at the University of Amsterdam, November 7-8
Friday Sept 30, 2011
(University of Amsterdam)
Friday June 10, 2011 (University of Utrecht)
1400h:
Seminar in A1.10
Speaker:
PierStefano Corasaniti
(LUTH, Observatory of Paris)
Title: A new approach to halo counting statistics: path-integral, non-spherical halo collapse and primordial non-Gaussianity
1530h: Journal club discussion
Speaker: Jan Pieter van der Schaar (University of Amsterdam)
Jan Pieter will lead a discussion about the article "The Multiverse Interpretation of Quantum Mechanics" by Susskind and Bousso, arXiv:1105.3796.
Title: A new approach to halo counting statistics: path-integral, non-spherical halo collapse and primordial non-Gaussianity
Abstract:
The mass distribution of dark matter halos in the universe
carries unique information on the non-linear gravitational processes
that have shaped the late time cosmic structure formation. Due to the
complexity of the non-linear collapse of dark matter density
fluctuations, the halo mass function has been mainly investigate using
numerical N-body simulations. In this talk I will review some
recent theoretical advancements based on a path-integral formulation of
the Excursion Set theory and present an analytical computation of the
halo mass function for Gaussian and non-Gaussian initial conditions in
the case of an effective stochastic barrier model which captures the
main features of the non-spherical collapse of dark matter halos. This
provides a mathematical description of halo mass function that
explicitly depends on physical model parameters and which we find to be
in remarkable agreement with Gaussian and non-Gaussian numerical N-body
simulation results.
1530h: Journal club discussion
Speaker: Jan Pieter van der Schaar (University of Amsterdam)
Jan Pieter will lead a discussion about the article "The Multiverse Interpretation of Quantum Mechanics" by Susskind and Bousso, arXiv:1105.3796.
Schedule 2010-2011
Friday June 10, 2011 (University of Utrecht)
1400h:
Seminar in Minnaert Gebouw 211 (lecture hall on second floor)
Speaker: David Polarski (Montpellier, France)
Title: Dark Energy
Abstract: The Universe has presumably entered a stage of accelerated expansion rate at low redshifts. This is a radical departure from conventional cosmology. Various ways to address this fundamental problem have been proposed and we will review some of them.
1530h: Seminar
Speaker: Richard Woodard
Title: The Graviton Propagator in de Donder Gauge on de Sitter Background
Abstract: We construct the graviton propagator on de Sitter background in exact de Donder gauge. We prove that it must break de Sitter invariance, just like the propagator of the massless, minimally coupled scalar. Our explicit solutions for its two scalar structure functions preserve spatial homogeneity and isotropy so that the propagator can be used within the larger context of inflationary cosmology, however, it is simple to alter the residual symmetry. Because our gauge condition is de Sitter invariant (although no solution for the propagator can be) renormalization should be simpler using this propagator than one based on a noncovariant gauge. It remains to be seen how other computational steps compare. Preprint: 1106.0925
Note: Richard is also giving an ITP Colloquium next Wed at 4pm (Title: "A Non-Technical (Would I Lie?) Discussion of the Problem of Quantum Gravity'')
Title: Dark Energy
Abstract: The Universe has presumably entered a stage of accelerated expansion rate at low redshifts. This is a radical departure from conventional cosmology. Various ways to address this fundamental problem have been proposed and we will review some of them.
1530h: Seminar
Speaker: Richard Woodard
Title: The Graviton Propagator in de Donder Gauge on de Sitter Background
Abstract: We construct the graviton propagator on de Sitter background in exact de Donder gauge. We prove that it must break de Sitter invariance, just like the propagator of the massless, minimally coupled scalar. Our explicit solutions for its two scalar structure functions preserve spatial homogeneity and isotropy so that the propagator can be used within the larger context of inflationary cosmology, however, it is simple to alter the residual symmetry. Because our gauge condition is de Sitter invariant (although no solution for the propagator can be) renormalization should be simpler using this propagator than one based on a noncovariant gauge. It remains to be seen how other computational steps compare. Preprint: 1106.0925
Note: Richard is also giving an ITP Colloquium next Wed at 4pm (Title: "A Non-Technical (Would I Lie?) Discussion of the Problem of Quantum Gravity'')
Friday May 6, 2011 (University of Leiden)
1400h:
Seminar in de Sitter Lecture Hall (NOTE ROOM CHANGE)
Speaker: Martin Sloth
(CERN)
Title: Cosmological Perturbations and IR Issues in quasi de Sitter Universes
Abstract: Using simple semiclassical relations it is possible to show that the conventional cosmological correlation functions are affected by significant IR corrections in quasi de Sitter space-times when averaged over very large volumes (in the "large box"). The IR effects apparently imply a breakdown of perturbation theory in the large box on sufficiently long time scales, for example the time between self-reproduction and reheating in chaotic inflation. An interpretation of the apparent breakdown of the perturbative expansion of gravity and the relation to the black hole information paradox will also be briefly discussed. Then we will show how one can define "IR-safe" observables seen by a post-inflationary observer today (in the "small box"), leading to a cosmological RG equation connecting "large box" and "small box" observers. Finally, we demonstrate how an observer today might be able to observe the beginning of the end of perturbative de Sitter imprinted in small statistical inhomogeneities/anisotropies at short scales.
1530h: Journal club discussion in Lorentz Seminar Room
Speaker: Pablo Ortiz (Leiden University)
Pablo will lead a discussion about the article "Gauge-flation: Inflation from non-abelan gauge fields" (arXiv:1102.1513).
Title: Cosmological Perturbations and IR Issues in quasi de Sitter Universes
Abstract: Using simple semiclassical relations it is possible to show that the conventional cosmological correlation functions are affected by significant IR corrections in quasi de Sitter space-times when averaged over very large volumes (in the "large box"). The IR effects apparently imply a breakdown of perturbation theory in the large box on sufficiently long time scales, for example the time between self-reproduction and reheating in chaotic inflation. An interpretation of the apparent breakdown of the perturbative expansion of gravity and the relation to the black hole information paradox will also be briefly discussed. Then we will show how one can define "IR-safe" observables seen by a post-inflationary observer today (in the "small box"), leading to a cosmological RG equation connecting "large box" and "small box" observers. Finally, we demonstrate how an observer today might be able to observe the beginning of the end of perturbative de Sitter imprinted in small statistical inhomogeneities/anisotropies at short scales.
1530h: Journal club discussion in Lorentz Seminar Room
Speaker: Pablo Ortiz (Leiden University)
Pablo will lead a discussion about the article "Gauge-flation: Inflation from non-abelan gauge fields" (arXiv:1102.1513).
Friday April 1, 2011 (University of Amsterdam)
1400h:
Seminar in C4.174
(right across the elevator on the 4th floor)
Speaker: James Fergusson
(DAMTP, Univ of Cambridge)
Title: Constraining nonGaussianity with the CMB
Abstract: Detection of nonGaussianity would be very significant as it would not only rule out single field slow roll inflation but it's form would provide a clear indication as to which other class of models would replace it. However due to the complexity of calculating higher order correlators, which are best suited to constraining it, work so far has focused exclusively on a couple of simple cases. In this talk I will propose a new approach which allows us not only to constrain nonGaussianity of any type, but to also generate simulated nonGaussian maps for any given model, detect and eliminate all known contaminants, and directly reconstruct the form of the nonGaussianity from the data both at late times and primordialy.
1600h: Colloquium (note special event, time and place) in room C1.12
Speaker: Amina Helmi (University of Groningen)
Title: Lessons from Near-field Cosmology
Abstract: Near-field cosmology is an active area of research in current astrophysics. It focuses on testing the cosmological model on the scales of the Milky Way galaxy and its nearest neighbours. I will review what we have learned from observations and modelling of these systems in recent years.
Title: Constraining nonGaussianity with the CMB
Abstract: Detection of nonGaussianity would be very significant as it would not only rule out single field slow roll inflation but it's form would provide a clear indication as to which other class of models would replace it. However due to the complexity of calculating higher order correlators, which are best suited to constraining it, work so far has focused exclusively on a couple of simple cases. In this talk I will propose a new approach which allows us not only to constrain nonGaussianity of any type, but to also generate simulated nonGaussian maps for any given model, detect and eliminate all known contaminants, and directly reconstruct the form of the nonGaussianity from the data both at late times and primordialy.
1600h: Colloquium (note special event, time and place) in room C1.12
Speaker: Amina Helmi (University of Groningen)
Title: Lessons from Near-field Cosmology
Abstract: Near-field cosmology is an active area of research in current astrophysics. It focuses on testing the cosmological model on the scales of the Milky Way galaxy and its nearest neighbours. I will review what we have learned from observations and modelling of these systems in recent years.
Friday March 4, 2011 (University of Amsterdam)
1400h:
Seminar in C4.174 (right across the elevator on the 4th floor)
Speaker: Leonardo Senatore
(Stanford University)
Title: The Effective Field Theory of Inflation and of Multifield Inflation
Abstract: I will describe the effective field theory of inflation and of multifield inflation, i.e. the most general theory describing the fluctuations around a quasi de Sitter background, in the case of single and multi-field models. This approach allows us to describe in a unique Lagrangian all possible inflationary models. It also allows us to fully explore the spectrum of the possible signatures that can be generated by inflation. Finally, it represents the most direct way of mapping cosmological observations into parameters of a fundamental Lagrangian. This is particularly important given the on-going experimental effort from the WMAP and Planck satellites, as well as from the Large Scale Structure surveys. I will describe how this effective Lagrangian is constructed, the most important signatures that we can infer from it, and finally how current observations are already beginning to constrain its parameters.
1530h: Journal club discussion in ITFA common room (C4.278)
Speaker: Ted van der Aalst (University of Leiden)
Ted will be leading the discussion about A Minimal Inflation Scenario, arXiv:1101.4948
Title: The Effective Field Theory of Inflation and of Multifield Inflation
Abstract: I will describe the effective field theory of inflation and of multifield inflation, i.e. the most general theory describing the fluctuations around a quasi de Sitter background, in the case of single and multi-field models. This approach allows us to describe in a unique Lagrangian all possible inflationary models. It also allows us to fully explore the spectrum of the possible signatures that can be generated by inflation. Finally, it represents the most direct way of mapping cosmological observations into parameters of a fundamental Lagrangian. This is particularly important given the on-going experimental effort from the WMAP and Planck satellites, as well as from the Large Scale Structure surveys. I will describe how this effective Lagrangian is constructed, the most important signatures that we can infer from it, and finally how current observations are already beginning to constrain its parameters.
1530h: Journal club discussion in ITFA common room (C4.278)
Speaker: Ted van der Aalst (University of Leiden)
Ted will be leading the discussion about A Minimal Inflation Scenario, arXiv:1101.4948
Friday February 4, 2011 (University of Leiden)
1400h:
Seminar in Lorentz Seminar Room
Speaker: Alexander Westphal (DESY)
Title: Simple exercises to flatten your potential
Abstract:
Speaker: Alexander Westphal (DESY)
Title: Simple exercises to flatten your potential
Abstract:
We show how backreaction of the
inflaton
potential energy on heavy scalar fields can flatten the inflationary
potential, as the heavy fields adjust to their most energetically
favorable configuration. This mechanism operates in previous
UV-complete examples of axion monodromy inflation - flattening a
would-be quadratic potential to one linear in the inflaton field - but
occurs more generally, and we illustrate the effect with several
examples. Special choices of compactification minimizing
backreaction may realize chaotic inflation with a quadratic potential,
but we argue that a flatter potential such as power-law inflation
$V(\phi) \propto \phi^p$ with $p<2$ is a more generic option at
sufficiently large values of $\phi$.
Speaker: Bret Underwood (McGill)
Title: A Breathing mode for Compactifications
Abstract: How do we study the
physics of theories with extra dimensions? The easiest thing to
do is to reduce the higher dimensional description to a 4-dimensional
effective description. This results in a number of scalar fields
describing, for instance, fluctuations of higher dimensional scalar
fields (dilaton) or the volume of the compact space (volume
modulus). But the fields in the effective theory must be
constructed with care: artifacts from the higher dimensions, such as
higher dimensional diffeomorphisms and constraint equations, can
restrict or remove putative degrees of freedom entirely. The
effective theory including these effects resembles in many ways
cosmological perturbation theory. The constraints and
diffeomorphisms generically lead the dilaton and volume modulus to
combine into a single degree of freedom in the effective theory, the
"breathing mode". This implies that models of inflation or moduli
stabilization involving extra dimensions which treat these moduli as
separate have the wrong degrees of freedom.