Oct. 9, 2019, 1:30 p.m.
Gravitational Waves: a new window onto the Early Universe
In anticipation of the next generation of gravitational wave experiments, I will discuss the opportunities for phenomenological studies of particle physics in the Early Universe. The focus of the talk will be on first order phase transitions in confining gauge theories. Such models may explain the strong CP-problem, baryogenesis, or flavour mass hierarchies. I will discuss several such examples and their gravitational wave phenomenology, and comment on complementarity with other experiments.
Oct. 16, 2019, 3 p.m.
Primordial Features in the BAO spectrum
One of the main challenges in cosmology is to characterise the physics of inflation. While a single weakly-coupled scalar field rolling down a very flat potential satisfies the basic requirements that observations impose on an inflationary scenario, a great number of phenomena that could take place during inflation are still unconstrained by data. Primordial features are one example of this phenomena and a well-motivated proof of the early universe in their own right. In this talk, we demonstrate that features in primordial spectra, much like the standard BAO themselves, are immune to the most basic nonlinear processes of the late universe and can be tested with the full statistical power of LSS surveys. We perform a full fledged analysis of the BOSS survey data and put constraints on linearly and logarithmically spaced primordial oscillations which are competitive with the ones obtained from CMB observations. Furthermore, we provide an extensive forecast of future surveys, such as EUCLID, DESI and SPHEREx, showing that the future of constraining primordial features is indeed in LSS observations.
Oct. 28, 2019, 11:30 a.m.
Generalized Josephson effects
The DC Josephon effect in superconductors is a current that flows between two samples without any voltage bias, purely due to the difference in order parameter phases. In this talk I show that a similar current exists for any type of spontaneous continuous symmetry breaking. It is identified as the DC (zero-wavenumber) Noether current associated with the broken symmetry, and can be expressed purely in terms of the broken symmetry generators. The generalized AC Josephson effect is due to an external asymmetric applied symmetry-generator field. This theory shows that the Josephson effect is an intrinsic property of symmetry breaking, and it applies to all known examples including superconductors, superfluids, magnets and non-Abelian condensates. Furthermore I predict a Josephson displacement current between two crystalline solids, which in this case also leads to a force periodic in the separation between the two samples. reference: arXiv:1907.13284 advertisement: lecture notes on spontaneous symmetry breaking arXiv:1909.01820
Oct. 30, 2019, 11:30 a.m.
Casimir room, Oort building
Statistics of radiation due to non-degenerate Josephson parametric down conversion
Oct. 30, 2019, 3 p.m.
Dark Energy Instabilities induced by Gravitational Waves
In this talk I will discuss the decay of gravitational waves (GW) into Dark Energy (DE) fluctuations $\pi$ in the context of the EFT of DE. In such theories, the time-dependence of the DE field spontaneously breaks Lorentz invariance. Therefore, as for light in a material, GW travelling in the cosmic medium are affected by dispersion phenomena and, at the quantum level, can decay into DE fluctuations. For cubic Horndeski and beyond Horndeski theories, a realistic GW acts as a classical background for $\pi$ and thus modifies its dynamics. In particular, for sufficiently large amplitudes of the wave, the kinetic term of $\pi$ becomes pathological, featuring gradient and ghost instabilities. Thus, by demanding that the effective theory of $\pi$ remains valid for LSS predictions we obtain strong constants on cubic and quartic Horndeski theories. For smaller amplitudes, $\pi$ fluctuations are described by a Mathieu equation and feature instability bands that grow exponentially. In such case the GW signal is affected by the $\pi$ back-reaction and this provides very stringent bounds quartic GLPV theories.
Nov. 6, 2019, 3 p.m.
De Sitter Meeting
Archisman Ghosh and Omar Contigiani
Nov. 13, 2019, 3 p.m.
Nov. 14, 2019, 11:30 a.m.
Chaos in the butterfly cone
A simple probe of chaos and operator growth in many-body quantum systems is the out of time ordered four point function. In a large class of local systems, the effects of chaos in this correlator build up exponentially fast inside the so called butterfly cone. It has been previously observed that the growth of these effects is organized along rays and can be characterized by a velocity dependent Lyapunov exponent. We prove a bound on this exponent that generalizes the chaos bound of Maldacena, Shenker and Stanford. We observe that many systems saturate this bound in a finite size region near the edge of the butterfly cone and the size of this region grows with the coupling. We discuss the connection to conformal Regge theory, where the velocity dependent exponent controls the four point function in an interpolating regime between the Regge and the light cone limit, and relate the aforementioned saturation of our bound to an exchange of dominance between the stress tensor and the pomeron.
Nov. 19, 2019, 1:30 p.m.
Multi-Scale Perturbation Theory for Cosmologies with Nonlinear Structure
Cosmological perturbation theory relies on the assumption that density contrasts are small. This assumption is valid for most of the history of the universe, but begins to break down at late times due to matter’s susceptibility to gravitational collapse. However, the post-Newtonian treatment of gravity is perfectly capable of dealing with highly nonlinear density contrasts, so long as the system under consideration is slow-moving and small in spatial extent - precisely the conditions present in large-scale structures such as superclusters! I will present a novel formalism for simultaneously applying a post-Newtonian expansion on short scales, while keeping a traditional approach to perturbation theory on large scales. This approach allows for the possibility of explicit coupling between terms from each sector. I will then use approximate solutions to calculate the matter bispectrum, using this statistic to highlight similarities and differences between traditional perturbation theory and our new multi-scale approach.
Nov. 20, 2019, 3 p.m.
De Sitter Meeting
Hidde Jense + Marius Cautun
Marius Cautun will present "The distribution of dark matter in hydrodynamical simulations and in the Milky Way” (https://arxiv.org/abs/1911.04557) Hidde Jense will discuss the formation of primordial black holes from an EFT for inflation and PBHs as dark matter candidates.
Nov. 27, 2019, 11:30 a.m.
Random-Matrix perspective on many-body localization
Nov. 27, 2019, 3 p.m.
Cosmological Parameters from the BOSS Galaxy Power Spectrum
I will present cosmological parameter measurements from the publicly available Baryon Oscillation Spectroscopic Survey (BOSS) data on anisotropic galaxy clustering in Fourier space. Assuming a minimal LCDM cosmology with varied massive neutrinos, fixing the primordial power spectrum tilt, and imposing the big bang nucleosynthesis (BBN) prior on the physical baryon density omega_b, the measured late-Universe parameters are: Hubble constant H_0 = 67.89 ± 1.06 km/s/Mpc, matter density fraction Omega_m = 0.295 ± 0.010, and the mass fluctuation amplitude sigma_8 = 0.721 ± 0.043. These parameters were measured directly from the BOSS data and independently of the Planck cosmic microwave background observations. I will also comment on combination of BOSS and Planck data and prospects for future spectroscopic surveys to put even tighter constraints on cosmological parameters.
Nov. 27, 2019, 7:30 p.m.
Gravitational waves: Physics at the Extreme
Jo van den Brand
The LIGO Virgo Consortium achieved the first detection of gravitational waves. A century after the fundamental predictions of Einstein, we report the first direct observations of binary black hole systems merging to form single black holes. The detected waveforms match the predictions of general relativity for the inspiral and merger of a pair of black holes and the ringdown of the resulting single black hole. Our observations provide unique access to the properties of space-time at extreme curvatures: the strong-field, and high velocity regime. It allows unprecedented tests of general relativity for the nonlinear dynamics of highly disturbed black holes. In 2017 the gravitational waves from the merger of a binary neutron star was observed. This discovery marks the start of multi-messenger astronomy and the aftermath of this merger was studied with 70 observatories on seven continents and in space, across the electromagnetic spectrum. The scientific impact of the recent detections will be explained. In addition key technological aspects will be addressed, such as the interferometric detection principle, optics, sensors and actuators. Attention is paid to Advanced Virgo, the European detector near Pisa. The presentation will close with a discussion of the largest challenges in the field, including plans for a detector in space (LISA), and Einstein Telescope, an underground observatory for gravitational waves science.
Nov. 28, 2019, 11:30 a.m.
Dec. 4, 2019, 3 p.m.
Weak field phenomenology of metric f(R) and hybrid metric-Palatini theories of gravity
The determination of the exact number of degrees of freedom pertaining to gravitational waves in metric f(R) theories has been the source of a long debate in the literature. This issue can be addressed by using gauge invariant variables, that allow to analyze the problem without any choice of gauge fixing. The same technique can be implemented to study gravitational waves in more complex extensions of General Relativity, such as a novel class of theories called Hybrid metric-Palatini gravity. A complete analysis of the weak field limit of such extended framework is performed, both from the perspective of gravitational waves and the PPN corrections to the Newtonian potential in the static case.
Dec. 11, 2019, 3 p.m.
De Sitter Meeting
Guadalupe Canas Herrera + Alessandro Sonnenfeld
- Dec. 11, 2019, 3 p.m. Guadalupe Canas Herrera + Alessandro Sonnenfeld (Leidein University - Lorentz Institute) De Sitter Meeting
Dec. 13, 2019, noon
- Dec. 13, 2019, noon CS Kaloian Lozanov (MPI garching) TBA
March 18, 2020, 2 p.m.
- March 18, 2020, 2 p.m. Gia Dvali (Lorentz Professor) first lecture
March 25, 2020, 2 p.m.
- March 25, 2020, 2 p.m. Gia Dvali (Lorentz Professor) second lecture
April 1, 2020, 2 p.m.
- April 1, 2020, 2 p.m. Gia Dvali (Lorentz professor) third lecture
LS = Lorentz Seminar, Casimir room (276), Oort building
CE = Colloquium Ehrenfestii, De Sitter lecture room, Oort building
SBM = Soft & Biological Matter Seminar, Casimir room (276), Oort building
CS = Cosmology Seminar, Casimir room (276), Oort building
ST = String Theory Seminar, Casimir room (276), Oort building