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25/05/2020, 10:00
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Giacomo Ciani25/05/2020, 10:25
The first trace left by a gravitational wave in a man-made detector in September 2015 marked the birth of gravitational wave astronomy. Less than four years from that first signal, gravitational wave detections have become routine, the LIGO and VIRGO instruments are standing up to their mission of being "observatories" and the trove of signals collected is enabling exciting new science and...
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Gianmassimo Tasinato25/05/2020, 11:45
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Yifan Wang25/05/2020, 12:35
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Aurélien Barrau25/05/2020, 14:00
I will show how quasinormal modes of black holes can be used to investigate new physics and quantum gravity. Some results on isospectrality will also be underlined.
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Suddhasattwa Brahma25/05/2020, 14:50
It is well-known that accelerating spacetimes form the basis of our understanding of early and late-time cosmology. On the other hand, there has been a pile of mounting evidence, mainly based on numerous results from String Theory (but not limited to them), that de Sitter space is difficult to embed in a quantum theory of gravity. Thus, these theoretical constraints that any consistent...
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Martin Bojowald25/05/2020, 15:45
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Sean Crowe25/05/2020, 16:35
In the recent article Phys. Rev. D 100, no. 4, 043533 (2019) a compact phase space generalization of
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the flat de Sitter cosmology has been proposed. The main advantages of the compactification is that
physical quantities are bounded, and the quantum theory is characterized by finite dimensional Hilbert
space. The purpose of this presentation is to discuss the extraction of semiclassical... -
Prof. Shinji Mukohyama (YITP, Kyoto University)26/05/2020, 10:00
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Hayato Motohashi26/05/2020, 10:50
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Kai Schmitz26/05/2020, 11:45
The type-I seesaw mechanism crucially depends on the presence of right-handed neutrinos (RHNs) with large Majorana masses. These heavy RHN neutrinos are, however, notoriously hard to produce in terrestrial experiments, which impedes their experimental discovery. In the present talk, I will therefore present a novel, cosmological window onto the seesaw mechanism: the gravitational-wave (GW)...
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Nils A. Nilsson26/05/2020, 12:35
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Prof. Jan Ambjørn (Bohr Ins.)26/05/2020, 14:00
Causal Dynamical Triangulations (CDT) is a lattice model which provides a non-perturbative, background independent formulation of four-dimensional quantum gravity. It provides an emergent background geometry and one can study the quantum fluctuations around this background geometry. The model has second order phase transition lines in the bare coupling constants. These transition lines may be...
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Zbigniew Drogosz26/05/2020, 14:50
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Daniel Németh26/05/2020, 15:45
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Giuseppe Clemente26/05/2020, 16:10
I will describe the current state of research on the application of spectral methods to the
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Quantum Gravity approach known as Causal Dynamical Triangulations (CDT).
Firstly, I will give an overview of the class of analysis methods based on graph theory
applied to the dual graphs of simplicial manifolds, arguing why they are inadequate, in some regimes,
to capture distance information,... -
Laura Johnson26/05/2020, 16:35
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Prof. Yifu Cai (University of Science and Technology of China)27/05/2020, 10:00
In this talk I plan to review the cosmological paradigm of nonsingular bounces, which is often regarded as an alternative to inflation in describing the very early universe. Such a scenario, while can avoid the big bang spacetime singularity, often suffers from conceptual challenges, namely, the dangerous growth of anisotropic stress, the possibly existence of ghosts, gradient instabilities or...
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Michael Kenna-Allis27/05/2020, 10:50
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Antonino Marciano27/05/2020, 11:45
We investigate the production of primordial Gravitational Waves (GWs)
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arising from First Order Phase Transitions (FOPTs) associated to
neutrino mass generation in the context of type-I seesaw schemes. We
examine both “high-scale” as well as “low-scale” variants, with either
explicit or spontaneously broken lepton number symmetry. In the latter
case, a pseudo-Goldstone boson, dubbed... -
Michal Artymowski27/05/2020, 12:35
Our understanding of the Universe is based on general relativity and on the standard model of fundamental interactions. This picture suffers from several issues that cannot be explained by GR or SM, like primordial singularity, inflation, dark energy or dark matter. I will show how unparticles may solve at least some these problems and generate realistic cyclic Universe and dark energy
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Dr Shi Pi (IPMU, Tokyo University)27/05/2020, 14:00
Our universe is fulfilled by stochastic background of gravitational waves with a large range of frequencies, which may have various astrophysical/cosmological origins in the early universe. As our universe is transparent to gravitational wave, it is a fossil recording the information of its generation and how our universe evolves. In this talk I will briefly review the stochastic background of...
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Dr Guillem Domenech (Heidelberg university)27/05/2020, 14:50
Gravitational waves (GWs) are unavoidably induced at second order in cosmological perturbation theory. The so-called induced GWs are a crucial counterpart of the primordial black hole scenario and might be observable by future space based gravitational waves detectors. However, only the generation during radiation and matter domination eras has been analytically studied. In this talk, I will...
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Nikodem Poplawski27/05/2020, 15:45
The conservation law for the total (orbital plus spin) angular momentum of a Dirac particle in the presence of gravity requires that spacetime is not only curved, but also has a nonzero torsion.
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The coupling between the spin and torsion in the Einstein-Cartan theory of gravity generates gravitational repulsion at extremely high densities, which should prevent a singularity in a black hole and... -
Taha Malik27/05/2020, 16:35
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Mr Matteo Fasiello (ICG)28/05/2020, 10:00
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Ms Ema Dimastrogiovanni (New South Wales U)28/05/2020, 10:35
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Sachiko Kuroyanagi28/05/2020, 11:45
Cosmic strings are one of the gravitational wave (GW) sources that can be probed by pulsar timing arrays (PTAs). In this work we develop a detection algorithm for the GW burst from a cusp on a cosmic string, and apply it to a Parkes PTA data release. We find four events with a false alarm probability less than 1\%. However further investigation shows that all of these are likely to be...
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Ogan Ozsoy28/05/2020, 12:35
In string theory inspired models of axion-like fields, sub-leading non-perturbative effects, if sufficiently large, can introduce steep cliffs and gentle plateaus onto the underlying scalar potential. During inflation, the motion of a spectator axion in this potential becomes temporarily fast, leading to exponential amplification of one helicity state of gauge fields. In this model, the axion-...
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Sabino Matarrese28/05/2020, 14:00
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Laura Iacconi28/05/2020, 14:50
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Macarena Lagos28/05/2020, 15:45
As we enter the era of precision cosmology, the behavior of gravity on large scales and the nature of the main constituents of the universe still remain debatable. Future data from the Cosmic Microwave Background and galaxy surveys, along with the advent of gravitational waves (GW) will provide us precise constraints that will help uncover some cosmological puzzles.
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In this talk, I will focus... -
William Wolf28/05/2020, 16:35
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Daniele Oriti29/05/2020, 10:00
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Marcus Reitz29/05/2020, 10:50
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Alejandro Perez29/05/2020, 11:45
I will argue that discreteness at the Planck scale (naturally expected to arise from quantum gravity) might manifest in the form of minute violations of energy-momentum conservation of the matter degrees of freedom when described in terms of (idealized) smooth fields on a smooth spacetime. In the context of applications to cosmology, such “energy diffusion” from the low energy matter degrees...
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Maria Jose Guzman29/05/2020, 12:35
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Włodzimierz Piechocki29/05/2020, 14:00
I will present the quantum model of the asymptotic dynamics underlying the Belinski-Khalatnikov-Lifshitz (BKL) scenario. The classical BKL scenario concerns generic singularity of general relativity. The quantum BKL scenario shows that gravitational singularity can be replaced by quantum bounce. I will suggest that quantum general relativity has a good chance to be free from singularities.
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Julien Grain29/05/2020, 15:20
Bouncing cosmologies is a popular alternative to (or an extension of) primordial inflation. However, the contracting phase preceding the bounce is known to be flawed with a shear instability with important consequences on the fate of the bouncing universe. Depending on the concrete model, this instability could either prevent the bounce to occur or drive the universe in an expanding phase...
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Mr Marcus Reitz (Radboud University, IMAPP)
An open question in quantum gravity is if and how small scale quantum fluctuations and inhomogeneities behave in such a way that at some larger scale they can be well approximated by a classical geometry with some number of exact symmetries. Causal Dynamical Triangulation (CDT) is a non-perturbative approach to quantum gravity, based on a lattice regularisation of space-time, in which these...
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Laura Iacconi (Institute of Cosmology and Gravitation (University of Portsmouth))
Understanding the laws of inflation can shed light on the processes that govern physics at very high energy scales, beyond current experimental limits. In particular, the characterisation and detection of primordial gravitational waves produced during inflation can be an excellent test for the particle content of the very early universe. We consider an inflationary realisation whose tensor...
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Dániel Németh (Németh Dániel)
Causal Dynamical Triangulations is an attempt to quantize gravity via lattice regularization, where 4-dimensional simplices play the role of the building blocks of space-time. Numerical simulations show that CDT has a well defined semi-classical limit. One of the questions of this approach which needs clarification is: whether the space-time foliation introduces a preferred time coordinate? By...
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Maria Jose Guzman (University of La Serena)
We present recent work on disformal transformations in the context of modified gravity based on the teleparallel equivalent of general relativity, and applications to f(T) gravity. We show the implications a disformal transformed tetrad has in the main geometric quantities, and explore the relation with the loss of local Lorentz invariance and the issue of the degrees of freedom in these...
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Mr Nils A. Nilsson (National Centre for Nuclear Research, Warsaw, Poland)
Searching for minuscule departures from exact Lorentz symmetry is an excellent
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probe of new physics; recently, there has been a large increase in gravity tests
of Lorentz symmetry. In the context of the Standard-Model Extension
effective field theory, we discuss and summarise recent developments in the search
for Lorentz violation. We also present recent work done in Lorentz-violating... -
Mr Taha Malik
The quantum null energy condition (QNEC) is a quantum generalization of the null energy condition which gives a lower bound on the null energy in terms of the second derivative of the von Neumann entropy or entanglement entropy of some region with respect to a null direction. The QNEC states that $⟨T_{kk}⟩p≥lim_{A→0}(\frac{ℏ}{2πA}S^{′′}_{out})$ where $S_{out}$ is the entanglement entropy...
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Prof. Włodzimierz Piechocki (National Centre for Nuclear Research )
We present the quantum model of the asymptotic dynamics underlying
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he Belinski-Khalatnikov-Lifshitz (BKL) scenario. The classical BKL
scenario concerns generic singularity of general relativity. The quantum
BKL scenario shows that gravitational singularity can be replaced by
quantum bounce that presents a unitary evolution of considered
gravitational system. Our results suggest that... -
Michael Kenna-Allison
Generalised Massive Gravity is an extension of de Rham-Gabadadze-Tolley theory where the translation invariance in the Stuckelberg field space is broken. This allows the mass parameters to be promoted to functions of the Stuckelberg fields. We consider an exact cosmological background in this theory and study the stability of perturbations. We derive conditions to avoid ghost, gradient and...
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Dr Lu Yin
Because of the universality of gravitational interactions, it is generally expected that a stochastic gravitational wave (GW) background could form during the reheating period when the inflation perturbatively decays with the emission of gravitons. Previously, only models in which the inflation dominantly decays into a pair of light scalar and/or fermion particles were considered in the...
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