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Prof. Luigi Pilo (University of L'Aquila and INFN L'Aquila )04/09/2019, 14:30Modified Gravity and Dark EnergyTalk
The low-energy dynamics of a generic self-gravitating media can be studied by using effective field theory in terms four derivatively coupled scalar fields and naturally gives rise to an interesting model of dark energy. Depending on internal symmetries, the theory describes fluids, superfluids, solid and supersolids. Dynamical and thermodynamical properties are also dictated by internal...
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Farbod Hassani (Université de Genève)04/09/2019, 14:55Modified Gravity and Dark EnergyTalk
The physical reason for the observed acceleration of the Universe is one of the most important mysteries in cosmology. This is also one motivation for the next generation of large galaxy surveys like Euclid, LSST or SKA that will observe billions of galaxies to provide galaxy number counts and weak lensing measurements.
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In the first part of my talk, I'm going to show a systematic extension of... -
Mr Hiroaki Tahara (RESCEU, The university of Tokyo)04/09/2019, 15:20Modified Gravity and Dark EnergyTalk
Perturbations on a static and spherically symmetric solution in the Horndeski theory were studied by previous researches. Their radial stability conditions were calculated but angular stability condition of the even-parity mode, which has more complicated form of perturbative equations of motions than the odd-parity mode, was not obtained. We have calculated it with high multipole limit and...
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Mr Simone Peirone (Leiden University)04/09/2019, 15:45Modified Gravity and Dark EnergyTalk
In my talk, I will present the impact of general, model independent conditions of theoretical stability and cosmological viability on the analysis of scalar-tensor theories with cosmological data. These conditions account for the avoidance of ghost and gradient instabilities as well as exponential growth of the scalar perturbations in the Dark Energy sector.
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As an example, I will show the... -
Bill Wright (Institute of Cosmology and Gravitation, University of Portsmouth)04/09/2019, 16:40Modified Gravity and Dark EnergyPoster
There is a well known degeneracy between the enhancement of the growth of large-scale structure produced by modified gravity models and the suppression due to the free-streaming of massive neutrinos at late times. This makes the matter power-spectrum alone a poor probe to distinguish between modified gravity and the concordance ΛCDM model when neutrino masses are not strongly constrained....
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Dr Axel de la Macorra (Physics Institute, UNAM - Mexico)04/09/2019, 17:05Modified Gravity and Dark EnergyTalk
We present a complete analysis of the observational constraints and cosmological implications of our Bound Dark Energy (BDE) model aimed to explain the late-time cosmic acceleration of the universe. BDE is derived from particle physics and corresponds to the lightest meson field $\phi$ dynamically formed at low energies due to the strong gauge coupling constant. The evolution of BDE is...
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Dr Yusuke Yamada (University of Tokyo)04/09/2019, 17:30Modified Gravity and Dark EnergyTalk
We discuss the embedding of the Horndeski model into supergravity. In the case of linearly realized supersymmetry, higher derivative interaction often leads to ghost and propagating auxiliary field problems. Therefore, supergravity realization of the Horndeski model has not been known so far.
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These issues can be circumvented in the recently proposed framework, called pure de Sitter... -
Mr Meng-Xiang Lin (University of Chicago)04/09/2019, 17:50Modified Gravity and Dark EnergyTalk
We discuss the ability of a dark fluid becoming relevant around the time of matter radiation equality to significantly relieve the tension between local measurements of the Hubble constant and CMB inference, within the $\Lambda$CDM model.
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We show the gravitational impact of acoustic oscillations in the dark fluid balance the effects on the CMB and result in an improved fit to CMB measurements... -
04/09/2019, 18:10
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Elisa Ferreira05/09/2019, 14:30Modified Gravity and Dark EnergyTalk
In this talk I present a novel model of a unified dark sector, where late-time cosmic acceleration emerges from the dark matter superfluid framework. We will start by reviewing the dark matter superfluid model and show how it describes the dynamics of dark matter in large and small scales. Then we will show that if the superfluid consists of a mixture of two distinguishable states with a small...
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Johannes Noller (ETH Zurich)05/09/2019, 14:55Modified Gravity and Dark EnergyTalk
I will present current observational bounds on general Horndeski scalar-tensor theories of gravity, using data from the Planck, SDSS/BOSS and 6dF surveys. Using such theories as an example, I will also show how combining these observational bounds with insights from theoretical particle physics (e.g. stability criteria and positivity bounds) can drastically improve constraints and therefore...
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Mr Tommi Markkanen (Imperial College London)05/09/2019, 15:20Modified Gravity and Dark EnergyTalk
In this talk I will discuss a scalar field model of dark energy that exhibits essentially no sensitivity to initial conditions and possesses a naturally suppressed effective mass and interactions in the late Universe. The magnitude of dark energy today is generated via an intricate conspiracy of numbers related to inflation, gravity and electroweak physics. arXiv:1905.00045
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Prof. Tsutomu Kobayashi (Rikkyo University)05/09/2019, 15:45Modified Gravity and Dark EnergyTalk
We consider a subclass of degenerate higher-order scalar-tensor (DHOST) theories in which gravitational waves propagate at the speed of light and do not decay into scalar fluctuations. The screening mechanism in DHOST theories evading these two gravitational wave constraints operates very differently from that in generic DHOST theories. We derive a spherically symmetric solution in the...
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Dr Carlos Martins (CAUP)05/09/2019, 16:40Modified Gravity and Dark EnergyTalk
Astrophysical tests of the stability of fundamental couplings such as the fine-structure constant $\alpha$ and the proton-to-electron mass ratio $\mu$ are a key probe of fundamental physics and cosmology. A new generation of high-resolution spectrographs and improved statistical analysis techniques are enabling tests with improved sensitivities and larger redshift ranges. I will present new...
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Mr Vicharit Yingcharoenrat05/09/2019, 17:05Modified Gravity and Dark EnergyTalk
In this talk, I will discuss the decay of gravitational waves (GWs) into dark energy fluctuations $\gamma \rightarrow \pi\pi$ taking into account the large occupation numbers. We study the decay due to the $m_3^3$- and $\tilde{m}_4^2$-operators in the context of the effective field theory (EFT) of dark energy. It turns out that, in the regime of small GW amplitude corresponding to narrow...
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Giovanni Tambalo (SISSA)05/09/2019, 17:30Modified Gravity and Dark EnergyTalk
In this talk I will discuss the classical decay of gravitational waves into dark energy fluctuations $\pi$ in the context of the EFT of Dark Energy. For cubic Horndeski and beyond Horndeski theories, the gravitational wave acts as a classical background for $\pi$ and thus modifies its dynamics. In particular, for a sufficiently large amplitude of the wave, the kinetic term of $\pi$ becomes...
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Katsuki Aoki (YITP, Kyoto University)05/09/2019, 17:55Modified Gravity and Dark EnergyTalk
Although quadratic curvature terms are well-motivated by leading quantum corrections to gravity and can be responsible for inflation, they generally lead to a massive spin-2 ghost. In this talk, instead of Riemannian geometry, we study quadratic curvature theories in four-dimensional Riemann-Cartan geometry where the torsion tensor does not vanish and can carry new degrees of freedom....
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Modified Gravity and Dark EnergyPoster
It is well-known that there are problems with the standard model of cosmology that hint at possible physics beyond the $\Lambda$CDM paradigm. In particular, the 4$\sigma$ tension in the values of $H_0$ coming from CMB and supernovae measurements is motivation enough to consider alternative cosmological models.
In this talk, I will introduce one such model, the interacting vacuum scenario....
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Modified Gravity and Dark EnergyPoster
Despite the good agreement between theoretical predictions and observational results, the cosmological constant is not a satisfactory explanation for the accelerated expansion of the universe. Hence an intense theoretical effort has been devoted to the study of models beyond General Relativity plus a cosmological constant.
In this talk, I will present ongoing work on the study of the...
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Modified Gravity and Dark EnergyPoster
The different observations coming from the late time Universe point to an accelerated expansion rate, dubbed to be originated from a Dark Energy component but its physical origin still remains unknown. Many theoretical models coming from scalar field theories for instance have been proposed. The contents of this talk were presented in https://doi.org/10.1103/PhysRevD.98.083530. In this work we...
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Modified Gravity and Dark EnergyPoster
We explore the implications of a rapid appearance of dark energy between the redshifts ($z$) of one and two on the expansion rate and growth of perturbations. Using both Gaussian process regression and a parameteric model, we show that this is the preferred solution to the current set of low-redshift ($z<3$) distance measurements if $H_0=73~\rm km\,s^{-1}\,Mpc^{-1}$ to within 1\% and the...
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Modified Gravity and Dark EnergyPoster
The nature of dark energy and dark matter remains a largely open question in cosmology and it is necessary to investigate if they could interact. I will discuss the possible nature of these interactions before focusing in on a particularly noteworthy sub category; momentum only interactions. I will explore the interesting features of these models before discussing the constraints on them...
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Modified Gravity and Dark EnergyPoster
Many scalar-tensor theories have more than 2 degrees of freedom because of additional scalar fields. However, there is a theory named “cuscuton” whose number of degrees of freedom is only 2 on a cosmological background. This theory has a nondynamical scalar field, which is called “cuscuton field.” In this talk, we consider inflation in the context of cuscuton gravity. We find a new exact...
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Modified Gravity and Dark EnergyPoster
We present a study of the KSVZ axion model with quasi-degenerate vacua as a minimal model for dark energy and dark matter. We demonstrate that the combination of the classical two-field potential for the Higgs and the PQ scalar, and quantum corrections, allows the existence of degenerate minima and of inflection points. We propose an explanation for dark energy in the form of the difference...
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Modified Gravity and Dark EnergyPoster
The f(R) theories of gravity rely on the chameleon mechanism to pass the solar system tests. Methods used in the literature are based in a scalar-tensorial identification in the Einstein frame. This approach has a disadvantage because it entails the definition of new variables being the inversion of the old variables not always well defined. To avoid this problem, we develop a novel and...
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Talk
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Modified Gravity and Dark EnergyPoster
One of the most pressing questions in modified gravity is how deviations from general relativity can manifest in upcoming galaxy surveys. This is especially relavant for theories exhibiting Vainshtein screening, which is known to be shape dependent: it is most effective around spherical sources, weaker around cylindrical sources and absent for planar sources. The cosmic web therefore offers a...
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Modified Gravity and Dark EnergyPoster
The late time acceleration of the Universe can be characterized in terms of an
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extra, time dependent, component of the universe -- dark energy. The simplest
proposal for dark energy is quintessence, a scalar field, $\phi$, whose
dynamics is solely dictated by its potential, $V(\phi)$. In this simple case,
just an extra function of the background is necessary to describe the
evolution of the...
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