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Mariateresa Crosta24/04/2017, 14:30Talk
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Alberto Vecchiato24/04/2017, 14:53
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Dr Konstantinos Dimopoulos (Lancaster University)24/04/2017, 15:15
Quintessential Inflation attempts to account for the tunings of the Hot Big Bang and for Dark Energy, using a single degree of freedom and a single theoretical framework, with the aim to avoid the extreme fine tuning needed for the cosmological constant in LambdaCDM. However, in the past the task proved to be very difficult. We will present how modern developments, e.g. in the context of...
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Prof. Seoktae Koh (Jeju National University)24/04/2017, 15:30
We consider an eight-dimensional Einstein-Yang-Mills theory to study whether Yang-Mills instantons formed in extra-dimensions can trigger cosmic inflation in our four-dimensional spacetime. We observe that the Yang-Mills instantons in extra dimensions and homogeneous in four dimensional spacetime act as a cosmological constant for the four-dimensional Einstein gravity. As a result,we study...
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Antonio Racioppi (National Institute of Chemical Physics and Biophysics (EE))24/04/2017, 15:45
We consider the most minimal scale invariant extension of the standard model that allows for successful radiative electroweak symmetry breaking and inflation. The framework involves an extra scalar singlet, that plays the role of the inflaton, and is compatibile with current experimental bounds owing to the non-minimal coupling of the latter to gravity.
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This inflationary scenario predicts a... -
Marco Zatta (University of Helsinki)24/04/2017, 16:30
Current measurements of the Higgs boson and top quark mass favor metastability of the electroweak vacuum in the Standard Model. This raises some questions when we consider the evolution of our universe: how did it end up in such an energetically disfavored state? Why it remained there during inflation? These problems can be addressed by assuming for the Higgs a direct coupling with the...
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Guillermo Ballesteros (CEA Paris-Saclay)24/04/2017, 16:45
I will present a minimal extension of the Standard Model that addresses dark matter, the strong CP problem, the smallness of neutrino masses, baryogenesis and primordial inflation. The model contains a new U(1) symmetry and a single new physics scale of the order of 10^11 GeV. Dark matter is made of axions, whose mass in predicted to be in a narrow range, which will be probed in the near...
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Ms Djuna Croon (University of Sussex)24/04/2017, 17:00
I will discuss the appeal of pseudo-Goldstone bosons (pGBs) for the generation of scales in Early Universe cosmology. In particular, I will show how Goldstone Inflation addresses the inflationary hierarchy problem (the tension between the Lyth bound and the scale of inflation as preferred by CMB anisotropies), while avoiding the problems with trans-Planckian scales that are typically...
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Scott Melville (Imperial College, London)24/04/2017, 17:15
In the conventional Big Bang picture, our current (perturbative) theories of gravity are not powerful enough to reliably capture the earliest moments of our Universe – they break down due to the large curvatures and high energies. An alternative early Universe scenario is a 'non-singular bounce’, in which an initially contracting phase bounces into an expanding Universe like the one we live in...
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Dr Kengo Shimada (LAPTh)24/04/2017, 17:30
If the electroweak sector of the standard model is described by classically conformal dynamics, we show that the electroweak phase transition can be triggered by the chiral condensation of six massless quarks in the standard model in the supercooled universe.
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The phase transition is first-order and occurs below the QCD scale temperature.
One of the phenomenological consequences of this... -
Tien-Tien Yu (CERN)24/04/2017, 17:45
Rotational superradiance was theoretically shown to occur in black hole spacetimes; in the presence of massive bosonic degrees of freedom, superradiance triggers an instability that leads to peculiar gravitational-wave signatures and black hole distribution in the spin-mass plane, which in turn can impose stringent constraints on ultralight fields. In this talk, I will demonstrate that a...
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Jose Beltran Jimenez (Universite d'Aix-Marseille)24/04/2017, 18:00
The discovery of the accelerated expansion of the universe triggered an intense activity in infrarred modifications of gravity with an additional scalar degree of freedom. This scalar is then used to replace the cosmological constant as the responsible for the cosmic acceleration. A common problem in these models is that this scalar must be very light to have cosmological effects today....
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Matthew McCullough (Oxford University)25/04/2017, 14:40Talk
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Dr Filippo Vernizzi (IPhT, CEA/Saclay)25/04/2017, 15:25
Most existing theories of dark energy and/or modified gravity, involving a scalar degree of freedom, can be conveniently described within the framework of the Effective Theory of Dark Energy. After reviewing this approach, I will extend it to consider Higher-Order Scalar Tensor Theories and discuss their degeneracy and phenomenological viability at the linear level.
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Mr Mancarella Michele (IPhT - CEA Saclay)25/04/2017, 15:40
The "Effective theory of dark energy" is a simple, general and effective way to bridge theory and observations in dark energy and modified gravity scenarios based on a single scalar field. I will illustrate its application to models that admit a kinetic mixing between matter and the scalar field, which I’ll call "Kinetic Matter Mixing". I will argue that this is a truly physical effect...
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Robert Hagala25/04/2017, 15:55
Many viable Scalar-Tensor theories for modified gravity introduce scalar fields that are coupled to matter. The equations that describe the evolution of the scalar fields are field equations similar to the Klein-Gordon equation, with additional source terms depending on the specific model. The usual way to solve this equation has been to apply the quasi-static approximation, neglecting the...
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Alessandra Silvestri (Leiden University)25/04/2017, 16:40Talk
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Levon Pogosian (Simon Fraser University)25/04/2017, 17:25
Constraining the dark energy equation of state, w, as well as modified growth of large structures predicted by alternatives to GR, are among the primary science goals of ongoing and future cosmological surveys. We derive the theoretical prior covariance for w predicted by a general class of theories of a scalar field dark energy (Horndeski theories). This is achieved by generating a large...
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Mr Damien Trinh (University of Manchester)25/04/2017, 17:40
In an attempt to explain dark energy numerous models and modified gravity theories have been constructed in order to better describe current cosmological observations. An obvious way to modify gravity is to introduce a new field other than the metric and make dark energy a dynamical component. In this talk I will present Generalized Einstein-Aether, a vector-tensor theory of gravity where the...
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Dr Francesco Pace (JBCA, University of Manchester)25/04/2017, 17:55
We present an application of the equation of state approach to dark sector perturbations as a comprehensive phenomenological framework to understand the evolution of perturbations in dark energy and modified gravity models. The
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approach is based on the observation that any modified gravity theory can be recast into an effective dark energy fluid. By eliminating the internal degree of freedom... -
Matthew Lewandowski (CEA Saclay)25/04/2017, 18:10
In the next few years, we are going to probe the low-redshift universe with unprecedented accuracy. Among the various fruits that this will bear, it will greatly improve our knowledge of the dynamics of dark energy, though for this there is a strong theoretical preference for a cosmological constant. We assume that dark energy is described by the so-called Effective Field Theory of Dark...
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Nathalie Palanque-Delabrouille (CEA)26/04/2017, 15:15Talk
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Dr Vincent Vennin (University of Portsmouth (UK), Institute of Cosmology and Gravitation)26/04/2017, 16:30
Cosmological inflation is one of the leading paradigms for explaining the physical conditions that prevailed in the early Universe. It consists in a phase of very high energy accelerated expansion that solves the hot big bang model problems. When combined with quantum mechanics, it also provides a causal mechanism for generating cosmological fluctuations on large scales.
In this talk I will...
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Mr Doogesh Kodi Ramanah (Institut d'Astrophysique de Paris)26/04/2017, 16:45
The Wiener filter has emerged as a standard tool for the inference of high dimensional signals, such as the large scale structures and cosmic microwave background (CMB) problems. Some particularly key applications of the Wiener filter in CMB data analysis include power spectrum estimation, map-making and the reconstruction of lensing potential. We present a new fast and robust iterative...
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Suvodip Mukherjee26/04/2017, 17:00
Measurements by WMAP and Planck have indicated nearly a $3\sigma$ departure from statistical isotropy in the temperature field of cosmic microwave background (CMB) at large scales, which is popularly known as Hemispherical Asymmetry. Such an anomalous signal is beyond the standard LCDM cosmological model and can lead to important consequences on cosmological parameters. Cosmological origin of...
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Victoria Yankelevich (Argelander-Institut für Astronomie, University of Bonn)26/04/2017, 17:15
The last decades witnessed huge progress in understanding the large-scale structure of the Universe. While homogeneous and isotropic on the largest scales, the matter and galaxy distributions display complex patterns on smaller scales where we observe elongated filaments, compact clusters and volume-filling underdense regions. These features are not captured by studies of two-point statistics...
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Guilhem Lavaux (Institut d'Astrophysique de Paris)26/04/2017, 17:30
The current and future galaxy surveys give us several challenge both in terms of data management and interpretation. The interpretation is made particularly complex by observational limitations, such as selection and foreground issues, and the extreme dynamical non-linearity of the galaxies. Such problems are generally taken into account a posteriori in the analysis, and are covered by putting...
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Luca Alberto Rizzo26/04/2017, 17:45
Consistency relations of large-scale structures provide exact nonperturbative results for cross-correlations of cosmic fields in the squeezed limit. They only depend on the equivalence principle and the assumption of Gaussian initial conditions, and remain nonzero at equal times for cross-correlations of density fields with velocity or momentum fields, or with the time derivative of density...
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Mr Pierros Delis26/04/2017, 18:00
The Cosmological Principle is one of the main pillars of the Friedman-Lemaître-Robertson-Walker models that constitute the the theoretical basis of ΛCDM concordance model. The Cosmological Principle states that the universe becomes homogeneous and isotropic at very large scale. While the isotropy of our universe is tested from several different probes and surveys, with the most well known, the...
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Kim Werner (Argelander Institut, University of Bonn)26/04/2017, 18:15
To extract cosmological information from large-scale galaxy clustering, we need accurate modeling of the relationship between dark matter and galaxies (galaxy bias). Recently, field-theory techniques have been used to provide a new description of galaxy biasing in terms of renormalised operators and counter terms, i.e. to build quantities that are not UV sensitive. We test these definitions of...
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Mr Martin Stref (Montpellier University)27/04/2017, 15:15
It is known that cold dark matter candidates lead to the structuring of matter on scales much smaller than typical galaxies. This clustering translates into a very large population of subhalos in galaxies, which must impact predictions for indirect searches of annihilating dark matter. I present a model (arXiv:1610:02233) consistently describing the subhalo population in a dynamically...
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Dr Thomas Lacroix (LUPM)27/04/2017, 15:30
In this presentation, I will demonstrate the unprecedented capabilities of the Event Horizon Telescope (EHT) to image the innermost dark matter profile in the vicinity of the supermassive black hole at the center of the M87 radio galaxy. I will present the first model of the synchrotron emission induced by dark matter annihilations from a spiky profile in the close vicinity of a supermassive...
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Vivian Poulin (LAPTh, Annecy-le-vieux)27/04/2017, 15:45
Although the existence of Dark Matter (DM) is by now well-established thanks to a variety of observations on many different scales, its nature is still unknown and so are many of its most basics properties, such as its lifetime. Moreover, even if obvious arguments require that most of the DM is stable on timescales of (at least) the lifetime of the universe, a fraction of it could be in the...
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Dr Francesco Muia27/04/2017, 16:30
According to the Standard Model of Cosmology, about 25% of the content of the universe is composed of Dark Matter (DM). From a theoretical point of view, there are many possible alternatives to explain its origin and composition, ranging from ultralight axions to supermassive black holes. However, despite many experimental efforts, the nature of DM is still obscure. One interesting possibility...
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Chu Xiaoyong27/04/2017, 16:45Talk
I will talk about a DM scenario in which the self-scattering rate today is regulated by kinematics and/or the abundance ratio, through the mass-splitting of two nearly degenerate states, emphasising the implications of the considered models and their prospect of solving astrophysical small-scale structure problems.
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Mr Joseph Kuruvilla27/04/2017, 17:00
Peculiar velocities affects the redshifts of distant galaxies and introduces distortions in all statistical measures of the reconstructed large-scale structure. These distortions are in general complex to model. In this talk, we focus on the streaming equation which is often used to model these distortions in configuration space. Current phenomenological models based on the streaming equation...
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Tommi Markkanen27/04/2017, 17:15
The exponentially expanding de Sitter solution is frequently encountered in cosmology due to its significance for the late and early Universe. However, its stability in a quantised theory has for a long time been the source of debate. In this talk we discuss this issue in the framework of semi-classical gravity. Based on a first principle calculation, we argue that when one considers only...
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Neven Bilic (Rudjer Boskovic Institute)27/04/2017, 17:30
We consider a model of a holographic braneworld universe in which a cosmological fluid occupies a 3+1 dimensional brane located at the boundary of the asymptotic AdS bulk. We combine the AdS/CFT correspondence and the second Randall-Sundrum
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(RSII) model to establish a relationship between the RSII braneworld cosmology and
the boundary metric induced by the time dependent bulk geometry. In the... -
Mr Thomas Schucker (CPT)27/04/2017, 17:45
The trajectory of light in a flat Robertson-Walker universe is presented taking due account of its spin. The off-set between the trajectories of positive and negative helicity states (birefringence) is of the order of a wave length and depends on the acceleration parameter. In 2008, using techniques of weak quantum measurement, an analogous birefringence in reflection, the Federov-Imbert...
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Alex Zucca (Simon Fraser University)
Cosmological symmetrons are usually assumed to have the symmetry breaking phase transition at low redshifts. In this talk I will explore the implications of relaxing (in a reasonable way) this assumption and I will present some preliminary constraints on such theories from cosmological data. I will also show some interesting features of the symmetron model from black holes physics.
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Alberto VecchiatoTalk
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