[RESCEU] Research Center for the Early Universe
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RESCEU Colloquium

RESCEU Colloquium No. 15
Date and Time: March 02, 2017, 16:00-17:00
Location: RESCEU seminar room on 1st Floor, Sci. Bldg. 4
Bernard Carr
(Queen Mary University of London)
Primordial black holes as dark matter and seeds for cosmic structure
Abstract
The possibility that the dark matter comprises primordial black holes (PBHs) is considered, with particular emphasis on the currently allowed mass windows at 1016 - 1017g, 1020 - 1024g and 10 - 103 M. The last possibility is of special interest in view of the recent detection of black-hole mergers by LIGO. All relevant constraints (lensing, dynamical, large-scale structure and accretion) are considered and various effects necessary for a precise calculation of the PBH abundance (non-Gaussianity, non-sphericity, critical collapse) are accounted for. It is difficult to put all the dark matter in PBHs if their mass function is monochromatic but this is still possible if the mass function is extended, as expected in many scenarios. A novel procedure for confronting observational constraints with an extended PBH mass spectrum is therefore introduced and this is applied for two inflationary models. Even if PBHs provide only a small fraction of the dark matter, they could generate cosmological structure through either the 'seed' effect on small scales or the 'Poisson' effect on large scales. For example, if supermassive PBHs with much less than the critical density seed galaxies, this naturally explains the proportionality between the mass of the central black hole and the galactic mass. On the other hand, if intermediate mass PBHs provide the dark matter, the first bound clouds of 106 M would form through Poisson fluctuations much earlier than usual. In principle, an extended PBH mass spectrum could permit them to fulfill all of these roles - providing the dark matter, the first bound clouds and galaxies. The gravitational wave background from the PBHs would then extend from the LIGO frequency (due to dark matter black holes) to the LISA frequency (due to galactic nuclei black holes).
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RESCEU Colloquium No. 14
Date and Time: February 20, 2017, 15:30-16:30
Location: RESCEU seminar room on 1st Floor, Sci. Bldg. 4
Alexei Starobinsky
(Landau Institute for Theoretical Physics RAS and RESCEU)
From generic classical curvature singularity in GR and f(R) gravity to inflation
Abstract
I discuss how generic is the onset of inflation from generic classical curvature singularity preceding it in GR and f(R), and which conditions are needed for it. For viable inflationary models in these kinds of gravity theory, the inflaton potential in the Einstein frame is not important near the singularity. Thus, its boundedness in models producing the best fit to observational data does not reduce the degree of generality of inflation. Space-time is asymptotically locally homogeneous near the singularity, despite the absence of causal connection, due to the very structure of field equations. However, an intermediate period when spatial gradients become important may well occur before the beginning of inflation. As a whole it seems that, for inflation to begin inside a patch including the observable part of the Universe, causal connection inside the whole patch is not necessary. However, it becomes obligatory for a graceful exit from inflation in order to have practically the same number of e-folds during inflation inside this patch. Also, the fact that inflation does not "solve" the singularity problem, i.e. it does not remove a curvature singularity preceding it, can be an advantage, not its weakness.
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RESCEU Colloquium No. 13
Date and Time: December 15, 2016, 14:00-15:30
Location: RESCEU seminar room on 1st Floor, Sci. Bldg. 4
Stefan Ballmer
(Syracuse University/LIGO)
What comes next for Gravitational-Wave Astronomy
Abstract
One year ago the Advanced LIGO detectors provided the first observation of gravitational waves from merging black holes. They just started to observe again this fall. I will discuss what we learned from the initial discovery, and where the detector sensitivity stands for the current observation run. Then I will look into the future, describing the next sensitivity upgrades for the detectors, and what we hope to observe with them. I will conclude by looking at possible future gravitational-wave observatories capable of observing binary mergers from an era when the first stars just started to form.
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RESCEU Colloquium No. 12
Date and Time: August 23, 2016, 16:00-17:00
Location: RESCEU seminar room on 1st Floor, Sci. Bldg. 4
Gonjie Li
(Harvard University)
Interactions of Planetary Systems with passing Stars and Binaries
Abstract
N/A
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RESCEU Colloquium No. 11
Date and Time: April 21, 2016, 14:00-15:00
Location: RESCEU seminar room on 1st Floor, Sci. Bldg. 4
Surhud More
(Kavli IPMU)
Detection of halo assembly bias and the splashback radius of galaxy clusters
Abstract
Dark matter halos are the basic building blocks that form the large scale structure in the Universe. I will present an overview of our knowledge about the internal structure of these halos, their large scale distribution, and the connection between the two, based on numerical simulations of cold dark matter in the concordance cosmological model. I will talk about some of the recent theoretical developments regarding the physical boundaries of dark matter halos, and their connection to the assembly history of these halos. I will present observational evidence supporting these new developments. In particular, I will highlight the recent detections of halo assembly bias on galaxy cluster scales, and the edges of galaxy clusters, and how these advances will help us to further our understanding of galaxy formation and the challenges they present to cosmological inferences.
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RESCEU Colloquium No. 10
Date and Time: March 17, 2016, 16:00-17:30
Location: RESCEU seminar room on 1st Floor, Sci. Bldg. 4
Krzysztof M. Gorski
(JPL/Kavli IPMU)
The Future of Cosmology with the CMB
Abstract
Observational cosmology has seen a remarkable quarter century of space exploration of the cosmic microwave background with the satellite missions COBE, WMAP, and Planck. I will briefly review the advances that these effort brought about, and discuss current prospects for the future, polarization measurements oriented CMB satellite proposals, including LiteBIRD in Japan, and the forthcoming suborbital CMB projects.
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RESCEU Colloquium No. 9
Date and Time: February 12, 2016, 16:30-18:00
Location: Room 1220 on the 2nd Floor, Sci. Bldg. 4
Kipp Cannon
(RESCEU)
Results From Advanced LIGO's First Science Run
Abstract
In its first 400 hours of operation, Advanced LIGO had already surveyed a larger space-time volume than all previous gravitational-wave detection experiments combined. I will discuss some of the conclusions drawn from this early effort.
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RESCEU Colloquium No. 8
Date and Time: December 08, 2015, 16:30-18:00
Location: RESCEU seminar room on the 1st Floor, Sci. Bldg. 4
Francois R. Bouchet
(Institut d'Astrophysique de Paris)
Cosmology with the Planck satellite
Abstract
Sketched out in 1992, selected by ESA in 1996, and launched in 2009, the Planck satellite was shut off in 2013, after a measuring mission that exceeded all expectations. The Planck collaboration delivered a first set of cosmological data and results in March 21st 2013, and the full set in February 2015. Part of the data delivery is a "definitive" map of the anisotropies of the Cosmic Microwave Background (CMB), its angular power spectrum together with their full statistical characterisation. The 2015 delivery also includes pioneering polarisation data. The temperature anisotropy map displays minuscule variations as a function of the observing direction, of rms ~100 microK, of the fossil radiation around its mean temperature of 2.725K. Other maps reveal the CMB polarisation. The anisotropies are the imprint of the primordial fluctuations which initiated the growth of the large scale structures of the Universe, as transformed by their evolution, in particular during the first 370 000 years. The polarisation is another imprint whose theoretical implications can then be confronted with those derived from the temperature field. I will describe some of our key results we obtained so far from temperature and polarisation data, both in terms of content of the universe and of characteristics of the primordial fluctuations, in particular concerning precision tests of key hypotheses of the standard model of cosmology, like the flat spatial geometry or Gaussianity, adiabaticity and per cent deviation from scale invariance of the primordial fluctuations.
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RESCEU Colloquium No. 7
Date and Time: November 09, 2015, 16:00-17:30
Location: RESCEU seminar room on the 1st Floor, Sci. Bldg. 4
Robert Wittenmyer
(The University of New South Wales)
The great unveiling: a new golden age of exoplanetary science
Abstract
Less than a generation ago, we wondered, as we had for millions of years before, whether there were any other planetary systems at all. Now, we are privileged to be in the first generation of humans to know that many of the points of light dusting our night sky are host to orbiting worlds, some of which may be like our Earth. With that privilege comes the mighty task of our time, to unlock the secrets of the diversity of worlds. I will give an overview of the "discovery revolution" that brought us here. I will then describe the tremendous challenges and opportunities awaiting us in exoplanetary science over the next decade. The next revolution will be one of understanding - a "great unveiling" as we learn the detailed properties of the planetary systems in the Solar neighbourhood.
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RESCEU Colloquium No. 6
Date and Time: July 08, 2015, 14:00-15:30
Location: RESCEU seminar room on the 1st Floor, Sci. Bldg. 4
Giuseppe Bono
(Univ. of Rome Tor Vergata)
On the distribution of neutron capture elements across the Galactic thin disk using Cepheids
Abstract
We present new results concerning the distribution of neutron capture (s-, r-) elements across the Galactic thin disk. We use young (classical Cepheids) stellar tracers for which we collected high spectral resolution, high signal to noise optical spectra with UVES at VLT (ESO). We found that the five (s: Y, La, Ce, Nd; r: Eu) investigated elements show well defined negative gradients when moving from the innermost to the outermost regions. Moreover, we also found that the gradients of the above elements are positive as a function of age/pulsation period. Thus suggesting a trend with age similar to alpha-elements. On the other hand, the slopes of [element/Fe] vs Galactocentric distance are more positive than for alpha-elements. We introduce plausible working hypothesis to take account of the difference, and perform a detailed comparison with similar abundances for dwarf and giant stars available in the literature. Finally, we discuss the abundance ratio between s- and r- elements (La/Eu) and between heavy and light s- elements (La/Y) and outline their impact on the chemical enrichment history of the Galactic thin disk.
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RESCEU Colloquium No. 5
Date and Time: July 03, 2015, 17:00-18:30
Location: RESCEU seminar room on the 1st Floor, Sci. Bldg. 4
Samaya Nissanke
(Radboud University Nijmegen, the Netherlands)
Follow the chirp: seeing and listening to the transient Universe
Abstract
The mergers of binary compact objects (black holes, neutron stars, white dwarfs) are amongst some of the most violent events in the Universe. The physics driving these events in strongly curved spacetimes are extremely complex, rich but still remain elusive. These cosmic laboratories present us now with both a challenge and an opportunity. The challenge is to explain the physics at play in strong-field gravity in Universe. The opportunity is to detect the accompanying electromagnetic (EM) and gravitational radiation for the first time with a suite of time-domain telescopes and newly upgraded gravitational wave (GW) detectors.In this pivotal new era of strong-field gravity astronomy, the most compelling astrophysical sources are neutron star binary mergers, which should emit both in electromagnetic and GWs. I will first review the most recent advances in this blossoming field of EM + GW astronomy, which combines two active disciplines: time-domain astronomy and general relativity. I will discuss the promises of this new convergence by illustrating the wealth of astrophysical information that a combined EM+GW measurement would immediately bring. I will then outline the main challenges that lie ahead for this new field in pinpointing the sky location of neutron star mergers using GW detectors and optical and radio wide-field synoptic surveys.
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RESCEU Colloquium No. 4
Date and Time: May 11, 2015, 14:00-15:30
Location: RESCEU seminar room on the 1st Floor, Sci. Bldg. 4
Anupam Mazumdar
(Physics Department, Lancaster University)
Universal laws of Gravity without Singularity
Abstract
I will discuss classical singularity theorem of General relativity, and then construct a general covariant theory of gravity which can avoid cosmological and blackhole singularities in the ultraviolet and reduces to the predictions of Einstein's theory of gravity in the infrared. I will also discuss how such an action may arise from string theory.
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RESCEU Colloquium No. 3
Date and Time: May 13, 2015, 14:00-15:30
Location: RESCEU seminar room on the 1st Floor, Sci. Bldg. 4
Shin'ichiro Ando
(GRAPPA, Univ. of Amsterdam)
Dark matter searches in anisotropic gamma-ray sky
Abstract
As a viable candidate of dark matter, weakly interacting massive particle (WIMP) has been studied. WIMP is considered to annihilate with itself, and as its consequence, to produce high-energy gamma rays. Since dark matter has been annihilating (if ever happens) since the beginning of the structure formation, it gives contributions to the diffuse gamma-ray background measured with the Fermi satellite. The measurement of the gamma-ray background spectrum already gives one of the tightest constraints on the annihilation cross section. Since Fermi already collected more than 5 million photons from the whole sky (above 1 GeV), it is possible to discuss anisotropy* of the gamma-ray background. I will discuss (1) the angular power spectrum, (2) one-point PDF of the gamma-ray flux, and (3) cross correlation with local galaxy catalogs, and prospects on discovering dark matter particles in the near future in the gamma-ray data.
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RESCEU Colloquium No. 2
Date and Time: April 22, 2015, 14:00-15:30
Location: RESCEU seminar room on the 1st Floor, Sci. Bldg. 4
Kipp Cannon
(Canadian Institute for Theoretical Astrophysics / University of Toronto)
Challenges in Gravitational-Wave Astronomy
Abstract
Gravitational radiation promises new knowledge about our world, but all attempts to observe gravitational waves (GWs) have been unsuccessful. There are many challenges to overcome in our quest to detect this elusive form of energy. I will describe how multivariate classifier techniques have been used to combat detector noise in searches for GWs from cosmic strings with LIGO and Virgo, and how the search for binary neutron star collisions has created new techniques for modeling collision waveforms.
Rapid detection of GWs will allow GW antennas like KAGRA to join a larger transient astronomy community and will provide exciting, new, information about the Universe. I will describe the analysis techniques used to achieve the extreme performance required to search for GWs from neutron star collisions with tens of seconds of latency. Finally, I will comment on some challenges that lay ahead for our community, and what might be done to address them.
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RESCEU Colloquium No. 1
Date and Time: April 20, 2015, 14:00-15:30
Location: RESCEU seminar room on the 1st Floor, Sci. Bldg. 4
Pisin Chen
(National Taiwan University)
Radiowave Detection of Ultra High Energy Cosmic Neutrinos and Cosmic Rays
Abstract
There has been tremendous progress in the field of particle astrophysics in recent years, exemplified by the results from the Pierre Auger Observatory in Argentina on ultra high energy cosmic ray (UHECR) detection and the IceCube at the South Pole on PeV cosmic neutrino observation. Here we introduce a novel methodology based on the detection of the radio wave signals emitted by the ultra high energy cosmic neutrinos (UHECN) and cosmic rays. Such radio wave signals can be either triggered by the Askaryan effect or the geosynchrotron effect. In this talk we will review the several projects based on this approach, namely ANITA, ARA, and TAROGE, that have been pursued by the Leung Center for Cosmology and Particle Astrophysics (LeCosPA) at the National Taiwan University. We will first review the science potentials in astrophysics and particle physics through the detection of UHECR and UHECN. We will then report on the history, status and the future prospect of ANITA, ARA, and TAROGE observatories, including their scientific results obtained so far.
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