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02/12/2019, 13:00
Studies of primordial black holes (PBHs) have often focused on constraints on their abundance since this has interesting implications for cosmology even if they never formed. However, in recent years attention has turned to the possibility that they actually exist and solve various cosmological conundra. The most exciting possibility is that they provide the dark matter, although this is only...
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02/12/2019, 13:50
I here describe how microlensing is powerful to constrain the abundance of PBH.
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02/12/2019, 14:40
I will talk about the general infrared behavior of the power spectrum of a stochastic gravitational wave background $\Omega_{GW}$ produced by stress tensor with bilinear structure, focusing on the gravitational waves induced by scalar perturbations. If the source term is bounded in both frequency and time and reenters the Hubble horizon in a radiation-dominated stage, we have a universal...
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03/12/2019, 10:00
The recent discovery of the Higgs and its mass suggests that our vacuum may by metastable. I will review how we calculate the probability of vacuum decay and discuss how black holes alter this rate. This leads to a constraint either on primordial black hole formation or the Higgs potential.
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03/12/2019, 11:10
I will discuss a novel class of scenarios for PBH formation, which do not place any particular requirements on inflation. A scalar field with a relatively small mass can develop a large VEV during inflation. Relaxation of such a field after inflation can result in fragmentation via a well-known instability, with formation of matter in the form of scalar lumps or Q-balls. If this kind of matter...
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03/12/2019, 13:00
Recent re-evaluations of PBH constraints show that the parameter space window for small PBHs to constitute all of the DM is significantly larger than previously thought. I will discuss how novel signals from tiny PBHs interacting with compact stars can not only lead to new insights into this difficult to probe parameter region of dark matter, but also contribute to resolution of long-standing...
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03/12/2019, 13:50
I discuss two topics: (1) A narrow range of masses for primordial metallicity supermassive stars exhibit a coincidence of three factors that may or may not set them up for explosion after the general relativistic instability initiates their collapse; and (2) Late vacuum phase transitions and a variety of other dark sector beyond-standard-model physics may generate fluctuations which give rise...
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03/12/2019, 14:40
Constant-roll inflation is an interesting phenomenological class of inflationary models in which the assumption of inflaton slow-roll is replaced by more general constant-roll condition, and the second slow-roll parameter is not necessarily negligible. The constant-roll inflation with small positive value of the constant-roll parameter has been known to produce a slightly red-tilted curvature...
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03/12/2019, 16:00
We formulate the two-point correlation function of primordial black holes (PBHs) at their formation time, based on the functional integration approach which has often been used in the context of halo clustering. We find that PBH clustering on super-Hubble scales could never be induced in the case where the initial primordial fluctuations are Gaussian, while it can be enhanced by the so-called...
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03/12/2019, 16:25
We discuss the effect of local type non-Gaussianity on the abundance of primordial black holes (PBH) based on the peak theory. We provide the PBH formation criterion based on the so-called compaction function and use the peak theory statistics associated with the curvature perturbation with the local type non-Gaussianity. Providing a method to estimate the PBH abundance, we demonstrate the...
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04/12/2019, 10:00
Primordial black holes (PBHs) have long been considered a viable candidate for the dark matter. While the abundance of PBHs with large masses has been constrained with a multitude of astrophysical observations, recent re-analyses of bounds on smaller PBHs have opened a significant window of the previously excluded parameter space for PBHs to constitute the dark matter (DM). In light of this,...
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04/12/2019, 11:10
Primordial Black Holes (PBHs) can be produced even in the early matter
dominated Universe due to collapses of regions which have large
curvature perturbation produced by inflation.I will review the current status of formations and evolutions of PBHs
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in the early matter dominated Universe. If time allows, I will also
mention cosmological and astrophysical constraints on PBHs with
introducing... -
04/12/2019, 13:00
Although there is a reasonably broad consensus that primordial black holes in the mass range detected by LIGO and Virgo cannot make up more than a small fraction of the dark matter, it remains possible that all of the black holes whose merger LIGO has detected were primordial in origin. I will briefly summarise the evidence and challenges behind this claim, and then focus on how current and...
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04/12/2019, 13:50
Abs: In the first part of this talk I will show that the threshold for PBHs formation, in a radiation dominated universe, can be analytically given by the use of a universal formula for the averaged compaction function. In the second part, I will present the full non-linear statistics of PBH abundance related to Gaussian curvature perturbations.
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04/12/2019, 14:40
We investigate the effect of inhomogeneity on primordial black hole formation in the matter dominated era. In the gravitational collapse of an inhomogeneous density distribution, a black hole forms if the apparent horizon prevents information of the central region of the configuration from leaking. Since information cannot propagate faster than the speed of light, we identify the threshold of...
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05/12/2019, 10:00
We present two scenarios for primordial black hole (PBH) formation. One is PBH formation
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by Affleck-Dine mechanism which produces high baryon bubbles after inflation.
Those high baryon bubbles produce high density contrasts and collapse, which leads to
formation of PBHs. This scenario can account for LIGO PBHs or seeds for supermassive BHs.
The other scenario is PBH formation from... -
05/12/2019, 11:10
A review is presented on the recent astronomical data, which indicate that the bulk of
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black holes in the universe in all mass ranges are mostly primordial. A mechanism of
PBH formation with the necessary properties is discussed. -
05/12/2019, 13:00
We will discuss some aspects of primordial black holes and how LISA will be able to detect the associated gravitational waves.
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05/12/2019, 13:50
I will discuss stability issues of classical fields in the Kerr black hole backgrounds.
In particular, I will describe mass bounds for instability of massive scalar and vector modes in the subcritical regime. In addition, some results on the construction of massive vector growing modes will be presented.Blackboard was used. No material files attached.
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05/12/2019, 14:40
The spin of black holes is one of the important observables in gravitational wave detection. As LIGO/Virgo have found a number of events of black hole mergers and some of them are of small effective spins, one possibility is that these black holes are primordial because it is believed that primordial black holes (PBH) have small spin. One important factor that affects the spin distribution of...
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06/12/2019, 10:00
I will discuss how we can infer the existence of primordial black holes. I will focus on stellar kinematics, merger rates and the possibility of a WIMP particle dark matter / primordial black hole co-existence using 1-point function statistics.
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06/12/2019, 11:10
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06/12/2019, 13:00
We investigate a possibility of primordial black hole (PBH) formation with a hierarchical mass spectrum in multiple phases of inflation. As an example, we find that one can simultaneously realize a mass spectrum that has recently attracted a lot of attention: stellar-mass PBHs (~O(10)M_\odot) as a possible source of binary black holes detected by LIGO/Virgo collaboration, asteroid-mass...
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06/12/2019, 13:25
Thomas Precession e?ect is purely a relativistic e?ect which has been studied extensively in the premises of Special Relativity. From a relativist's perspective, it is due to the non-commutative nature of Lorentz groups. Thomas Precession in the context of general relativity can be realized as a Fermi-Walker transport equa- tion. In this paper, we study Thomas Precession of spin vector upon a...
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06/12/2019, 13:50
The spatial configuration near local extrema of the primordial density perturbation restricts the statistics of high-density peaks valid for the formation of
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primordial black holes (PBHs). We argue that the condition for density extrema to be maxima in the peak statistics leads to an universal enhancement to the extended mass function of PBH estimated by the Press-Schechter method. For the...
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