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Introduction
Education
September 2008 - June 2011
September 2004 - June 2008
Publications
Publications (20)
Light axion fields, if they exist, can be sourced by neutron stars due to their coupling to nuclear matter, and play a role in binary neutron star mergers. We report on a search for such axions by analyzing the gravitational waves from the binary neutron star inspiral GW170817. We find no evidence of axions in the sampled parameter space. The null...
Light axion fields, if they exist, can be sourced by neutron stars due to their coupling to nuclear matter, and play a role in binary neutron star mergers. We report on a search for such axions by analysing the gravitational waves from the binary neutron star inspiral GW170817. We find no evidence of axions in the sampled parameter space. The null...
The observation of gravitational waves from a binary neutron star merger by LIGO/VIRGO and the associated electromagnetic counterpart provides a high precision test of orbital dynamics, and therefore a new and sensitive probe of extra forces and new radiative degrees of freedom (d.o.f.). Axions are one particularly well-motivated class of extension...
We show that gravitational floating orbits may exist for black holes with rotating hairs. These black hole hairs could originate from the superradiant growth of a light axion field around the rotating black hole. If a test particle rotates around the black hole, its tidal field may trigger the dynamical transition between a co-rotating state and a...
The observation of gravitational waves from a binary neutron star merger by LIGO/VIRGO and the associated electromagnetic counterpart provides a high precision test of orbital dynamics, and therefore a new and sensitive probe of extra forces and new radiative degrees of freedom. Axions are one particularly well-motivated class of extensions to the...
The mass of the graviton, if nonzero, is usually considered to be very small, e.g. of the Hubble scale, from several observational constraints. In this paper, we propose a gravity model where the graviton mass is very small in the usual weak gravity environments, below all the current graviton mass bounds, but becomes much larger in the strong grav...
Observations of gravitational radiation from compact binary systems provide an unprecedented opportunity to test General Relativity in the strong field dynamical regime. In this paper, we investigate how future observations of gravitational radiation from binary neutron star mergers might provide constraints on finite-range forces from a universall...
Observations of gravitational radiation from compact binary systems provide an unprecedented opportunity to test General Relativity in the strong field dynamical regime. In this paper, we investigate how future observations of gravitational radiation from binary neutron star mergers might provide constraints on finite-range forces from a universall...
Vacuum bubbles may nucleate and expand during the inflationary epoch in the
early universe. After inflation ends, the bubbles quickly dissipate their
kinetic energy; they come to rest with respect to the Hubble flow and
eventually form black holes. The fate of the bubble itself depends on the
resulting black hole mass. If the mass is smaller than a...
Many theories of the early universe predict the existence of a multiverse
where bubbles continuously nucleate giving rise to observers in their interior.
In this paper, we point out that topological defects of several
dimensionalities will also be produced in de Sitter like regions of the
multiverse. In particular, defects could be spontaneously nu...
According to classical GR, Anti-de Sitter (AdS) bubbles in the multiverse
terminate in big crunch singularities. It has been conjectured, however, that
the fundamental theory may resolve these singularities and replace them by
nonsingular bounces. This may have important implications for the beginning of
the multiverse. Geodesics in cosmological sp...
According to classical GR, negative-energy (AdS) bubbles in the multiverse
terminate in big crunch singularities. It has been conjectured, however, that
the fundamental theory may resolve these singularities and replace them by
non-singular bounces. Here we explore possible dynamics of such bounces using a
simple modification of the Friedmann equat...
We study the preheating process in a model of DBI inflation with a DBI-type
inflaton coupling to a canonical entropy field. At the end of inflation, the
inflaton field oscillates around its vacuum which can arise from an infrared
cutoff parameter on the warp factor and correspondingly the evolution of its
fluctuations can be approximately described...
We show a model of the slow expansion, in which the scale invariant spectrum
of curvature perturbation is adiabatically induced by its increasing mode, by
applying a generalized Galileon field. In this model, initially \epsilon << -1,
which then is rapidly increasing, during this period the universe is slowly
expanding. There is not the ghost insta...
Cyclic cosmology, in which the universe will experience alternating periods
of gravitational collapse and expansion, provides an interesting understanding
of the early universe and is described as "The Phoenix Universe". In usual
expectation, the cyclic universe should be homogeneous, however, with studying
the cosmological perturbations, we find t...
The phantom inflation predicts a slightly blue spectrum of tensor
perturbation, which might be tested in coming observations. In normal inflation
models, the introduction of step in its potential generally results in an
oscillation in the primordial power spectrum of curvature perturbation. We will
check whether there is a similar case in the phant...
We analytically and numerically show that through the cycles with nonsingular bounce, the amplitude of curvature perturbation on a large scale will be amplified and the power spectrum will redden. In some sense, this amplification will eventually destroy the homogeneity of the background, which will lead to the ultimate end of cycles of the global...
We analytically and numerically show that through the cycles with nonsingular bounce the amplitude of curvature perturbation on large scale will be amplified and the power spectrum will be redden. In some sense, this amplification will eventually destroy the homogeneity of background, which will lead to the ultimate end of cycles of global universe...
In a landscape with metastable minima, the bubbles will inevitably nucleate.
We show that during the bubbles collide, due to the dramatically oscillating of
the field at the collision region, the energy deposited in the bubble walls can
be efficiently released by the explosive production of the particles. In this
sense, the collision of bubbles is...
In this paper we study a curvaton model obtained by considering a probe anti-D3-brane with angular motion at the bottom of a KS throat with approximate isometries. We calculate the spectrum of curvature perturbations and the non-Gaussianities of this model. Specifically, we consider the limit of relativistic rotation of the curvaton brane which lea...
Questions
Question (1)
Atomists want to find things that are fundamental. But the question is what do we mean by "fundamental".
An intuitional way of doing this is to keep looking for things on a smaller scale. So we built accelerators and "cut" things into pieces as small as possible. But the particles we look for are so massive it makes me wonder, do we really divide things, not build?
Or, is what we are looking for just something exactly identical. So we can use it as the fundamental blocks of our theory, since the more identical the blocks are, the more promising our theory is. But these things have not to be the blocks of our world, it could be just a particular state of the "matters".
And a following question is whether there is something fundamental. Maybe the definition of "fundamental" depends on our point of view. In some cases, particles like electrons are fundamental (as far as we know), but we still have freedom of choosing other things as fundamental blocks, which depends on how we build our theory.