A5100321828- Cosmology and Gravitation Theories
- Black Holes and Theoretical Physics
- Galaxies: Formation, Evolution, Phenomena
- Dark Matter and Cosmic Phenomena
- Geophysics and Gravity Measurements
- Solar and Space Plasma Dynamics
- Noncommutative and Quantum Gravity Theories
- Pulsars and Gravitational Waves Research
- Physics of Superconductivity and Magnetism
- Astro and Planetary Science
- Planetary Science and Exploration
- Particle physics theoretical and experimental studies
- Advanced Differential Geometry Research
- Theoretical and Computational Physics
- Magnetic and transport properties of perovskites and related materials
- Relativity and Gravitational Theory
- Radio Astronomy Observations and Technology
- Computational Physics and Python Applications
- Space Science and Extraterrestrial Life
- Quantum Mechanics and Applications
- Magnetic properties of thin films
- Quantum Electrodynamics and Casimir Effect
- Magnetic Properties of Alloys
- Quantum and electron transport phenomena
- Spacecraft and Cryogenic Technologies
Hong Kong University of Science and Technology
2016-2025
University of Hong Kong
2016-2025
China Academy of Space Technology
2019-2024
Hong Kong Jockey Club
2017-2022
Central Academy of Fine Arts
2022
University of Cambridge
2014-2016
University of Science and Technology of China
1996-2016
Istituto Nazionale di Fisica Nucleare, Sezione di Trieste
2014
Scuola Internazionale Superiore di Studi Avanzati
2014
McGill University
2009-2014
We review the problem of dark energy, including a survey theoretical models and some aspects numerical studies.
In quasi-single field inflation models, massive isocurvature modes, that are coupled to the inflaton and have mass of order Hubble parameter, can nontrivial impacts on density perturbations, especially non-Gaussianities. We study a simple example in terms turning trajectory. Large bispectra with one-parameter family novel shapes arise, lying between well-known local equilateral shape. The trispectra also be very large its magnitude tNL much larger than fNL squared.
We study the slow-roll inflation models, where inflaton slow-rolls along a trajectory whose orthogonal directions are lifted by potentials with masses of order Hubble parameter. In these models large non-Gaussianities can be generated through transformation from isocurvature modes to curvature mode, once turns. find bispectra one-parameter family novel shapes, interpolating between equilateral and local shape. According in-in formalism, shapes different simple projection non-Gaussian...
The specific heat of the layered organic superconductor $\ensuremath{\kappa}\mathrm{\text{\ensuremath{-}}}(\mathrm{BEDT}\mathrm{\text{\ensuremath{-}}}\mathrm{TTF}{)}_{2}\mathrm{Cu}(\mathrm{NCS}{)}_{2}$, where BEDT-TTF is bisethylenedithio-tetrathiafulvalene, has been studied in magnetic fields up to 28 T applied perpendicular and parallel superconducting layers. In above 21 T, transition becomes first order, which signals that Pauli-limiting field reached. Instead saturating at this value,...
We investigate the implications of entropic force formalism proposed by Verlinde. show that an UV/IR relation Cohen et al., as well uncertainty principle Hogan can be derived from formalism. applying to cosmology, there is additional term in Friedmann equation, which identified holographic dark energy. also propose intuitive picture screen, thought improvement Susskind's screen.
We present a systematic introduction to the diagrammatic method for practical calculations in inflationary cosmology, based on Schwinger-Keldysh path integral formalism. show particular that rules can be derived directly from classical Lagrangian even presence of derivative couplings. Furthermore, we use quasi-single-field inflation model as an example how this formalism, combined with trick mixed propagator, significantly simplify calculation some in-in correlation functions. The resulting...
We calculate 1-loop corrections to the Schwinger-Keldysh propagators of Standard-Model-like fields spin-0, 1/2, and 1, with all renormalizable interactions during inflation. pay special attention late-time divergences loop corrections, show that can be resummed into finite results in limit using dynamical renormalization group method. This is our first step toward studying both Standard Model new physics primordial universe.
The inflationary universe can be viewed as a "cosmological collider" with an energy of the Hubble scale, producing very massive particles and recording their characteristic signals in primordial non-Gaussianities. To utilize this collider to explore any new physics at high scales, it is prerequisite understand background from particle standard model. In Letter we describe model cosmological collider.
Abstract We consider a Bardeen-Cooper-Schrieffer (BCS)-like model in the inflationary background. show that with an axial chemical potential, attractive quartic fermion self-interaction can lead to BCS-like condensation. In rigid-de Sitter (dS) limit of inflation where backreaction from inflaton and graviton is neglected, we perform first computation non-perturbative effective potential includes full spacetime curvature effects presence subject mean-field approximation whose validity has...
We compute the large scalar four-point correlation functions in general single field inflation models, where inflaton Lagrangian is an arbitrary function of and its first derivative. find that leading order trispectra have four different shapes determined by three parameters. study features these can be used to distinguish among themselves, between them local form. For purpose data analyses, we give two simple representative forms for ``equilateral trispectra''. also effects on if initial...
In this paper we place observational constraints on the interaction and spatial curvature in holographic dark energy model. We consider three kinds of phenomenological interactions between matter, i.e., term Q is proportional to densities (ρΛ), matter (ρm), plus (ρm+ρΛ). For probing model, use latest data including type Ia supernovae (SNIa) Constitution data, shift parameter cosmic microwave background (CMB) given by five-year Wilkinson Microwave Anisotropy Probe (WMAP5) observations, baryon...
We study cosmological perturbations in Ho\ifmmode \check{r}\else \v{r}\fi{}ava-Lifshitz Gravity, a recently proposed potentially ultraviolet-complete quantum theory of gravity. consider scalar metric fluctuations about homogeneous and isotropic space-time. Starting from the most general metric, we work out complete second order action for perturbations. then make use residual gauge invariance constraint equations to reduce number dynamical degrees freedom. At first glance, it appears that...
We study the perturbation of holographic dark energy and find it to be stable. fate universe when interacting is present, discuss a simple phenomenological classification models. also cosmic coincidence problem in context energy. that cannot completely solved by adding an term. Inflation may provide better solution problem.
We study the effect of massive isocurvaton on density perturbations in quasi-single field inflation models, when mass M becomes larger than order Hubble parameter H. analytically compute correction to power spectrum, leading coupling but exact for all values mass. This verifies previous numerical results range 0<M<3H/2 and shows that, large limit, is H^2/M^2.
We have measured electromagnetic energy harvesting properties of all-thin-film magnetoelectric (ME) heterostructures on Si cantilevers. The devices are built a silicon oxide/nitride/oxide stack, and the ME layers consist magnetostrictive Fe0.7Ga0.3 thin film Pb(Zr0.52Ti0.48)O3 piezoelectric film. harvested peak power at 1 Oe is 0.7 mW/cm3 (RMS) resonant frequency (3.8 kHz) with load 12.5 kΩ. was found to display DC bias magnetic field dependence indicative magnetization canting respect...
We review the theory of inflationary perturbations. Perturbations at both linear and nonlinear orders are reviewed. also a variety inflation models, emphasizing their signatures on cosmic
Oscillating massive fields in the primordial universe can be used as Standard Clocks. The ticks of these oscillations induce features density perturbations, which directly record time evolution scale factor universe, thus if detected, provide a direct evidence for inflation scenario or alternatives. In this paper, we construct full inflationary model Clock and study its predictions on perturbations. This provides realization several key proposed previously. We compare theoretical from...
A bstract We study the cosmological collider phenomenology of neutrinos in an effective field theory. The mass spectrum and their characteristic oscillatory signatures squeezed limit bispectrum are computed. Both dS-covariant slow-roll corrections considered, so is scenario electroweak symmetry breaking during inflation. Interestingly, we show that background inflaton provides a chemical potential for neutrino production. greatly amplifies signal makes observably large heavy without need fine tuning.
A bstract The quantum fluctuations of the Higgs field during inflation could be a source primordial density perturbations through Higgs-dependent inflaton decay. By measuring non-Gaussianities, this so-called Higgs-modulated reheating scenario provides us unique chance to probe interactions at extremely high energy scale, which we call Cosmological Collider (CHC). We realize CHC in simple where decays into Higgs-portal scalars, taking account decay fluctuation amplitude after inflation. also...
Our current understanding of the Universe is established through pristine measurements structure in cosmic microwave background (CMB) and distribution shapes galaxies tracing large scale (LSS) Universe. One key ingredient that underlies cosmological observables field sources observed assumed to be initially Gaussian with high precision. Nevertheless, a minimal deviation from Gaussianityis perhaps most robust theoretical prediction models explain Universe; itis necessarily present even...
Hořava-Lifshitz gravity is a potentially UV complete theory with important implications for the very early universe. In particular, in presence of spatial curvature it possible to obtain non-singular bouncing cosmology. The bounce realized as consequence higher order terms gravitational action. Here, we extend study linear cosmological perturbations coupled matter case when present. As without curvature, find that there no extra dynamical degree freedom scalar metric perturbations. We...
We study the tilt of primordial gravitational waves spectrum. A hint blue is shown from analyzing BICEP2 and POLARBEAR data. Motivated by this, we explore possibilities tensor spectra very early universe cosmology models, including null energy condition violating inflation, inflation with general initial conditions, string gas cosmology, etc. For simplest G-inflation, spectrum also implies scalar In general, models indicate large non-Gaussianities. On other hand, predicts highly Gaussian...