Since the release of the DESI DR2 data, dynamic dark energy, particularly the quintom dark energy it suggests, has garnered significant attention. Quintom dark energy represents a characteristic that lies between quintessence and phantom behavior, indicating that the equation-of-state of dark energy will cross $-1$ during its evolution. In this talk, I will investigate the realization of...
Curvaton mechanism provides an alternative way to explain the origin of the observed primordial scalar fluctuations in the Cosmic Microwave Background (CMB) radiation. In this scenario, the curvaton is a scalar field which nearly remains frozen during inflation but produces isocurvature perturbations. It starts to evolve after the end of inflation, and at the time of it's decay it converts the...
The fact that graviton propagator contains not only one but two tensorial components excludes a unique definition of the running behavior of the gravitational constant, while at low energies gravitation is characterized solely by Newton's constant. How these two facts are reconciled when massive quantum fields are present remains unanswered. In this work, by non-minimally coupling gravity to a...
SMEFT Wilson coefficients are subject to various positivity bounds in order to be consistent with the fundamental principles of S-matrix. Previous bounds on dimension-8 SMEFT operators have been obtained using the positivity part of UV partial wave unitarity and form a (projective) convex cone. We derive a set of linear UV unitarity conditions that go beyond positivity and are easy to...
In this talk, I will briefly review the story of scattering amplitudes, mostly the color-ordering amplitudes. Based on the open-string topology- the real Riemann surface, a stringy integral has been proposed to unify the scalar, pion, and gluon amplitudes. The more interesting thing is now I propose a new stringy integral for the color-ordering form factor, which is inspired by the open &...
Positivity bounds in effective field theories (EFTs) can be extracted through the moment problem approach, utilizing well-established results from the mathematical literature. We generalize this formalism using the matrix moment approach to derive positivity bounds for theories with multiple field components. The sufficient conditions for
obtaining optimal bounds are identified and applied to...
At electroweak scale there are two EFTs: SMEFT and HEFT. In SMEFT, the Higgs and Goldstones are linearly realized around the vacuum expectation value. In HEFT, they are non-linearly realized and the Goldstones are encapsulated in an exponential matrix. HEFT encompasses SMEFT. Through matching a UV model to both EFTs, we study their distinctions. For general scalar extensions of the SM, there...
I will present a novel method to compute classical observables for two-body scattering systems. The on-shell radial action is treated as a generating function to directly extract observables, with full spin dependence. To account for the spin supplementary condition and other constraints, we compute the corresponding Dirac brackets. The observables, such as momentum impulse and spin kick, are...
We discuss a new classical action that enables efficient computation of the gluonic tree amplitudes but does not contain any triple point vertices. This new formulation is obtained via a canonical transformation of the light-cone Yang-Mills action, with the field transformations based on Wilson line functionals. In addition to MHV vertices, the action contains also $N^k$MHV vertices, where...
In this presentation, I will introduce part of our paper, which is a collaboration between my advisor Anna Tokareva, my academic siblings and friends Yong-jun and Long-Qi, and myself. I will begin with a brief overview of some fundamental concepts of effective field theory (EFT). Then, I will explain how, by applying dispersion relations, we can separate the infrared (IR) and ultraviolet (UV)...
We derive the Schwinger-Keldysh effective field theories for diffusion including
the lowest non-hydrodynamic degree of freedom from holographic Gubser-Rocha
systems. At low temperature the dynamical non-hydrodynamic mode could be either an IR mode or a slow mode, which is related to IR quantum critical excitations
or encodes the information of all energy scales. This additional dynamical...
In this talk, I will introduce the effective field theory (EFT) approach as a powerful tool for studying the dynamics of compact binary systems in scalar-tensor and Einstein-scalar-Gauss-Bonnet (ESGB) gravity. I will discuss state-of-the-art progress in deriving the conservative dynamics for both spinless and spinning binaries, emphasizing the efficiency of the EFT framework. These results...
Perturbative nonrenormalizability of gravity based on Hilbert-Einstein or Palatini actions prompted vast research in higher-derivative theories. The actions that are at least quadratic in curvature lead to a renormalizable theory, but they bring along the issue of possible unitarity violation from ghost and tachyonic degrees of freedom. Whether ghosts can or cannot be quantized consistently,...
In recent years, the gravitational self-force (GSF) has been successfully studied in Schwarzschild and Kerr black hole (BH) spacetimes. A test particle perturbing these spacetimes models a gravitational two-body system. After decoupling the radial and angular equations and performing a Fourier transform in the time variable, one is ultimately left with a main radial equation. This equation can...
