arXiv subjects

Ji-Yuan Ke

Publications and source records attributed to Ji-Yuan Ke.

3 recordsLinked to original sources

arXiv2026

Splitting Rules from Kinematic Flow: Local Evolution and Emergent Time

The differential equations satisfied by the wavefunction coefficients of conformally coupled scalars in a power-law cosmology can be recast as an iterative differential system of basis functions. These functions can be encoded within graph tubings and are governed by a set of rules describing how they flow in kinematic space. In this paper, we formulate a set of splitting rules equivalent to the kinematic flow at tree level by reversing the flow direction of graph tubings. Specifically, for any basis function, these rules identify all other basis functions whose total differentials contain it. From the splitting perspective, we uncover deeper physical information captured by graph tubings, such as the formation of singularity structures and the realization of local evolution. In an alternative basis based on time ordering, the splitting processes correspond to the emergence of time integrals. These rules can also be generalized naturally to the $\mathrm{tr}\,ϕ^3$ theory beyond individual graphs, providing a physical interpretation of the structure of the associahedron. This suggests that graph tubings and the kinematic flow may be more fundamental objects than the differential equations, and may have a life of their own.

hep-th↗

arXiv2025

Precision calculation of the EFT likelihood with primordial non-Gaussianities

We perform a precision calculation of the effective field theory (EFT) conditional likelihood for large-scale structure (LSS) using the saddle-point expansion method in the presence of primordial non-Gaussianities (PNG). The precision is manifested at two levels: one corresponding to the consideration of higher-order noise terms, and the other to the inclusion of contributions around the saddle points. In computing the latter, we encounter the same issue of the negative modes as in the context of false vacuum decay, which necessitates deforming the original integration contour into a combination of the steepest descent contours to ensure a convergent and real result. We demonstrate through detailed calculations that, upon incorporating leading-order PNG, both types of extensions introduce irreducible field-dependent contributions to the conditional likelihood. This insight motivates the systematic inclusion of additional effective terms within the forward modeling framework. Our work facilitates Bayesian forward modeling under non-Gaussian initial conditions, thereby enabling more stringent constraints on the parameters describing PNG.

astro-ph.CO↗

arXiv2025

Calculating the EFT likelihood via saddle-point expansion

In this paper, we extend the functional approach for calculating the EFT likelihood by applying the saddle-point expansion. We demonstrate that, after suitable reformulation, the likelihood expression is consistent with the path integral required to be computed in the theory of false vacuum decay. In contrast to the saddle-point approximation, the application of the saddle-point expansion necessitates more nuanced considerations, particularly concerning the treatment of the negative eigenvalues of the second derivative of the action at the saddle point. We illustrate that a similar issue arises in the likelihood calculation, which requires approximating the original integral contour through the combination of the steepest descent contours in the field space. As a concrete example, we focus on calculating the EFT likelihood under a Gaussian distribution and propose a general procedure for computing the likelihood using the saddle-point expansion method for arbitrary partition functions. Precise computation of the likelihood will benefit Bayesian forward modeling, thereby enabling more reliable theoretical predictions.

hep-ph↗