arXiv subjects

Yanda Wu

Publications and source records attributed to Yanda Wu.

5 recordsLinked to original sources

arXiv2026

Electroweak Baryogenesis: Advances in Sphaleron Rate Calculations and Implications of Thermal Phase Transitions

This thesis reviews recent advances in calculating the sphaleron rate, with particular emphasis on electroweak baryogenesis. It also provides pedagogical introductions to sphaleron- and instanton-induced baryon-number violation, the vacuum structure of non-Abelian gauge theories, and other topological field configurations, and suggests "an zi" as a possible Chinese term for "sphaleron" (see p. 3). Broader implications of first-order phase transitions for collider searches and primordial black hole formation are also discussed.

hep-ph↗

arXiv2025

An Effective Sphaleron Awakens

Using thermal effective field theory, we present a self-consistent perturbative formulation of the Higgs phase sphaleron rate after a radiatively-induced first-order phase transition. This gauge-invariant formulation is based on dimensionally reduced effective field theory (3D EFT) at high temperatures and paves a way for including higher order corrections within the 3D EFT perturbation theory without double counting. Concretely, we compute the Higgs phase sphaleron rate in a semi-classical approximation within the two-loop resummed 3D EFT. We find compact results for the sphaleron rate and the baryon washout factor as well as criteria for the baryon number preservation by providing a clear connection to the results obtained using a similar 3D EFT description for the bubble nucleation. We demonstrate these calculations for the real triplet-extended Standard Model, and conclude that when all two-loop thermal effects for the matching are accounted, no sufficiently strong one-step electroweak phase transitions exist within the parameter space regime that can be mapped onto the 3D EFT we have considered.

hep-ph↗

arXiv2024

Super-exponential Primordial Black Hole Production via Delayed Vacuum Decay

If a cosmological first-order phase transition occurs sufficiently slowly, delayed vacuum decay may lead to the formation of primordial black holes. Here we consider a simple model as a case study of how the abundance of the produced black holes depends on the model's input parameters. We demonstrate, using both numerical and analytical arguments and methods, that the black hole abundance is controlled by a double, ``super''-exponential dependence on the three-dimensional Euclidean action over temperature at its minimal value. We show that a modified expansion rate during the phase transition, such as one driven by an additional energy density component, leads to a weaker dependence on the underlying model parameters, but maintains the same super-exponential structure. We argue that our findings generalize to any framework of black hole production via delayed vacuum decay.

hep-ph↗

arXiv2023

Phase transitions, anomalous baryon number violation and electroweak multiplet dark matter

We perform a comprehensive analysis of baryon number violation during an electroweak phase transition (EWPT) within the framework of a scalar electroweak multiplet extension of the Standard Model. We classify the multiplet representations, topological properties, and corresponding thermal histories. Sphaleron or monopole topological field solutions emerge during the EWPT depending on the stage of the phase transition and the hypercharge of the new scalar multiplet. Furthermore, the monopole field solution pertains when the neutral component of the additional scalar multiplet is a viable dark matter candidate. We further analyze other formal considerations, including the construction of the \lq\lq sphaleron matrix\rq\rq\, for higher dimensional representations, computation of the sphaleron and monopole masses, and the choice of boundary conditions when solving the field equations of motion. We apply these considerations to the computation of sphaleron energy and monopole mass within the context of a multi-step EWPT, employing the SU(2)$_L$ septuplet scalar extension to the Standard Model (SM) as a case of study from the minimal dark matter paradigm. For the first step of a two-step EWPT, we delineate the relationship between the monopole mass and the parameters relevant to dark matter phenomenology.

hep-ph↗

arXiv2022

Study of Electroweak Phase Transition in Exotic Higgs Decays at the CEPC

A strong first-order electroweak phase transition (EWPT) can be induced by light new physics weakly coupled to the Higgs. This study focuses on a scenario in which the first-order EWPT is driven by a light scalar $s$ with a mass between 15-60 GeV. A search for exotic decays of the Higgs boson into a pair of spin-zero particles, $h \to ss$, where the $s$-boson decays into $b$-quarks promptly is presented. The search is performed in events where the Higgs boson is produced in association with a $Z$ boson, giving rise to a signature of two charged leptons (electrons or muons) and multiple jets from $b$-quark decays. The analysis is considering a scenario of analysing 5000 fb$^{-1}$ $e^+ e^-$ collision data at $\sqrt{s} = 240 $ GeV from the Circular Electron Positron Collider (CEPC). This study with $4b$ final state conclusively tests the expected sensitivity of probing the light scalars in the CEPC experiment. The sensitivity reach is significantly larger than that can be achieved at the LHC.

hep-ex↗