arXiv subjects

Xu-Xiang Li

Publications and source records attributed to Xu-Xiang Li.

9 recordsLinked to original sources

arXiv2026

Logarithmic Wavelets for Dark Matter--Phonon Scattering

Phonon excitations in crystals are a promising detection channel for sub-GeV dark matter (DM), and anisotropic targets add directional sensitivity through the daily modulation of the rate. Exploiting these capabilities requires evaluating six-dimensional rate integrals across DM models, target materials, detector orientations, and times of day. The vector space integration method factorizes the calculation into projections of the DM velocity distribution and of the material response -- each computed once and reused -- contracted with an analytic kinematic matrix, reducing such scans to fast matrix algebra. In the phonon channel, however, the relevant momentum transfers span six orders of magnitude, and the linearly spaced Haar wavelet basis of existing implementations falls short: light mediator models demand an impractically large basis, and a single projection reused across DM masses loses its effective resolution for light DM. We introduce a logarithmic Haar wavelet basis that resolves both obstacles, and present a package VectorPhonoDark that implements the approach. On an Al$_2$O$_3$ daily modulation benchmark, it reproduces results from PhonoDark's direct numerical integration while reducing the computational cost by orders of magnitude. Though developed here for phonons, the logarithmic wavelet basis generalizes to any DM detection channel spanning a wide range of momentum transfers, enabling efficient scans over DM models and detection strategies.

hep-ph↗

arXiv2026

Astrophysical Uncertainties in Sub-GeV Dark Matter Detection via Single Phonon Excitations

We present the first systematic study of how local dark matter velocity distribution uncertainties propagate into direct detection rates for dark matter--single phonon scattering. We consider three benchmark halo models -- Standard Halo Model, Tsallis and empirical -- and vary the astrophysical parameters within observationally motivated ranges. To compare halo models on equal footing, we introduce an rms-matching prescription that holds the mean dark matter kinetic energy fixed across models. With this prescription, differences between halo models prove subdominant to parameter variations within each model, so that astrophysical uncertainties can be effectively captured by varying parameters within the Standard Halo Model alone. We find $\mathcal{O}(1\%)$ to $\mathcal{O}(100\%)$ fractional deviations in the predicted rates across the dark matter mass range of interest. For the daily modulation signal, astrophysical parameter variations rescale the amplitude but leave the phase robust. These results provide timely input for reliably interpreting upcoming phonon-based direct detection experiments targeting sub-GeV dark matter.

hep-ph↗

arXiv2025

Multi-step phase transition and gravitational wave from general $\mathbb{Z}_2$ scalar extensions

Multi-step phase transition provides a paradigm in which a broken symmetry during phase transition can be restored, enriching the phenomena of both dark matter and baryon asymmetry. We study the dynamics of the multi-step phase transition in the standard model extension with additional isospin $N$-plet scalar field $Φ_2$ under a discrete $\mathbb{Z}_2$ symmetry. We find that the multi-step phase transition could be triggered if there is a moderately large coupling between the Higgs and the $Φ_2$ and this coupling is required to be larger as the mass of the $Φ_2$ and/or isospin increase. The first-order phase transition at the first (second) step can be realized by the thermal loop (tree-level barrier) effects. Thus it is more likely that a detectable spectrum of gravitational waves can be produced at the second step of the phase transition.

hep-ph↗

arXiv2025

Geometric Building Blocks of Effective Field Theory Amplitudes

On-shell amplitudes are invariant under field redefinitions. Nonderivative field redefinitions have a natural interpretation as coordinate transformations on the target manifold. General field redefinitions, which may involve derivatives, can be viewed as coordinate transformations on the field configuration manifold. We present a unified perspective for the geometry of both the target manifold and the field configuration manifold for scalar effective field theories. In both cases, we identify vertices that can be used to build the tree-level amplitudes, with the property that they transform covariantly in the vacuum and on-shell limits. We identify a choice of metric on the field configuration manifold, for which amplitude expressions on the target manifold can be easily reproduced from their counterparts on the field configuration manifold. This clarifies the relation between the well-established framework of field space geometry and recent proposals for functional geometry.

hep-th↗

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

The Geometric Universal One-Loop Effective Action

We derive universal formulae for integrating out heavy degrees of freedom in scalar field theories up to one-loop level in terms of covariant quantities associated with the geometry of the field manifold. The universal matching results can be readily applied to phenomenologically interesting extensions of the Standard Model, as we demonstrate using a singlet scalar example. We also discuss the role of field redefinitions in effective field theory matching and simplifications resulting from going to a field basis where interactions are encoded in a nontrivial metric on the field manifold.

hep-ph↗

arXiv2023

A complete tree-level dictionary between simplified BSM models and SMEFT (d $\leq$ 7) operators

Finding all possible UV resonances of effective operators is an important task in the bottom-up approach of effective field theory. We present all the tree-level UV resonances for the dimension-5, -6 and -7 operators in the Standard Model effective field theory (SMEFT), and then obtain the correspondence between the UV resonances and the effective operators from the relations among their Wilson coefficients, through the functional matching and operator reduction procedure. This provides a cross-dimension UV/IR dictionary for the SMEFT at tree-level, and the methods used here, especially the on-shell construction of general UV Lagrangian and the systematic reduction of operators, are extendable for UV resonances of $d \geq 8$ operators in SMEFT and other EFTs.

hep-ph↗

arXiv2022

Neutrino seesaw models at one-loop matching: Discrimination by effective operators

Using the functional method, one-loop matching of the type-I, -II and -III seesaw models are investigated and the results are presented in both the Green's and the Warsaw bases. Although these models generate the same dimension-5 Weinberg operator, they could induce quite different types of dimension-6 effective operators that can be utilized for model discrimination. We also find the threshold effects from one-loop matching could be significant, which turn out to allow triggering electroweak symmetry breaking radiatively in type-II seesaw while forbid that in type-I/-III models. An analytical criterion for such radiative symmetry breaking is also derived in type-II seesaw. Finally, we investigate the indirect signatures from different types of dimension-6 operators at high-energy colliders, low-energy precision experiments and forward physics facilities for model discrimination.

hep-ph↗

arXiv2021

Electroweak phase transition triggered by fermion sector

To realize first-order electroweak phase transition, it is necessary to generate a barrier in the thermal Higgs potential, which is usually triggered by scalar degree of freedom. We instead investigate phase transition patterns in pure fermion extensions of the standard model, and find that additional fermions with mass hierarchy and mixing could develop such barrier and realize strongly first-order phase transition in such models. In the Higgs potential with polynomial parametrization, the barrier can be generated in the following two patterns: (I) positive quadratic term, negative cubic term and positive quartic term or (II) positive quadratic term, negative quartic term and positive higher dimensional term, such as dimensional 6 operator.

hep-ph↗