arXiv subjects

Yan Shao

Publications and source records attributed to Yan Shao.

At least 19 recordsLinked to original sources

arXiv2026

Rescuing flavor-symmetry-forbidden leptogenesis within the left-right symmetric framework

While the type-I seesaw model provides a unified framework for explaining the origin of neutrino masses and the baryon asymmetry of the Universe, flavor symmetries offer an attractive approach to understanding the observed neutrino mixing pattern. However, in many flavor-symmetry-based type-I seesaw models, either the Dirac neutrino mass matrix $M^{}_{\rm D}$ or the right-handed-neutrino mass matrix $M^{}_{\rm R}$ is constrained to be proportional to the identity matrix, which prevents the conventional leptogenesis mechanism from working. In this paper, without breaking the original flavor structure dictated by the employed flavor symmetries, we investigate whether such forbidden leptogenesis scenarios can be rescued within the framework of the left-right symmetric model. We show that, in these scenarios, the contribution of the Higgs triplet present in the left-right symmetric model to the CP asymmetries of right-handed neutrino decays can successfully reproduce the observed baryon asymmetry.

hep-ph↗

arXiv2026

Flavon assisted low scale leptogenesis

Low-scale leptogenesis scenarios, such as the resonant or ARS leptogenesis, typically require a highly degenerate mass spectrum of right-handed neutrinos (RHNs). This requirement can be circumvented by extending the seesaw framework with a scalar singlet $S$ that couples to RHNs via the $S N^{}_I N^{}_J$ terms (with $I \neq J$), which opens up new decay channels $N^{}_I \to N^{}_J S$ and provides additional sources of CP violation, thereby enabling successful leptogenesis at the TeV scale without the need for mass degeneracy. In this work, we point out that the flavon fields, which are introduced in many flavor-symmetry neutrino mass models to be responsible for the generation of RHN masses through the acquisition of non-zero vacuum expectation values, serve as ideal candidates for the $S$ field. Taking as an example a flavor-symmetry neutrino mass model that naturally realizes the experimentally allowed TM1 mixing pattern and has the attractive features that only one flavon field plays the role of $S$ and that it couples to only two RHNs, we demonstrate that the observed neutrino masses and mixing angles can be consistently reproduced, while the observed baryon asymmetry can be achieved within a parameter space compatible with current experimental constraints.

hep-ph↗

arXiv2026

Neutrino mass anarchy and leptogenesis

In this paper, we investigate leptogenesis under the neutrino mass anarchy hypothesis in both type-I and type-II seesaw models. We first revisit the corresponding study in the type-I seesaw framework with two improvements: in contrast to Ref.[25], where an approximate $U(1)$ flavor symmetry was imposed to ensure sizable hierarchies among the right-handed neutrino masses and Yukawa couplings, we adopt a fully general anarchy scenario with completely random and structureless neutrino mass and Yukawa matrices; moreover, given the crucial role of lepton flavors in both the generation and washout of the lepton asymmetry, flavor effects are consistently incorporated throughout our analysis. We then extend our investigation to the type-II seesaw framework, in which leptogenesis proceeds via the out-of-equilibrium decays of a scalar triplet.

hep-ph↗

arXiv2026

Leptogenesis in the littlest inverse seesaw model

The littlest inverse seesaw (LIS) model represents the first low-scale seesaw framework to successfully account for all six physical observables of the neutrino sector with merely two effective free parameters, making it highly worthy of in-depth investigation. In this work, we investigate realizations of leptogenesis in this framework. We consider two distinct scenarios. In the first, the two pseudo-Dirac sterile neutrino pairs are initially exactly degenerate and subsequently acquire small mass splittings via the RGE effects, enabling resonant leptogenesis to occur across different PD pairs and consequently enhancing leptogenesis. In the second, the two PD pairs feature a hierarchical mass spectrum, and leptogenesis proceeds via sterile neutrino oscillations through the ARS mechanism. We show that the observed baryon asymmetry can be successfully reproduced in sizable regions of the parameter space without introducing additional free parameters, demonstrating that the LIS framework provides a viable and predictive setting for low-scale leptogenesis.

hep-ph↗

arXiv2025

Linear seesaw leptogenesis before/after electroweak symmetry breaking

The linear seesaw (LSS) model provides a natural framework for generating small neutrino masses at low energy scales, thereby offering promising testability prospects. However, in generic LSS models, the exact mass degeneracy (before the electroweak symmetry breaking) between the two sterile neutrinos that form a Dirac pair precludes the generation of CP asymmetries from their interplay, posing a significant challenge to explaining the observed baryon (or lepton) asymmetry of the Universe via the leptogenesis mechanism. In this work, we explore two well-motivated approaches to generate a suitable mass splitting for the two sterile neutrinos that form a Dirac pair, and consequently naturally realize a resonantly enhanced generation of baryon (and lepton) asymmetry. First, we demonstrate that the renormalization group evolution effects can naturally induce the desired mass splitting for the sterile neutrinos, resulting in a successful generation of the observed baryon asymmetry of the Universe. Second, motivated by the recent result from the EMPRESS collaboration that indicates the possible existence of a large lepton asymmetry of the Universe, we explore the possibility that a large lepton asymmetry might naturally follow from the electroweak symmetry breaking which automatically induces the desired mass splitting for the sterile neutrinos.

hep-ph↗

arXiv2025

How Auxiliary Reasoning Unleashes GUI Grounding in VLMs

Graphical user interface (GUI) grounding is a fundamental task for building GUI agents. However, general vision-language models (VLMs) struggle with this task due to a lack of specific optimization. We identify a key gap in this paper: while VLMs exhibit significant latent grounding potential, as demonstrated by their performance measured by Pointing Game, they underperform when tasked with outputting explicit coordinates. To address this discrepancy and bypass the high data and annotation costs of current fine-tuning approaches, we propose three zero-shot auxiliary reasoning methods. By providing explicit spatial cues such as axes, grids and labeled intersections as part of the input image, these methods enable VLMs to better articulate their implicit spatial understanding capabilities. We evaluate these methods on four GUI grounding benchmarks across seven open-source and proprietary VLMs. Experimental results show substantial gains from auxiliary reasoning. Mark-Grid Scaffold boosts Gemini-3.1-Pro from 11.72\% under direct inference to 95.20\% on ScreenSpot-v2, achieves state-of-the-art performance on ScreenSpot, and approaches the strongest fine-tuned methods on ScreenSpot-v2 and UI-I2E-Bench. Our code is available at https://github.com/liweim/AuxiliaryReasoning.

cs.CV↗

arXiv2025

Rescuing leptogenesis in inverse seesaw models with the help of non-Abelian flavor symmetries

The inverse seesaw (ISS) model provides an attractive framework that can naturally explain the smallness of neutrino masses while accommodating some sterile neutrinos potentially accessible at present or future experiments. However, in generic ISS models with hierarchical pseudo-Dirac (PD) sterile neutrino pairs, the generation of the observed baryon asymmetry of the Universe via the leptogenesis mechanism is extremely challenging. In this paper, we investigate rescuing leptogenesis in the ISS model with the help of non-Abelian flavor symmetries which have the potential to explain the observed peculiar neutrino mixing pattern: we first implement non-Abelian flavor symmetries to naturally enforce mass degeneracies among different pseudo-Dirac sterile neutrino pairs and then break them in a proper way so that resonant leptogenesis among different PD sterile neutrino pairs can arise, thus enhancing the generated baryon asymmetry. To be specific, we have considered the following two well-motivated approaches for generating the tiny mass splittings among different PD sterile neutrino pairs: one approach makes use of the renormalization-group corrections to the sterile neutrino masses, while the other approach invokes non-trivial flavor structure of the $\mu_{\rm s}$ matrix. For these two scenarios, we aim to explore the viability of leptogenesis and to identify the conditions under which the observed baryon asymmetry can be successfully reproduced.

hep-ph↗

arXiv2024

Towards Building a Robust Knowledge Intensive Question Answering Model with Large Language Models

The development of LLMs has greatly enhanced the intelligence and fluency of question answering, while the emergence of retrieval enhancement has enabled models to better utilize external information. However, the presence of noise and errors in retrieved information poses challenges to the robustness of LLMs. In this work, to evaluate the model's performance under multiple interferences, we first construct a dataset based on machine reading comprehension datasets simulating various scenarios, including critical information absence, noise, and conflicts. To address the issue of model accuracy decline caused by noisy external information, we propose a data augmentation-based fine-tuning method to enhance LLM's robustness against noise. Additionally, contrastive learning approach is utilized to preserve the model's discrimination capability of external information. We have conducted experiments on both existing LLMs and our approach, the results are evaluated by GPT-4, which indicates that our proposed methods improve model robustness while strengthening the model's discrimination capability.

cs.CL↗

arXiv2024

Low scale leptogenesis under neutrino $\mu$-$\tau$ reflection symmetry

In the literature, the neutrino $\mu$-$\tau$ reflection symmetry (which has the interesting predictions $\theta^{}_{23} =\pi/4$ and $\delta = \pm \pi/2$ for the atmospherical neutrino mixing angle and Dirac CP phase) is an attractive and widely studied candidate for the flavor symmetries in the neutrino sector. But it is known that, when the seesaw model is furnished with this symmetry, the leptogenesis mechanism (which provides an elegant explanation for the baryon-antibaryon asymmetry of the Universe) can only work in the two-flavor regime (which only holds for the right-handed neutrino masses in the range $10^9-10^{12}$ GeV). This prohibits us to have a low scale seesaw model (which has the potential to be directly accessed by running or upcoming collider experiments) that can have the $\mu$-$\tau$ reflection symmetry and successful leptogenesis simultaneously. In this paper, for the first time, we demonstrate that the successful leptogenesis may also be achieved in low scale seesaw models furnished with the $\mu$-$\tau$ reflection symmetry, by means of the flavor non-universality of the conversion efficiencies from the flavored lepton asymmetries to the baryon asymmetry via the sphaleron process. We perform the study in both the resonant leptogenesis regime and the leptogenesis via oscillations (ARS leptogenesis) regime.

hep-ph↗

arXiv2024

Large Language Models Understand Layout

Large language models (LLMs) demonstrate extraordinary abilities in a wide range of natural language processing (NLP) tasks. In this paper, we show that, beyond text understanding capability, LLMs are capable of processing text layouts that are denoted by spatial markers. They are able to answer questions that require explicit spatial perceiving and reasoning, while a drastic performance drop is observed when the spatial markers from the original data are excluded. We perform a series of experiments with the GPT-3.5, Baichuan2, Llama2 and ChatGLM3 models on various types of layout-sensitive datasets for further analysis. The experimental results reveal that the layout understanding ability of LLMs is mainly introduced by the coding data for pretraining, which is further enhanced at the instruction-tuning stage. In addition, layout understanding can be enhanced by integrating low-cost, auto-generated data approached by a novel text game. Finally, we show that layout understanding ability is beneficial for building efficient visual question-answering (VQA) systems.

cs.CL↗

arXiv2024

Unusual charge density wave introduced by Janus structure in monolayer vanadium dichalcogenides

As a fundamental structural feature, the symmetry of materials determines the exotic quantum properties in transition metal dichalcogenides (TMDs) with charge density wave (CDW). Breaking the inversion symmetry, the Janus structure, an artificially constructed lattice, provides an opportunity to tune the CDW states and the related properties. However, limited by the difficulties in atomic-level fabrication and material stability, the experimental visualization of the CDW states in 2D TMDs with Janus structure is still rare. Here, using surface selenization of VTe2, we fabricated monolayer Janus VTeSe. With scanning tunneling microscopy, an unusual root13-root13 CDW state with threefold rotational symmetry breaking was observed and characterized. Combined with theoretical calculations, we find this CDW state can be attributed to the charge modulation in the Janus VTeSe, beyond the conventional electron-phonon coupling. Our findings provide a promising platform for studying the CDW states and artificially tuning the electronic properties toward the applications.

cond-mat.mtrl-sci↗

arXiv2024

Consequences of the $\mu$-$\tau$ reflection symmetry for leptogenesis in a seesaw model with diagonal Dirac neutrino mass matrix

In this paper, we have studied the consequences of the $\mu$-$\tau$ reflection symmetry for leptogenesis in the type-I seesaw model with diagonal Dirac neutrino mass matrix. We have first obtained the phenomenologically allowed values of the model parameters, which show that there may exist zero or equal entries in the Majorana mass matrix for the right-handed neutrinos, and then studied their predictions for three right-handed neutrino masses, which show that there may exist two nearly degenerate right-handed neutrinos. Then, we have studied the consequences of the model for leptogenesis. Due to the $\mu$-$\tau$ reflection symmetry, leptogenesis can only work in the two-flavor regime. Furthermore, leptogenesis cannot work for the particular case of $r=1$. Accordingly, for some benchmark values of $r \neq 1$, we have given the constraints of leptogenesis for relevant parameters. Furthermore, we have investigated the possibilities of leptogenesis being induced by the renormalization group evolution effects for two particular scenarios. For the particular case of $r=1$, the renormalization group evolution effects will break the orthogonality relations among different columns of $M^{}_{\rm D}$ and consequently induce leptogenesis to work. For the low-scale resonant leptogenesis scenario which is realized for nearly degenerate right-handed neutrinos, the renormalization group evolution effects can break the $\mu$-$\tau$ reflection symmetry and consequently induce leptogenesis to work.

hep-ph↗

arXiv2024

Leptogenesis consequences of trimaximal mixing and $\mu$-$\tau$ reflection symmetry in the most minimal seesaw model

In this paper we have studied the realizations of the popular TM1 neutrino mixing and neutrino $\mu$-$\tau$ reflection symmetry (which are well motivated from the neutrino oscillation data and lead to interesting phenomenological consequences) in the most minimal seesaw model with a pseudo-Dirac pair of right-handed neutrinos, and their consequences for leptogenesis. In order to realize the low-scale resonant leptogenesis scenario, we have considered two possible ways of generating the tiny mass splitting between the two right-handed neutrinos: one way is to modify their Majorana mass matrix to a form as shown in Eq. (25); the other way is to consider the renormalization-group corrections for their masses. For the $\mu$-$\tau$ reflection symmetry, in order for leptogenesis to work, we have further considered the flavor-dependent conversion efficiencies from the lepton asymmetry to the baryon asymmetry during the sphaleron processes, and its breaking via the renormalization-group corrections.

hep-ph↗

arXiv2021

Graph Attention Network-based Multi-agent Reinforcement Learning for Slicing Resource Management in Dense Cellular Network

Network slicing (NS) management devotes to providing various services to meet distinct requirements over the same physical communication infrastructure and allocating resources on demands. Considering a dense cellular network scenario that contains several NS over multiple base stations (BSs), it remains challenging to design a proper real-time inter-slice resource management strategy, so as to cope with frequent BS handover and satisfy the fluctuations of distinct service requirements. In this paper, we propose to formulate this challenge as a multi-agent reinforcement learning (MARL) problem in which each BS represents an agent. Then, we leverage graph attention network (GAT) to strengthen the temporal and spatial cooperation between agents. Furthermore, we incorporate GAT into deep reinforcement learning (DRL) and correspondingly design an intelligent real-time inter-slice resource management strategy. More specially, we testify the universal effectiveness of GAT for advancing DRL in the multi-agent system, by applying GAT on the top of both the value-based method deep Q-network (DQN) and a combination of policy-based and value-based method advantage actor-critic (A2C). Finally, we verify the superiority of the GAT-based MARL algorithms through extensive simulations.

cs.MA↗

arXiv2020

Spontaneous Formation of a Superconductor-Topological Insulator-Normal Metal Layered Heterostructure

The discovery of graphene has spurred vigorous investigation of 2D materials, revealing a wide range of extraordinary properties and functionalities. 2D heterostructural materials have recently been fabricated by assembling isolated planes layer-by-layer in a desired sequence. Unusual properties and novel physical phenomena have been unveiled in such layered heterostructures. For example, Hofstadter's butterfly, an intriguing pattern of the energy states of Bloch electrons, was predicted several decades ago to be observable only under unfeasibly strong magnetic fields in conventional materials. But it has been observed recently under current experimental conditions in graphene/BN layered heterostructures, one of the outstanding new kinds of 2D materials. Moreover, another amazing physics phenomenon, Majorana fermions was predicted to exist in heterostructural systems consisting of a superconductor (SC) and a topological insulator (TI) Journal.

cond-mat.mes-hall↗

arXiv2018

82 Treebanks, 34 Models: Universal Dependency Parsing with Multi-Treebank Models

We present the Uppsala system for the CoNLL 2018 Shared Task on universal dependency parsing. Our system is a pipeline consisting of three components: the first performs joint word and sentence segmentation; the second predicts part-of- speech tags and morphological features; the third predicts dependency trees from words and tags. Instead of training a single parsing model for each treebank, we trained models with multiple treebanks for one language or closely related languages, greatly reducing the number of models. On the official test run, we ranked 7th of 27 teams for the LAS and MLAS metrics. Our system obtained the best scores overall for word segmentation, universal POS tagging, and morphological features.

cs.CL↗

arXiv2018

Universal Word Segmentation: Implementation and Interpretation

Word segmentation is a low-level NLP task that is non-trivial for a considerable number of languages. In this paper, we present a sequence tagging framework and apply it to word segmentation for a wide range of languages with different writing systems and typological characteristics. Additionally, we investigate the correlations between various typological factors and word segmentation accuracy. The experimental results indicate that segmentation accuracy is positively related to word boundary markers and negatively to the number of unique non-segmental terms. Based on the analysis, we design a small set of language-specific settings and extensively evaluate the segmentation system on the Universal Dependencies datasets. Our model obtains state-of-the-art accuracies on all the UD languages. It performs substantially better on languages that are non-trivial to segment, such as Chinese, Japanese, Arabic and Hebrew, when compared to previous work.

cs.CL↗

arXiv2017

Character-based Joint Segmentation and POS Tagging for Chinese using Bidirectional RNN-CRF

We present a character-based model for joint segmentation and POS tagging for Chinese. The bidirectional RNN-CRF architecture for general sequence tagging is adapted and applied with novel vector representations of Chinese characters that capture rich contextual information and lower-than-character level features. The proposed model is extensively evaluated and compared with a state-of-the-art tagger respectively on CTB5, CTB9 and UD Chinese. The experimental results indicate that our model is accurate and robust across datasets in different sizes, genres and annotation schemes. We obtain state-of-the-art performance on CTB5, achieving 94.38 F1-score for joint segmentation and POS tagging.

cs.CL↗