The 2nd Workshop on Grand Unified Theories: Phenomenology and Cosmology (GUTPC 2025)

17 Apr 2025, 12:00 → 22 Apr 2025, 14:00 Asia/Shanghai

The Workshop on Grand Unified Theory, Phenomenology and Cosmology (GUTPC) will be hosted in Hangzhou Institute for Advanced Study (HIAS), University of Chinese Academy of Sciences (UCAS), on April 17-22, 2025, including registration day and leaving day. 

The aim of the workshop is to discuss recent progresses in Grand Unified Theories (GUT), which unifies all fundamental particle forces. Inspired by undergoing and upcoming gravitational wave observatories and precision measurements in neutrino experiments, we will focus on particle phenomenology and cosmology related to GUT.

Registration fee: 1500 CNY for staffs, 1000 CNY for students

Registration and abstract submission deadline: April 8th, 2025

Time: April 17-22, 2025 (arrival on 17, departure on 22)

Address: Conference Hall on Floor 2A, B3, Yunyi Campus of HIAS, UCAS

国科大杭州高等研究院云艺园区 3号楼 2楼报告厅

We have a panel session for 50th Anniversary of SO(10) GUT.
Time: 4:00-5:30pm, Friday
Welcome to join via the zoom link below (only for the panel) if you cannot appear personally

https://zoom.us/j/7189000175?pwd=akRSTjBjMExVQytIaTFVcGdPdyszZz09&omn=98895233920

Contact: 
Ms. Jing Wang (SLXY@ucas.ac.cn)
Ms. Shutong Liu (liushutong@ucas.ac.cn)

Poster

Thursday, 17 April

Registration

Friday, 18 April

Registration

Plenary: Session 1

Convener: Yi Liao (IQM, South China Normal University)

1 Small Instantons and the Post-Inflationary QCD Axion in a Special Product GUT

We present a new framework of grand unification that is equipped with an axion solution to the strong CP problem without a domain wall problem when the Peccei-Quinn (PQ) symmetry is spontaneously broken after inflation. Our grand unified theory (GUT) is based on a symmetry breaking pattern, SU(10)×SU(5)1→SU(5)V⊃SU(3)C×SU(2)L×U(1)Y, where SU(5)1 and a special embedding of SU(5)2⊂SU(10) are broken to a diagonal subgroup SU(5)V. The model contains a vector-like pair of PQ-charged fermions that transform as (anti-)fundamental representations under SU(10), so that the domain wall number is one. However, after the GUT symmetry breaking, the number of vector-like pairs of PQ-charged colored fermions is larger than one, which seems to encounter the domain wall problem. This apparent inconsistency is resolved by small instanton effects on the axion potential which operate as a PQ-violating bias term and allow the decay of domain walls. We propose a domain-wall-free UV completion for an IR model where the domain wall number appears larger than one. The model gives a prediction for a dark matter axion window, which is different from that of the ordinary post-inflationary QCD axion with domain wall number one.

Speaker: Yuichiro Nakai (Shanghai Jiao Tong University)

GUT2025.pdf

2 E6

I will motivate the use of E6 grand unified theory and describe a
realistic E6 GUT which gives rise to novel possible intermediate stages.

Speaker: Prof. Borut Bajc (J. Stefan Institute)

3 A simple and safe way to break PQ at the GUT scale

I will present a set of simple KSVZ-type axion models, with a breaking scale similar to the GUT-scale, and which doesn't have a domain wall problem or fine-tuning in the initial misalignment angle. I will use this model to argue that it is experimentally difficult to distinguish whether PQ symmetry is broken before or after inflation. I will describe how GW probes could provide vital information in this direction, giving us a concrete handle of relevant particle physics parameters and the UV physics.

Speaker: Andrew Cheek (TDLI, SJTU)

CHEEK_GUTPC.pdf

4 Unification of Particles and Symmetries in An Affine SU(8) Lie Algebra

We present the recent progresses of a unified framework based on an affine SU(8) Lie algebra. This is found to be the minimal Lie algebra where three-generational SM fermions can transform differently. Accordingly, we describe how to generate the observed SM quark/lepton mass hierarchies and the CKM mixing patterns with one unique SM Higgs boson. We also discuss the gauge coupling unification in this framework, where one unique SUSY extension with anti-symmetric superfields is allowed.

Speaker: 宁/Ning 陈/Chen (Nankai University)

SU8_talk.pdf

Coffee break

Lunch

Plenary: Session 2

Convener: Zhi-Wei Wang (University of Electronic Science and Technology of China (UESTC))

5 Understanding the SM gauge group from SMEFT

We discuss heavy particles that can be used to pin down the faithful Standard Model (SM) gauge group and their patterns in the SM effective field theory (SMEFT). These heavy particles are not invariant under a specific $\mathbb{Z}_6$ subgroup of $SU(3)_c\times SU(2)_L \times U(1)_Y$, which however acts trivially on all the SM particles, hence the faithful SM gauge group remains undetermined. Different realizations of the faithful SM gauge group correspond to different spectra of heavy particles, and they also correspond to distinct sets of line operators with one-form global symmetry acting on them. We show that the heavy particles not invariant under the $\mathbb{Z}_6$ group cannot appear in tree-level ultraviolet completions of SMEFT, this enforces us to consider one-loop UV completions of SMEFT to identify the $\mathbb{Z}_6$ non-invariant heavy particles. We demonstrate with examples that correlations between Wilson coefficients provide an efficient way to examine models with $\mathbb{Z}_6$ non-invariant heavy particles. Finally, we prove that all the scalars that can trigger electroweak symmetry breaking must be invariant under the $\mathbb{Z}_6$ group, hence they cannot be used to probe the faithful SM gauge group.

Speaker: Dr Hao-Lin Li (Zhongshan University)

SMGroup_HaolinLi.pdf

6 Testing Frogatt-Nielsen flavour models with gravitational waves

I will present a recent work where we assessed the capability of Gravitational Wave (GW) experiments to probe the origin of the flavour sector of the Standard Model. Within the context of the Froggatt-Nielsen mechanism to generate the hierarchical patterns of fermion masses and mixing based on a gauged U(1) flavour symmetry, we investigated the formation of cosmic strings and the resulting GW background (GWB), estimating the sensitivity to the model’s parameter space of future GW observatories. Comparing these results with the bounds from low-energy flavour observables, we found that these two types of experimental probes of the model are nicely complementary. In certain scenarios, the combination of flavour constraints and future GW bounds can bring about a complete closure of the parameter space, which (once again) illustrates the potential of GWB searches to test fundamental interactions at ultra-high energy scales beyond the reach of laboratory experiments.

Speaker: Lorenzo Calibbi (Nankai University)

calibbi-GUTPC.pdf

7 Enhancing Phase Transition Calculations through Polynomial Fitting and Neural Network Approximation

The computation of bounce action in a phase transition involves solving partial differential equations, inherently introducing non-negligible uncertainty. Deriving characteristic temperatures and properties of this transition necessitates both differentiation and integration of the action, thereby exacerbating the uncertainty. In this work, we use polynomial fitting to approximate the action function of temperature, aimed at mitigating the uncertainties inherent in calculation of the nucleation temperature, the percolation temperature, and the inverse transition duration. We find that the sixth-order polynomial can provide an excellent fit for the groomed action in the toy model. In a realistic model, the singlet extension of the Standard Model, this method performs satisfactorily across most of the parameter space after trimming the fitting data. This approach not only enhances the accuracy of phase transition calculations but also systematically reduces computation time and facilitates error estimation, particularly in models involving multiple scalar fields.

Speaker: Yang Zhang (Henan Normal University)

8 Detecting Gravitational Waves from Cosmic Phase Transitions

Symmetry breaking in the early universe is manifested in the form of cosmological
phase transitions, and more desirably first order ones, during which a stochastic
background of gravitational waves can be generated. I will discuss how to detect
such gravitational waves using future space-based detectors, and how future measurements of such signals help us learn about the underlying particle physics
models.

Speaker: Huaike Guo (UCAS (ICTP-AP))

Huaike Guo.pdf

Coffee break

Panel discussion: 50th Anniversary of SO(10) GUT

Convener: Zhi-zhong XING (IHEP, Beijing)

Zoom link

9 50th Anniversary of SO(10) GUT; Moderator: Zhi-zhong Xing; Panelists: John Ellis, Steve King, Tian-Jun Li, Ray Volkas, Zhi-Wei Wang

Dinner: Reception

Saturday, 19 April

Plenary: Session 3

Convener: Huaike Guo (UCAS (ICTP-AP))

10 Flavoured GUTs

I will discuss Beyond Standard frameworks that can address the flavour problem and unification, including strategies for reconciling unification with distinct flavour structures between lepton and quark sectors.

Speaker: Ivo de Medeiros Varzielas (CFTP, IST)

GUTPC.pdf

11 Yukawa textures from selection rules without group actions

We study the coupling selection rules associated with non-group symmetries, i.e., $\mathbb{Z}_2$ gauging of $\mathbb{Z}_M$ symmetries. We clarify which Yukawa textures can be derived by our selection rules for $M=3, 4$, and $5$, and obtain various textures including the the nearest neighbor interaction type and its extension. Some of them cannot be realized by a conventional group-like symmetry. They lead to interesting phenomenology such as a solution to the strong CP problem without axion.

Speaker: Hajime Otsuka

Otsuka_GUTPC2025.pdf

12 High-quality Peccei-Quinn symmetry from the interplay of vertical and horizontal gauge symmetries

We explore a class of axion models where an accidental U(1) Peccei-Quinn (PQ)
symmetry automatically arises from the interplay of vertical (grand-unified)
and horizontal (flavor) gauge symmetries. Focusing on a specific SO(10) or Pati-Salam realization, we analyze the quality of the PQ symmetry and demonstrate that
the model non-trivially reproduces the Standard Model flavor structure. A high-quality axion, immune to the PQ quality problem, is obtained for ma ≳ 0.01 eV, corresponding to a post-inflationary PQ-breaking scenario. A distinctive feature of this setup is the presence of parametrically light fermions, known as anomalons, introduced to cancel the gauge anomalies of the flavor symmetry. We
investigate their cosmological production in the early universe, highlighting
how measurements of ∆Neff could serve as a low-energy probe of the UV dy-
namics addressing the PQ-quality problem.

Speaker: Giacomo Landini (CSIC-IFIC)

Axion_GUTPC25.pdf

Photo

Coffee break

Plenary: Session 4

Convener: Anna Tokareva (HIAS)

13 Degeneracy Enhancement of Neutron-Antineutron Oscillation in Neutron Star

We explore the fermion oscillation in a degenerate environment. The direct consequence is introducing a Pauli blocking factor 1−fi, where fi is the phase space distribution function, for each intermediate mass eigenstate during propagation. It is then much easier for a state with larger existing fraction or density to oscillate into other states with less degeneracy while the reversed process is not enhanced. This can significantly modify the oscillation behaviors. We apply this degenerate fermion oscillation to a concrete scenario of neutron-antineutron oscillation in neutron star. It turns out antineutrons receive a standing fraction to annihilate with the environmental neutrons. The subsequent neutron star heating can put an extremely stringent bound on the baryon number violating cross mass term between neutron and antineutron.

Speaker: Shao-Feng Ge (SJTU)

250419_HIAS.pdf

14 Appeal and challenges of natural SUSY GUT (with spontaneous SUSY breaking)

I introduce the appeal and remaining challenges of natural GUT and then discuss possible solutions to these problems. After that, I delve into the appeal and issues concerning scenarios of spontaneous supersymmetry breaking within natural grand unified theories.

Speaker: Nobuhiro MAEKAWA (KMI, Nagoya Univ.)

Hanzou25.pdf

Lunch

Plenary: Session 5

Convener: Shao-Feng Ge (SJTU)

15 Consequencies of phase transitions happened during inflation

I will talk about phonmenological consequencies induced by phase transitions occurred during inflation, including gravitational waves, primordial black holes, primordial non-gaussianity, baryogenesis, dark matter production.

Speaker: Haipeng An (Tsinghua University)

HGY_2025_HaipengAN.pdf

16 Kahler moduli inflation in large volume compactifications

TBA

Speaker: Prof. Georgios Leontaris (Ioannnia U)

17 A model builder's guide to cosmological collider physics

I will introduce the basics and recent developments of cosmological collider physics, with a focus on the model-building aspects. In particular, I will describe the essential knowledge and techniques required for particle model builders to study the cosmological collider phenomenology of their favorite BSM new physics.

Speaker: Prof. Zhong-Zhi Xianyu (Tsinghua University)

CosmoCollider_HIAS2025.pdf

18 Gravitational Waves of GUT Phase Transition during Inflation

GUT phase transition is generally considered unobservable due to its ultra-high energy scale, and the monopole problem associated with GUT phase transition is one motivation of inflation. We propose that if a first-order GUT phase transition happens during inflation, the induced gravitational waves (GWs) are redshifted and deformed, and might be observed today in GW observatories. We review the formalism of inflated GWs and derive the general deformation function between inflated and uninflated GW spectra in the instant-source or transitory-source application. It is valid for any e-folding number of instant or transitory source. Applying the formalism to GUT phase transition, we find that the e-folding number at 15 or 25 can shift the GWs to 10 Hz or mHz hands, respectively, which might be tested in the future ground-based or space-based interferometers. We further generalise the discussion to inflated GWs via phase transition below the GUT scale. It is worth mentioning that, due to the deformation of the spectrum, the peak of inflated GWs is not simply a redshift of the peak of uninflated GWs.

Speaker: Mr Xi-He Hu (HIAS, UCAS)

XiHeHu_Hangzhou_2025.4.19_v.2.pdf

Coffee break

Plenary: Session 6

Convener: Shun Zhou (University of Electronic Science and Technology of China (UESTC))

19 Asymptotic unification in supersymmetric E6 theory

The ultimate dream of unification models consists in combining both gauge and Yukawa couplings into one unified coupling. This is achieved by using a supersymmetric exceptional E6 gauge symmetry together with asymptotic unification in compact five-dimensional space-time. The ultraviolet fixed point requires exactly three fermion generations: one in the bulk, and the two light ones localised on the SO(10) boundary in order to cancel gauge anomalies. A second option allows to preserve baryon number and to lower the compactification scale down to the typical scales of the intermediate Pati-Salam gauge theory.

Speaker: Roman Pasechnik (University of Lund)

20 Boundary breaking of multiple modular flavor symmetry, SUSY mu-problem and modulus stabilization mechanism in modular flavor GUT models

In this talk, we would like to discuss the breaking of multiple modular flavor symmetry by boundary conditions in flipped SU(5) unification model. We would also like to discuss the solution of SUSY mu-problem in the framework of modular flavor symmetry. Relevant modulus stabilization mechanism with SUSY breaking contributions from nilpotent constrained superfield will also be discussed. .

Speaker: Fei Wang (Department of Physics, ZhengZhou University)

21 Asymptotic grand unification in SO(10) with one extra dimension

Asymptotic grand unification provides an alternative approach to gradually unify gauge couplings in the UV limit, where they reach a non-trivial UV fixed point. Using an economical and realistic particle content setup, we demonstrate that asymptotic grand unification can be achieved in $SO(10)$ with one extra dimension. The top, bottom and tau masses are split, and the smallness of the neutrino mass is explained via seesaw mechanisms. One intermediate scale, the Pati-Salam symmetry breaking scale, is included below the compactification scale. Due to the restricted Higgs content, gauge couplings exhibit asymptotic safety and are thus asymptotically unified, regardless of their initial values. In contrast, Yukawa couplings exhibit asymptotic freedom, requiring explicit unification at the compactification scale if decomposed from the same couplings in $SO(10)$. Asymptotic freedom of the 't Hooft Yukawa couplings is realized when the negative gauge contribution dominates over the positive Yukawa contribution in the competition within the beta functions. The widely-used 126-dimensional Higgs is not recommended in this asymptotic $SO(10)$ GUT with one extra dimension.

Speaker: Gao-Xiang Fang (HIAS)

Dinner: Banquet

22 Caixun Yuanzi Restaurant 采寻院子餐厅

Sunday, 20 April

Plenary: Session 7

Convener: Hajime Otsuka

23 General chiral structures for BNV nucleon decays and applications to hydrogen decay

We examine the general nucleon decay interactions that involve only three light quarks without any derivatives acting on them. We identify eight generic operator structures that correspond to eight different chiral representations, {$\pmb{8}_{\tt L}\otimes \pmb{1}_{\tt R}$, $\bar{\pmb{3}}_{\tt L}\otimes \pmb{3}_{\tt R}$, $\pmb{6}_{\tt L}\otimes \pmb{3}_{\tt R}$, $\pmb{10}_{\tt L}\otimes \pmb{1}_{\tt R}$}, along with their chiral partners under the interchange of ${\tt L}\leftrightarrow {\tt R}$. The four structures, $\pmb{8}_{\tt L(R)}\otimes \pmb{1}_{\tt R(L)}$ and
$\bar{\pmb{3}}_{\tt L(R)}\otimes \pmb{3}_{\tt R(L)}$, have been extensively discussed in the literature, while the remaining four are identified for the first time. We perform the chiral matching for these interactions at leading chiral order and find that there is a unique hadronic operator for each quark-level interaction. Notably, the hadronic counterparts of the new structures with $\pmb{6}_{\tt L(R)}\otimes \pmb{3}_{\tt R(L)}$ representations can appear at the same order as those of the four well-known ones, while those with $\pmb{10}_{\tt L(R)}\otimes \pmb{1}_{\tt R(L)}$ representations appear at a higher chiral order, involving derivatives of the meson octet matrix. Besides, we study BNV hydrogen decays. We employ a robust EFT approach to estimate the decay widths of two-body decays of hydrogen atom into SM particles, by utilizing the constraints on the EFT cutoff scale derived from conventional nucleon decay processes. By applying the bounds on the WCs from conventional nucleon decays, we provide a conservative estimate on hydrogen BNV decays. Our findings indicate that the bounds on the inverse partial widths of all dominant two-body decays exceed $10^{44}$ years. Among these modes, the least constrained diphoton decay ${\tt H}\to \gamma\gamma$ might be astrophysically interesting, although the monochromatic photon signal from our Sun is difficult to detect with current near-Earth telescopes.

Speaker: 昊琳/Hao-Lin 王/Wang (SCNU)

24 Exotic proton decays and the GUT Models

In the first part we discuss exotic proton decay processes within grand unification that are characterized by non-minimal embeddings of the Standard Model matter fields within the irreducible representations of the grand unified group. We take $SU(7)$ as the grand unified group and allow for different options for the dominant proton decay processes, depending on the details of the $SU(7)$ symmetry breaking and the embedding of the quarks and leptons in $SU(7)$ multiplets.

Proton decay scenarios include: two-body processes via $B+L$ or $B-L$ conserving channels, three-body processes, or the proton can be made exactly stable.

All nonzero proton decay processes appear at one or higher loop orders, with exotic states in the loops that are odd with respect to an emergent $Z_2$ symmetry, similar to scotogenic scenarios for neutrino masses. The approach also allows for several possible dark matter candidates and a variety of possible scenarios for the neutrino sector.

In the second part , we explore scenarios within grand unification in which proton decay can be suppressed and possibly eliminated due to novel embeddings of the Standard Model matter fields into irreducible representations of the grand unified group and residual symmetries.

The scenarios are based on an $SU(7)$ gauge group, in which the matter fields are embedded within an anomaly-free set of fields that can be realized as a natural subgroup of the fundamental spinor representation of an $SO(14)$ gauge symmetry.

Depending on the embedding, proton decay can either be forbidden at tree level and generated via one-loop diagrams, or the proton can be made stable by forcing it to decay channels that must have an even number of leptons, independently of the bosonic content of the theory. We describe the theoretical and phenomenological implications of such scenarios, including their implications for dark matter and neutrino masses.

Speaker: Dr Oleg Popov (Shenzhen MSU-BIT University)

PopovO_GUTPC2025.pdf

25 Phenomenology of a supersymmetric Pati-Salam model

We present a supersymmetric Pati-Salam model with small representations as a potential candidate for physics beyond the Standard Model. The model features a Higgs sector with bifundamental fields $H_R+\bar H_R=(4,1,2)+(\bar 4,1,2)$, $H_L+\bar H_L=(4,2,1)+(\bar 4,2,1)$ as well as a pair of bi-doublet fields $h_a=(1,2,2)$ where $ a=1,2$, with three families of fermions accommodated in $ (4,2,1)+(\bar 4,1,2)$ as usual. The matter spectrum is augmented with three copies of neutral singlets that mix with ordinary neutrinos to realize the seesaw mechanism. The model introduces supersymmetric R-symmetry and a global discrete $\mathbb{Z}_n$ symmetry ($n > 2$) that prevents disastrous superpotential couplings, while its spontaneous breaking implies the existence of domain walls that are successfully addressed. Interestingly, the one-loop beta coefficient of the $SU(4)_C$ gauge coupling is zero in the minimal $\mathbb{Z}_3$ model, rendering the corresponding gauge coupling near-conformal in the UV. Meanwhile, Landau poles are avoided up to the Planck scale and proton decay is suppressed, resulting in a proton lifetime beyond current experimental bounds. By virtue of the extended Higgs sector, the key advantage of this PS model is its ability to disentangle quark and lepton masses through higher-dimensional effective operators, addressing a common limitation in GUT models with small Higgs representations. This makes the model more economical and easier to be constructed from string theory, particularly in several heterotic and F-theory models where Higgses in the adjoint representation are absent.

Speaker: Ruiwen Ouyang

Coffee break

Plenary: Session 8

Convener: Ye-Ling Zhou (Hangzhou Institute for Advanced Study)

26 Leptogenesis via symmetry non-restoration

In this talk, we present a novel electron-assisted Baryogenesis mechanism that does not require explicit B-L violation, which is essential for the traditional Leptogenesis mechanism. This scenario is based on the assumption of high-scale electroweak symmetry restoration, which implies that the electron Yukawa interaction, crucial for the mechanism, does not reach thermal equilibrium before the electroweak sphaleron process is quenched in the early universe. Primordial charge asymmetries for chiral electrons, which can be generated through various mechanisms such as axion inflation, the evaporation of primordial black holes, or the CP-asymmetric decays of a heavy Higgs doublet, serve as the initial condition for the amplification of the baryon asymmetry through transport equations. Right-handed electron asymmetry is almost irrelevant to the baryon asymmetry due to high-scale electroweak symmetry restoration, leading to both a non-zero baryon asymmetry and the electron asymmetry. We dub this mechanism as the Eogenesis.

Speaker: Wei Chao (BNU)

27 Testing Leptogenesis from Observable Gravitational Waves

We are going to show within a scalar extended seesaw models, leptogenesis can successfully generate sufficient BAU as the CP asymmetry is enhanced by the scalar interactions in the loop. In the meantime, the same scalar is responsible for a first-order electroweak phase transition, which can lead to observable gravitational waves~(GWs) in the near future experiments such as eLISA and ultimate-DECIGO. In this scenarios, the BAU is highly correlated to the magnitude of GWs, so can be tested by them.

Speaker: Wei（刘威） Liu (Nanjing University of Science and Technology（南京理工）)

28 SO(10)-inspired Leptogenesis with flavour coupling effects

In the past few decades, leptogenesis has been widely studied as a solution to the matter–antimatter asymmetry problem. However, certain theoretical effects that could alter the predictions have not yet been fully considered. In this talk, I will discuss the impact of flavour coupling effects on the predictions of SO(10)-inspired leptogenesis for low-energy neutrino parameters. I will show that only the first octant is allowed and that a large range of values for the Dirac CP phase is excluded. I will also discuss how flavour coupling effects modify the allowed parameter space in strong thermal leptogenesis, a scenario that assumes a possible pre-existing asymmetry generated in the very early universe.

Speaker: Xubin Hu (University of Southampton)

SO(10)lepto-Xubin.pdf

Lunch

Excursion

29 Black Myth: Wukong Art Exhibition + Leisure in Hefang Street

Video Tour: https://www.bilibili.com/video/BV1oSdPYnETo/?vd_source=f49c3b8c30becae8270d8cec5555b83b

Monday, 21 April

Plenary: Session 9

Convener: Borut Bajc (J. Stefan Institute)

30 Non-Abelian Domain Walls

Domain wall is one of the topological defects that can be generated during phase transitions. When a non-abelian discrete symmetry is broken, different types of domain walls can be created. Starting from a real scalar model with $S_4$ symmetry, we study the properties of different types of domain walls and then extend the analysis to models with $A_4$ symmetry as well as complex scalar models.

Speaker: Bowen Fu (Northeastern University, Shenyang)

31 Dark Chiral Phase Transition Driven by Chemical Potential

In this article, for the first time, we explore the scenario that the dark-QCD sector has a large chemical potential μ (on the order of magnitude of temperature) of dark quarks. It leads to a complex-valued Polyakov loop and tilts the partial confinement effect, driving the dark-QCD phase transition to a first-order one in the early universe. We present a toy model via the Affleck-Dine mechanism that could generate degenerate dark quarks. Our study, in the framework of PNJL, focuses on the dynamical impacts of a large chemical potential on the chiral phase transition without turning on the KMT instanton term. We plot the phase diagram of the dark-QCD in the chiral limit. Following the phase diagram, we find that increasing μ can considerably prolong the duration of the phase transition and also the release of latent heat.

Speaker: 召丰/Zhaofeng 康/Kang (N)

32 Cold darkogenesis: Dark matter and baryon asymmetry in light of the PTA signal

We build upon the intriguing possibility that the recently reported nano-Hz gravitational wave signal by Pulsar Timing Array (PTA) experiments is sourced by a strong first-order phase transition from a nearly conformal dark sector. The phase transition has to be strongly supercooled to explain the signal amplitude, while the critical temperature has to be in the (GeV) range, as dictated by the peak frequency of the gravitational wave spectrum. However, the resulting strong supercooling exponentially dilutes away any pre-existing baryon asymmetry and dark matter, calling for a new paradigm of their productions. We then develop a mechanism of cold darkogenesis that generates a dark asymmetry during the phase transition from the textured dark 𝑆𝑈(2)D Higgs field. This dark asymmetry is transferred to the visible sector via neutron portal interactions, resulting in the observed baryon asymmetry. Furthermore, the mechanism naturally leads to the correct abundance of asymmetric dark matter, with self-interaction of the scale that is of the right order to solve the diversity problem in galactic rotation curves. Collider searches for mono-jets and dark matter direct detection experiments can dictate the viability of the model.

Speaker: Mr Zhihao Zhang (上海交通大学李政道研究所)

Coffee break

Plenary: Session 10

Convener: Georgios Leontaris (Ioannnia U)

33 Gravitational waves and neutrino masses in conformal models

TBA

Speaker: Prof. Danny Marfatia (Hawaii U)

34 Cosmological Signatures of Neutrino Seesaw Mechanism

The tiny neutrino masses are most naturally explained by the seesaw mechanism through singlet right-handed neutrinos, which can further explain the matter-antimatter asymmetry in the universe. In this work, we propose a new approach to study cosmological signatures of neutrino seesaw through the interaction between inflaton and right-handed neutrinos. After inflation the inflaton predominantly decays into right-handed neutrinos and its decay rate is modulated by the fluctuations of Higgs field which act as the source of curvature perturbations. We demonstrate that this modulation produces primordial non-Gaussian signatures, which can be measured by the forthcoming large-scale structure surveys. We find that these surveys have the potential to probe a large portion of the neutrino seesaw parameter space, opening up a new window for testing the high scale seesaw mechanism.

Speaker: 成成/Chengcheng 韩/Han (Sun Yat-sen University)

35 Silk damping in induced gravitational waves: a novel probe for new physics

The early universe is a natural laboratory for high-energy physics, and gravitational waves, as direct probes of this epoch, inherently carry rich information related to high-energy physics. Silk damping, resulting from dissipation in the cosmic fluid, is a significant physical phenomenon in the early universe. In this talk, I will introduce our first study on Silk damping in induced gravitational waves. Silk damping notably suppresses the spectrum of induced gravitational waves on scales comparable to a diffusion scale at the decoupling of weakly-interacting particles. This characteristic suppression offers a novel and general observable for detecting the underlying particle interaction, especially for those mediated by heavy gauge bosons beyond the Standard Model. We anticipate that pulsar timing arrays are sensitive to gauge bosons with masses ∼ 10³−10⁴ GeV, while space- and ground-based interferometers to those with masses ∼ 10⁷−10¹² GeV, leading to essential complements to traditional high-energy physics experiments.

Speaker: Yan-Heng Yu (IHEP, CAS)

Lunch

Plenary: Session 11

Convener: Kohei Kamada (HIAS, UCAS)

36 Dark Matter Decay in Dark Unification

As with the standard grand unification, we may have a similar structure in the dark sector. The dark-sector counterpart of baryons plays a role of the dark matter at the low-energy scale when the particle-antiparticle asymmetries are shared in the Standard Model and dark sectors. Through the portal interaction sharing asymmetry, dark matter particles can decay into antineutrinos and dark-sector counterparts of mesons (dark mesons) or dark photon. Subsequent cascade decay of the dark mesons and the dark photon can also provide electromagnetic fluxes at late times of the Universe. We perform comprehensive studies on the DM decay by combining the astrophysical constraints from electron, positron, and gamma-ray. The characteristic DM mass in the range of 1 — 10 GeV requires the precise analysis for the cosmic-ray constraints. We derive constraints on the lifetime of dark matter decay in the composite ADM scenario from the astrophysical observations of the cosmic-ray fluxes. The constraints from cosmic-ray positron measurements by AMS-02 are the most stringent above 2 GeV: a lifetime should be larger than the order of 10^{26} s, corresponding to the cutoff scale of the portal interaction of about 10^8 — 10^9 GeV. We also perform the precise analysis for the neutrino monoenergetic signals at Super-Kamiokande and Hyper-Kamiokande due to the atmospheric neutrino background in the energy range of our interest.

Speaker: Takumi Kuwahara (Peking University)

37 Minimal dark matter in SU(5) grand unification

Minimal dark matter is an attractive candidate for dark matter because it is stabilized without the need to impose additional symmetries. It is known that the SU(2)L quintuplet fermion can serve as a minimal dark matter candidate, with its mass predicted to be around 14 TeV, based on the thermal production mechanism. In this work, we embed the quintuplet dark matter within non-supersymmetric SU(5) grand unified theories. We find that two pairs of colored sextet fermions are required at the O(1-10) TeV scale to achieve gauge coupling unification, with the unification scale near the reduced Planck scale. These colored sextet fermions become metastable because their interactions are suppressed by the unification scale. Our model can be tested through comprehensive searches for colored sextet fermions in collider experiments, as well as through indirect and direct detection methods for minimal dark matter. Once the minimal dark matter scenario has been experimentally confirmed, it will have implications for modifying string theories.

Speaker: Takashi Toma (Kanazawa University)

38 Pseudo-Nambu-Goldstone Boson Dark Matter Inspired by Grand Unification

A pseudo-Nambu-Goldstone boson (pNGB) is a compelling candidate for
dark matter (DM), as it naturally evades the stringent constraints
from current DM direct detection experiments. In this framework, the
pNGB DM model can be embedded within an SO(10) grand unified theory,
where SO(10) is first broken to the Pati-Salam gauge group at the
unification scale and subsequently to the Standard Model gauge group
at an intermediate scale. Constraints from DM lifetime and gamma-ray
observations suggest that the pNGB DM mass must be below O(100) GeV.
We find that the thermal relic abundance remains consistent with all
constraints when the DM mass is close to half the mass of the CP-even
Higgs boson.

Reference: arXiv:2104.13523

Speaker: Prof. Koji Tsumura (Kyushu University)

39 Gravitational Waves from Dark Sector Phase Transitions

We discuss the phenomenological consequences of the decay of the meta-stable dark sector during the thermal expansion of the universe. We consider that the latent heat is much larger than the plasma energy density in the dark sector. In this case, the Lorentz factor of the bubble walls can be extremely large and the effect of bubble propagation after collisions can not be ignored. We use a $2048^3$ lattice to simulate the evolution of the scalar fields in the dark sector and directly calculate the gravitational waves generated by the bubble collisions during the decay of the meta-stable vacuum in RD era. The results show that the IR region of the power spectrum of GW is flatter than the $k^3$ law produced by envelop approximation.

Speaker: Tingyu Li (Department of Physics, Tsinghua University)

Coffee break

Plenary: Session 12

Convener: Jiang-Hao Yu (ITP, CAS)

40 Studies on Domain Walls, Cosmic strings, and Their Gravitational Wave Signatures

In various new physics theories, the spontaneous breaking of symmetries can lead to the formation of topological defects, such as domain walls and cosmic strings, in the early universe. The motion and collapse of domain walls, as well as relativistic oscillations of cosmic string loops, can generate significant stochastic gravitational waves, offering a unique opportunity to probe new physics. In one of our recent studies, we consider quantum and thermal corrections to the effective potential and explore their impact on the dynamics of domain walls and the resulting gravitational wave signatures. In another study, we investigate how an early matter-dominated era in cosmic history influences the dynamics of cosmic strings and the gravitational waves they produce.

Speaker: Dr 钊焕/Zhao-Huan 余/Yu (Sun Yat-sen University)

41 Proton Lifetime in Minimal Supersymmetric SU(5) with Gauge Mediation

In this paper, we discuss the predicted proton lifetimes in minimal supersymmetric (SUSY) $SU(5)$ grand unified theory (GUT) with gauge mediated supersymmetry breaking (GMSB). We focus on the case of $\mathbf{5} + \mathbf{\bar{5}}$ messengers and determine the low-scale mass spectrum of the scalar particles and gauginos using the renormalization group equations. With the obtained mass spectrum, we calculate the dominant proton decay mode for SUSY $SU(5)$ GUT, $p \to K^+ \bar{\nu}$. In our setup, we assume the messenger scale to be $\mathcal{O}(10^3)$ TeV in order to obtain a proper Higgs mass in GMSB scenario. For this messenger scale, we find the proton lifetime is consistent with current experimental limits and can be tested by future proton decay experiments.

Speaker: Yoshihiro SHIGEKAMI (Henan Normal University)

42 GW from Metastable Cosmic String in Delayed Scaling Scenario —— A Cosmological Prospective of View

Recent observations from pulsar timing arrays (PTAs) suggest the existence of a stochastic gravitational wave background (GWB) in the nanohertz frequency range. One of the most promising explanations is a GWB generated by metastable cosmic strings.

However, the standard formation scenario for (meta)stable cosmic strings—based on the Kibble-Zurek mechanism triggered by a thermal phase transition—faces several challenges. Notably, the GWB spectrum predicted by a cosmic string network with a relatively large string tension, as required to explain the PTA results, is in tension with the null detections by ground-based interferometers such as LIGO-Virgo-KAGRA (LVK) at higher frequencies. Moreover, in conventional setups, a monopole-forming phase transition preceding the cosmic string-forming symmetry breaking often disrupts the subsequent formation of the string network.

These issues can be avoided in the delayed scaling scenario, in which cosmic strings are generated during inflation and their network is diluted away, beginning to evolve and emit gravitational waves only at a later time. In this framework, a cosmic string network with large tension can naturally evade LVK constraints while still accounting for the PTA signal.

In this talk, I will present predictions for the stochastic GWB spectrum from metastable cosmic strings in the delayed scaling scenario and identify in which case it is consistent with current observations. I will also discuss implications for inflationary dynamics and possible ultraviolet completions such as grand unified theories.

Speaker: Yifan Hu (School of Fundamental Physics and Mathematical Sciences, Hangzhou Institute for Advanced Study, UCAS)

43 Effective Field Theories from GUT Scale to Nuclear Probes

We discuss the whole procedure from GUT scale to nuclear probes through the effective field theories. The procedure includes the UV models from SO(10) GUT symmetry breaking and the matching between UV models and SMEFT operators. The nuclear probes of proton decay will be obtained through the matching from the SMEFT to the LEFT which would be matched into Chiral EFT.

Speaker: Chuan-Qiang Song (HIAS, UCAS)