Effective Field Theories, Gravity and Cosmology

24 Apr 2025, 15:00 → 29 Apr 2025, 14:00 Asia/Shanghai

Building 3, 2A-223 (国科大杭州高等研究院 Hangzhou Institute for Advanced Study (UCAS))

Description

本次会议旨在汇集有效场论方法、经典和量子引力以及早期宇宙学方面的专家，探讨包括粒子物理、引力、宇宙学中的各种有效场论方法，以及暴胀宇宙学、散射振幅、正定性约束以及超出广义相对论的黑洞物理等主题。

The conference aims to bring together experts in effective field theory approaches, classical and quantum gravity, and early Universe cosmology. More specifically, the covered topics include various EFT methods in particle physics, gravity and inflationary cosmology, scattering amplitudes, positivity bounds, and black hole physics beyond general relativity. 

Organizers

• Chao-Qiang Geng (HIAS)
• Anna Tokareva (HIAS)
• Shuang-Yong Zhou (USTC)
• Tao Zhu (Zhejiang U. Tech.)

Young researcher's session

青年研究者报告环节

我们欢迎青年研究者（学生和博士后）注册并申请口头报告。报告申请和摘要提交的截止日期为4月20日。会议报告用英文或中文皆可。

We welcome young researchers to register and apply for contributed talks. The deadline of the talk application and abstract submission is April 20. The talks can be in Chinese or English languages.

Registration fee

注册费

会议现场将收取500元人民币的注册费。受邀报告人可以免缴注册费。

A registration fee of 500 rmb will be taken at the place of the meeting. Invited speakers are exempt from paying the fee.

conference notice.pdf

Thursday 24 April

15:00 → 20:00 Registration

Friday 25 April

08:00 → 09:00 Registration

09:00 → 10:00 Cosmology

Convener: Prof. Hong-Wei Yu

09:00 Cosmological collider from particle physics viewpoint

The Higgs boson was discovered in the LHC experiment, but given the current lack of physics beyond the Standard Model of particle physics, such as supersymmetry, the importance of the universe as a means of exploring more fundamental laws of physics at high energies is expected to increase. In more fundamental theories beyond the Standard Model, it is believed that many new particles exist in addition to those of the Standard Model, but their mass scales are, of course, unknown. Although particles on the order of a few TeV may be found in the near future using ground-based accelerators, it will be almost impossible to directly produce particles with masses far beyond the TeV scale using ground-based accelerators even in the future. Therefore, the only way to elucidate the nature of such new particles is to look for their traces in the universe. In this talk, we will explain how to extract information about physics beyond the Standard Model through the properties of primordial density perturbations produced during inflation.

Speaker: Prof. Masahide Yamaguchi (IBS, Korea)

09:30 Progress of higher derivative scalar-tensor theory: parity violation and multi-scalar extensions

Scalar-tensor theory not only serves as one of the most important tools for constructing models in cosmology and gravitational wave research but also offers a broad playground for exploring modified gravity. In this talk, I will first review the development of scalar-tensor theory over the past two decades. In particular, I will present our efforts to utilize spatially covariant gravity as an effective and efficient framework for developing higher-derivative scalar-tensor theories without introducing ghost degrees of freedom. I will then discuss our recent results in constructing two new classes of scalar-tensor theories based on this approach: one featuring parity-violating effects and the other incorporating multiple scalar fields. These developments expand the scope of scalar-tensor theories and open new avenues for theoretical exploration.

Speaker: Prof. Xian Gao (Sun Yat-sen U)

10:00 → 10:20 Group photo

10:20 → 11:00 Coffee break

11:00 → 12:00 Cosmology

Convener: Prof. Kohei Kamada (HIAS)

11:00 TBA

Speaker: Prof. Shi Pi (ITP CAS)

11:30 Thermal production of gravitational waves in the early universe

We investigate a novel gravitational wave (GW) production mechanism from gravitons generated during the pre-thermal phase of cosmic reheating, where the energy density is dominated by non-thermalized inflaton decay products, dubbed reheatons. We consider multiple production channels, including: i) pure inflaton-inflaton annihilation, ii) graviton Bremsstrahlung from inflaton decay, iii) scatterings between an inflaton and a reheaton, and iv) scatterings among reheatons. To determine the resulting GW spectrum, we solve the Boltzmann equation to obtain the graviton phase-space distribution for each channel. We find that the third channel, iii), dominates due to the large occupation number of reheatons at highly-energetic states during the pre-thermalization phase. Notably, in scenarios with a low inflaton mass, the GW spectrum could fall within the sensitivity range of future experiments such as the Einstein Telescope, the Cosmic Explorer, the Big Bang Observer, and ultimate DECIGO.

Speaker: Xun-Jie XU (IHEP, China)

12:00 → 14:00 Lunch

14:00 → 15:30 Cosmological correlators

Convener: Anna Tokareva (Hangzhou Institute for Advanced Study)

14:00 Massive Inflationary Amplitudes: Differential Equations and Complete Solutions for General Trees

We construct and solve a complete system of differential equations for general tree-level inflation correlators with an arbitrary number of massive scalar exchanges and time-dependent couplings. Any massive tree correlators can be uniquely fixed by solving this system of equations with appropriate boundary conditions. We take a hybrid approach to solve this system, using the differential equation to get the inhomogeneous solution and the bulk time integrals to determine the homogeneous solution. Altogether, we obtain analytical results for all tree-level massive inflation correlators with generic kinematics, expressed as multivariate hypergeometric series of energy ratios. The result can be neatly organized as a sum of the completely inhomogeneous solution, which we call the massive family tree, and all of its cuts. As simple applications, we provide full analytical expressions for tree correlators with one, two, and three massive exchanges.

Speaker: Zhong-Zhi Xianyu (Tsinghua University)

14:30 Next-to-leading order corrections to the conserved current three-point correlators in the large N expansion

The conserved currents three-point correlators have broad applications in several directions, including the conformal field theories, early time cosmology and quantum gravity through AdS/CFT correspondence. In this talk, I will explain the perturbative computations to the conserved current three-point correlators to the subleading order in the large N expansion. The techincal chanllenge includes the three-loop integrals with three external momenta, which are hard to evaulate analytically. I will introduce a novel method by employing the strong constraints from the conformal symmetry, which provides strong restrictions on the conserved current three-point correlators and can help to simplify the three-loop integrals significantly. I will breifly explain the applications of this method in conformal field theories and inflation theories.

Speaker: Prof. ZhiJin Li (Southeast U)

15:00 Effective field theory of inflation with strongly non-geodesic motion

In models of inflation with multiple scalar fields, the inflaton describes a curve in the internal space spanned by the fields. When this curve deviates strongly from a geodesic, interesting observational signatures arise, including enhanced fluctuations and peculiar non-Gaussianities. In this talk I will review the application of effective field theory methods to this class of models, before presenting recent work on the issue of perturbative control and loop corrections.

Speaker: Prof. Sebastian Garcia-Saenz (SUSTech)

15:30 → 16:00 Coffee break

16:00 → 17:20 Contributed talks: Gravity and cosmology

16:00 Modified gravity realizations of quintom dark energy

Since the release of the DESI DR2 data, dynamic dark energy, particularly the quintom dark energy it suggests, has garnered significant attention. Quintom dark energy represents a characteristic that lies between quintessence and phantom behavior, indicating that the equation-of-state of dark energy will cross $-1$ during its evolution. In this talk, I will investigate the realization of quintom scenario for dynamical dark energy within modified gravity theories that can efficiently fit the recent observational datasets.

Speaker: Yuhang Yang (University of Science and Technology of China)

16:20 A Semi-analytic Approach Towards Curvaton

Curvaton mechanism provides an alternative way to explain the origin of the observed primordial scalar fluctuations in the Cosmic Microwave Background (CMB) radiation. In this scenario, the curvaton is a scalar field which nearly remains frozen during inflation but produces isocurvature perturbations. It starts to evolve after the end of inflation, and at the time of it's decay it converts the isocurvature perturbations to the observed scalar fluctuations. The estimation of the CMB observables i,e the scalar power spectrum and bispectrum relies on the form of curvaton potential. For a quadratic curvaton potential the observables can be estimated analytically, but for a non-trivial potential numerical methods are required. Though analytical methods are applied to deal with the non-trivial potentials, these methods often approximate that the energy density of the curvaton behaves similar to that of a quadratic potential. In this talk we will present an alternative semi-analytic method to deal with general curvaton potential, which is based on the $\delta N$ formalism. Our method is more precise than the existing methods and known results can be reproduced in the quadratic limit.

Speaker: Abhishek Naskar (ShanghaiTech University)

16:40 Uniqueness of gravitational constant at low energies from the connection between spin-2 and spin-0 sectors

The fact that graviton propagator contains not only one but two tensorial components excludes a unique definition of the running behavior of the gravitational constant, while at low energies gravitation is characterized solely by Newton's constant. How these two facts are reconciled when massive quantum fields are present remains unanswered. In this work, by non-minimally coupling gravity to a one loop massive scalar, we show that this potential conflict is resolved by the non-trivial equivalence between the residues of the two propagator components. Such equivalence is based on a hidden connection between the spin-2 and spin-0 sectors of the propagator. It is verified that this connection also makes the two quantum-corrected gravitational potentials be characterized by the same gravitational constant at large distances. In addition, we find that the potentials in our case as well as the quantum-corrected Coulomb potential can be expressed concisely in a unified formulation. By comparing these results with experiments, we establish a new upper bound on the magnitude of the non-minimal coupling parameter $\xi$.

Speaker: Duojie Jimu (Utrecht University)

17:00 Quasi-normal modes in non-perturbative quantum gravity

Non-pertrubative quantum gravity formulated as a unitary four-dimensional theory suggests that certain amount of non-locality, such as infinite-derivative operators, can be present in the action, in both cases of Analytic Infinite Derivative gravity and Asymptotically Safe gravity. Such operators lead to the emergence of Background Induced States on top of any background deviating from the flat spacetime. We analyze Quasi-normal modes (QNMs) corresponding to these excitations with the use of an example of a static nearly Schwarzschild black hole. We mainly target micro-Black Holes, given that they are strongly affected by the details of UV completion for gravity, while real astrophysical black holes can be well described in EFT framework. We find that frequencies of QNMs are deviating from those in a General Relativity setup and, moreover, that the unstable QNMs are also possible. This leads to the necessity of constraints on gravity modifications or lower bounds on masses of the stable micro-Black Holes or both.

Speaker: Chenxuan Li

Saturday 26 April

09:00 → 10:00 Bootstrap methods

Convener: Prof. Shuang-Yong Zhou

09:00 Bootstrapping Lattice Yang-Mills Theory

We discuss some recent progress on applying the positivity bootstrap approach to SU(3) lattice Yang-Mills (YM) theory, extending previous studies of large N and SU(2) theories by incorporating multiple-trace Wilson loop operators. Utilizing Hermitian and reflection positivity conditions, along with Schwinger-Dyson (SD) loop equations, we compute rigorous bounds for the expectation values of plaquette Wilson loop in 2D, 3D, and 4D YM theories.

Speaker: Gang Yang (Institute of Theoretical Physics, CAS)

09:30 Kaluza-Klein Correlators at Five Points and Hidden Structures

I will report some recent progress on the study of 1/2-BPS correlators that describe tree-level scattering of five gluons or gravitons in AdS backgrounds, with arbitrary Kaluza-Klein charge configurations for the external operators. After motivating this exploration, I will describe the analytic bootstrap method and its use in the computation of the gluon case. This results in a unified formula, which serves as the first concrete confirmation for the existence of the hidden higher-dimensional symmetries at the level of five-point scattering. In the end I will comment on some efforts made in the study of gravitons.

Speaker: 野 袁 (浙江大学)

10:00 → 10:30 Coffee break

10:30 → 12:00 Bootstrap methods

Convener: Prof. Gang Yang (Institute of Theoretical Physics, CAS)

10:30 New Factorizations of Yang-Mills Amplitudes

We propose a new factorization pattern for tree-level Yang-Mills (YM) amplitudes, where they decompose into a sum of gluings of two lower-point amplitudes by setting specific two-point nonplanar Mandelstam variables within a rectangular configuration to zero. This approach manifests the hidden zeros of YM amplitudes recently identified. Furthermore, by setting specific Lorentz products involving polarization vectors to zero, the amplitudes further reduce to a sum of products of three currents. These novel factorizations provide a fresh perspective on the structure of YM amplitudes, potentially enhancing our understanding and calculation of these fundamental quantities.

Speaker: Prof. Yong Zhang (Ningbo University)

11:00 Locality and unitarity from hidden zeros

Hidden zeros are a novel feature of quantum field theory, corresponding to special kinematic configurations where scattering amplitudes unexpectedly vanish across a broad class of theories. In this talk, I will show that these hidden zeros are precisely equivalent to a previously unnoticed form of Britto-Cachazo-Feng-Witten (BCFW) scaling, governing the high-energy behavior of amplitudes. Using this equivalence, I prove that, under the assumption of locality, the tree-level amplitudes of Tr($\phi^3$) theory are uniquely fixed by hidden zeros — demonstrating that unitarity is not a fundamental principle, but rather an emergent consequence. I also extend such results to loop-level.

Speaker: Laurentiu Rodina (BIMSA)

11:30 Bosonic Fortuity from the Structure of Loop Space at Finite N

The space of gauge invariants for a single matrix is generated by traces containing at most N matrices per trace. We extend this analysis to multi-matrix models at finite N. Using the Molien-Weyl formula, we compute partition functions for various multi-matrix models at different N and interpret them through trace relations. This allows us to identify a complete set of invariants, naturally divided into two distinct classes: primary and secondary. The full invariant ring of the multi-matrix model is reconstructed via the Hironaka decomposition, where primary invariants act freely, while secondary invariants satisfy quadratic relations. Significantly, while traces with at most N matrices are always present, we also find invariants involving more than N matrices per trace. The primary invariants correspond to perturbative degrees of freedom, whereas the secondary invariants emerge as non-trivial background structures. The growth of secondary invariants aligns with expectations from black hole entropy, suggesting deep structural connections to gravitational systems. We also observe an analog of the fortuity mechanism whereby invariants that are secondary transition to primary invariants as N is increased.

Speaker: Prof. Robert de Mello Koch (Huzhou U)

12:00 → 14:00 Lunch

14:00 → 15:00 Holography

Convener: Prof. Alexey Koshelev (ShanghaiTech University)

14:00 Quantum-Corrected Wilson Loop Correlators and Super-Yang-Mills Theory at Infrared

Confinement is a well-known phenomenon in the infrared regime of (supersymmetric) Yang-Mills theory. Although experiments and numerical simulations have solidly confirmed confinement, its physical origin remains mysterious today, and finding a theoretical explanation for it is a long-standing and challenging problem in physics and mathematics. Inspired by the recent progress in quantum Jackiw-Teitelboim gravity, we compute the Wilson loop correlators of the large-$N$ limit of $\mathcal{N}=4$ super-Yang-Mills theory holographically in an extremal AdS$_5$ Reissner-Nordstrom black brane background. The quantum gravity fluctuations of the near-horizon region are considered, which consequently affect the holographic Wilson loop correlators. Within this framework, the results suggest that the confinement of the super-Yang-Mills theory is induced by the near-horizon quantum gravity fluctuations of the bulk extremal AdS$_5$ black brane. Similar to the confinement, the mass gap of (supersymmetric) Yang-Mills theory can also be generated by the near-horizon quantum gravity fluctuations. In the talk, we will discuss these aspects, which are based on some of my recent papers with collaborators.

Speaker: Jun Nian (University of Chinese Academy of Sciences)

14:30 Application of solving inverse scattering problem in holographic bulk reconstruction

This talk will show that the bulk metric of a planar symmetric asymptotically anti-de Sitter static black brane can be reconstructed from its boundary frequency 2-point correlation functions by solving Gel’fand-Levitan-Marchenko integral equation. Since the correlation function is easily handled in experiments and theories, this paper not only proposes a new method to “measure” the corresponding holographic spacetime for a material that has holographic dual but also provides an approach to experimentally check if a system has holographic dual.

Speaker: Run-Qiu Yang (Tianjin University)

15:00 → 15:30 Coffee break

15:30 → 16:50 Contributed talks: Amplitudes, bootstrap, positivity bounds

15:30 Two-sided positivity bounds for dim-8 Higgs operators

SMEFT Wilson coefficients are subject to various positivity bounds in order to be consistent with the fundamental principles of S-matrix. Previous bounds on dimension-8 SMEFT operators have been obtained using the positivity part of UV partial wave unitarity and form a (projective) convex cone. We derive a set of linear UV unitarity conditions that go beyond positivity and are easy to implement in an optimization scheme with dispersion relations in a multi-field EFT. Using Higgs scattering as an example, we demonstrate how to obtain closed bounds in the space of the three relevant dimension-8 coefficients, making use of the UV unitarity conditions as well as so-called null constraints that arise from full crossing symmetry. Specifically, we show that they are bounded by inequalities schematically going like C < O 􏰂(4π)2􏰃. We compare the newly obtained upper bounds with the traditional perturbative unitarity bounds from within the EFT, and discuss some phenomenological implications of the two-sided positivity bounds in the context of experimental probes of Vector Boson Scattering.

Speaker: Qing Chen (Anhui University of Science and Technology)

15:50 String-inspired methods for scattering amplitudes and form factors

In this talk, I will briefly review the story of scattering amplitudes, mostly the color-ordering amplitudes. Based on the open-string topology- the real Riemann surface, a stringy integral has been proposed to unify the scalar, pion, and gluon amplitudes. The more interesting thing is now I propose a new stringy integral for the color-ordering form factor, which is inspired by the open & closed string disk amplitudes. The stringy form factor reduces to the form factor in the field theory, manifests the hidden properties of the field-theory form factors, and uncovers more non-trivial relations between form factors and scattering amplitudes.

Speaker: Qu Cao (Zhejiang University)

16:10 Matrix moment approach to positivity bounds and UV reconstruction from IR

Positivity bounds in effective field theories (EFTs) can be extracted through the moment problem approach, utilizing well-established results from the mathematical literature. We generalize this formalism using the matrix moment approach to derive positivity bounds for theories with multiple field components. The sufficient conditions for
obtaining optimal bounds are identified and applied to several example field theories, yielding results that match precisely the numerical bounds computed using other methods. The upper unitarity bounds can also be easily harnessed in the matrix case. Furthermore, the moment problem formulation also provides a means to reverse engineer the UV spectrum from the EFT coefficients, often uniquely, as explicitly demonstrated in examples such as string amplitudes and the $stu$ kink theory.

Speaker: Shi-Lin Wan (University of Science and Technology of China)

16:30 De-projecting the EFT-hedron at loop level

In the bottom-up approach to Effective Field Theory (EFT), we systematically construct the most general Lagrangian by writing all operators allowed by the symmetries of the system, each multiplied by an arbitrary Wilson coefficient. For instance, in the case of a scalar field with shift symmetry, this procedure leads to an infinite tower of derivative interactions. However, not all such EFTs admit a consistent ultraviolet (UV) completion. By imposing fundamental principles such as causality, unitarity, locality, and Lorentz invariance, we obtain powerful constraints on the allowed values of Wilson coefficients. These constraints carve out a nontrivial geometric region in the space of EFT parameters—known as the EFT-hedron. Interestingly, when full unitarity is imposed, this geometry exhibits a non-projective structure, revealing deep connections between low-energy EFT data and high-energy consistency conditions. This presentation explores the construction of EFTs, the geometric nature of the allowed Wilson coefficient space, and how the EFT-hedron emerges as a manifestation of fundamental physical principles.

Speaker: Yongjun Xu (HIAS)

17:30 → 19:00 Banquet

Sunday 27 April

09:00 → 10:00 EFTs in phenomenology

Convener: Prof. Chao-Qiang Geng (HIAS)

09:00 Recent results on pipi and piN scatterings

Speaker: Prof. Han-Qing Zheng (Sichuan U)

09:30 Towards a Quantum Simulation of Sphaleron Configuration

We revisited the sphaleron configuration in a 1+1-dimensional (1+1D) field theory model, achieved by introducing linear additional terms into the action of the $O(3)$ nonlinear $\sigma$-model. We discretize the Lagrangian of the aforementioned 1+1D model and construct a Hamiltonian representation based on unitary quantum gate forms, enabling the construction of quantum-simulated sphaleron. Subsequently, we devise a sophisticated adiabatic simulation method based on the field space properties of quantum-bits and the corresponding structure of the model field, obtaining the quantum-simulated 1D sphaleron states.

Speaker: Prof. Hao Zhang (Theoretical Physics Division, Institute of High Energy Physics, Chinese Academy of Sciences)

10:00 → 10:30 Coffee break

10:30 → 12:00 EFTs in phenomenology

10:30 Positivity bounds at one-loop level

Parameters in an effective field theory can be subject to certain positivity bounds if one requires a UV completion that obeys the fundamental principles of quantum field theory. These bounds are relatively straightforward at the tree level, but would become more obscure when loop effects are important. Using scalar theories as examples, we carefully exam the positivity bounds in a case where the leading contribution to a forward elastic amplitude arises at the one-loop level, and point out certain subtleties in terms of the implications of positivity bounds on the theory parameter space. In particular, the one-loop generated dimension-8 operator coefficients and their beta functions are generally not subject to positivity bounds as they might correspond to interference terms of the cross sections under the optical theorem, which could have either sign. A strict positivity bound can only be implied when all contributions at the same loop order are considered, including the ones from dim-4 and dim-6 operator coefficients, which have important effects at the one-loop level. We also consider similar examples in scalar QED, where gauge invariance puts strong constraints on the form of the UV completion and plays an important role in the interpretation of positivity bounds.

Speaker: Prof. Jiayin Gu (Fudan University)

11:00 TBA

Speaker: Prof. Yingli Zhang (Tongji U)

11:30 Bootstrapping the Chiral-Gravitational Anomaly

We analyze causality and unitarity constraints
in graviton scattering amplitudes, aiming to establish new bounds on theories with $U(1)$-gravitational anomalies, such as axion models
or strongly-coupled gauge theories. For this purpose, we show the necessity of coupling these theories to gravity. We obtain a universal scale $\Lambda_{\rm caus}$ at which states with $J\geq 4$ must appear in the theory. We show that this scale can lie below the quantum gravity scale. For axion models, we get $\Lambda_{\rm caus}\sim\sqrt{M_P f_a}$ where $f_a$ is the axion decay constant.
In strongly-coupled gauge theories in the large-$N_c$ limit,
the presence of glueballs allows to evade these bounds, provided the number of fermions $N_F\ll N_c$ and the 'tHooft coupling is not large.
Nevertheless, for models that have a holographic 5D dual (large 'tHooft coupling), $\Lambda_{\rm caus}$ emerges as a new cutoff scale, unless certain conditions on the parameters of the 5D models are satisfied.

Speaker: Prof. Teng Ma (University of Chinese Academy of Sciences)

12:00 → 14:00 Lunch

14:00 → 15:00 Amplitudes for black holes

Convener: Prof. Alexander Ochirov

14:00 Effective field theory for classical two-body dynamics

High-precision theoretical predictions for the motion of compact binary systems are essential for maximizing the discovery potential of current and next-generation gravitational-wave observations, such as LIGO-Virgo-Kagra, Taiji, TianQin, and the Einstein Telescope. The Effective Field Theory (EFT) methodology, integrated with state-of-the-art multi-loop computational techniques, has proven exceptionally powerful for analytically tackling the classical two-body problem. This talk explores recent advancements in modern EFT methods and their application to computing gravitational two-body dynamics in the post-Minkowskian approximation.

Speaker: Prof. Zhengwen Liu (Southeast University)

14:30 Generic spinning binaries from the scattering amplitude perspective

In conventional world-line formalism for spinning binaries in general relativity, one assumes that the dynamical degrees of freedom for spin are the completely captured by the rest frame canonical spin. A spin supplementary condition (SSC) is then necessary to remove redundancies. We study this problem from an amplitude-based field theory perspective. In higher spin field theories, it is notoriously difficult to impose transverse and traceless conditions when interactions are included. We take an alternative approach and keep the additional degrees of freedom. We see that for generic Wilson coefficients, we obtain a system with additional physical degrees of freedom that has physical effect starting at the quadrupole level. It will decouple when we choose special values for Wilson coefficients, and we land back on the dynamics of conventional spinning binaries. The situation is very similar to a symmetry breaking in the classical limit. We also construct a world-line Lagrangian and a classical effective Hamiltonian that completely match the physics mentioned above, which incorporates such additional dynamical degree of freedom. Such generic spinning objects are realized in a world-line formalism, in which the additional degrees of freedom can be removed through a world-line shift when Wilson coefficients take special values. Finally, we propose a few candidates for such generic spinning bodies.

Speaker: Prof. Fei Teng (Fudan U)

15:00 → 15:30 Coffee break

15:30 → 17:10 Contributed talks: EFT methods

15:30 A Non-linear Representation of General Scalar Extensions of the Standard Model for HEFT Matching

At electroweak scale there are two EFTs: SMEFT and HEFT. In SMEFT, the Higgs and Goldstones are linearly realized around the vacuum expectation value. In HEFT, they are non-linearly realized and the Goldstones are encapsulated in an exponential matrix. HEFT encompasses SMEFT. Through matching a UV model to both EFTs, we study their distinctions. For general scalar extensions of the SM, there commonly exists another VEV source, which cause the matching between HEFT and UV model become complicated if we start from the UV model's linear form. We thus build a non-linear representation, in which the Goldstones' exponential matrix are separate from heavy states, so that to "integrate out" heavy states in UV model and get a HEFT becomes straightforward. Under this non-linear representation we firstly give a matching between HEFT and a real Higgs triplet extension of the SM.

Speaker: xia wan (Shaanxi Normal University)

15:50 Extracting observables for black hole binary with generic spin orientation

I will present a novel method to compute classical observables for two-body scattering systems. The on-shell radial action is treated as a generating function to directly extract observables, with full spin dependence. To account for the spin supplementary condition and other constraints, we compute the corresponding Dirac brackets. The observables, such as momentum impulse and spin kick, are obtained by iteratively applying a differential operator, constructed by inserting the radial action into the first slot of the Dirac bracket, to the initial value of the observable. As an explicit case, we consider a spinning probe in the Kerr background and compute the radial action up to O(G^6 s^4). It is then used to efficiently calculate the momentum impulse and spin kick. Via analytic continuation, this radial action also provides information about bound orbits such as their fundamental frequencies.

Speaker: Canxin Shi (Institute of Theoretical Physics, Chinese Academy of Sciences)

16:10 On-Shell EFT Matching through d-Dimensional Generalized Unitary Cuts

We present a novel framework for effective field theory (EFT) matching that leverages generalized unitarity cuts to generate one-loop integrands directly from tree-level amplitudes. This on-shell approach effectively eliminates contributions from unphysical degrees of freedom. Furthermore, by extending the on-shell prescription to d dimensions, our method recovers the rational terms essentially in matching process. The resulting framework achieves a precise mapping of ultraviolet amplitudes onto EFT Wilson coefficients, and seamlessly integrates with on-shell EFT operator bases. This work offers a promising pathway toward more efficient and systematic EFT calculations with broad applications in high-energy physics.

Speaker: 子正 周 (itp-cas)

16:30 Wilson line-based action for gluonic interactions at classical and quantum level

We discuss a new classical action that enables efficient computation of the gluonic tree amplitudes but does not contain any triple point vertices. This new formulation is obtained via a canonical transformation of the light-cone Yang-Mills action, with the field transformations based on Wilson line functionals. In addition to MHV vertices, the action contains also $N^k$MHV vertices, where $1≤k≤n−4$, and $n$ is the number of external legs. We computed tree-level amplitudes up to 9 gluons and found agreement with standard results. The classical action is however not sufficient to obtain rational parts of loop amplitudes. In order to systematically develop quantum corrections to this new action, we derive the one-loop effective action, in such a way there are no quantum contributions missing at one loop.

Speaker: Hiren Kakkad (ShanghaiTech University)

16:50 EFT-Hedron and positivity bounds in loop level

In this presentation, I will introduce part of our paper, which is a collaboration between my advisor Anna Tokareva, my academic siblings and friends Yong-jun and Long-Qi, and myself. I will begin with a brief overview of some fundamental concepts of effective field theory (EFT). Then, I will explain how, by applying dispersion relations, we can separate the infrared (IR) and ultraviolet (UV) contributions in EFT. This separation allows us to derive constraints on low-energy (IR) EFT coefficients based on the well-behaved properties of the high-energy (UV) sector.
Recently, a method known as the EFT-hedron was developed by Nima Arkani-Hamed, Yu-tin Huang, and their collaborators. Using this approach, the authors were able to analytically derive bounds on the ratios g_3/g_2 and g_4/g_2 at tree level, which remarkably match the results obtained through numerical methods (see arXiv:2011.02957). However, beyond tree level, the appearance of \log t terms leads to divergences in the forward limit (t \to 0), making it challenging to include loop-level contributions. After briefly reviewing these results, I will discuss how to address the divergence problem associated with loop-level amplitudes, then present our modified bounds and offer a discussion of this modification.

Speaker: Mr Guangzhuo Peng (UCAS-HIAS)

Monday 28 April

09:00 → 10:00 Black holes

Convener: Prof. Tao Zhu

09:00 Nonlinear evolution of unstable charged de Sitter black holes with hyperboloidal formalism

Speaker: Prof. Yu Tian (UCAS)

09:30 Thermodynamics of dyonic black holes with Chern-Simons interactions

Thermodynamics of black holes offers a promising avenue for exploring the quantum nature of black holes and quantum gravity. We investigate the thermodynamic properties of dyonic black holes in 5-dimensional Einstein-Maxwell-Chern-Simons theory with free Chern-Simons coupling parameter. We demonstrate that the standard form of the first law of thermodynamics is inconsistent with the quantum statistical relation widely adopted in black hole physics. We address a protocol that solves this issue by employing the on-shell variation of the Euclidean action and the Iyer-Wald formalism. We analytically derive the standard form of the first law and Smarr formula for the dyonic black holes. Moreover, our findings are corroborated by numerical tests and hydrodynamics.

Speaker: Prof. Li Li (ITP CAS)

10:00 → 10:30 Coffee break

10:30 → 12:00 Approaches beyond EFT

Convener: Prof. Ye-Ling Zhou (HIAS-UCAS)

10:30 TBA

Speaker: Prof. Zhiwei Wang (UESTC)

11:00 Not Quite Black Holes

Speaker: Prof. Jing Ren (IHEP)

11:30 Black Hole singularity resolution in infinite derivative gravity theories

In my talk I will briefly outline the higher and infinite derivative gravity generalizations. Aspects of unitarity and renormalizability will be emphasized. As the main question I will discuss how a black hole singularity gets inevitably resolved as a consequence of a model self-consistency. If time permits, I will explain how causality is preserved in infinite derivative gravity models.

Speaker: Prof. Alexey Koshelev (ShanghaiTech University)

12:00 → 14:00 Lunch

14:00 → 15:00 Amplitudes for black holes

Convener: Prof. Jiang-Hao Yu

14:00 On-shell approach to black hole mergers

We develop an on-shell approach to study black hole mergers. Since, asymptotically, the initial and final states can be described by point-like spinning particles, we propose a massive three-point amplitude for the merger of two Schwarzschild black holes into a Kerr black hole. This three-point amplitude and the spectral function of the final state are fully determined by kinematics and the model-independent input about the black hole merger which is described by a complete absorption process. Using the Kosower-Maybee-O’Connell (KMOC) formalism, we then reproduce the classical conservation laws for momentum and angular momentum after the merger. As an application, we use the proposed three-point to compute the graviton emission amplitude, from which we extract the merger waveform to all orders in spin but leading in gravitational coupling. Up to sub-subleading order in spin, this matches the classical soft graviton theorem. We conclude with a comparison to black hole perturbation theory, which gives complementary amplitudes which are non-perturbative in the gravitational coupling but to leading order in the extreme mass ratio limit. This also highlights how boundary conditions on a Schwarzschild background can be used to rederive the proposed on-shell amplitudes for merger processes.

Speaker: Prof. Katsuki Aoki (Yukawa Institute, Japan)

14:30 Chiral Approach to Massive Higher Spins

Quantum field theory of higher-spin particles is a formidable subject,
where preserving the physical number of degrees of freedom in the
Lorentz-invariant way requires a host of auxiliary fields. They can be
chosen to have a rich gauge-symmetry structure, but introducing
consistent interactions in such approaches is still a non-trivial task,
with massive higher-spin Lagrangians specified only up to three points.
In this talk, I will discuss a new, chiral description for massive
higher-spin particles, which in four spacetime dimensions allows to do
away with the unphysical degrees of freedom. This greatly facilitates
the introduction of consistent interactions. I will focus on three
theories, in which higher-spin matter is coupled to electrodynamics,
non-Abelian gauge theory or gravity. These simple theories are the first
ever models for consistently interacting massive higher-spin fields.

Speaker: Prof. Alexander Ochirov (ShanghaiTech)

15:00 → 15:30 Coffee break

15:30 → 16:50 Contributed talks: Gravity side

15:30 Holographic Schwinger-Keldysh effective field theories including a non-hydrodynamic mode

We derive the Schwinger-Keldysh effective field theories for diffusion including
the lowest non-hydrodynamic degree of freedom from holographic Gubser-Rocha
systems. At low temperature the dynamical non-hydrodynamic mode could be either an IR mode or a slow mode, which is related to IR quantum critical excitations
or encodes the information of all energy scales. This additional dynamical vector
mode could be viewed as an ultraviolet sector of the diffusive hydrodynamic theory.
We construct two different effective actions for each case and discuss their physical
properties. In particular we show that the Kubo-Martin-Schwinger symmetry is
preserved.

Speaker: Xin-Meng Wu (Shanghai Jiao Tong University)

15:50 The Two-Body Problem in Beyond-General Relativity: Precision Modeling in Scalar-Tensor and ESGB Gravity

In this talk, I will introduce the effective field theory (EFT) approach as a powerful tool for studying the dynamics of compact binary systems in scalar-tensor and Einstein-scalar-Gauss-Bonnet (ESGB) gravity. I will discuss state-of-the-art progress in deriving the conservative dynamics for both spinless and spinning binaries, emphasizing the efficiency of the EFT framework. These results provide important insights into deviations from General Relativity, offering testable predictions for gravitational wave observations and probing the validity of modified gravity theories.

Speaker: Gabriel Luz Almeida (University of Science and Technology of China)

16:10 Quadratic gravity with propagating torsion and asymptotic freedom

Perturbative nonrenormalizability of gravity based on Hilbert-Einstein or Palatini actions prompted vast research in higher-derivative theories. The actions that are at least quadratic in curvature lead to a renormalizable theory, but they bring along the issue of possible unitarity violation from ghost and tachyonic degrees of freedom. Whether ghosts can or cannot be quantized consistently, is still a matter of debate. Tachyons, on the other hand, are generally considered unhealthy, and they can be avoided by an appropriate choice of couplings. Within the Wilsonian definition of the renormalization group flow, such choice leads to uncontrolled growth of the couplings in the UV. I will consider a class of actions quadratic in curvature and torsion, which is a natural generalization of metric quadratic gravity. Using the heat kernel technique, I compute the torsion contributions to the one-loop counterterms. Vectorial and axial components of torsion preserve the qualitative picture of the renormalization group flow of the metric sector. However, there exists a specific nonminimal kinetic term for the pure tensorial (hook-antisymmetric traceless) component of torsion that switches the sign of the beta function of the $R^2$ term while preserving the negative sign in front of the $\text{Weyl}^2$ term. This behavior renders the gravitational couplings asymptotically free in the absence of tachyons.

Speaker: Oleg Melichev (ShanghaiTech University)

16:30 Scalar perturbations in Topological star spacetimes

In recent years, the gravitational self-force (GSF) has been successfully studied in Schwarzschild and Kerr black hole (BH) spacetimes. A test particle perturbing these spacetimes models a gravitational two-body system. After decoupling the radial and angular equations and performing a Fourier transform in the time variable, one is ultimately left with a main radial equation. This equation can be solved perturbatively using various approximation schemes: the Post-Newtonian (PN) expansion, which assumes slow motion; the Post-Minkowskian (PM) expansion, which assumes a weak field; and the Mano-Suzuki-Takasugi (MST) expansion, which uses hypergeometric functions that satisfy the correct boundary conditions—purely ingoing waves at the horizon and outgoing waves at infinity.

These same techniques are now being applied to recently discovered solutions of the Einstein-Maxwell equations in five dimensions, which include both electric and magnetic fluxes and are known as Topological Stars (TS). In a certain parameter regime, this solution describes a smooth, horizonless geometry; in the complementary regime, it reduces to a Schwarzschild solution with an extra compactified dimension.

The emission of scalar waves due to the presence of a small massive particle moving along circular and hyperbolic-like geodesics in the TS geometry is investigated. Furthermore, fundamental observables such as energy and angular momentum losses are computed, along with the deflection angle in geodesic scattering.

Speaker: Giorgio Di Russo (Hangzhou Institute for Advanced Study)

Tuesday 29 April

08:00 → 12:00 Free discussions and departure