We assess the impact of measuring deeply virtual Compton scattering (DVCS) off protons using the planned detector at the Electron-Ion Collider in China (EicC), which is proposed as an upgrade to the High Intensity Heavy-Ion Accelerator Facility (HIAF). We develop a neural-network architecture to flexibly parameterize Compton form factors (CFFs), reliably extrapolate into unmeasured kinematic regions, and provide robust uncertainty estimates using the replica method. The framework is fitted to available worldwide DVCS data using the $ {\mathrm{Gepard}}$ software. We find a significant reduction in the uncertainties of all CFFs after incorporating pseudo-data from single and double polarization asymmetries at the EicC, with particularly strong improvements in the sea-quark region.

China

Yuan-Yuan Huang

Xu Cao

Taifu Feng

Croatia

Krešimir Kumerički

Yu Lu

Assessing the impact of the Electron-Ion Collider in China on deeply virtual Compton scattering * Supported by the National Key R&D Program of China (2023YFA1606703), the National Natural Science Foundation of China (12547111, 12235008, 12405105) and (PK.1.1.10.0004) co-financed by the European Union and through the European Regional Development Fund - Competitiveness and Cohesion Programme 2021-2027. TF also thanks the Hebei Natural Science Foundation (A2022201017, A2023201041) and Natural Science Foundation of Guangxi Autonomous Region (2022GXNSFDA035068)

The quark-mass dependence of the $ N^*(920) $ pole is analyzed using the $\textit{K}$-matrix method, with the $ \pi N $ scattering amplitude calculated up to the $ O(p^3) $ order in the chiral perturbation theory. As the quark mass increases, the $ N^*(920) $ pole gradually approaches the real axis in the complex $\textit{w}$-plane (where $ w=\sqrt{s} $ ). Eventually, in the $ O(p^2) $ case, it crosses the $\textit{u}$-cut on the real axis and enters the adjacent Riemann sheet when the pion mass reaches $ 526\; {\rm{MeV}} $ . At order $ O(p^3) $ , the rate at which it approaches the real axis decreases; however, it remains uncertain whether it will ultimately cross the $\textit{u}$-cut and enter the adjacent Riemann sheet. In addition, the trajectory of the $N^*(920)$ pole is in qualitative agreement with the results from the linear $\textit{σ}$ model calculation.

Xu Wang

Kai-Ge Kang

Qu-Zhi Li

Zhiguang Xiao

Han-Qing Zheng

Studies on quark-mass dependence of the $\textit{N}$ $^{*}$(920) pole from unitarized $\textit{πN}$ $\textit{χ}$PT amplitudes * Supported by China National Natural Science Foundation (12335002, 12375078) and the Fundamental Research Funds for the Central Universities

<p>We explore the fundamental but untested possibility that the photon is a continuous spin particle (CSP) with a small but nonzero spin Casimir <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>ρ</mi></math>. When <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>ρ</mi><mo>≠</mo><mn>0</mn></math>, the familiar polarization modes of the photon transform nontrivially under Lorentz boosts, leading to deviations from familiar QED. Surprisingly, these deviations are strongest at low energy, but smoothly vanish in the <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>ρ</mi><mo stretchy="false">→</mo><mn>0</mn></math> limit. In this letter, we compute corrections to the hydrogen 21-cm transition rate, which is expected to be particularly sensitive given the small hyperfine energy splitting <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>ω</mi></math>. We find deviations from <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>QED</mi><mo>∝</mo><msup><mi>ρ</mi><mn>2</mn></msup><msup><mi>α</mi><mn>2</mn></msup><mo>/</mo><msup><mi>ω</mi><mn>2</mn></msup></math> at leading order, suggesting experimental constraints <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>ρ</mi><mo>≲</mo><mn>1</mn><mtext> </mtext><mtext> </mtext><mi>meV</mi></math>. Building on this work, we expect that a range of other atomic, molecular, or condensed matter systems could be used to provide even more stringent tests of <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>ρ</mi></math> in electromagnetic interactions.</p>

United States

Aidan Reilly

Alessandro Russo

Philip Schuster

Natalia Toro

Hydrogen 21-cm constraints on the photon’s spin scale

<p>We investigate abelian Chern-Simons gauge theory on a strip geometry with two spatial boundaries. In the presence of boundaries, gauge invariance is broken by boundary conditions, leading to physical edge excitations. By deriving the most general local boundary conditions consistent with power counting in the sense of Symanzik, we show that the bulk equations of motion determine the boundary degrees of freedom through a broken gauge Ward identity, yielding boundary Kac-Moody current algebras with opposite central charges on the two edges. The corresponding two-dimensional boundary actions are of Tomonaga-Luttinger type and describe chiral bosons propagating in opposite directions along the two boundaries. A consistency condition, interpreted as a holographic-like bulk-boundary matching, relates the Chern-Simons coupling constant and the boundary parameters to the physical edge velocities. Within this framework, the equality and opposite sign of the two velocities in a symmetric setup follow directly from the boundary structure rather than from model-dependent assumptions about confining potentials, and the velocities are independent of the strip width. Our analysis provides a fully field-theoretic realization of bulk-boundary correspondence in Chern-Simons theory with two boundaries, with direct applications to edge physics in quantum Hall systems and related topological/hydrodynamic settings.</p>

Ireland

Erica Bertolini

Michael Doyle

Italy

Nicola Maggiore

Conor Murphy

Carlotta Piras

Edge modes in Chern-Simons theory on a strip

The photon sphere, a hypersurface of null circular geodesics, plays a fundamental role in characterizing black hole spacetimes, influencing phenomena such as black hole shadows, gravitational lensing, and quasinormal modes. In this work, we derive both upper and lower bounds on the photon sphere radius for static, spherically symmetric, asymptotically flat black holes within $\textit{n}$-dimensional Einstein gravity $$(n\ge 4)$$ , assuming an anisotropic matter field satisfying the weak energy condition and a non-positive trace of the energy–momentum tensor. For the upper bound, we obtain $$r_\gamma \le [(n-1)M]^{\frac{1}{n-3}},$$ where $\textit{M}$ is the ADM mass. In the four-dimensional case $$(n=4)$$ , this reduces to $$r_\gamma \le 3M,$$ in agreement with previous results. For the lower bound, under the additional assumption that $$|r^{n-1}p_r(r)|$$ is monotonically decreasing, we prove $$r_\gamma \ge (\frac{n-1}{2})^{1/(n-3)}r_H,$$ where $$r_H$$ is the radius of the outer event horizon; for $$n=4$$ this gives $$r_\gamma \ge \frac{3}{2}r_H,$$ also consistent with previous four-dimensional result. These results provide dimension-dependent geometric constraints that generalize well-known four-dimensional bounds to a specific class of higher-dimensional black holes (described by a Tangherlini-type metric) and deepen our understanding of spacetime structure in higher-dimensional gravitational theories.

Yong Song

Jiaqi Fu

Yiting Cen

Bounds on the photon sphere radius for spherically symmetric black holes in $${\varvec{n}}$$ -dimensional Einstein gravity

We derive model-independent constraints on finite-time inflationary initial states by combining an EFT with physical cutoff $$\Lambda $$ , backreaction control at the initialization time, and a UV–IR reflection principle imposed only on a logarithmic “trans-Planckian band” about the cutoff pivot. For Gaussian, homogeneous and isotropic states, Bogoliubov data $$\beta _k$$ determine the excitation energy density, and backreaction finiteness selects a natural weighted Hilbert norm on this data. We introduce a windowed symmetry defect on the band and an explicit local completion map that enforces the reflection without constraining modes outside the band. Requiring that completion does not move admissible data by an order-one amount in the backreaction norm yields a parametric lower bound on the excitation energy density in terms of cutoff-scale Bogoliubov jets. In the narrow-band regime the defect admits a universal jet expansion, so generic non–Bunch–Davies data require tuned cancellations among cutoff derivatives or a nonzero excitation floor.

Douglas Watson

Tiziano Valentinuzzi

Stability bounds on inflationary initial states from UV–IR reflection on a trans-Planckian band

In this paper, we update constraints on the Holographic Dark Energy (HDE) model and the Interacting Holographic Dark Energy (IHDE) models in a non-flat universe, building upon our previous work in which the flat HDE and IHDE models were tested using same datasets, including DESI DR2 BAO, the five-year supernovae sample from DES, CMB distance priors, observational Hubble parameter data, and the local measurement of Hubble constant. Our results indicate that in the HDE model, an open universe is supported at $$6\sigma $$ , whereas in the IHDE models a closed universe is favored at over $$3\sigma $$ . The model parameter $\textit{c}$ is anti-correlated with $$H_0$$ in all these models, implying that a resolution to $$H_0$$ tension by reducing the parameter $\textit{c}$ comes at the expense of a Big Rip fate. Furthermore, using AIC, BIC, DIC, and Bayes evidence, we find that within the non-flat framework, the $$\Lambda $$ CDM model remains the most strongly supported by the data, while the HDE model is the most disfavored. Compared with the HDE model, the IHDE models demonstrate markedly improved agreement with the data, and the most strongly supported IHDE model is the one with the interaction term $$Q=3\beta H_{\textrm{0}}\frac{\rho _{\textrm{dm}}\rho _{\textrm{de}}}{\rho _{\textrm{dm}}+\rho _{\textrm{de}}}$$ .

Xiaofang Shen

Bing Xu

Kaituo Zhang

Xiangyun Fu

Qihong Huang

Liangliang Ren

Zelin Zhang

Updated observational constraints on interacting holographic dark energy models in a non-flat universe

The nucleation of bubbles in first-order phase transitions is traditionally characterised by the critical bubble: defined as the saddle-point solution of the Euclidean action that separates collapsing from expanding field configurations. While this picture is exact in the noiseless, zero-temperature limit, thermal fluctuations introduces stochasticity which can influence the behaviour of the field configuration. In this work, we develop a purely statistical criterion for identifying the critical bubble by leveraging the concept of the “committor” probability: the likelihood that a given local field configuration evolves to the true vacuum before returning to the false vacuum. Using ensembles of lattice simulations with controlled thermal noise, we extract the committor probability during the evolution of a bubble from sub- to super-criticality. We find this approach to be robust, accounts for finite-temperature effects, and allows independent verification of bounce-based predictions. To demonstrate this, we compare the average profile obtained via the committor probability method to standard theory for a given model and find strong agreement, particularly at the core of the bubble. Importantly, we also observe that the behaviour of the committor probability with time is smooth and well defined. This method establishes a robust, simulation-driven framework for studying nucleation dynamics in thermal field theories and may be especially applicable in cases where analytical control might be limited.

South Korea

Tomasz Dutka

Committing to bubbles: finding the critical configuration on the lattice

Spread complexity uses the distribution of support of a time-evolving state in the Krylov basis to quantify dispersal across accessible dimensions of a Hilbert space. Here, we describe how variations in initial conditions, the Hamiltonian, and the dimension of the Hilbert space affect spread complexity and Krylov basis structure. We introduce $\textit{Koherence}$, the entropy of coherence between perturbed and unperturbed Krylov bases, which can, e.g., quantify dynamical amplification of differences in initial conditions in chaos. To illustrate, we show that dynamics on SL(2, $\textit{ℝ}$), SU(2), and Heisenberg-Weyl group manifolds, often used as paradigmatic settings for contrasting chaotic and integrable (semi-)classical behavior, display distinctively different responses to variations of the initial state or Hamiltonian. We then describe a lattice model that displays linear growth of spread complexity, saturating for bounded lattices and continuing forever in a thermodynamic limit. The latter example illustrates a breakdown of continuum/classical effective descriptions of complexity growth in bounded quantum systems.

Belgium

Vijay Balasubramanian

Japan

Poland

Sweden

Pawel Caputa

United Kingdom

Joan Simón

Variations on a theme of Krylov

Multi-parton distribution functions (mPDFs) are non-perturbative objects that are important in the prediction of multiple scattering rates at hadron colliders. In the case where the scales associated with all partons in the mPDF are the same, we have two theoretical constraints on the mPDF. These are symmetry in exchange of the parton indices, and the number and momentum sum rules. In a previous publication $\textit{JHEP}$ 02 (2023) 090 we found that the equal-scale mPDFs from the P model could not satisfy both of these constraints simultaneously. In this paper we introduce an algorithm for constructing equal-scale mPDFs that is based on the P procedure but has three additional modifications, such that it yields symmetric mPDFs that should satisfy the sum rules to an improved extent. We test the construction for the case of the double and triple parton distribution functions (dPDFs and tPDFs), finding that the sum rules are obeyed to within 10% over the vast majority of the phase space for the scales tested (and deviations only being mildly above this level). We use our dPDFs to compute rapidity asymmetries for same-sign $\textit{WW}$ and $\textit{ZZ}$ production via double parton scattering, and compare the results to predictions obtained using P and the GS09 dPDFs of $\textit{JHEP}$ 03 (2010) 005.

Finland

Oleh Fedkevych

Cyprus

Jonathan Gaunt

Seonagh Smith

Improving on the PYTHIA modelling of equal-scale multi-parton distribution functions