Hadron-hadron interactions, being nonperturbative in nature, play a significant role in addressing phenomenological questions in particle physics. Femtoscopy is a powerful tool in heavy-ion collision experiments, enabling the extraction of hadron-hadron interactions via momentum-correlation functions (CFs). These CFs are typically expressed as a convolution of source functions and hadron-hadron wave functions, with the latter encoding information about the interactions. However, source functions remain poorly constrained and are commonly approximated by a Gaussian form. Reconstructing source functions from experimental correlation data constitutes an 'inverse problem.' To address this, we propose a toy model based on Tikhonov regularization. Using a square-well potential with four distinct strengths, we calculate the CFs for inputs of single Gaussian source functions and mixed Gaussian source functions. The resulting CFs are then used to reconstruct the source functions via Tikhonov regularization. Our results show that the Gaussian source function can be successfully reconstructed, highlighting the potential of this approach for extracting realistic source functions from hadron pairs of interest.

China

Ao-Sheng Xiong

Qi-Wei Yuan

Ming-Zhu Liu

Fu-Sheng Yu

Zhi-Wei Liu

Li-Sheng Geng

Solving the inverse source problem in femtoscopy with a toy model * Supported in part by the Fundamental and Interdisciplinary Disciplines Breakthrough Plan of the Ministry of Education of China (JYB2025XDXM204) and the National Natural Science Foundation of China (W2543006, 12435007). Ming-Zhu Liu acknowledges support from the National Natural Science Foundation of China (12575086). Zhi-Wei Liu acknowledges support from the National Natural Science Foundation of China (12405133) and from the Shenzhen Science and Technology Program (ZDSYS20230626091501002). Fu-Sheng Yu and Ao-Sheng Xiong acknowledge support from the Scientific Research Innovation Capability Support Project for Young Faculty (ZYGXQNJSKYCXNLZCXM-P2) and from the Fundamental Research Funds for the Central Universities (lzujbky-2023-stlt01, lzujbky-2024-oy02, lzujbky-2025-eyt01)

We investigate the vacuum-induced current density for a charged scalar field in a (<math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><mi>D</mi><mo>+</mo><mn>1</mn></mrow></math>)-dimensional cosmic dispiration spacetime threaded by a magnetic flux. This background combines a cosmic string and a screw dislocation, yielding a nontrivial helical geometry. By constructing the normalized mode functions of the Klein-Gordon equation, we evaluate the Wightman function and obtain the vacuum expectation value of the current density. We show that, in addition to the azimuthal component describing a persistent current around the defect, a nonvanishing axial component is induced as a direct consequence of the helical structure of the spacetime. Both components are periodic functions of the magnetic flux depending only on its fractional part, reflecting the Aharonov-Bohm nature of the effect. Closed expressions are obtained for massive and massless fields in arbitrary dimensions. We demonstrate that the screw dislocation parameter plays a crucial role in the behavior of the induced currents, leading to the regularization of the components at the origin and controlling their magnitude. Their asymptotic behavior is also analyzed in detail. Our results reduce to known expressions in the absence of the screw dislocation, providing a consistency check. In particular, we examine the physically relevant (<math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><mn>3</mn><mo>+</mo><mn>1</mn></mrow></math>)-dimensional case, where numerical analysis reveals nontrivial features arising from the interplay between topology and gauge effects.

Brazil

Herondy Mota

Vacuum-induced current density from a magnetic flux threading a cosmic dispiration in (<math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>D</mi><mo>+</mo><mn>1</mn></math>)-dimensional spacetime

We introduce a streamlined method for evaluating in-in loop integrals using dimensional regularization for diagrams with an arbitrary number of external legs and vertices, which complements earlier work and facilitates the extraction of the ultraviolet contributions. The method leads us to identify an apparent difficulty to renormalize with Hamiltonian counterterms within the in-in formalism. We also discuss the importance of the finite parts of loop corrections that can be distinguished from their associated counterterm contributions. As an application, we examine the one-loop primordial bispectrum in the context of the effective field theory of inflation, considering a specific set of interactions, and identifying a contribution distinguishable from its tree-level counterpart.

Spain

Guillermo Ballesteros

Jesús Egea

Italy

Flavio Riccardi

Finite parts of inflationary loops II: A streamlined UV in-in algorithm and distinguishable signatures

In earlier work we proposed a string theory dual to two dimensional Yang-Mills theory at zero coupling (which can also be thought of as a $\textit{BF}$ theory), given by a Polyakov-like generalization of Hořava’s topological rigid string theory, and we showed that it correctly reproduces (in the 1/$\textit{N}$ expansion) several partition functions of $\textit{SU}$ ($\textit{N}$) Yang-Mills theory. In the present paper, we generalise this to Wilson loop expectation values by adding boundaries with one Dirichlet and one Neumann boundary condition to our string worldsheets. We discuss in detail several examples, including examples where the worldsheet has branch points or orientation-reversing tubes, or where the Wilson loop has one or more self-intersections, and we show that in all of them the string theory reproduces the known Yang-Mills expectation values. We argue that examples with orientation-reversing tubes or self-intersecting Wilson loops cannot be brought to the conformal gauge, so we analyse them in a different gauge.

Israel

Ofer Aharony

Suman Kundu

Tal Sheaffer

A string theory for two dimensional Yang-Mills theory. Part II

We compute three-loop QCD corrections to the scattering amplitude of a Higgs boson and three partons interfered with its tree level counterpart. Specifically, we derive our results in the generalized leading color limit. Our results are represented in terms of so-called multiple polylogarithms and thus are ready for use in phenomenological predictions. We provide the three-loop amplitudes necessary to compute the production cross section of a Higgs boson and a hadronic jet at hadron colliders and the decay probability of a Higgs boson to three hadronic jets at lepton colliders.

Switzerland

Xiang Chen

United States

Xin Guan

Bernhard Mistlberger

Three-loop QCD corrections to the production of a Higgs boson and a jet

We match the real Higgs triplet model (RHTM) onto Higgs effective field theory (HEFT) under different parameter choices and power-counting schemes, thereby obtaining several representative HEFT formulations and clarifying their relations. We establish the primary HEFT (pHEFT) as a benchmark framework, demonstrating that alternative HEFT constructions can be systematically derived from it. A key advantage of the pHEFT construction is its parameter choice, which maintains linear relations between the UV Lagrangian parameters and squared heavy masses. By strictly employing the inverse squared heavy masses as the expansion parameters without imposing additional constraints, pHEFT preserves maximal UV information and ensures higher perturbative accuracy by avoiding the additional truncations inherent in more complex nonlinear formulations or extra constraints. Through the analysis of the <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msub><mi>Z</mi><mn>2</mn></msub></math>-symmetric real singlet model and the two-Higgs-doublet model, we illustrate the criteria for identifying viable primary HEFT constructions in UV models with scalar extensions. Furthermore, for the first time, we derive the HEFT operators of the RHTM involving fermions.

Zizhou Ge

South Korea

Huayang Song

Xia Wan

Establishing the primary HEFT as a precision benchmark for UV-HEFT matching

The Karlsruhe Tritium Neutrino (KATRIN) experiment measures the neutrino mass from a precise measurement of the endpoint region of the kinematic tritium $$\upbeta $$ -decay spectrum by using a spectrometer combining magnetic adiabatic collimation and electrostatic filtering (MAC-E filter). For calibration purposes, KATRIN uses a monoenergetic angular-selective photoelectron source. We present an upgrade of this source, which was installed in the KATRIN beamline in February 2022. The source allows for a wide range of accessible electron energies up to 32keV and a variation of the angle with regard to the magnetic field. These features are used for precise measurements of electron scattering effects off tritium molecules in KATRIN’s gaseous tritium source, for investigations of angular-dependent backscattering for example at KATRIN’s focal-plane detector, and for studies on adiabatic transport in the main spectrometer.

Germany

S. Schneidewind

R. Sack

F. Block

S. Enomoto

V. Hannen

C. Köhler

A. Lokhov

A. Marsteller

H.W. Ortjohann

R.W.J. Salomon

L. Schimpf

K. Schlösser

S. Wüstling

C. Weinheimer

A precision 32 keV angular-selective photoelectron source for calibration measurements at the KATRIN experiment

We propose that simple neural networks (NNs) trained on crossing symmetry can reconstruct conformal correlators restricted to a line to remarkable accuracy. The input is minimal: an external scaling dimension, a spectral gap, and the value of the correlator at a single point. We present evidence across a wide range of conformal theories and dimensions, for both four-point and thermal two-point functions. We attribute these observations to the <italic>spectral bias</italic> of gradient-based NN training, which appears to align with an intrinsic smoothness property of conformal field theory. This suggests a novel variational principle for conformal correlators and opens a path towards a powerful new computational framework for non-perturbative quantum field theory.

United Kingdom

Kausik Ghosh

Sidhaarth Kumar

Greece

Vasilis Niarchos

Andreas Stergiou

Neural networks reveal a universal bias in conformal correlators

We classify the non-Abelian anomaly of the Euclidean conformal group $\textit{SO}$(2$\textit{n}$ + 1$\textit{,}$ 1) in 2$\textit{n}$ dimensions via Stora-Zumino descent from its Euler invariant polynomial in 2$\textit{n}$ + 2 dimensions. In this way, we place the conformal anomaly on the same footing as ordinary perturbative ’t Hooft anomalies. We also explore the relation of the non-Abelian anomaly to the known $\textit{type-A Weyl anomaly}$, which involves projecting into a Weyl cocycle. We discuss implications for anomaly inflow, and ’t Hooft anomaly matching for the full conformal group with a Wess-Zumino-Witten term. In 4d, this enables the construction of a dilaton effective action matching the full non-Abelian $\textit{SO}$(5, 1) conformal anomaly.

Gleb Aminov

Csaba Csáki

Ofri Telem

Shimon Yankielowicz

Non-Abelian and type-A conformal anomalies from Euler descent

We apply localization techniques to topologically $\textit{A}$-twisted 𝒩 = (2, 2) supersymmetric theories of vector and chiral multiplets on $\textit{S}$ and derive a novel exact formula for abelian observables, described by a distribution integrated along the real line. The distributional integral formula is verified by evaluating the correlator of the $\textit{A}$-twisted ℂℙ gauged linear sigma model and confirming the standard selection rule. Finally, we use hyper-functions to demonstrate the equivalence between the distributional and complex contour integral descriptions of the ℂℙ correlator, and find agreement with the Jeffrey-Kirwan residue prescription.

Denmark

Türkiye

Emil Leeb-Lundberg

Hyperfunctions in $\textit{A}$-model localization