The precise reconstruction of the mass peak of long-lived heavy neutral leptons (HNLs) helps to improve the sensitivity for sterile neutrino searches in both fixed-target and collider environments (e.g., SHiP and the LHC). We present an analytical framework for reconstructing the HNL mass peak in the semileptonic HNL decay channel $$N \rightarrow \ell \rho $$ with $$\rho \rightarrow \pi \pi ^0$$ , using only the lepton and the charged pion emerging from the decay vertex together with kinematic constraints and the known particle masses. Incorporating mass constraints from intermediate resonances (e.g., the $$\rho $$ meson) or the parent particle (e.g., the $$W$$ boson at the collider experiments), we propose two methods, suitable for experiments with displaced vertex tracking capabilities. The particle-level simulation’s results demonstrate that the $$\rho $$ -mass constraint method yields promising HNL mass resolution in both beam-dump and collider-based environments. The W-mass constraint method, limited to the HNLs produced via $$W$$ -boson decays at the collider-based experiments, shows better HNL mass resolution than the $$\rho $$ -mass constraint method.

Germany

Marzieh Bahmani

Alessandro Guida

Maral Khandan

Heiko Lacker

Anupama Reghunath

Techniques for mass peak reconstruction in searches for long-lived heavy neutral leptons decaying to a lepton and a $$\rho $$ meson

An efficient numerical algoritm is proposed for the calculation of the modified Lüscher zeta-function in the presence of a long-range force. Using the formalism developed in ref. JHEP05(2024)168 for the analysis of synthetic data on the finite-volume energy levels in a toy model, it is demonstrated that, in contrast to the standard Lüscher approach, the truncation of the higher partial waves has very little effect on the final result. Furthermore, the regularization and renormalization of the modified Lüscher zeta-function is discussed in detail, as well as the problems arising within the cutoff regularization. It is shown that, using the renormalization scheme proposed in the present paper, one obtains modified effective range expansion parameters of natural size in all partial waves.

Rishabh Bubna

Hans-Werner Hammer

Bai-Long Hoid

China

Jin-Yi Pang

Georgia

Akaki Rusetsky

Jia-Jun Wu

Modified Lüscher zeta-function and the modified effective range expansion in the presence of a long-range force

Two models for Schwarzschild-like black holes with quantum corrections, derived from the Hamiltonian constraints approach to quantum gravity while preserving general covariance, have been developed in Zhang et al. (Phys. Rev. D , L081504, 2025, [gr-qc]). In this work, we study the quasinormal modes of a massive scalar field and demonstrate that the spectrum includes arbitrarily long-lived modes, known as quasi-resonances. Precise calculations using the Leaver method show good agreement with WKB data and time-domain integration within the range where these methods are reliable, specifically for small field masses.

Russia

S. Bolokhov

Long lived quasinormal modes in the effective quantum gravity

In a supersymmetry scenario with R-parity violation (RPV), neutralinos with GeV-scale mass, which are necessarily bino-like, are allowed by all constraints and can be produced in association with a baryon in $\textit{B}$-meson decays via certain $$ \overline{U}\overline{D}\overline{D} $$ operators. In this work, we investigate this scenario with two non-vanishing RPV couplings at the low-energy scale. With one RPV coupling governing the neutralino production rate and another determining its lifetime, this scenario can lead to observable signals with displaced-vertex signatures in the tracking volume of $\textit{B}$-factories. To maximize the sensitivity to such signals, we develop a new partial-reconstruction technique that yields high efficiency and utilizes most of the decays of relatively heavy, long-lived particles, achieving much better sensitivity than standard full reconstruction. We consider potential background sources and devise selection criteria to suppress their event yields to very low levels. Using a parameterized model of the detector, we estimate in detail the displaced-vertex reconstruction efficiency as a function of neutralino lifetime and mass. For squark masses beyond the LHC limits, we calculate the signal sensitivity of Belle II, showing that the experiment can probe the RPV couplings well beyond the present bounds, obtained from searches for dinucleon decays, baryon-antibaryon oscillations, and $\textit{B}$ → $\textit{p}$ + missing.

Israel

Emilie Bertholet

Chile

Claudio Dib

Sara Gandelman

Juan Helo

Valery Lyubovitskij

India

Minakshi Nayak

Nicolás Neill

Abner Soffer

Zeren Wang

Searching for long-lived light neutralinos from $\textit{B}$-meson decays with baryonic R-parity violation at Belle II

Dark matter candidates with masses around the Planck scale are theoretically well-motivated, and it has been suggested that it might be possible to search for dark matter solely via gravitational interactions in this mass range. In this work, we explore the pathway towards searching for dark matter candidates with masses around the Planck scale using mechanical sensors while considering realistic experimental constraints, and develop analysis techniques needed to conduct such searches. These dark matter particles are expected to leave tracks as their signature in mechanical sensor arrays, and we show that we can effectively search for such tracks using statistical approaches to track-finding. We analyze a range of possible experimental setups and compute sensitivity projections for searches for ultraheavy dark matter coupling to the Standard Model via long-range forces. We find that while a search for Planck-scale dark matter purely via gravitational couplings would be exceedingly difficult, requiring <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mo>∼</mo><mn>80</mn><mtext> </mtext><mtext> </mtext><mi>dB</mi></math> of quantum noise reduction with a <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msup><mn>100</mn><mn>3</mn></msup></math> array of devices, there is a wide range of currently unexplored dark matter candidates which can be searched for with already existing or near-term experimental platforms.

United States

Juehang Qin

Dorian W.P. Amaral

Sunil A. Bhave

Erqian Cai

Daniel Carney

Rafael F. Lang

Shengchao Li

Alberto M. Marino

Giacomo Marocco

Claire Marvinney

Jared R. Newton

Jacob M. Taylor

Christopher Tunnell

Mechanical sensors for ultraheavy dark matter searches via long-range forces

A new dark matter candidate is proposed that arises as the lightest baryon from a confining <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>S</mi><mi>U</mi><mo stretchy="false">(</mo><mi>N</mi><mo stretchy="false">)</mo></math> gauge theory which equilibrates with the Standard Model only through electroweak interactions. Surprisingly, this candidate can be as light as a few GeV. The lower bound arises from the intersection of two competing requirements: (i) the equilibration sector of the model must be sufficiently heavy, at least several TeV, to avoid bounds from colliders, and (ii) the lightest dark meson (that may be the dark <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msup><mi>η</mi><mo>′</mo></msup></math>, <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>σ</mi></math>, or the lightest glueball) has suppressed interactions with the SM and must decay before big bang nucleosynthesis. The low-energy dark sector consists of one flavor that is electrically neutral and an almost electroweak singlet. The dark matter candidate is the lightest baryon consisting of <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>N</mi></math> of these light flavors leading to a highly suppressed elastic scattering rate with the Standard Model (SM). The equilibration sector consists of vectorlike dark quarks that transform under the electroweak group, ensuring that the dark sector can reach thermal equilibrium with the SM in the early Universe. The lightest dark meson lifetimes vary between <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msup><mn>10</mn><mrow><mo>−</mo><mn>3</mn></mrow></msup><mo>≲</mo><mi>c</mi><mi>τ</mi><mo>≲</mo><msup><mn>10</mn><mn>7</mn></msup><mtext> </mtext><mtext> </mtext><mi mathvariant="normal">m</mi></math>, providing an outstanding target for LHC production and experimental detection. We delineate the interplay between the lifetime of the light mesons, the suppressed direct detection cross section of the lightest baryon, and the scale of equilibration sector that can be probed at the LHC.

George T. Fleming

Graham D. Kribs

Ethan T. Neil

United Kingdom

David Schaich

Pavlos M. Vranas

Hyperstealth dark matter and long-lived particles

We study quasinormal modes and time-domain profiles of a massive scalar field in the background of black holes arising in Einstein–Gauss–Bonnet–Proca gravity. The black holes in this theory possess $\textit{primary Proca hair}$, which modifies the effective potential and gives rise to distinctive dynamical phenomena. Using three complementary numerical techniques – the WKB method with Padé resummation, time-domain integration, and the Frobenius (Leaver) method – we obtain accurate spectra of quasinormal frequencies. Our analysis shows that increasing the scalar-field mass leads to arbitrarily long-lived states, known as quasi-resonances, a behavior shared by both the fundamental mode and the first overtone. The real part of the quasinormal mode decreases for the first and higher overtones and starting from the second overtone it reaches zero at some critical value of mass of the field. When the effective potential develops an additional peak, the late-time signal exhibits a sequence of echoes. Furthermore, the time-domain evolution reveals distinct regimes of intermediate power-law tails $$\sim t^{-4/3-\ell }\sin (A(\mu )t)$$ and a universal asymptotic tails $$\sim t^{-5/6}\sin (\mu t)$$ .

Czechia

B. Lütfüoğlu

Long-lived quasinormal modes and echoes in the Einstein–Gauss–Bonnet–Proca theory

We construct light-cone sum rules for various types of effective form factors in the Λ → Λ$\textit{ℓ}$ $\textit{ℓ}$ and Λ → Λ$\textit{γ}$ decays by analyzing vacuum-to-Λ (or $\textit{γ}$ -to-Λ ) correlation functions with the light Λ-baryon interpolating current. These form factors, defined via hadronic matrix elements within soft-collinear effective theory (SCET), enter the next-to-leading-power QCD factorization formulas for large-recoil transitions. Implementing the perturbative matching from SCET to heavy quark effective theory, we determine the hard-collinear functions at next-to-leading-order accuracy. Based on light-cone sum rule predictions for the Λ → Λ form factors, we compute the $\textit{q}$ -dependent differential branching fraction, forward-backward asymmetry and dilepton longitudinal polarization fraction for Λ → Λ$\textit{ℓ}$ $\textit{ℓ}$ decay, as well as the branching fraction for Λ → Λ$\textit{γ}$ decay.

Long-Shun Lu

Cai-Dian Lü

Yue-Long Shen

Yan-Bing Wei

SCET sum rules for Λ

The radiative leptonic $$B \rightarrow \gamma \ell \nu _{\ell }$$ decay serves as an ideal platform to determine the $\textit{B}$-meson inverse moment which is a fundamental nonperturbative parameter for the $\textit{B}$ meson. In this paper, we explore precise QCD contributions to this decay with an energetic photon. We reproduce the next-to-next-to-leading-logarithmic resummation formula for the decay amplitude at leading power in $$\Lambda _\textrm{QCD}/m_b$$ . Employing operator identities, we calculate subleading-power contributions from the expansion of the hard-collinear propagator of the internal up quark and the heavy-quark expansion of the bottom quark. We update the contributions from the hadronic structure of the photon to the $$B \rightarrow \gamma \ell \nu _{\ell }$$ process with the dispersion technique. Together with other yet known power corrections, phenomenological applications including the partial branching fraction and ratio of the branching fractions of the radiative $\textit{B}$ decay are investigated.

Bo-Yan Cui

Chao Wang

QCD factorization for the $$B \rightarrow \gamma \ell \nu _{\ell }$$ decay beyond leading power

Long-range field configurations exist in the Proca theory and their non-equilibrium evolution is of interest in this work. General arguments suggest that a charge can be assigned to them and that its evolution is governed by the law of periodic charge oscillations. We discuss an elegant analytically-solvable example of a field configuration in the Proca theory respecting such a law. We also identify a weak point in the aforementioned general arguments, construct the counterexample to the law of periodic charge oscillations in the Proca theory, and comprehensively analyze it. The Gibbs-Wilbraham phenomenon is discussed in the course of these studies.

Poland

Bogdan Damski

Non-equilibrium dynamics of long-range field configurations in the Proca theory and the counterexample to the law of periodic charge oscillations