Screened scalars are ubiquitous in many dark-sector models. They give rise to nontrivial fifth forces while evading experimental constraints through density-dependent screening mechanisms. We propose equipping a 10 m-scale long-baseline atom interferometer with an annular planar source mass inside the vacuum chamber to search for such screened fifth forces. Two key challenges arise: distinguishing the static fifth force from backgrounds, and isolating it from the plate’s Newtonian gravity. We introduce the <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>Q</mi></math>-flip protocol, which alternates between interferometry sequences to induce controllable time-dependence, aiding signal extraction and detrending of transient noise. We further develop an in situ calibration procedure to characterize the plate’s Newtonian gravity and reach shot-noise-limited sensitivity. We show that our proposal could test theoretically motivated parameter space, advancing existing bounds on chameleon and symmetron screened scalar models by 1 to 1.5 orders of magnitude. Our proposal is directly applicable to forthcoming experiments, such as AION-10 or VLBAI, and is readily extensible to broader theoretical models and longer baselines.

United States

United Kingdom

Hannah Banks

John Carlton

Benjamin Elder

Thomas Hird

Christopher McCabe

Searching for screened scalar forces with long-baseline atom interferometers

Accelerator-based neutrino experiments offer a competitive environment to search for long-lived particles with sub-GeV masses. Yet, many theoretical models involving such particles predict very similar phenomenology and nearly identical final-state signatures. In view of this, we study the capabilities of upcoming experiments—specifically the DUNE near detectors—to distinguish between different classes of long-lived particles and the mechanisms by which they are produces. We expound how the experiment’s excellent energy resolution, combined with the possibility to move the detector off-axis (the DUNE-PRISM concept), work in tandem to improve the discrimination power.

Kevin J. Kelly

Mudit Rai

Long-lived particle production through the DUNE-PRISM concept

Alpha decay is an important competing process in astrophysical nucleosynthesis. In this work, thermal effects on several long-lived <italic>&#945;</italic> decays relevant to the <italic>s</italic>-, <italic>r</italic>-, and <italic>p</italic>-processes are investigated within a microscopic coupled-channels framework combined with an effective- <math altimg='si12.svg'><msub><mi mathvariant='script'>Q</mi><mi>&#945;</mi></msub></math> approach. The <italic>&#945;</italic>-daughter interaction is described by a temperature-dependent double-folding potential based on the density-dependent Migdal interaction, and the thermal contribution of nuclear excitations is evaluated by including both experimentally known discrete levels and the continuum part of the level density. Calculations for twelve selected long-lived <italic>&#945;</italic>-emitters show that the direct thermal modification of the <italic>&#945;</italic>-daughter potential is negligible at typical stellar temperatures, whereas the dominant thermal effect arises from the increase in the effective decay energy associated with the thermal population of parent states. The magnitude of the enhancement is found to depend on both the low-lying level structure of the parent nucleus and the ground-state decay energy. In contrast to the very large enhancements suggested in the early pioneering work of Perrone and Clayton [ <inter-ref xmlns:ns0='http://www.w3.org/1999/xlink' id='intrrf0001' ns0:href='https://doi.org/10.1007/BF00649638'>Astrophys. Space~Sci. 11, 451 (1971)</inter-ref> ], the present results indicate a more moderate thermal enhancement for the nuclei considered here. For most cases, the half-life reduction remains limited in the astrophysically relevant temperature range, although several low- <math altimg='si12.svg'><msub><mi mathvariant='script'>Q</mi><mi>&#945;</mi></msub></math> nuclei exhibit stronger enhancements toward the higher temperatures. These results provide updated estimates of thermal modifications to long-lived <italic>&#945;</italic>-decay half-lives under astrophysical conditions, which may be useful for future studies in nuclear astrophysics.

China

Zhen Wang

Zhongzhou Ren

Thermal effects on long-lived <italic>&#945;</italic> decays in astrophysical nucleosynthesis

We study the prospects of the proposed $\textit{μ}$TRISTAN experiment, running in the energy asymmetric $\textit{μ}$ $\textit{e}$ mode, in probing long lived particles (LLPs) arising from the decay of the Standard Model Higgs boson. We focus on the proposed runs with $$ \left\{{E}_{\mu^{+}},{E}_{e^{-}}\right\} $$ = {1 TeV, 30 GeV} and $$ \left\{{E}_{\mu^{+}},{E}_{e^{-}}\right\} $$ = {3 TeV, 50 GeV} and we show that, owing to the boosted nature of the produced events, a far detector placed along the beam line can collect a large fraction of the LLP flux. This allows one to set bounds on the exotic Higgs branching ratio which, for specific $\textit{ϕ}$ decay modes, can surpass those expected at the end of the High Luminosity LHC in the regime of large LLPs proper decay lengths. On the other hand, we find that the proposed strategy will not be able to further extend the limits that might be set by proposed LHC far detectors such as CODEX-b, ANUBIS and MATHUSLA.

Italy

Daniele Barducci

Boosting long lived particles searches at $\textit{μ}$TRISTAN

We study axionlike particles (ALPs) in beam dump experiments, focusing on the Search for Hidden Particles (SHiP, at CERN) experiment and the Beam Dump eXperiment (BDX, at JLab). Many existing projections for sensitivity to ALPs in beam dump experiments have focused on production from either the primary proton/electron beam, or—in the case of SHiP—the secondary (high-energy) photons produced by neutral meson decays (e.g., <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msup><mi>π</mi><mn>0</mn></msup><mo stretchy="false">→</mo><mi>γ</mi><mi>γ</mi></math>). In this work, we study the subsequent production of axions from the full electromagnetic shower in the target, finding order-of-magnitude enhancements in the visible decay yields across a wide range of axion masses. We update SHiP’s sensitivity curve and provide new projections for BDX. Both experiments will be able to reach currently unexplored regions of ALP parameter space.

Samuel Patrone

Canada

Nikita Blinov

CERN

Ryan Plestid

Long-lived axionlike particles from electromagnetic cascades

The $ e^+e^- $ annihilation of unpolarized beams is free from initial hadron states or initial anisotropy around the azimuthal angle. Hence, it is ideal for studying the correlations of dynamical origin via final state jets. We investigate the planar properties of multi-jet events employing the relevant event-shape observables at next-to-next-to-leading order ( $ {\cal{O}} $ ( $ \alpha_{s}^{3} $ )) in perturbative Quantum Chromodynamics (QCD). In particular, the azimuthal angle correlations on the long pseudo-rapidity (polar angle) range (Ridge correlation) between the inclusive jet momenta are calculated. We demonstrate that the significant planar properties and the strong correlations as the consequence are natural results of the energy-momentum conservation of the perturbative QCD radiation dynamics. Our study provides benchmarks of a hard strong interaction background for investigating the collective and/or thermal effects via the Ridge-like correlation observables for various scattering processes.

Xuan Chen

Yuesheng Dai

Shi-Yuan Li

Zong-Guo Si

Huiting Sun

Planar property and long-range azimuthal correlation in $\textit{e}$ $^{+}$ $\textit{e}$ $^{–}$ annihilation * Supported by the National Science Foundation of China (NSFC) (12475085, 12275157, 12321005, 12235008)

Recently, the study of long-lived particles (LLPs) has attracted increasing attention. In this work, we analyze the full parameter space of the Type-I Two-Higgs-Doublet Model (2HDM) that allows for light long-lived scalar ($\textit{H}$) and pseudoscalar ($\textit{A}$) particles. When involving a light beyongd Standard Model (BSM) Higgs, the ∆$\textit{S}$ could be the main contribution during the global fit of the oblique parameters, which is different to ∆$\textit{T}$ being the main factor for heavy BSM Higgs cases. By imposing theoretical constraints such as vacuum stability and perturbative unitarity, together with current experimental bounds, we summarize a complete region for a potential light $\textit{H}$ with cos($\textit{β}$ − $\textit{α}$) ≃ $$ \frac{1}{\tan \beta } $$ , light $\textit{A}$ with cos($\textit{β}$ − $\textit{α}$) ≃ $$ \frac{1}{\tan \beta}\frac{2{m}_H^2-{m}_h^2}{m_H^2-{m}_h^2} $$ , and point out the invisible Higgs decay is the most important constraint. We further identify viable regions for LLPs and propose four benchmark regions that simultaneously accommodate a light long-lived particle and the CDF-II measured $\textit{W}$ boson mass. For these benchmarks, we present the reaches of FASER and FASER 2, where FASER 2 improves the sensitivity by approximately two orders of magnitude compared to FASER.

Xueying Qi

South Korea

Huayang Song

Wei Su

Complete light long-lived particles searches in Type-I 2HDM

The factorization proposal claims that the codimension one “pinning defect,” on which a local relevant operator is integrated, factorizes the space into two halves in general conformal field theories in the infrared limit. In this paper, we study a two-dimensional long-range Ising model at criticality with a line defect or an interface, which physically corresponds to changing the local temperature on it. We show that in the perturbative regime, it is not factorizing even in the infrared limit. An intuitive explanation of the nonfactorization is that the long-range Ising model is equivalent to a local conformal field theory in higher dimensions. In this picture, the space is still connected through the “extra dimension” across the defect line.

Japan

Dongsheng Ge

Yu Nakayama

Nonfactorizing interface in the two-dimensional long-range Ising model

The scale of the seesaw mechanism is typically much larger than the electroweak scale. This hierarchy can be naturally explained by U(1) symmetry, which after spontaneous symmetry breaking, simultaneously generates Majorana masses for neutrinos and produces a network of cosmic strings. Such strings generate a gravitational wave (GW) spectrum which is expected to be almost uniform in frequency unless there is a departure from the usual early radiation domination. We explore this possibility in Type I, II and III seesaw frameworks, finding that only for Type-I, long-lived right-handed neutrinos (RHN) may provide a period of early matter domination for parts of the parameter space, even if they are thermally produced. Such a period leaves distinctive imprints in the GW spectrum in the form of characteristic breaks and a knee feature, arising due to the end and start of the periods of RHN domination. These features, if detected, directly determine the right-handed neutrino mass $\textit{M}$, and associated left-handed effective neutrino mass $$ \overset{\sim }{m} $$ of the dominating RHN. We find that GW detectors like LISA and ET could probe RHN masses in the range $\textit{M}$ ∈ [0.1, 10 ] GeV and effective neutrino masses in the $$ \overset{\sim }{m} $$ ∈ [10 , 10 ] eV range. We investigate the phenomenological implications of long-lived right-handed neutrinos for both local and global U(1) strings, focusing on dark matter production and leptogenesis. We map the viable and detectable parameter space for successful baryogenesis and asymmetric dark matter production from right-handed neutrino decays. We derive analytical and semi-analytical relations correlating the characteristic gravitational-wave frequencies to the neutrino parameters $$ \overset{\sim }{m} $$ and $\textit{M}$, as well as to the relic abundances of dark matter and baryons. We find that the detectable parameter space reaches the boundary of hierarchical leptogenesis and encompasses a substantial portion of the near-resonant regime.

Satyabrata Datta

Poland

Anish Ghoshal

Angus Spalding

Graham White

Gravitational wave spectral shapes as a probe of long lived right-handed neutrinos, leptogenesis and dark matter. Global versus local $\textit{B}$ − $\textit{L}$ cosmic strings

Heavy neutral leptons (HNLs) and axion-like particles (ALPs) are both considered well-motivated candidates for beyond the standard model (BSM) physics. If ALPs with sizable couplings to gluons exist, they will be abundantly produced at the LHC. Therefore, HNLs produced via the ALP portal may provide unprecedented sensitivities to HNL parameters. Here, we study the prospects for the high-luminosity LHC to search for long-lived HNLs. We consider future far detectors as well as ATLAS in our simulations. In the limit where the ALP mass is above the TeV scale, HNLs are effectively produced by a dimension-8 operator connecting HNL pairs to gluons. For completeness, we therefore also calculate future LHC sensitivities for HNLs produced via $\textit{N}$ SMEFT operators with gluons.