<p>We report on a search for axion dark matter in the frequency range near 5.9 GHz, conducted using the haloscope technique. The experiment employed an 8-cell microwave resonator designed to extend the accessible frequency range by a multifold factor relative to conventional single-cell configurations, while maintaining a large detection volume. To enhance sensitivity, a flux-driven Josephson parametric amplifier operating near the quantum noise limit was utilized, together with a sideband-summing method that coherently combines mirrored spectral components generated by the Josephson parametric amplifier. Data were acquired over the frequency range 5.83–5.94 GHz. With no statistically significant excess observed, we exclude axion-photon couplings <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><msub><mrow><mi>g</mi></mrow><mrow><mi>a</mi><mi>γ</mi><mi>γ</mi></mrow></msub></mrow></math> down to <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><mn>1.2</mn><mo>×</mo><msup><mrow><mn>10</mn></mrow><mrow><mo>−</mo><mn>14</mn></mrow></msup><mtext> </mtext><mtext> </mtext><mrow><msup><mrow><mi>GeV</mi></mrow><mrow><mo>−</mo><mn>1</mn></mrow></msup></mrow></mrow></math> at a 90% confidence level. The achieved sensitivity approaches the Kim-Shifman-Vainshtein-Zakharov benchmark prediction, setting the most stringent limits to date in this range.</p>

South Korea

Saebyeok Ahn

Çağlar Kutlu

Soohyung Lee

SungWoo Youn

Sergey V. Uchaikin

Sungjae Bae

Sweden

Junu Jeong

Japan

Arjan F. van Loo

Yasunobu Nakamura

Seongjeong Oh

Jihn E. Kim

Yannis K. Semertzidis

Probing Kim-Shifman-Vainshtein-Zakharov Axion Dark Matter near 5.9 GHz Using an 8-Cell Cavity Haloscope

<p>Axions, originally proposed to resolve the <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><mi>C</mi><mi>P</mi></mrow></math> problem in the strong interaction, remain a leading dark matter candidate. While cavity haloscopes offer the most sensitive technique for detecting axions, searches have largely been limited to masses below <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><mn>10</mn><mtext> </mtext><mtext> </mtext><mi>μeV</mi></mrow></math>. We report a sensitive search for axion dark matter with masses around <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><mn>21</mn><mtext> </mtext><mtext> </mtext><mi>μeV</mi></mrow></math>, utilizing the <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><msub><mrow><mi>TM</mi></mrow><mrow><mn>020</mn></mrow></msub></mrow></math> mode of a cylindrical cavity equipped with an innovative tuning mechanism. Our search achieved a sensitivity of <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mn>1.7</mn><mo>×</mo></math> the Kim-Shifman-Vainshtein-Zakharov benchmark over a 100-MHz range, representing a significant advance in this mass range. These results demonstrate that higher-order modes provide a viable strategy for extending haloscope searches into previously unexplored higher-mass regions.</p>

Germany

Younggeun Kim

Jinsu Kim

Seonjeong Oh

Taehyeon Seong

Sergey Uchaikin

Axion Dark Matter Search with Sensitivity near the Kim-Shifman-Vainshtein-Zakharov Benchmark Using the <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><msub><mrow><mi>TM</mi></mrow><mrow><mn>020</mn></mrow></msub></mrow></math> Mode

We propose a deep learning-based search strategy for pair production of doubly charged scalars undergoing three-body decays to   <math> <msup> <mi>W</mi> <mo>+</mo> </msup> <mi>t</mi> <mover> <mi>b</mi> <mo>¯</mo> </mover> </math>  $$ {W}^{+}t\overline{b} $$  in the same-sign lepton plus multi-jet final state. This process is motivated by composite Higgs models with an underlying fermionic UV theory. We demonstrate that for such busy final states, jet image classification with convolutional neural networks outperforms standard fully connected networks acting on reconstructed kinematic variables. We derive the expected discovery reach and exclusion limit at the high-luminosity LHC.

Thomas Flacke

Jeong Kim

Manuel Kunkel

Pyungwon Ko

Jun Pi

Werner Porod

Leonard Schwarze

Uncovering doubly charged scalars with dominant three-body decays using machine learning

It has been known for some time that the cosmological bound on the invisible axion scale can be avoided by an early phase of strong QCD. While most approaches rely on theories where the strong coupling constant is determined through the expectation value of some scalar field, we show that this mechanism can also be implemented into the benchmark Kim-Shifman-Vainshtein-Zakharov and Dine-Fischler-Srednicki-Zhitnitsky models when the early phase of strong QCD emerges by the modification of the running coupling during inflation. For both models the physics that are responsible for making QCD strong do not displace the axions minimum by too much, so that the efficiency of the relaxation is controlled by parameters of the theory and the number of inflationary <math><mi>e</mi></math>-folds. In particular, we consider the case of very efficient relaxation where the axion abundance is dominated by inflationary quantum and postinflationary thermal fluctuations. Within this situation we identify the parameter space compatible with all cosmological constrains and derive conditions on the reheating temperature and the QCD scale during inflation that result in the axion making up all the dark matter. Because of duality below the Peccei-Quinn scale and a minor influence of the Kim-Shifman-Vainshtein-Zakharov and Dine-Fischler-Srednicki-Zhitnitsky fields on the running, our findings also apply to a minimal two-form implementation of the axion.

Emmanouil Koutsangelas

Removing the cosmological bound on the axion scale in the Kim-Shifman-Vainshtein-Zakharov and Dine-Fischler-Srednicki-Zhitnitsky models

The Higgs potential is vital to understand the electroweak symmetry breaking mechanism, and probing the Higgs self-interaction is arguably one of the most important physics targets at current and upcoming collider experiments. In particular, the triple Higgs coupling may be accessible at the HL-LHC by combining results in multiple channels, which motivates to study all possible decay modes for the double Higgs production. In this paper, we revisit the double Higgs production at the HL-LHC in the final state with two b-tagged jets, two leptons and missing transverse momentum. We focus on the performance of various neural network architectures with different input features: low-level (four momenta), high-level (kinematic variables) and image-based. We find it possible to bring a modest increase in the signal sensitivity over existing results via careful optimization of machine learning algorithms making a full use of novel kinematic variables.

China

Li Huang

Su-beom Kang

United States

Kyoungchul Kong

Portraying double Higgs at the Large Hadron Collider II

The mirror twin Higgs model (MTH) is a solution to the Higgs hierarchy problem that provides well-predicted cosmological signatures with only three extra parameters: the temperature of the twin sector, the abundance of twin baryons, and the vacuum expectation value (VEV) of twin electroweak symmetry breaking. These parameters specify the behavior of twin radiation and the acoustic oscillations of twin baryons, which lead to testable effects on the cosmic microwave background (CMB) and large-scale structure (LSS). While collider searches can only probe the twin VEV, through a fit to cosmological data we show that the existing CMB (Planck18 TTTEEE+lowE+lowT+lensing) and LSS (KV450) data already provide useful constraints on the remaining MTH parameters. Additionally, we show that the presence of twin radiation in this model can raise the Hubble constant H 0 while the scattering twin baryons can reduce the matter fluctuations S 8, which helps to relax the observed H 0 and S 8 tensions simultaneously. This scenario is different from the typical ΛCDM + ∆N eff model, in which extra radiation helps with the Hubble tension but worsens the S 8 tension. For instance, when including the SH0ES and 2013 Planck SZ data in the fit, we find that a universe with ≳ 20% of the dark matter comprised of twin baryons is preferred over ΛCDM by ∼ 4σ. If the twin sector is indeed responsible for resolving the H 0 and S 8 tensions, future measurements from the Euclid satellite and CMB Stage 4 experiment will further measure the twin parameters to O(1 − 10%)-level precision. Our study demonstrates how models with hidden naturalness can potentially be probed using precision cosmological data.

Saurabh Bansal

Christopher Kolda

Matthew Low

Yuhsin Tsai

Mirror twin Higgs cosmology: constraints and a possible resolution to the H 0 and S 8 tensions

The study of the Higgs boson’s properties is a cornerstone of the LHC and future collider programs. In this paper, we examine the potential to directly probe the Higgs-top interaction strength and CP-structure in the   <math> <mi>t</mi> <mover> <mi>t</mi> <mo>¯</mo> </mover> <mi>h</mi> </math>  $$ t\overline{t}h $$  channel with the Higgs boson decaying to bottom-quark pairs and top-quarks in the di-leptonic mode. We adopt the BDRS algorithm to tag the boosted Higgs and exploit the M 2-assisted reconstruction to compute observables sensitive to the CP-phase at the   <math> <mi>t</mi> <mover> <mi>t</mi> <mo>¯</mo> </mover> </math>  $$ t\overline{t} $$  rest frame, where the new physics sensitivity can be enhanced. Performing a side-band analysis at the LHC to control the continuum   <math> <mi>t</mi> <mover> <mi>t</mi> <mo>¯</mo> </mover> <mi>b</mi> <mover> <mi>b</mi> <mo>¯</mo> </mover> </math>  $$ t\overline{t}b\overline{b} $$  background, we find that the Higgs-top strength and CP-phase can be probed up to   <math> <msub> <mi>δ</mi> <msub> <mi>κ</mi> <mi>t</mi> </msub> </msub> </math>  $$ {\delta}_{\kappa_t} $$  ≲ 20% and |α| ≲ 36° at 95% CL, respectively. We also derive that a similar analysis at a 100 TeV future collider could further improve the precision to   <math> <msub> <mi>δ</mi> <msub> <mi>κ</mi> <mi>t</mi> </msub> </msub> </math>  $$ {\delta}_{\kappa_t} $$  ≲ 1% and |α| ≲ 1.5°, where the CP-odd observables play a crucial role, boosting the sensitivity on the CP-phase.

Dorival Gonçalves

Yongcheng Wu

Direct Higgs-top CP-phase measurement with   <math> <mi>t</mi> <mover> <mi>t</mi> <mo>¯</mo> </mover> <mi>h</mi> </math>  $$ t\overline{t}h $$  at the 14 TeV LHC and 100 TeV FCC

Heavy particles with masses much bigger than the inflationary Hubble scale H *, can get non-adiabatically pair produced during inflation through their couplings to the inflaton. If such couplings give rise to time-dependent masses for the heavy particles, then following their production, the heavy particles modify the curvature perturbation around their locations in a time-dependent and scale non-invariant manner. This results into a non-trivial spatial profile of the curvature perturbation that is preserved on superhorizon scales and eventually generates localized hot or cold spots on the CMB. We explore this phenomenon by studying the inflationary production of heavy scalars and derive the final temperature profile of the spots on the CMB by taking into account the subhorizon evolution, focusing in particular on the parameter space where pairwise hot spots (PHS) arise. When the heavy scalar has an   <math> <mi>O</mi> </math>  $$ \mathcal{O} $$ (1) coupling to the inflaton, we show that for an idealized situation where the dominant background to the PHS signal comes from the standard CMB fluctuations themselves, a simple position space search based on applying a temperature cut, can be sensitive to heavy particle masses M 0 /H * ∼   <math> <mi>O</mi> </math>  $$ \mathcal{O} $$ (100). The corresponding PHS signal also modifies the CMB power spectra and bispectra, although the corrections are below (outside) the sensitivity of current measurements (searches).

Soubhik Kumar

Adam Martin

Cosmological particle production and pairwise hotspots on the CMB

In this paper, we explore the impact of extra radiation on predictions of   <math> <mi>pp</mi> <mo>→</mo> <mi>t</mi> <mover> <mi>t</mi> <mo>¯</mo> </mover> <mi>X</mi> <mo>,</mo> <mi>X</mi> <mo>=</mo> <mi>h</mi> <mo>/</mo> <msup> <mi>W</mi> <mo>±</mo> </msup> <mo>/</mo> <mi>Z</mi> </math>  $$ pp\to \mathrm{t}\overline{\mathrm{t}}\mathrm{X},\mathrm{X}=\mathrm{h}/{\mathrm{W}}^{\pm }/\mathrm{Z} $$  processes within the dimension-6 SMEFT framework. While full next-to-leading order calculations are of course preferred, they are not always practical, and so it is useful to be able to capture the impacts of extra radiation using leading-order matrix elements matched to the parton shower and merged. While a matched/merged leading-order calculation for   <math> <mi>t</mi> <mover> <mi>t</mi> <mo>¯</mo> </mover> <mi>X</mi> </math>  $$ \mathrm{t}\overline{\mathrm{t}}\mathrm{X} $$  is not expected to reproduce the next-to-leading order inclusive cross section precisely, we show that it does capture the relative impact of the EFT effects by considering the ratio of matched SMEFT inclusive cross sections to Standard Model values,   <math> <msub> <mi>σ</mi> <mtext>SMEFT</mtext> </msub> <mfenced> <mrow> <mi>t</mi> <mover> <mi>t</mi> <mo>¯</mo> </mover> <mi>X</mi> <mo>+</mo> <mi>j</mi> </mrow> </mfenced> <mo>/</mo> <msub> <mi>σ</mi> <mi>SM</mi> </msub> <mfenced> <mrow> <mi>t</mi> <mover> <mi>t</mi> <mo>¯</mo> </mover> <mi>X</mi> <mo>+</mo> <mi>j</mi> </mrow> </mfenced> <mo>≡</mo> <mi>μ</mi> </math>  $$ {\sigma}_{\mathrm{SM}\mathrm{EFT}}\left(\mathrm{t}\overline{\mathrm{t}}\mathrm{X}+\mathrm{j}\right)/{\sigma}_{\mathrm{SM}}\left(\mathrm{t}\overline{\mathrm{t}}\mathrm{X}+\mathrm{j}\right)\equiv \mu $$ . Furthermore, we compare leading order calculations with and without extra radiation and find several cases, such as the effect of the operator   <math> <mfenced> <mrow> <msup> <mi>φ</mi> <mo>†</mo> </msup> <mi>i</mi> <msub> <mover> <mi>D</mi> <mo>↔</mo> </mover> <mi>μ</mi> </msub> <mi>φ</mi> </mrow> </mfenced> <mfenced> <mrow> <mover> <mi>t</mi> <mo>¯</mo> </mover> <msup> <mi>γ</mi> <mi>μ</mi> </msup> <mi>t</mi> </mrow> </mfenced> </math>  $$ \left({\varphi}^{\dagger }i{\overleftrightarrow{D}}_{\mu}\varphi \right)\left(\overline{t}{\gamma}^{\mu }t\right) $$  on   <math> <mi>t</mi> <mover> <mi>t</mi> <mo>¯</mo> </mover> <mi>h</mi> </math>  $$ \mathrm{t}\overline{\mathrm{t}}\mathrm{h} $$  and   <math> <mi>t</mi> <mover> <mi>t</mi> <mo>¯</mo> </mover> <mi>W</mi> </math>  $$ \mathrm{t}\overline{\mathrm{t}}\mathrm{W} $$ , for which the relative cross section prediction increases by more than 10% — significantly larger than the uncertainty derived by varying the input scales in the calculation, including the additional scales required for matching and merging. Being leading order at heart, matching and merging can be applied to all operators and processes relevant to   <math> <mi>pp</mi> <mo>→</mo> <mi>t</mi> <mover> <mi>t</mi> <mo>¯</mo> </mover> <mi>X</mi> <mo>,</mo> <mi>X</mi> <mo>=</mo> <mi>h</mi> <mo>/</mo> <msup> <mi>W</mi> <mo>±</mo> </msup> <mo>/</mo> <mi>Z</mi> <mo>+</mo> <mi>jet</mi> </math>  $$ pp\to \mathrm{t}\overline{\mathrm{t}}\mathrm{X},\mathrm{X}=\mathrm{h}/{\mathrm{W}}^{\pm }/\mathrm{Z}+\mathrm{jet} $$ , is computationally fast and not susceptible to negative weights. Therefore, it is a useful approach in   <math> <mi>t</mi> <mover> <mi>t</mi> <mo>¯</mo> </mover> <mi>X</mi> </math>  $$ \mathrm{t}\overline{\mathrm{t}}\mathrm{X} $$  + jet studies where complete next-to-leading order results are currently unavailable or unwieldy.

Reza Goldouzian

Kevin Lannon

Kelci Mohrman

Andrew Wightman

Matching in   <math> <mi>pp</mi> <mo>→</mo> <mi>t</mi> <mover> <mi>t</mi> <mo>¯</mo> </mover> <mi>W</mi> <mo>/</mo> <mi>Z</mi> <mo>/</mo> <mi>h</mi> <mo>+</mo> </math>  $$ pp\to t\overline{t}W/Z/h+ $$  jet SMEFT studies

We studied the feasibility of an experiment searching for sub-millicharged particles (χs) using 30 GeV proton fixed-target collisions at J-PARC. The detector is composed of two layers of stacked scintillator bars and PMTs and is proposed to be installed 280 m from the target. The main background is a random coincidence between two layers due to dark counts in PMTs, which can be reduced to a negligible level using the timing of the proton beam. With N POT = 1022 which corresponds to running the experiment for three years, the experiment provides sensitivity to χs with the charge down to 5 × 10 −5 in m  χ  &lt; 0.2 GeV/c2 and 8 × 10 −4 in m  χ  &lt; 1.6 GeV/c2. This is the regime largely uncovered by previous experiments. We also explored a few detector designs to achieve optimal sensitivity to χs. The photoelectron yield is the main driver, but the sensitivity does not have a strong dependence on detector configuration in the sub-millicharge regime.

In Hwang

Jae Yoo

Search for sub-millicharged particles at J-PARC