We consider the transverse momentum ($\textit{q}$ ) distribution of neutral charged bosons at hadron colliders. We perform the resummation of the logarithmically-enhanced effects due to simultaneous QCD and QED initial-state radiation, up to mixed next-to-next-to-leading logarithmic (NNLL) accuracy. We study the impact of such mixed QCD⊗QED resummed contributions on top of pure QCD corrections, finding percent-level effects.

Spain

Andrea Autieri

Switzerland

Stefano Camarda

Leandro Cieri

Italy

Giancarlo Ferrera

German Sborlini

Transverse-momentum resummation at mixed QCD⊗QED NNLL accuracy for $\textit{Z}$ boson production at hadron colliders

The Three-Higgs-Doublet Model (3HDM) extends the Standard Model by introducing two additional scalar doublets, leading to a rich spectrum of new particles: three neutral CP-even Higgs bosons $$(h_1,$$ $$H_2,$$ $$H_3),$$ two neutral CP-odd Higgs bosons $$(A_2,$$ $$A_3),$$ and two charged Higgs bosons $$(H_2^+,$$ $$H_3^+).$$ In this work, we present a phenomenological study of the 3HDM at the future International Linear Collider (ILC) with a center-of-mass energy of $$\sqrt{s} = 1000\,\text {GeV}.$$ Applying a comprehensive set of theoretical and experimental constraints, we identify promising new physics signals with sufficiently large production cross-sections. Our analysis shows that $$e^+e^- \rightarrow H_2 A_2,$$ $$e^+e^- \rightarrow H_2 H_2 Z,$$ $$A_2 A_2 Z,$$ $$H_2 H_2^{\pm } W^{\mp },$$ $$A_2 H_2^{\pm } W^{\mp }$$ and $$H_1 H_2 A_2$$ are among the most sensitive channels to probe this extended Higgs sector. We demonstrate that a future ILC would offer a powerful platform to test these interactions and discover these heavier Higgs bosons thus providing evidence of physics beyond the Standard Model.

India

Baradhwaj Coleppa

Akshat Khanna

Gokul Krishna

ILC phenomenology of the $$Z_3$$ symmetric type-Z three Higgs doublet model

We identify two distinct repulsive mechanisms in the Cho-Maison monopole-antimonopole pair (MAP) configuration. Our results show that the Higgs-mediated repulsion exhibits a nonmonotonic dependence on both topological charge and Higgs self-coupling, confirming its topological origin while revealing a mass-controlled range transition that deviates from the exponential form of a Yukawa potential. Simultaneously, the <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>Z</mi></math>-boson field generates localized repulsive cores of radius <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msub><mi>R</mi><mi>c</mi></msub><mo>≈</mo><mn>0.8</mn><msubsup><mi>m</mi><mi>W</mi><mrow><mo>−</mo><mn>1</mn></mrow></msubsup></math>, consistent with the weak interaction scale. The collaborative effect of these mechanisms—operating in different physics regimes—counteracts the magnetic attraction, establishing a stabilization paradigm for the Cho-Maison MAP that extends naturally to other topological solitons in the Standard Model.

China

Dan Zhu

Xurong Chen

Malaysia

Khai-Ming Wong

Topological stabilization via Higgs and Z-boson mediated repulsions in electroweak monopole-antimonopole pairs

The decay <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>A</mi><mo stretchy="false">→</mo><mi>Z</mi><mi>H</mi></math> is a characteristic signal of two-Higgs-doublet models (2HDMs), where <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>A</mi></math> and <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>H</mi></math> lie primarily within the same <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>S</mi><mi>U</mi><mo stretchy="false">(</mo><mn>2</mn><msub><mo stretchy="false">)</mo><mi>L</mi></msub></math> multiplet, leading to a coupling of order <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msub><mi>g</mi><mn>2</mn></msub></math> to the <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>Z</mi></math> boson. The subsequent decay <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>H</mi><mo stretchy="false">→</mo><mi>t</mi><msup><mi>t</mi><mrow><mo stretchy="false">(</mo><mo>*</mo><mo stretchy="false">)</mo></mrow></msup></math> is particularly promising, as it gives rise to distinct final states involving multiple leptons and <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>b</mi></math>-jets. The required splitting between <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msub><mi>m</mi><mi>A</mi></msub></math> and <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msub><mi>m</mi><mi>H</mi></msub></math> can naturally occur near the electroweak scale while being consistent with perturbative unitarity. Whereas dedicated ATLAS and CMS searches focused on the region with both top-quarks on-shell, we cover lower masses where one top quark is off-shell by recasting Standard Model <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>t</mi><mover accent="true"><mi>t</mi><mo stretchy="false">¯</mo></mover><mi>Z</mi></math> measurements of ATLAS and CMS. The obtained limits on <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>σ</mi><mo stretchy="false">(</mo><mi>A</mi><mo stretchy="false">→</mo><mi>Z</mi><mi>H</mi><mo stretchy="false">)</mo><mo>×</mo><mi>Br</mi><mo stretchy="false">(</mo><mi>H</mi><mo stretchy="false">→</mo><mi>t</mi><mover accent="true"><mi>t</mi><mo stretchy="false">¯</mo></mover><mo stretchy="false">)</mo></math> are between 0.12 pb and 0.62 pb. Interestingly, we observe these stringent limits despite a preference (up to <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mn>2.5</mn><mi>σ</mi></math>) for a nonzero new physics signal, most pronounced around for <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><msub><mrow><mi>m</mi></mrow><mrow><mi>A</mi></mrow></msub><mo>≈</mo><mn>450</mn><mi>–</mi><mn>460</mn><mtext> </mtext><mtext> </mtext><mi>GeV</mi></mrow></math> and <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msub><mi>m</mi><mi>H</mi></msub><mo>≈</mo><mn>290</mn><mtext> </mtext><mtext> </mtext><mi>GeV</mi></math>, with a best-fit value of <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>σ</mi><mo stretchy="false">(</mo><mi>A</mi><mo stretchy="false">→</mo><mi>Z</mi><mi>H</mi><mo stretchy="false">)</mo><mo>×</mo><mi>Br</mi><mo stretchy="false">(</mo><mi>H</mi><mo stretchy="false">→</mo><mi>t</mi><mover accent="true"><mi>t</mi><mo stretchy="false">¯</mo></mover><mo stretchy="false">)</mo><mo>≈</mo><mn>0.3</mn><mtext> </mtext><mtext> </mtext><mi>pb</mi></math>. This cross section can be accommodated within a top-philic 2HDM for a top-Yukawa coupling of the second Higgs doublet of <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mn>0.16</mn><mo>≲</mo><msub><mi>μ</mi><mi>t</mi></msub><mo>≲</mo><mn>0.33</mn></math>.

Germany

Saiyad Ashanujjaman

Guglielmo Coloretti

Andreas Crivellin

South Africa

Siddharth P. Maharathy

Bruce Mellado

Constraining <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>A</mi><mo stretchy="false">→</mo><mi>Z</mi><mi>H</mi></math> with <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>H</mi><mo stretchy="false">→</mo><mi>t</mi><mover accent="true"><mi>t</mi><mo stretchy="false">¯</mo></mover></math> in the low-mass region

We present the phenomenology of the charged Higgs boson $\textit{H}$ appearing in a fermionic dark matter model mediated by an additional scalar doublet. In order to couple the dark matter fermion to the scalar doublet, we introduce a U(1) gauge symmetry, which is spontaneously broken at electroweak symmetry breaking, resulting in a massive $\textit{Z′}$ gauge boson. Since $\textit{Z′}$ is generically light, the model is subject to strong constraints from electroweak precision observables. As a result, the charged Higgs boson mass allowed by current experimental bounds is typically light in this model, 110 GeV $\textit{<}$ $$ {m}_{H^{\pm }} $$ $\textit{<}$ 170 GeV. Such a light charged Higgs boson will be produced mainly through top-quark decays at the LHC. Additionally, depending on the mass of the additional neutral Higgs boson $\textit{h}$ and the dark gauge boson $\textit{Z′}$, the direct production channels $\textit{pp}$ → $\textit{H}$ $\textit{Z′}$ and $\textit{pp}$ → $\textit{H}$ $\textit{h}$ can become sizable. We investigate the corresponding signal processes at the LHC to assess the discovery potential for $\textit{H}$ . Current ATLAS and CMS searches for light charged Higgs bosons already impose further constraints on the model. We also discuss the implications of dark matter in relation to the charged Higgs boson phenomenology.

South Korea

Kyu Bae

Jinn-Ouk Gong

Dong-Won Jung

Kang Lee

Chaehyun Yu

Chan Park

Charged Higgs boson phenomenology in the dark $\textit{Z}$ mediated fermionic dark matter model

We improve the theoretical predictions for rare <italic>Z</italic>-boson decays, <math altimg='si1.svg'><mrow><mi>Z</mi><mo>&#8594;</mo><mi>V</mi><msup><mi>&#8467;</mi><mo>+</mo></msup><msup><mi>&#8467;</mi><mo>&#8722;</mo></msup></mrow></math> ( <math altimg='si9.svg'><mrow><mi>&#8467;</mi><mo linebreak='goodbreak'>=</mo><mi>e</mi></mrow></math> or <italic>&#956;</italic>), where <italic>V</italic> denotes a heavy vector quarkonium including <italic>J</italic>/&#936;, &#936;(2 <italic>S</italic>), and &#933;( <italic>nS</italic>) with <math altimg='si10.svg'><mrow><mi>n</mi><mo linebreak='goodbreak'>=</mo><mn>1</mn><mo>,</mo><mn>2</mn><mo>,</mo><mn>3</mn></mrow></math>. These processes are thought to be dominated by the electromagnetic fragmentation transition, i.e., <math altimg='si11.svg'><mrow><mi>Z</mi><mo>&#8594;</mo><msup><mi>&#947;</mi><mo>*</mo></msup><msup><mi>&#8467;</mi><mo>+</mo></msup><msup><mi>&#8467;</mi><mo>&#8722;</mo></msup></mrow></math> followed by <italic>&#947;</italic>*&#8239;&#8594;&#8239; <italic>V</italic>. The present study includes all of the relevant tree-level Feynman diagrams, which contribute to these decays in the standard model. Our analysis shows that, for the charmonium final states, the fragmentation transition almost saturates the whole contribution and the other diagrams can be neglected; while for the bottomonium final states, the inclusion of other diagrams can increase their branching fractions by 4%&#8239;&#8764;&#8239;9%. Further investigation of the differential distributions, especially the angular distributions, indicates that forward-backward asymmetries for final leptons in these processes would be zero in the standard model. Therefore, in future experimental facilities with large number of <italic>Z</italic>-boson events accumulated, studies of these rare <italic>Z</italic> decays may help both to test the standard model and to probe its interesting extensions.

Li Ang

Dao-Neng Gao

Improved analysis of rare <italic>Z</italic>-boson decays into a heavy vector quarkonium plus lepton pair

We show that a very clear signal of the presence of a strong magnetic field during the early stage of a high-energy heavy-ion collision is provided by the decay of the <math xmlns="http://www.w3.org/1998/Math/MathML"><msup><mi>Z</mi><mn>0</mn></msup></math> into dimuon pairs. We find that the process is highly anisotropic, producing pairs mainly out of plane, as signaled by a negative value of <math xmlns="http://www.w3.org/1998/Math/MathML"><msub><mi>v</mi><mn>2</mn></msub></math>, and leads to an antimuon transverse momentum distribution which peaks at a higher value of the transverse momentum compared to the peak of the muon transverse momentum distribution. We also show that the process does not produce a significant distortion of the <math xmlns="http://www.w3.org/1998/Math/MathML"><msup><mi>Z</mi><mn>0</mn></msup></math> spectral function. The signal can be identified by comparing the dimuon-invariant mass and the individual muon and antimuon spectra produced in semicentral heavy-ion collisions with the corresponding scaled spectra produced in <math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><mi>p</mi><mo>+</mo><mi>p</mi></mrow></math> collisions at the <math xmlns="http://www.w3.org/1998/Math/MathML"><msup><mi>Z</mi><mn>0</mn></msup></math> peak.

Mexico

Brazil

Alejandro Ayala

Chile

Ana Julia Mizher

Javier Rendón

Asymmetric muon-antimuon emission from <math xmlns="http://www.w3.org/1998/Math/MathML"><msup><mi>Z</mi><mn>0</mn></msup></math> decays: A potential magnetometer in relativistic heavy-ion collisions

We investigate the discovery prospects of a leptophilic gauge boson $ Z_\ell $ at future $ e^+e^- $ colliders, focusing on a comparative study of the Circular Electron–Positron Collider (CEPC) and the International Linear Collider (ILC). Such a state naturally arises from an additional $ U(1)'_\ell $ gauge symmetry, under which quarks remain neutral while all leptons carry a universal charge, motivated by neutrino oscillations and scenarios of physics beyond the Standard Model. As a clean benchmark, we study the process $ e^+e^- \to \mu^+\mu^- $ , including realistic effects of initial-state radiation and beamstrahlung. Our results indicate that the CEPC, with its very high luminosity at $ \sqrt{s}=240 $ GeV, can probe couplings down to $ g_\ell \approx 10^{-3} $ for $ Z_\ell $ masses up to about 220 GeV. The ILC extends the sensitivity to heavier states in the multi-hundred GeV range through its higher $ \sqrt{s} $ stages. These findings demonstrate the strong complementarity of circular and linear colliders in exploring purely leptophilic interactions.

S.O. Kara

Discovery prospects for a leptophilic gauge boson Z$_{ℓ}$ at CEPC and ILC

One-loop contributions for the decay process $ H^{\pm} \rightarrow W^{\pm}Z $ within the Two-Higgs-Doublet Model (THDM) are computed in the general $ {\cal{R}}_{\xi} $ gauge, and its phenomenological applications at future muon–TeV colliders are investigated. Analytic results are confirmed by several consistency tests, including those of $\textit{ξ}$-independence, renormalization-scale stability, and the ultraviolet finiteness of the one-loop amplitude. We first perform an updated parameter scan of the Type-X THDM in phenomenological studies. The production of charged Higgs boson pairs at future muon–TeV colliders is then investigated through two processes: $ \mu^+\mu^- \rightarrow H^+H^- \rightarrow W^{\pm}W^{\mp}Zh $ and $ \mu^+\mu^- \rightarrow \gamma\gamma \rightarrow H^+H^- \rightarrow W^{\pm}W^{\mp}Zh $ . Both signal events and their significance are evaluated considering the corresponding Standard Model backgrounds. We find that the signal significances can exceed $ 5\sigma $ at several benchmark points in the viable parameter space of the Type-X THDM.

Vietnam

Dzung Tri Tran

Quang Hoang-Minh Pham

Khoa Ngo-Thanh Ho

Khiem Hong Phan

One-loop expressions for ${H^\pm \rightarrow W^\pm Z} $ and their implications at muon-TeV colliders * This research is funded by Vietnam National Foundation for Science and Technology Development (NAFOSTED) (103.01-2023.16)

Rare decays of the Z boson provide a sensitive probe for physics beyond the standard model. This study investigates the <math altimg='si49.svg'><mrow><msup><mi>e</mi><mo>+</mo></msup><msup><mi>e</mi><mo>&#8722;</mo></msup><mo>&#8594;</mo><mi>Z</mi><mo>&#8594;</mo><mi>&#957;</mi><mover accent='true'><mi>&#957;</mi><mo>&#175;</mo></mover><mi>&#947;</mi></mrow></math> process within the context of the Tera-Z programmes at future colliders such as the FCC-ee and CEPC. The SM predicts a one-loop branching ratio of <math altimg='si50.svg'><mrow><mn>7.16</mn><mo linebreak='goodbreak'>&#215;</mo><msup><mn>10</mn><mrow><mo>&#8722;</mo><mn>10</mn></mrow></msup></mrow></math> for <math altimg='si6.svg'><mrow><mi>Z</mi><mo>&#8594;</mo><mi>&#957;</mi><mover accent='true'><mi>&#957;</mi><mo>&#175;</mo></mover><mi>&#947;</mi></mrow></math>, a value four times smaller than the current experimental limit from the LEP. To explore this window for new physics, we parameterize anomalous <math altimg='si1.svg'><mrow><mi>Z</mi><mi>&#957;</mi><mover accent='true'><mi>&#957;</mi><mo>&#175;</mo></mover><mi>&#947;</mi></mrow></math> interactions using an Effective Field Theory framework, considering both dimension-6 and dimension-8 operators. A detailed simulation is performed by generating signal and background events with MadGraph, modeling particle showers with Pythia, and simulating detector effects with Delphes. The analysis employs key kinematic variables-including the photon energy ( <italic>E<inf>&#947;</inf></italic>), missing transverse energy ( <math altimg='si51.svg'><mrow><mi>E</mi><msub><mi>&#824;</mi><mi>T</mi></msub></mrow></math>), and the missing transverse energy significance ( <math altimg='si18.svg'><msub><mi>S</mi><mrow><mi>E</mi><msub><mi>&#824;</mi><mi>T</mi></msub></mrow></msub></math>) to isolate the signal. The results yield upper limits on the anomalous couplings, from which we infer branching ratios for <math altimg='si6.svg'><mrow><mi>Z</mi><mo>&#8594;</mo><mi>&#957;</mi><mover accent='true'><mi>&#957;</mi><mo>&#175;</mo></mover><mi>&#947;</mi></mrow></math> on the order of <math altimg='si52.svg'><msup><mn>10</mn><mrow><mo>&#8722;</mo><mn>9</mn></mrow></msup></math>. This represents a significant improvement of several orders of magnitude over the LEP sensitivity. Consequently, this study demonstrates the unique potential of the Tera-Z runs not only to test the SM loop-level predictions with unprecedented precision but also to tightly constrain or reveal new anomalous interactions.

Türkiye

H. Denizli

A. Senol

M. Köksal

Search for new physics effects in <math altimg='si26.svg'><mrow><mi>&#957;</mi><mover accent='true'><mi>&#957;</mi><mo>&#175;</mo></mover><mi>&#947;</mi></mrow></math> production at a tera-Z factory