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

An analytical and numerical systematic study of the neutrino mass matrix with one texture zero is presented in a basis where the charged leptons are diagonal. Under the assumption that neutrinos are Dirac particles, the analysis is conducted in detail for the normal and inverted hierarchy mass spectra. Our study is performed without any approximations, first analytically and then numerically, using current neutrino oscillation data. The analysis constrains the parameter space in such a way that, among the six possible one-texture-zero patterns, only four are favored in the normal hierarchy and one in the inverted hierarchy by current oscillation data at the $3 \sigma$ level. Phenomenological implications for the lepton CP-violating phase and neutrino masses are also explored.

Colombia

Richard H. Benavides

Yessica Lenis

John D. Gómez

William A. Ponce

One texture zero for Dirac neutrinos in a diagonal charged lepton basis * Richard H. Benavides acknowledges additional financial support from Minciencias (CD82315 CT ICETEX 2021-1080)

Heavy Majorana neutrinos ($\textit{N}$) are predicted in many models of physics beyond the Standard Model. In this work, we explore the production and detection prospects of TeV-scale heavy neutrinos ( $ m_N \gtrsim 1 $ TeV) at a future 3 TeV Compact Linear Collider (CLIC). We focus on two distinct decay topologies: (i) $ N \to \ell^\pm W^\mp $ with hadronic $\textit{W}$ boson decay, leading to a final state with one charged lepton and a hadronic fat jet $ J_W $ ; and (ii) $ N \to \nu h $ with subsequent Higgs decay $ h \to b\bar{b} $ , yielding a Higgs-tagged fat jet $ J_h $ and $\not {E}_T$ . Based on comprehensive detector-level simulations and background analysis, we present both $ 2\sigma $ exclusion limits and $ 5\sigma $ discovery reaches in the $ m_N $ – $ |V_{\ell N}|^2 $ plane. We further extract 95% confidence level upper limits on the mixing parameter $ |V_{\ell N}|^2 $ and perform a detailed comparison with existing constraints from direct searches at future colliders and indirect global fits. Our findings demonstrate that a 3 TeV CLIC can improve the sensitivity to $ |V_{\ell N}|^2 $ by about two orders of magnitude compared with the projected reaches of future hadron colliders while remaining competitive with other CLIC search channels.

China

Yao-Bei Liu

Jing-Wei Lian

Searches for heavy neutrinos at a 3 TeV CLIC in fat jet final states * Yao-Bei Liu is supported by the Natural Science Foundation of Henan Province, China (252300421988), Jing-Wei Lian is supported by the National Natural Science Foundation of China (12447140) and the Natural Science Foundation of Henan Province, China (252300421771)

We study a three-loop induced neutrino mass scenario from a non-holomorphic modular $\textit{A}$ $_{4}$ flavor symmetry and obtain the minimum scenario leading to predictions of the lepton masses, mixing angles, and Dirac and Majorana phases, which are shown through chi square analyses. In addition, we discuss the lepton flavor violations, muon anomalous magnetic moment, lepton universality, and relic density of the dark matter candidate. Moreover, we show that our model can be extended to satisfy the observed relic density of dark matter within the limit of perturbation by adding one singlet scalar boson without changing predictions in the neutrino sector.

Takaaki Nomura

Hiroshi Okada

Neutrino mass model at a three-loop level from a non-holomorphic modular $\textit{A}$ $_{4}$ symmetry * Takaaki Nomura is supported by the Fundamental Research Funds for the Central Universities. Hiroshi Okada is supported by Zhongyuan Talent (Talent Recruitment Series) Foreign Experts Project

This investigation develops two exact anisotropic solutions determined by the Chaplygin equation of state within the context of Einstein’s gravity theory using the minimal geometric deformation. In order to accomplish this, we start with the anisotropic fluid acting as the seed source inside a static spherical interior. The gravitational interaction between the additional matter source and the seed (parent) fluid is then included in a Lagrangian that describes a new source. We compute the field equations for the full matter configuration and then transform the radial component to produce two independent systems of equations. Each set is imposed by different constraints that allow them to solve separately and leading to novel solutions. By matching the interior and exterior geometries using the suitable junction conditions, the constants that appear in the interior solutions are determined. The observed mass and radius of the compact star candidates $$Vela~X-1$$ and $$Cen~X-3$$ are then used to graphically examine the resulting models. We show that our solutions fulfill all the physical feasibility requirements for the chosen parameter values, indicating the workability of the gravitational decoupling approach in the current scenario.

Pakistan

Azerbaijan

Tayyab Naseer

M. Sharif

Aleena Tehreem

Saudi Arabia

Hamdy Thabet

Abdel-Haleem Abdel-Aty

Theoretical models of radially deformed relativistic stellar structures within the context of a realistic equation of state

We study lepton-flavor-violation (LFV) effects occurring in the <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>e</mi><mo>−</mo><mi>μ</mi></math> conversion in nuclei and in the rare radiative decays <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>η</mi><mo stretchy="false">(</mo><msup><mi>η</mi><mo>′</mo></msup><mo stretchy="false">)</mo><mo stretchy="false">→</mo><mi>γ</mi><mi>μ</mi><mi>e</mi></math> of the <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>η</mi></math> and <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msup><mi>η</mi><mo>′</mo></msup></math> mesons with a special impact of the sub-GeV mass vector mediator (dark photon). In the case of the lepton conversion, we make estimates for running and future experiments operating with electron beams at fixed target. Obtained results are implemented in analysis of the LFV decays <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>η</mi><mo stretchy="false">(</mo><msup><mi>η</mi><mo>′</mo></msup><mo stretchy="false">)</mo><mo stretchy="false">→</mo><mi>γ</mi><mi>μ</mi><mi>e</mi></math>.

JINR

Russia

Alexey S. Zhevlakov

Chile

Sergey Kuleshov

Germany

Valery E. Lyubovitskij

Evgenie O. Oleynik

Electron-muon conversion in nuclei and rare decays induced by a lepton-flavor-violating dark photon

We investigate the fermion system excited by a free Dirac spinor field near the throat of a global monopole wormhole, characterized by the equation-of-state parameter $$\xi $$ of the exotic fluid supporting the wormhole and the symmetry-breaking scale $$\eta $$ of the monopole. From the perspective of the spacetime metric alone, there have no significant distinction for different values of $$\xi $$ and $$\eta $$ . However, when the spinor field is introduced as a probe and macroscopic physical quantities, such as fermion condensation, energy density, radial pressure, and angular stress, are calculated, we find that these quantities are able to uncover distinct physical behaviors corresponding to different combinations of $$\xi $$ and $$\eta $$ . Meanwhile, we find that the fermion condensation is closely related to the strong energy condition and undergoes a notable phase transition as $$\eta $$ increases. Furthermore, the free energy density is analyzed to investigate the stability of the fermion system under varying parameter combinations of $$\xi $$ and $$\eta $$ . Besides, both scenarios of normal fermions and exotic fermions are considered in this analysis, highlighting the contrasting physical properties between these two cases.

Spain

Ai-chen Li

Xin-Fei Li

Vacuum polarization of fermions near the throat of a global monopole wormhole

Using proton-proton collision data collected by the CMS experiment at <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><msqrt><mrow><mi>s</mi></mrow></msqrt><mo>=</mo><mn>13</mn><mtext> </mtext><mtext> </mtext><mi>TeV</mi></mrow></math> in 2016–2018, corresponding to an integrated luminosity of <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><mn>140</mn><mtext> </mtext><mtext> </mtext><msup><mrow><mi>fb</mi></mrow><mrow><mo>−</mo><mn>1</mn></mrow></msup></mrow></math>, the first full reconstruction of the three vector <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>B</mi></math> meson states, <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><msup><mrow><mi>B</mi></mrow><mrow><mo>*</mo><mo>+</mo></mrow></msup></mrow></math>, <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><msup><mrow><mi>B</mi></mrow><mrow><mo>*</mo><mn>0</mn></mrow></msup></mrow></math>, and <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><msubsup><mrow><mi>B</mi></mrow><mrow><mi>s</mi></mrow><mrow><mo>*</mo><mn>0</mn></mrow></msubsup></mrow></math>, is performed. The mass differences between the excited mesons and their corresponding ground states are measured to be <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><mrow><mi>m</mi><mo stretchy="false">(</mo><msup><mrow><mi>B</mi></mrow><mrow><mo>*</mo><mo>+</mo></mrow></msup><mo stretchy="false">)</mo></mrow><mo>−</mo><mrow><mi>m</mi><mo stretchy="false">(</mo><msup><mrow><mi>B</mi></mrow><mrow><mo>+</mo></mrow></msup><mo stretchy="false">)</mo></mrow><mo>=</mo><mn>45.277</mn><mo>±</mo><mn>0.039</mn><mo>±</mo><mn>0.027</mn><mtext> </mtext><mtext> </mtext><mi>MeV</mi></mrow></math>, <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><mrow><mi>m</mi><mo stretchy="false">(</mo><msup><mrow><mi>B</mi></mrow><mrow><mo>*</mo><mn>0</mn></mrow></msup><mo stretchy="false">)</mo></mrow><mo>−</mo><mrow><mi>m</mi><mo stretchy="false">(</mo><msup><mrow><mi>B</mi></mrow><mrow><mn>0</mn></mrow></msup><mo stretchy="false">)</mo></mrow><mo>=</mo><mn>45.471</mn><mo>±</mo><mn>0.056</mn><mo>±</mo><mn>0.028</mn><mtext> </mtext><mtext> </mtext><mi>MeV</mi></mrow></math>, and <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><mrow><mi>m</mi><mo stretchy="false">(</mo><msubsup><mrow><mi>B</mi></mrow><mrow><mi>s</mi></mrow><mrow><mo>*</mo><mn>0</mn></mrow></msubsup><mo stretchy="false">)</mo></mrow><mo>−</mo><mrow><mi>m</mi><mo stretchy="false">(</mo><msubsup><mrow><mi>B</mi></mrow><mrow><mi>s</mi></mrow><mrow><mn>0</mn></mrow></msubsup><mo stretchy="false">)</mo></mrow><mo>=</mo><mn>49.407</mn><mo>±</mo><mn>0.132</mn><mo>±</mo><mn>0.041</mn><mtext> </mtext><mtext> </mtext><mi>MeV</mi></mrow></math>, where the first uncertainties are statistical and the second are systematic. These results improve on the precision of previous measurements by an order of magnitude.

Armenia

A. Hayrapetyan

V. Makarenko

A. Tumasyan

Austria

W. Adam

J.W. Andrejkovic

L. Benato

T. Bergauer

M. Dragicevic

C. Giordano

P.S. Hussain

M. Jeitler

N. Krammer

A. Li

D. Liko

M. Matthewman

I. Mikulec

J. Schieck

R. Schöfbeck

D. Schwarz

M. Shooshtari

M. Sonawane

W. Waltenberger

C.E. Wulz

Belgium

T. Janssen

H. Kwon

D. Ocampo Henao

T. Van Laer

P. Van Mechelen

J. Bierkens

N. Breugelmans

J. D’Hondt

S. Dansana

A. De Moor

M. Delcourt

F. Heyen

Y. Hong

P. Kashko

S. Lowette

I. Makarenko

D. Müller

J. Song

S. Tavernier

M. Tytgat

G.P. Van Onsem

S. Van Putte

D. Vannerom

B. Bilin

B. Clerbaux

A.K. Das

I. De Bruyn

G. De Lentdecker

H. Evard

L. Favart

P. Gianneios

A. Khalilzadeh

F.A. Khan

A. Malara

M.A. Shahzad

L. Thomas

M. Vanden Bemden

C. Vander Velde

P. Vanlaer

F. Zhang

M. De Coen

D. Dobur

G. Gokbulut

J. Knolle

L. Lambrecht

D. Marckx

K. Skovpen

N. Van Den Bossche

J. van der Linden

J. Vandenbroeck

L. Wezenbeek

S. Bein

A. Benecke

A. Bethani

G. Bruno

A. Cappati

J. De Favereau De Jeneret

C. Delaere

A. Giammanco

A.O. Guzel

V. Lemaitre

J. Lidrych

P. Malek

P. Mastrapasqua

S. Turkcapar

Brazil

G.A. Alves

M. Barroso Ferreira Filho

E. Coelho

C. Hensel

T. Menezes De Oliveira

C. Mora Herrera

P. Rebello Teles

M. Soeiro

E.J. Tonelli Manganote

A. Vilela Pereira

W.L. Aldá Júnior

H. Brandao Malbouisson

First Exclusive Reconstruction of the <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><msup><mrow><mi>B</mi></mrow><mrow><mo>*</mo><mo>+</mo></mrow></msup></mrow></math>, <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><msup><mrow><mi>B</mi></mrow><mrow><mo>*</mo><mn>0</mn></mrow></msup></mrow></math>, and <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><msubsup><mrow><mi>B</mi></mrow><mrow><mi>s</mi></mrow><mrow><mo>*</mo><mn>0</mn></mrow></msubsup></mrow></math> Mesons and Precise Measurement of Their Masses

A fast-rolling axion can transfer its kinetic energy to gauge fields via the Chern-Simons coupling, leading to copious production of gauge quanta during inflation. The amplified gauge fields act as a source for both scalar and tensor perturbations. In this work, we propose a mechanism for suppressing scalar perturbations while sourcing strong tensor perturbations. We present an implementation of such a mechanism, demonstrating that sourced tensor perturbations are expected to be detected by upcoming next-generation cosmic microwave background experiments.

Kai-Ge Zhang

Jian-Feng He

Chengjie Fu

Zong-Kuan Guo

Suppression of scalar perturbations due to a heavy axion

The <math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><msup><mi>π</mi><mo>+</mo></msup><mi>p</mi></mrow></math> elastic scattering process is studied, using an effective Lagrangian approach that incorporates the <math xmlns="http://www.w3.org/1998/Math/MathML"><mi>s</mi></math>-, <math xmlns="http://www.w3.org/1998/Math/MathML"><mi>u</mi></math>-, and <math xmlns="http://www.w3.org/1998/Math/MathML"><mi>t</mi></math>-channel amplitudes, including <math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><msup><mi mathvariant="normal">Δ</mi><mrow><mo>+</mo><mo>+</mo></mrow></msup><mrow><mo>(</mo><mn>1232</mn><mo>)</mo></mrow></mrow><mo>,</mo><mo> </mo><mrow><msup><mi mathvariant="normal">Δ</mi><mn>0</mn></msup><mrow><mo>(</mo><mn>1232</mn><mo>)</mo></mrow></mrow></math>, neutron, and <math xmlns="http://www.w3.org/1998/Math/MathML"><msup><mi>ρ</mi><mn>0</mn></msup></math> contributions. By constructing the spin-density matrices from the scattering amplitudes, the von Neumann (entanglement) entropy is derived and associated with the spin degrees of freedom of the initial and final state particles. The entropy is computed by performing a partial trace over the spin subsystems, and its behavior is analyzed as a function of the center-of-mass energy <math xmlns="http://www.w3.org/1998/Math/MathML"><mi>W</mi></math> and scattering angle <math xmlns="http://www.w3.org/1998/Math/MathML"><mi>θ</mi></math>. It is found that entropy exhibits nontrivial angular and energy dependences, reflecting the interplay among resonance contributions and background amplitudes. In particular, the <math xmlns="http://www.w3.org/1998/Math/MathML"><msup><mi mathvariant="normal">Δ</mi><mrow><mo>+</mo><mo>+</mo></mrow></msup></math> region shows relatively low entanglement, suggesting spin coherence dominated by the specific resonant contribution, while the background contributions increase entropy due to mixed spin configurations. These results indicate that entanglement entropy can serve as a novel probe into the quantum structure of hadronic scattering amplitudes, providing complementary insights beyond conventional cross-section analyses.

South Korea

Seung-il Nam

Entanglement entropy for <math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><msup><mi>π</mi><mo>+</mo></msup><mi>p</mi></mrow></math> elastic scattering using a spin-density matrix