Recent observations from the DESI Collaboration indicate a preference for quintom dark energy, i.e., its equation of state evolves across the cosmological constant boundary $$w=-1$$ . It is well known that models with single perfect fluid or single scalar field minimally coupled to Einstein gravity develop perturbative instabilities around the crossing, thereby cannot realize the quintom scenario. In this paper, we propose a method to circumvent the instability problem of these models by considering the coupling of dark energy to the Nieh–Yan density within the framework of teleparallel gravity. We show that with this coupling the background evolution is not affected, but the dark energy perturbation is removed from the menu of dynamical degrees of freedom, thus avoiding the inherent difficulties in the old models. Furthermore, the Nieh–Yan coupling causes parity violation in gravitational waves, and this can be considered as a clear prediction of this mechanism.

China

Yuxuan Kang

Mingzhe Li

Changzhi Yi

Realization of quintom dark energy after DESI DR2 in Nieh–Yan modified teleparallel gravity

Hadronic electromagnetic form factors and radiative decay properties offer a crucial window into the nonperturbative dynamics of quantum chromodynamics (QCD). In this work, we employ the light-cone sum rules (LCSR) method to systematically investigate the M1 radiative decay of vector mesons. Our study covers processes including <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msup><mi>K</mi><mrow><mo>*</mo><mo>−</mo></mrow></msup><mo stretchy="false">→</mo><msup><mi>K</mi><mo>−</mo></msup><mi>γ</mi></math>, <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msup><mi>D</mi><mo>*</mo></msup><mo stretchy="false">→</mo><mi>D</mi><mi>γ</mi></math>, <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msup><mi>B</mi><mo>*</mo></msup><mo stretchy="false">→</mo><mi>B</mi><mi>γ</mi></math>, <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msubsup><mi>D</mi><mi>s</mi><mrow><mo>*</mo><mo>+</mo></mrow></msubsup><mo stretchy="false">→</mo><msubsup><mi>D</mi><mi>s</mi><mo>+</mo></msubsup><mi>γ</mi></math>, and <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msubsup><mi>B</mi><mi>s</mi><mo>*</mo></msubsup><mo stretchy="false">→</mo><msub><mi>B</mi><mi>s</mi></msub><mi>γ</mi></math>, and further extends to the excited charmonium state <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>ψ</mi><mo stretchy="false">(</mo><mn>2</mn><mi>S</mi><mo stretchy="false">)</mo></math>. Our calculations yield decay widths for <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msup><mi>K</mi><mo>*</mo></msup></math> and <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>ψ</mi><mo stretchy="false">(</mo><mn>2</mn><mi>S</mi><mo stretchy="false">)</mo></math> that are in excellent agreement with experimental data. For the charm and bottom meson decays, where precise measurements are lacking, we provide theoretical predictions and compare them with other theoretical approaches. Most notably, our analysis reveals a universal linear dependence of the decay width on a function A(x) in the logarithmic coordinate system, which originates from the two-body decay dynamics and the ratio of the initial and final state decay constants. This relationship holds for the ground state <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>V</mi><mo stretchy="false">→</mo><mi>P</mi><mi>γ</mi></math> processes here and suggests a broader applicability to radiative decays of ground-state vector mesons.

Zhi Jun Wang

Russia

Di Gao

Kai Kai Zhang

Yuan Yuan Ma

Yan Jun Sun

Radiative decays of vector mesons with light-cone sum rules

We perform a complete calculation of the next-to-next-to-leading order (NNLO) electroweak fermionic corrections to fermion-pair production processes, where “fermionic” refers to contributions with closed fermion loops. We do this via a semi-numerical technique that uses dispersion relations for the fermion sub-loop in two-loop box and vertex diagrams and dispersion relations and Feynman parameters for vertex diagrams with fermionic triangle sub-loops. UV and IR divergences are treated with suitable subtraction terms. We present numerical results for the cross-sections of $$ {e}^{+}{e}^{-}\to {\mu}^{+}{\mu}^{-}/u\overline{u}/d\overline{d} $$ and differential distributions at representative center-of-mass energies. The NNLO corrections are found to modify the NLO cross-section on the order of 1%.

United States

Ayres Freitas

E. Wallace

Fermionic electroweak two-loop corrections to Drell-Yan and related processes

We propose a novel method for extracting non-singlet (NS) fragmentation functions (FFs) of light charged hadrons from charge asymmetries measured in hadron fragmentation using data from both single-inclusive electron-positron annihilation and semi-inclusive deep-inelastic scattering processes. We determine the NS FFs for pions and kaons at next-to-next-to-leading order in Quantum Chromodynamics through a comprehensive uncertainty analysis. The extracted FFs reveal a scaling index of approximately 0.7 at large momentum fractions and low energy scales, a strangeness suppression factor of approximately 0.5, and universality in fragmentation of light mesons. Our findings establish a valuable benchmark for testing non-perturbative QCD models and Monte Carlo event generators, and serve as crucial inputs for future electron-ion colliders.

Jun Gao

Chong-Yang Liu

Bin Zhou

Determination of fragmentation functions from charge asymmetries in hadron production * The work of Jun Gao is supported by the National Natural Science Foundation of China (NSFC) (12275173), the Shanghai Municipal Education Commission (2024AIZD007) and open fund of Key Laboratory of Atomic and Subatomic Structure and Quantum Control (Ministry of Education)

The Fermilab E906/SeaQuest collaboration performed measurements of the Drell-Yan process using 120 GeV proton beams bombarding liquid hydrogen and liquid deuterium targets. A combined analysis of all collected data was performed to obtain the final results for the <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msub><mi>σ</mi><mrow><mi>p</mi><mi>d</mi></mrow></msub><mo>/</mo><mn>2</mn><msub><mi>σ</mi><mrow><mi>p</mi><mi>p</mi></mrow></msub></math> Drell-Yan cross section ratio covering the kinematic region of <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mn>0.13</mn><mo>&lt;</mo><mi>x</mi><mo>&lt;</mo><mn>0.45</mn></math>. The <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>x</mi></math> dependencies of <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><mover accent="true"><mrow><mi>d</mi></mrow><mrow><mo stretchy="false">¯</mo></mrow></mover><mrow><mo stretchy="false">(</mo><mi>x</mi><mo stretchy="false">)</mo></mrow><mo>/</mo><mover accent="true"><mrow><mi>u</mi></mrow><mrow><mo stretchy="false">¯</mo></mrow></mover><mrow><mo stretchy="false">(</mo><mi>x</mi><mo stretchy="false">)</mo></mrow></mrow></math> and <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mover accent="true"><mi>d</mi><mo stretchy="false">¯</mo></mover><mrow><mo stretchy="false">(</mo><mi>x</mi><mo stretchy="false">)</mo></mrow><mo>−</mo><mover accent="true"><mi>u</mi><mo stretchy="false">¯</mo></mover><mrow><mo stretchy="false">(</mo><mi>x</mi><mo stretchy="false">)</mo></mrow></math> are extracted from these cross section ratios. It is found that <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mover accent="true"><mi>d</mi><mo stretchy="false">¯</mo></mover><mrow><mo stretchy="false">(</mo><mi>x</mi><mo stretchy="false">)</mo></mrow></math> is greater than <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mover accent="true"><mi>u</mi><mo stretchy="false">¯</mo></mover><mrow><mo stretchy="false">(</mo><mi>x</mi><mo stretchy="false">)</mo></mrow></math> over the entire measured <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>x</mi></math> range, with improved statistical accuracy compared to previous measurements. The new results on <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mover accent="true"><mi>d</mi><mo stretchy="false">¯</mo></mover><mrow><mo stretchy="false">(</mo><mi>x</mi><mo stretchy="false">)</mo></mrow><mo>/</mo><mover accent="true"><mi>u</mi><mo stretchy="false">¯</mo></mover><mrow><mo stretchy="false">(</mo><mi>x</mi><mo stretchy="false">)</mo></mrow></math> and <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mover accent="true"><mi>d</mi><mo stretchy="false">¯</mo></mover><mrow><mo stretchy="false">(</mo><mi>x</mi><mo stretchy="false">)</mo></mrow><mo>−</mo><mover accent="true"><mi>u</mi><mo stretchy="false">¯</mo></mover><mrow><mo stretchy="false">(</mo><mi>x</mi><mo stretchy="false">)</mo></mrow></math> are compared to various parton distribution functions and theoretical calculations.

C.H. Leung

J. Dove

Taiwan

Japan

K. Nagai

K. Nakano

S. Prasad

A.S. Tadepalli

C.A. Aidala

J. Arrington

C. Ayuso

C.L. Barker

W.C. Chang

A. Chen

D.C. Christian

B.P. Dannowitz

L. El Fassi

D.F. Geesaman

R. Gilman

Y. Goto

R.S. Guo

L. Guo

T.J. Hague

R.J. Holt

M.F. Hossain

L.D. Isenhower

E.R. Kinney

A. Klein

D. Kleinjan

P.J. Lin

K. Liu

M.X. Liu

W. Lorenzon

R.E. McClellan

P.L. McGaughey

M.M. Medeiros

Y. Miyachi

S. Miyasaka

D.H. Morton

K. Nakahara

J.C. Peng

A.J.R. Puckett

A. Pun

B.J. Ramson

P.E. Reimer

J.G. Rubin

F. Sanftl

S. Sawada

T. Sawada

M.B.C. Scott

T.A. Shibata

D.S. Su

M. Teo

R. Towell

S. Uemura

S.G. Wang

J. Wu

N. Wuerfel

Z.H. Ye

Final SeaQuest Results on the Flavor Asymmetry of the Proton Light-Quark Sea with Proton-Induced Drell-Yan Process

We propose the “naive” <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>T</mi></math>-odd Collins-Soper moments in the Drell-Yan process as probes of previously unexplored directions in the Standard Model effective field theory (SMEFT) parameter space. We show that the moments <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msub><mi>A</mi><mn>6</mn></msub></math> and <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msub><mi>A</mi><mn>7</mn></msub></math> in the high invariant mass and transverse momentum region are sensitive to dimension-8 <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><mi>C</mi><mi>P</mi></mrow></math>-odd semileptonic four-fermion operators with an additional gluon field strength tensor. Using the projected integrated luminosity of a future high-luminosity LHC, we show that effective ultraviolet scales in the few-TeV range can be probed with this process.

Frank Petriello

Kaan Şimşek

Naive <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>T</mi></math>-odd Drell-Yan angular coefficients as a probe of the dimension-8 SMEFT

In this paper we present the first application of the MiNLO method to the calculation of QED NLO corrections to the production of a neutral vector boson in Drell–Yan processes. We consider only the case of initial-state radiation, when the $\textit{Z}$ boson decays into neutrinos. We illustrate the abelianization procedure of the MiNLO formulae and discuss the impact that it has on the differential cross section. We then propose a variant of the MiNLO formulae in order to circumvent some of the problems that arise when dealing with QED emissions. Since this is a case study, we use ad-hoc parton distribution functions and a larger value of the electromagnetic coupling constant, in order to emphasize potential discrepancies with respect to the expected behavior of the MiNLO formulae. We quantify the uncertainties connected with the proposed method, also for a physical value of the electromagnetic coupling. The study presented here is a necessary first step towards incorporating full electroweak effects into the $$\text {MiNNLO}_{\text {PS}}$$ framework.

Italy

Filippo Belloni

Mauro Chiesa

Carlo Oleari

Emanuele Re

Towards the inclusion of NLO EW corrections in the MiNLO method in Drell–Yan processes: the QED case

A striking prediction of QCD on the properties of the novel Transverse Momentum Dependent (TMD) distribution functions is that the time-reversal odd Sivers and Boer-Mulders functions extracted from semi-inclusive deep-inelastic scattering (SIDIS) will undergo a sign reversal in the Drell-Yan (DY) process. This prediction has been tested by experiments that have focused on the Sivers functions so far. We review the current status on the theoretical prediction and experimental extraction of the signs of the Boer-Mulders functions from SIDIS and DY. We note that the existing SIDIS and DY data are consistent with the predicted sign reversal of the Boer-Mulders functions for proton’s valence quark distribution. Prospects for future experiments at EIC capable of testing the sign reversal of the pion Boer-Mulders functions are also discussed.

Jen-Chieh Peng

Ming-Xiong Liu

Guanghua Xu

Sign reversal of Boer-Mulders functions from semi-inclusive deep-inelastic scattering to the Drell-Yan process

In this study, we investigate the possibility of enhancing the di-jet resonance searches by tagging the final state radiation (FSR) jet using an event-level deep neural network. It is found that solely relying on the 4-momenta of the leading three jets allows the algorithm to achieve good discriminating power that can identify the hardest FSR jet in the signal while rejecting other soft jets. Once the invariant mass is corrected with the tagged FSR jet, the mass resolution of the signal is greatly enhanced, and the sensitivity of the search is also improved by more than 10%. By crafting the input variables carefully, the algorithm introduces minimal mass sculpting for the background, and its applicability extends to a broad mass range. This work proves that FSR jet tagging can potentially enhance di-jet resonance searches, suiting various stages of the physics programmes at the Large Hadron Collider (LHC) and High-Luminosity LHC (HL-LHC).

Bingxuan Liu

Yuxuan Shen

Yuanshunzi Sui

Enhancing di-jet resonance searches via a final-state radiation jet tagging algorithm * Bingxuan Liu is supported by Shenzhen Campus of the Sun Yat-sen University under project 74140-12255011, and by the Young Scientists Fund (C Class) of the National Natural Science Foundation of China (12405122). Both Yuxuan Shen and Yuanshunzi Sui are supported by College Students’ Innovative Entrepreneurial Training Plan Program

We investigate the collider signatures of a maximally flavor-violating $ U(1)_{L_\mu-L_\tau} $ model, where a new gauge boson $ Z^\prime $ and scalar triplets induce lepton flavor-changing interactions in the $\textit{μ}$-$\textit{τ}$ sector. Focusing on four-lepton final states at multi-TeV lepton colliders, we conduct a detailed analysis of cross sections, asymmetries, and polarization effects. We show that the signal cross section is highly sensitive to $ m_{Z^\prime} $ and the effective parameters $ \tilde{g}/m_{Z^\prime} $ , whereas it remains largely insensitive to the triplet Yukawa couplings within the phenomenologically allowed region. The forward-backward asymmetry exhibits a characteristic monotonic dependence on $ m_{Z^\prime} $ , and beam polarization can significantly suppress the Standard Model backgrounds while enhancing new physics contributions. We find that, in the phenomenologically allowed parameter space, the predicted observables remain highly sensitive to the underlying model parameters. These results show that multi-lepton final states are powerful probes of the $ U(1)_{L\mu - L_\tau} $ framework and can offer valuable guidance for future searches at muon and electron-positron colliders.

Jianing Qin

Fei Huang

Honglei Li

Zhi-Long Han

Jin Sun

Collider probes of four-lepton final states in maximally flavor-violating ${U(1)_{L_\mu-L_\tau}} $ model * Supported by National Natural Science Foundation of China (12505112, 11805081), Shandong Province Natural Science Foundation (ZR2024QA138, ZR2022MA056) and State Key Laboratory of Dark Matter Physics, University of Jinan Disciplinary Cross-Convergence Construction Project 2024 (XKJC- 202404) and Jin Sun is supported by IBS under the project code, (IBS-R018-D1)