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Valery E. Lyubovitskij

Publications and source records attributed to Valery E. Lyubovitskij.

At least 19 recordsLinked to original sources
arXiv2026

Quantum states in an AdS-invariant theory

We note that the description of elementary particles in anti-de Sitter (AdS) quantum theory differs radically from standard approaches. Since the Cartan subalgebra of the AdS algebra has rank 2, it is necessary to consider only those elements that explicitly depend on the eigenvalues of operators in the irreducible representations (IRs) of the algebra. In the literature, AdS symmetry is widely invoked in various quantum applications, such as AdS/QCD. However, such frameworks typically do not take into account the unconventional properties of the AdS algebra IRs investigated in the present paper.

hep-th↗
arXiv2026

Charge-exchange reactions with pion and kaon beams in the NA64h experiment at CERN

We discuss a new approach to search for dark sector coupled to quarks in the invisible decays and oscillations of light neutral mesons produced in the charge-exchange (CEX) reactions with pion and kaon beams $π^-(K^-)+ (A, Z) \to π^0, η, η' (\bar K^0) + (A,Z-1)$ at nuclei target $(A,Z)$ in the NA64h experiment at CERN for $P_{\rm Lab}$ running in the interval from 5 to 50 GeV. For estimating of the projection sensitivity for the proposed searches the knowledge of the meson yield is crucial. This work is dedicated to the accurate evaluation of CEX cross sections for the wide range of energies and target nuclei which could be also useful for other experiments.

hep-ph↗
arXiv2026

Nonlocal Portal to the Dark Sector

We propose a nonlocal realization of the Stueckelberg portal between the Standard Model and Dark Sector, which decouple in the local limit. This implies that the mediator, $U(1)_{D}$ Dark Photon $A'$ with a Stueckelberg mass, interacts nonlocally with the Standard Model quarks and leptons. We study phenomenological implications of this scenario for the meson decays into semi-invisible and invisible channels. We discuss the experimental limitations on the model parameters, including the nonlocality scale.

hep-ph↗
arXiv2026

Constraints on dark axion portal: missing energy and fermion EDMs

We study a model in which a new interactions between the Standard Model (SM) photon and both the dark photon ($γ_D)$ and an ALP ($a$) are described by the dark axion portal operator. The implications of this dark axion portal scenario for electron fixed-target experiments are presented. In particular, we investigate the missing energy signatures associated with production of dark photons and their subsequent invisible decays into stable dark sector fermions, $γ_D \to χ\barχ$. We discuss the discovery potential for such a scenario and derive projected sensitivity curves for the NA64$e$ and LDMX experiments. Furthermore, novel constraints of the NA64$e$ for $9.37\times 10^{11}$ electrons on target are derived by considering two production mechanisms for invisible states: (i)~the bremsstrahlung-like emission of an $aγ_D$ pair, $e N \to e N γ^* (\to a γ_D)$, and (ii)~the exclusive vector meson photoproduction, $γ^* N \to N V$, followed by the invisible decays of vector mesons, $V \to a γ_D$. Additionally, the constraints on the parameter space of $CP$-violating, fermion-specific ALP and dark photon couplings are established. These constraints are derived from current experimental bounds on the electric dipole moments (EDMs) of SM fermions, incorporating loop-induced contributions to the EDMs of the electron, muon, and neutron.

hep-ph↗
arXiv2026

Electron-muon conversion in nuclei and rare decays induced by LFV dark photon

We study lepton-flavor violation (LFV) effects occurring in the $e-μ$ conversion in nuclei and in the rare radiative decays $η(η') \to γμe$ of the $η$ and $η'$ 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 $η(η') \to γμe$.

hep-ph↗
arXiv2026

Long Range Outlook for Short-Range Correlations

Short range correlated (SRC) N N pairs are pairs of nucleons with high relative momentum (prel > kF where kF ~ 250 MeV/c is the Fermi momentum in medium to heavy nuclei) and lower center of mass momentum. The motivation for studying SRC pairs ranges from a desire to achieve a more comprehensive understanding of the many-body nuclear wave-function at high-resolution to searching for explicit QCD-dynamics effects within the nuclear medium, not to mention connections to many other open problems in nuclear physics. Exploring short-range correlations was one of the physics motivations for building CEBAF (now Jefferson Lab). Scientists used the high luminosity and high energy of this cutting-edge machine to find kinematics that cleanly showed the signals of short-range correlations. This paved the way in the last two decades for tremendous progress understanding these correlations. This paper reviews recent progress and highlights outstanding questions and areas that need further study.

nucl-ex↗
arXiv2026

Probing millicharged particles with NA64$μ$ and LDMX

Millicharged particles emerge as compelling candidates in numerous theoretically well-motivated extensions of the Standard Model. These hypothetical particles, characterized by an electric charge that is a small fraction of the elementary charge, have attracted significant attention in contemporary experimental physics. Their potential existence motivates dedicated search strategies across multiple experimental platforms, leveraging their distinctive electromagnetic interactions while evading conventional detection methods. In the present paper we estimated the projected sensitivity of fixed-target experiments, specifically NA64$μ$ and LDMX, to the parameter space of millicharged particles. For the NA64$μ$ experiment, with an anticipated muon flux of $\mbox{MOT}\lesssim 10^{14}$, our analysis reveals a detectable mass window of $10~\mbox{MeV} \lesssim m_χ\lesssim 150~\mbox{MeV}$ and charge parameter range $10^{-4} \lesssim ε\lesssim 7\times 10^{-4}$. This sensitivity arises from the bremsstrahlung-like missing energy signature $μN \to μN γ^{*}( \to χ\barχ)$. Furthermore, we evaluate the discovery potential of the LDMX facility, considering its projected electron beam statistics, $\mbox{EOT}\lesssim 2\times 10^{16}$, and energy, $E_{\rm e}\simeq 8~\mbox{GeV}$. Our results demonstrate that LDMX can probe heavier MCPs in the mass range $250~\mbox{MeV} \lesssim m_χ\lesssim 400 ~\mbox{MeV}$, with sensitivities reaching $10^{-3} \lesssim ε\lesssim 1.5 \times 10^{-3}$. This parametric window can be accessible through the distinctive invisible decay channel $ρ\to χ\barχ$, where $ρ$-meson photo-production $γN \to N ρ$ plays a pivotal role.

hep-ph↗
arXiv2025

Searching for long-lived light neutralinos from $B$-meson decays with baryonic R-parity violation at Belle II

In a supersymmetry scenario with R-parity violation (RPV), neutralinos with GeV-scale mass, which are necessarily bino-like, are allowed by all constraints and can be produced in association with a baryon in $B$-meson decays via certain $\bar U \bar D \bar D$ operators. In this work, we investigate this scenario with two non-vanishing RPV couplings at the low-energy scale. With one RPV coupling governing the neutralino production rate and another determining its lifetime, this scenario can lead to observable signals with displaced-vertex signatures in the tracking volume of $B$-factories. To maximize the sensitivity to such signals, we develop a new partial-reconstruction technique that yields high efficiency and utilizes most of the decays of relatively heavy, long-lived particles, achieving much better sensitivity than standard full reconstruction. We consider potential background sources and devise selection criteria to suppress their event yields to very low levels. Using a parameterized model of the detector, we estimate in detail the displaced-vertex reconstruction efficiency as a function of neutralino lifetime and mass. For squark masses beyond the LHC limits, we calculate the signal sensitivity of Belle~II, showing that the experiment can probe the RPV couplings well beyond the present bounds, obtained from searches for dinucleon decays, baryon-antibaryon oscillations, and $B^+\to p +\text{missing}$.

hep-ph↗
arXiv2025

Probing leptophobic dark sector with a pseudoscalar portal in the NA64 experiment at CERN

We propose the possibility of discovering a light pseudoscalar particle $a$, axion-like particle (ALP), interacting mainly with quarks using the electron and photon scattering reaction chain $e + Z \rightarrow e + γ+ Z$; $γ+ Z \rightarrow a + Z$ on nuclei in the NA64 experiment at the CERN SPS. We consider the mixing of ALP with light pseudoscalar mesons $P = π, η, η'$ with taking into account of the ALP mass explicitly breaking the Peccei-Quinn symmetry. It could open invisible channels of ALP decaying into dark fermion matter by analogy with $P$ mesons decays. New bounds on the coupling strengths of the ALP with quarks and of pseudoscalar mesons with dark fermions are obtained by using existing upper bounds on invisible decay modes of $P$s including those recently derived by NA64. We also study a scenario when the $a$ plays the role of a messenger in the communication between our world and the dark sector. New upper limits on axion couplings with quarks and its mixing parameters with $π, η, η'$ mesons are established.

hep-ph↗
arXiv2025

Formation of true muonium in the Drell-Yan dimuon production

We suggest a new mechanism for the formation of true muonium ($T\!M$), the QED $(μ^+ μ^-)$ bound state, due to the Coulomb interaction of muons from $μ^+ μ^-$ pairs generated in the Drell-Yan reaction of protons off nuclei of a thin foil target. The $T\!M$ atoms produced in the $^3S_1$ long-lived triplet state ($oT\!M$) could escape from the foil to vacuum followed by their decay into $e^+e^-$ pairs. Observation of $e^+e^-$ events with a displaced vertex, and an invariant mass and decay time consistent with the mass and lifetime of the $oT\!M$ is used as a signature of the discovery of $T\!M$. We present estimates of the $T\!M$ yield and briefly discuss an experiment which could lead to such a discovery.

hep-ph↗
arXiv2024

Transverse momentum dependence of the $T$-even hadronic structure functions in the Drell-Yan process

We present detailed analysis of the $T$-even lepton angular distribution in the Drell-Yan process including $γ/Z^0$ gauge boson exchange and using perturbative QCD based on the collinear factorization scheme at leading order in the $α_s$ expansion. We focus on the study of the transverse momentum $Q_T$ dependence of the corresponding hadronic structure functions and angular coefficients up to next-next-to-leading order in the $Q_T^2/Q^2$ expansion. We analyze $Q_T$ dependence numerically and compare $T$-even angular coefficients integrated over rapidity with available data of the ATLAS Collaboration at LHC. Additionally, we present our results for the forward-backward asymmetry and compare it with data.

hep-ph↗
arXiv2024

Perturbative $T$-odd asymmetries in the Drell-Yan process revisited

We calculate the perturbative $T$-odd contributions to the lepton angular distribution in the Drell-Yan process. Using collinear factorization, we work at the first order in QCD perturbation theory where these contributions appear, ${\cal O}(α_s^2)$, and address both $W^\pm$ and $γ/Z^0$ boson exchange. A major focus of our calculation is on the regime where the boson's transverse momentum $Q_T$ is much smaller than its mass $Q$. We carefully expand our results up to next-to-next-to-leading power in $Q_T/Q$. Our calculation provides a benchmark for studies of $T$-odd contributions that employ transverse-momentum dependent parton distribution functions. In the neutral-current case we compare our results for the $T$-odd structure functions to available ATLAS data.

hep-ph↗
arXiv2023

Lepton flavor violating dark photon

We study possible impact of dark photons on lepton flavor phenomenology. We derive the constraints on non-diagonal dark photon couplings with leptons by analyzing corresponding contributions to lepton anomalous magnetic moments, rare lepton decays and the prospects of fixed-target experiments aiming for search for light dark matter based on missing energy/momentum techniques.

hep-ph↗
arXiv2023

Test of vector portal with dark fermions in the charge-exchange reactions in the NA64 experiment at CERN SPS

We consider an experiment to search for dark sector particles in dark photon kinetic mixing model by analyze invisible and semi-invisible decays of neutral mesons $M^0 = π^0$, $η$, $η'$, $ω$, $f_2(1270)$, produced in the NA64 experiment at the CERN SPS. The approach proposed in Ref.~\cite{Gninenko:2014sxa} is to use the charge-exchange reactions $π^- + (A, Z) \to M^0 + (A,Z-1); M^0 \to$ invisible or semi-invisible of high-energy pions (or kaons) at a nuclei target as a source of $M^0$s, which subsequently decay invisibly into dark sector. This reaction chain would lead to a striking signature of the signal event - the complete disappearance of the beam energy in the setup. Using data obtained from the study of charge-exchange reactions at IHEP (Protvino) and Fermilab (Batavia) we show that the integral cross sections $σ$ for production of the neutral mesons $M^0$ are slightly deviate from phenomenological formula $σ\sim Z^{2/3}$, where $Z$ is the nuclei charge. In particular, we present the formulas for the differential and integral sections that explicitly depend on the Mandelstam and $Z$ variables. Derived formulas are used to predict the cross sections as a function of beam energy for several target nuclei, and to estimate the projection sensitivity for the proposed search for the $M^0\to$ semi-invisible and $M^0\to$ invisible decays through the vector portal to dark sector. Sensitivity to different semi-invisible decay modes of neutral pseudoscalar mesons is studied.

hep-ph↗
arXiv2023

Study of the nonleptonic decay $Ξ^0_c \to Λ^+_c π^-$ in the covariant confined quark model

The nonleptonic decay $Ξ^0_c \to Λ^+_c π^-$ with $ΔC=0$ is systematically studied in the framework of the covariant confined quark model with accounting for both short and long distance effects. The short distance effects are induced by four topologies of external and internal weak $W^\pm$ exchange, while long distance effects are saturated by an inclusion of the so-called pole diagrams with an intermediate $\frac12^+$ and $\frac12^-$ baryon resonances. The contributions from $\frac12^+$~resonances are calculated straightforwardly by accounting for single charmed $Σ^0_c$ and $Ξ^{'\,+}_c$~baryons whereas the contributions from $\frac12^-$~resonances are calculated by using the well-known soft-pion theorem in the current-algebra approach. It allows to express the parity-violating S-wave amplitude in terms of parity-conserving matrix elements. It is found that the contribution of external and internal $W$-exchange diagrams is significantly suppressed by more than one order of magnitude in comparison with data. The pole diagrams play the major role to get consistency with experiment.

hep-ph↗
arXiv2023

Bulk-to-boundary propagators with arbitrary total angular momentum $J$ in soft-wall AdS/QCD

We derive the equations of motion for the bulk-to-boundary propagators of the anti-de Sitter (AdS) boson and fermion fields with arbitrary total angular momentum $J$, in a soft-wall AdS/QCD model and solve it analytically. It provides the opportunity to study transition form factors induced by these bulk-to-boundary propagators, both for on-shell and off-shell hadrons. This is a continuation of our study of hadron form factors induced by the bulk-to-boundary propagator with total angular momentum $J=1$ (e.g., electromagnetic form factors of mesons, nucleons, and nucleon resonances).

hep-ph↗
arXiv2023

Probing invisible vector meson decay mode with hadronic beam in the NA64 experiment at SPS/CERN

We test a novel idea of using a $π^-$ beam in the fixed-target experiments to search for New Physics in the events with missing energy. Bounds for invisible vector $ρ$ meson decay were derived, analyzed, and compared with the current limits on searching Dark Matter in the accelerator based experiments. We demonstrate that the new approach can be effective tool to probe sub-GeV Dark Matter parameter space.

hep-ph↗