New articles on High Energy Physics - Phenomenology


[1] 2503.07713

$ν$ limits from Super-Kamiokande on dark matter-electron scattering in the Sun

Particle dark matter scattering on electrons in the Sun may gravitationally capture and self-annihilate inside it to neutrinos and anti-neutrinos, or other final states that in turn decay to them. Using up-to-date measurements by Super-Kamiokande of the fluxes of atmospheric electron-type and muon-type neutrinos, we set the most stringent limits on the electron scattering cross sections of dark matter down to about $10^{-40}-10^{-39}$ cm$^2$ over a mass range of 4$-$200 GeV. These outdo direct searches for dark matter-electron scattering and previously set limits at IceCube. We also derive corresponding reaches at Hyper-K, and show that atmospheric neutrino observations restricted to the direction of the Sun can improve sensitivities.


[2] 2503.07722

Direct Detection of Ultralight Dark Matter via Charged Lepton Flavor Violation

We propose a dark matter direct-detection strategy using charged particle decays at accelerator-based experiments. If ultralight $(m_\phi \ll \text{eV})$ dark matter has a misalignment abundance, its local field oscillates in time at a frequency set by its mass. If it also couples to flavor-changing neutral currents, rare exotic decays such as $\mu \to e \phi$ and $\tau\to e(\mu)\phi$ inherit this modulation. Focusing on such charged lepton flavor-violating decays, we show that sufficient event samples can enable detection of ultralight dark matter candidates at Mu3e, Belle-II, and FCC-ee.


[3] 2503.07724

Analytic results for electroweak precision observables at NLO in SMEFT

We present analytic results for electroweak precision observables (EWPO) at next-to-leading order (NLO) in dimension-six SMEFT, with no assumptions on the flavour structure of SMEFT Wilson coefficients. The results are given in five different electroweak input schemes, thus offering a simple means, along with scale variations, of estimating theory uncertainties related to higher-order terms in the SMEFT expansion. Our results will be useful to assess the constraining power of existing and future lepton colliders for new physics scenarios.


[4] 2503.07752

Neutrino masses and mixing: Entering the era of subpercent precision

We perform an updated global analysis of the known and unknown parameters of the standard $3\nu$ framework as of 2025. The known oscillation parameters include three mixing angles $(\theta_{12},\,\theta_{23},\,\theta_{13})$ and two squared mass gaps, chosen as $\delta m^2=m^2_2-m^2_1>0$ and $\Delta m^2=m^2_3-{\textstyle\frac{1}{2}}(m^2_1+m^2_2)$, where $\alpha=\mathrm{sign}(\Delta m^2)$ distinguishes normal ordering (NO, $\alpha=+1$) from inverted ordering (IO, $\alpha=-1$). With respect to our previous 2021 update, the combination of oscillation data leads to appreciably reduced uncertainties for $\theta_{23}$, $\theta_{13}$ and $|\Delta m^2|$. In particular, $|\Delta m^2|$ is the first $3\nu$ parameter to enter the domain of subpercent precision (0.8\% at $1\sigma$). We underline some issues about systematics, that might affect this error estimate. Concerning oscillation unknowns, we find a relatively weak preference for NO versus IO (at $2.2\sigma$), for CP violation versus conservation in NO (1.3$\sigma$) and for the first $\theta_{23}$ octant versus the second in NO ($1.1\sigma$). We discuss the status and qualitative prospects of the mass ordering hint in the plane $(\delta m^2,\,\Delta m^2_{ee})$, where $\Delta m^2_{ee}=|\Delta m^2|+{\textstyle\frac{1}{2}}\alpha(\cos^2\theta_{12}-\sin^2\theta_{12})\delta m^2$, to be measured by the JUNO experiment with subpercent precision. We also discuss upper bounds on nonoscillation observables. We report $m_\beta<0.50$~eV and $m_{\beta\beta}<0.086$~eV ($2\sigma$). Concerning the sum of neutrino masses $\Sigma$, we discuss representative combinations of data, with or without augmenting the $\Lambda$CDM model with extra parameters accounting for possible systematics or new physics. The resulting $2\sigma$ upper limits are roughly spread around the bound $\Sigma < 0.2$~eV within a factor of three. [Abridged]


[5] 2503.07776

Explaining the KM3-230213A Detection without Gamma-Ray Emission: Cosmic-Ray Dark Radiation

Recently, a high-energy neutrino event, designated KM3-230213A, was observed by the KM3NeT/ARCA detector in the Mediterranean Sea. This event is characterized by a reconstructed muon energy of approximately 120 PeV, corresponding to a median neutrino energy of roughly 220 PeV. To understand the origin, it is essential to investigate consistency with multi-messenger observations--particularly gamma-ray constraints--in various theoretical scenarios within and beyond the Standard Model. Motivated by this, we explore the possibility that the detected event does not originate from conventional neutrinos but rather from right-handed neutrinos (sterile neutrinos) mixing with active neutrinos, leading to the observed muon signal. Such cosmic-ray dark radiation may have originated either in the early Universe or through dark matter decay in the present epoch. We show that in both cases, while satisfying existing general constraints on light sterile neutrinos, the stringent multi-messenger gamma-ray limits can be significantly alleviated. A distinct prediction of this scenario is that such events can arrive from directions through Earth that would typically attenuate conventional neutrinos. A related scenario involving cosmic-ray boosted WIMP dark matter is also discussed.


[6] 2503.07866

A Brief History of Mass

It has been known since the 1950's that an unstable particle is associated with a complex pole in the propagator. This had to be rediscovered twice: in the early 1970's in the context of hadronic resonances, and in the early 1990's in the context of the $Z$ boson. The physical mass of the particle is the real part of the pole in the complex energy plane. In hadronic physics, this replaced the ``Breit-Wigner mass,'' which was found to depend on the parameterization of the ``energy-dependent width.'' In $Z$ physics, it replaced the ``on-shell'' mass, which was found to be gauge dependent. Although the mass defined from the complex pole position has been widely discussed in the literature, it has not yet made its way into quantum field theory textbooks.


[7] 2503.07867

The Pierre Auger Observatory and Physics Beyond the Standard Mode

The Pierre Auger Observatory, the world's largest cosmic ray detector, plays a pivotal role in exploring the frontiers of physics beyond the standard model of particle physics. By the observation of ultra-high energy cosmic rays, Auger provides critical insights into two major scenarios: super heavy dark matter and Lorentz invariance violation. Super heavy dark matter, hypothesized to originate in the early universe, offers a compelling explanation for the dark matter problem and is constrained by Auger through searches for photons and neutrinos resulting from its decay. Lorentz invariance violations, motivated by quantum gravity theories implying deviations from fundamental symmetries, are probed by Auger through alterations of the particle dispersion relation and the energy thresholds of their interactions with astrophysical photons backgrounds.


[8] 2503.07962

Discriminative versus Generative Approaches to Simulation-based Inference

Most of the fundamental, emergent, and phenomenological parameters of particle and nuclear physics are determined through parametric template fits. Simulations are used to populate histograms which are then matched to data. This approach is inherently lossy, since histograms are binned and low-dimensional. Deep learning has enabled unbinned and high-dimensional parameter estimation through neural likelihiood(-ratio) estimation. We compare two approaches for neural simulation-based inference (NSBI): one based on discriminative learning (classification) and one based on generative modeling. These two approaches are directly evaluated on the same datasets, with a similar level of hyperparameter optimization in both cases. In addition to a Gaussian dataset, we study NSBI using a Higgs boson dataset from the FAIR Universe Challenge. We find that both the direct likelihood and likelihood ratio estimation are able to effectively extract parameters with reasonable uncertainties. For the numerical examples and within the set of hyperparameters studied, we found that the likelihood ratio method is more accurate and/or precise. Both methods have a significant spread from the network training and would require ensembling or other mitigation strategies in practice.


[9] 2503.08210

Constraints on new vector boson mediated electron-nucleus interactions from spectroscopy of polar diatomic molecules

A measurement of parity violation in the hyperfine structure of $^{138}$Ba$^{19}$F [E. Altunta\c{s} et al. Phys. Rev. Lett. 120, 142501 (2018)] is reinterpreted with density functional theory calculations in terms of beyond Standard Model vector boson mediated electron-nucleus interactions. Our results set constraints on previously unexplored, new boson mediated axial vector-vector nucleus-electron interactions. Similar bounds are obtained by analyzing the atomic parity violation experiment with $^{133}$Cs. Moreover, we show that future experiments with cold heavy diatomic molecules like $^{225}$RaF will improve on the present sensitivity to axial vector-vector nucleon-nucleus interactions by at least four orders of magnitudes assuming current experimental resolution.


[10] 2503.08273

Neutrino Mass Matrix with broken Scaling in light of LMA and Dark-LMA Solutions

In the present work we have investigated some patterns of broken ``scaling" ansatz of the neutrino mass matrix. The scaling neutrino mass matrix is disallowed by the current neutrino oscillation data as, among others, it predicts vanishing reactor angle ($\theta_{13}=0$). We study its possible breaking scenarios in light of the large mixing angle (LMA) and Dark-LMA solutions suggested by current neutrino oscillation data. The normal hierarchical neutrino mass spectrum is ruled out in all three possible breaking patterns. Also, one of the interesting features of these breaking scenarios is the interplay between $\theta_{23}$-octant and possible CP violation. We find that the model allows maximal CP violation for $\theta_{23}$ above $6\%$ of its maximal value which, interestingly, is close to its current best-fit value for inverted hierarchical neutrino masses. We have, also, investigated the implications for effective Majorana neutrino mass parameter $|M_{ee}|$ for allowed breaking patterns. The correlation behavior of Majorana CP phases, which can be probed in $0\nu\beta\beta$ decay experiments, is found to have the capability of distinguishing LMA and Dark-LMA solutions.


[11] 2503.08313

Suppressed Drell-Yan process by an external magnetic field

The strongest electromagnetic fields in nature are created in high energy nuclear collisions and expected to change the dynamic scattering processes in the early stage. The magnetic field effect on the Drell-Yan process is investigated in this work. The single photon decay into quark pairs and lepton pairs in an external magnetic field leads to a significant Drell-Yan suppression in low and intermediate invariant mass region. The calculation up to the Landau level $n-1$ is complete in the energy region $s<2/3n(eB)$, and the enlarged phase space at higher landau levels may enhance the dilepton spectrum in the high mass region.


[12] 2503.08428

Relativistic spin hydrodynamics from novel relaxation time approximation

With the help of a semi-classical kinetic theory, a new collision kernel is proposed, which simultaneously conserves the energy-momentum tensor and the spin tensor of a relativistic fluid of spin-1/2 particles irrespective of the frame and matching conditions, even when relaxation time is momentum dependent. The relativistic Boltzmann's equation is solved using this new collision kernel to obtain the expressions of the transport coefficients with general definitions for the frame and matching conditions. The results indicate the expected existence of Barnett-like effect and the non-existence of Einstein--de-Haas-like effects.


[13] 2503.08433

Superkick Effect in Vortex Particle Scattering

Vortex states of photons or electrons are a novel and promising experimental tool across atomic, nuclear, and particle physics. Various experimental schemes to generate high-energy vortex particles have been proposed. However, diagnosing the characteristics of vortex states at high energies remains a significant challenge, as traditional low-energy detection schemes become impractical for high-energy vortex particles due to their extremely short de Broglie wavelength. We recently proposed a novel experimental detection scheme based on a mechanism called "superkick" that is free from many drawbacks of the traditional methods and can reveal the vortex phase characteristics. In this paper, we present a complete theoretical framework for calculating the superkick effect in elastic electron scattering and systematically investigate the impact of various factors on its visibility. In particular, we argue that the vortex phase can be identified either by detecting the two scattered electrons in coincidence or by analyzing the characteristic azimuthal asymmetry in individual final particles.


[14] 2503.08439

Testing the dark origin of neutrino masses with oscillation experiments

The origin of neutrino masses remains unknown to date. One popular idea involves interactions between neutrinos and ultralight dark matter, described as fields or particles with masses $m_\phi \ll 10\,\mathrm{eV}$. Due to the large phase-space number density, this type of dark matter exists in coherent states and can be effectively described by an oscillating classical field. As a result, neutrino mass-squared differences undergo field-induced interference in spacetime, potentially generating detectable effects in oscillation experiments. We demonstrate that if $m_\phi\gg 10^{-14}\,\mathrm{eV}$, the mechanism becomes sensitive to dark matter density fluctuations, which suppresses the oscillatory behavior of flavor-changing probabilities as a function of neutrino propagation distance in a model-independent way, thereby ruling out this regime. Furthermore, by analyzing data from the Kamioka Liquid Scintillator Antineutrino Detector (KamLAND), a benchmark long-baseline reactor experiment, we show that the hypothesis of a dark origin for the neutrino masses is disfavored for $m_\phi \ll 10^{-14}\,\mathrm{eV}$, compared to the case of constant mass values in vacuum. This result holds at more than the 4$\sigma$ level across different datasets and parameter choices. The mass range $10^{-17}\,\mathrm{eV} \lesssim m_\phi \lesssim 10^{-14}\,\mathrm{eV}$ can be further tested in current and future oscillation experiments by searching for time variations (rather than periodicity) in oscillation parameters.


[15] 2503.08440

Strong decays of $P_ψ^N(4440)^+$ and $P_ψ^N(4457)^+$ within the Bethe-Salpeter framework

By combining the effective Lagrangian and Bethe-Salpeter framework, we studied the mass spectra, wave functions, and strong decay widths of the two pentaquark states $P_\psi^N(4440)^+$ and $P_\psi^N(4457)^+$ reported by LHCb in 2019. We calculate the one-boson-exchange interaction kernel of $\bar D^*\Sigma_c$ in the isospin-$\frac12$ configuration. Then we present the Bethe-Salpeter equation(BSE) and wave functions for the bound states of a vector meson and a $\frac12$ baryon with $J^P={\frac12}^-$ and ${\frac32}^-$. By solving the BSE we obtain 2 bound states for both ${\frac12}^-$ and ${\frac32}^-$ spin-parity configuration, and the mass results favor the $(\frac32)^-$ and $(\frac12)^-$ configuration for the $P_\psi^N(4440)$ and $P_\psi^N(4457)$. Combining the effective Lagrangians and the obtained BS wave functions, we further calculate the strong decay channels $\bar D^{(*)0}\Lambda_c^+$, $J/\psi(\eta_c) p$, and $\bar D\Sigma_c^{(*)}$ for the two $P_\psi^N$ states. In the favored $\frac32^-$ and $\frac12^-$ configuration, the obtained total widths are 34.8 MeV and $2.2$ MeV for $P_\psi^N(4440)$ and $P_\psi^N(4457)$, respectively, which are substantially consistent with the LHCb data. The obtained decay widths suggest that $\bar D^{*0}\Lambda_c^+$ and $\bar D\Sigma_c$ are the dominant decay channels to detect $P_\psi^N(4440)$ and $P_\psi^N(4457)$. Taking into account both the mass spectra and decay widths, our results favor the interpretation of $P_\psi^N(4440)$ and $P_\psi^N(4457)$ as the isospin-$\frac12$ $[\bar D^*\Sigma_c]$ molecular states with $J^P$ configuration $(\frac{3}{2})^-$ and $(\frac12)^-$ respectively.


[16] 2503.08447

Investigating the broadening phenomenon in two-particle correlations induced by gluon saturation

It has been found that the gluon density inside the proton grows rapidly at small momentum fractions. Quantum Chromodynamics (QCD) predicts that this growth can be regulated by nonlinear effects, ultimately leading to gluon saturation. Within the color glass condensate framework, nonlinear QCD effects are predicted to suppress and broaden back-to-back angular correlations in collisions involving heavy nuclei. While suppression has been observed in various experiments in $d/p$$+$A collisions compared to $p$$+$$p$ collisions, the predicted broadening remains unobserved. This study investigates the contributions of intrinsic transverse momentum ($k_T$), which is associated with saturation physics, as well as parton showers and transverse motion from fragmentation ($p_T^{\mathrm{frag}}$), which are not saturation dependent, to the width of the correlation function. Our findings show that the non-saturation dependent effects, especially the initial-state parton shower and $p_T^{\mathrm{frag}}$, which occur independently of the collision system, smear the back-to-back correlation more than gluon saturation does, making the broadening phenomenon difficult to observe.


[17] 2503.08624

Light-by-Light scattering in ultraperipheral heavy ion collisions: Estimating inelastic contributions

The current state-of-the-art theoretical estimations lead to cross-sections for $AA \to \gamma \gamma AA$ which are somewhat smaller than the measured ones by the ATLAS and CMS Collaborations, which motivates the searching and calculation of subleading corrections disregarded in these previous studies. In this paper, we estimate the contribution of inelastic channels to the Light - by - Light (LbL) scattering in ultraperipheral collisions of heavy ions (UPHICs), in which one or both of the incident nuclei dissociate ($A A \to \gamma \gamma X Y$ where $X, Y = A, A'$) due to the photon emission. These new mechanisms are related to extra emissions that are rather difficult to identify at the LHC and can be mistakenly interpreted as enhanced $\gamma \gamma \to \gamma \gamma$ scattering compared to the Standard Model result. We include processes of coupling of photons to individual nucleons (protons and neutrons) in addition to coherent coupling to the whole nuclei (called standard approach here). Both elastic (nucleon in the ground state) and inelastic (nucleon in an excited state) in the couplings of photons to nucleons are taken into account. The inelastic nucleon fluxes are calculated using CT18qed photon in nucleon PDFs. The inelastic photon fluxes are shown and compared to standard photon fluxes in the nucleus. In addition, we show the ratio of the inelastic corrections to the standard contribution as a function of diphoton invariant mass and photon rapidity difference. We find the maximal effect of the inelastic corrections at $M_{\gamma \gamma} \sim$ 14 GeV for the ATLAS rapidity and transverse momentum acceptance. Furthermore, the inelastic contribution increases gradually with photon rapidity difference. Our results indicate that the inelastic contributions can increase locally by 10-15 \% the traditional (no nuclear excitation) predictions for the LbL scattering in UPCs.


[18] 2503.08651

Hydrogenlike molecules composed of $D_1D_1$, $D_1D^*_2$ and $D^*_2D^*_2$

We systematically explore the S-wave $D_1D_1$, $D_1D^*_2$ and $D^*_2D^*_2$ states with various isospin-spin-orbit ($ISL$) configurations in the quark model. We propose nine stable dimeson states with the $ISL$ configurations, $ISL=001$, $010$, $012$, $100$, $102$, $110$, $112$, $120$, and $122$, against dissociation into their constituent mesons. Those bound states are hydrogenlike molecular states, where the two subclusters are moderately overlapped and the QCD covalent bond is formed due to the delocalization of light quarks. The QCD covalent bond serves as the primary binding mechanism in the bound states with $I=1$. However, the exchange of $\pi$ and $\sigma$-meson plays a pivotal role in the bound states with $I=0$. The coupled-channel effect is essential in the formation of the bound states with $ISL=001$, $010$, $012$, $100$, and $102$.


[19] 2503.08659

On new physics off the Z peak in $H \rightarrow \ell^+\ell^- γ$

Motivated by a small but intriguing excess observed in the decay mode $ H\rightarrow \ell^+\ell^- \gamma$ reported by both the ATLAS and CMS collaborations, we explore the possibility that new physics contributes directly to the effective $ H \ell \overline{\ell} \gamma $ coupling rather than modifying the $ Z $ peak. Concretely, we consider a dimension-8 operator that could arise from new particles via box diagrams. Such non-resonant contribution may provide an alternative origin for current or future excesses. We examine how experimental cuts may distinguish between possible modifications of the $ Z $ peak and non-resonant contributions. The currently measured excess requires that the new physics scale is relatively low $( \Lambda_R \sim v $). However, we show that it may remain within current experimental bounds. In particular, we illustrate this using a simplified model, motivated by the dark matter problem, and discuss its other experimental constraints.


[20] 2503.07668

Heavy-flavored meson spectrum under the action of external magnetic field

In this paper, the Schr{\"o}dinger equation in a magnetic field is utilized to study the effect of the magnetic field on $B$ mesons. The mass spetrum of $B$ mesons are numerically calculated for different magnetic field strengths by solving the Schr{\"o}dinger equation under the non-relativistic Cornell potential model, incorporating the Zeeman effect and the harmonic oscillator basis vector expansion method. The external magnetic field is assumed to be sufficiently strong in the calculations, so that the spin-orbit interaction energies can be omitted in comparison with the energies induced by the field. The Zeeman term in the Schr{\"o}dinger equation is taken to be $ \frac{eB_s}{2m_ec}(m\pm1)$ where $m=0, \pm1$. The results demonstrate Zeeman splitting of energy levels in the external magnetic field.


[21] 2503.07718

Deciphering the Sources of Cosmic Neutrinos

More than a decade ago, the IceCube Neutrino Observatory discovered a diffuse flux of 10 TeV - 10 PeV neutrinos from our Universe. This flux of unknown origin most likely emanates from an extragalactic population of neutrino sources, which are individually too faint to appear as bright emitters. We review constraints on extragalactic neutrino source populations based on the non-detection of the brightest neutrino source. Extending previous work, we discuss limitations of source populations based on general neutrino luminosity functions. Our method provides more conservative but also statistically more robust predictions for the expected number of observable sources. We also show that the combined search of the brightest neutrino sources via weighted stacking searches or the analysis of non-Poissonian fluctuations in event-count histograms can improve the discovery potential by a factor of 2-3 relative to the brightest source.


[22] 2503.07732

Photoproduction, Paramagnetic Anisotropic Plasma, IR Log-Gravitational-DBI Renormalization and $G_2$-Structure Induced (Almost) Contact 3-Structures in Hot Strongly Magnetic MQCD at Intermediate Coupling

After obtaining the flavor $D6$-brane gauge fields/their fluctuations in the type IIA dual of T>T_c QCD-like theories at intermediate coupling (via the ${\cal M}$-theory uplift's ${\cal O}(R^4)$ corrections) in the absence/presence of a strong magnetic field, we compute the photoproduction spectral function and get a nice agreement with gauged supergravity backgrounds arXiv:2204.00024 [hep-th]. We demonstrate from the EoS that the holographic dual, in principle, could correspond to several $T>T_c$ scenarios: stable wormhole, stable wormhole transitioning via a smooth crossover to dark energy as the universe cools, and a paramagnetic pressure/energy-anisotropic plasma. Given that $T>T_c$ QGP is expected to be paramagnetic, see Bali et al '14, the third possibility appears to be the preferred one. We also show that it is not possible that the anisotropic plasma leads to the formation of a compact star. IR renormalization of the DBI action requires a boundary Log-det-Ricci-tensor counter term. {\it Noting (i) photoproduction spectral function, speed of sound, etc. determined from gauge field fluctuations receiving ${\cal O}(R^4)$-corrections, if complexified, include a non-analytic-complexified gauge-coupling dependence, and correspond to Contact 3-Structures; (ii) pressure/energy density, etc. determined from world-volume gauge fields and not ${\cal O}(R^4)$-corrected, if complexified, are analytic in the complexified gauge coupling, and correspond to Almost Contact 3-Structures (AC3S) both induced from the $G_2$ structure of a closed seven-fold, we conjecture (i) the lack of $N$-path connectedness in the parameter space associated with AC3S and C3S arXiv:2211.13186[hep-th] to be equivalent to that gauge field fluctuations can not be finite, and (zero-instanton sector) ${\cal O}(R^4)$ non-renormalized gauge fields produce ${\cal O}(R^4)$-corrected gauge fluctuation; (ii) C3S--UV--> AC3S.


[23] 2503.07788

Effects of the Cosmic Neutrino Background Capture on Astrophysical Objects

Low-energy neutrinos from the cosmic background are captured by objects in the sky that contain material susceptible of single beta decay. Neutrons, which compose most of a neutron star, capture low-energy neutrinos from the cosmic neutrino background and release a high-energy electron in the MeV range. Also, planets contain unstable isotopes that capture the cosmic neutrinos. We show that this process is feasible and results in a non-negligible flux of electrons in the MeV range in neutron stars. We present a novel observable, the redshift evolution of the temperature of neutron stars due to neutrino capture, that could provide a route for detection of the cosmic neutrino background from future gravitational waves observatories. For planets the flux is significantly smaller and a measurement is not possible with currently envisioned technology. While the signature from neutron stars is small and challenging, it could result in a novel way to detect the cosmic neutrino background.


[24] 2503.07803

Feynman integrals at large loop order and the $\log$-$Γ$ distribution

We find empirically that the value of Feynman integrals follows a $\log$-$\Gamma$ distribution at large loop order. Our study of the primitive contribution to the scalar $\phi^4$ beta function in four dimensions up to 18 loops provides accompanying evidence. Guided by instanton considerations, we extrapolate the value of this contribution to all loop orders.


[25] 2503.07947

Oscillations of the black hole photon ring as a probe of ultralight dilaton fields

Recent advancements of very long baseline interferometry (VLBI) have facilitated unprecedented probing of superradiant phenomena in the vicinities of supermassive black holes (SMBHs), establishing an ideal laboratory to detect ultralight bosons beyond the Standard Model. In this study, we delve into how ultralight dilaton clouds, formed via SMBH superradiance, impact the black hole photon rings. Our focus is on the dilaton-electromagnetic coupling term of the form $f(\phi)F_{\mu\nu}F^{\mu\nu}$. By integrating geometric optics with plasma refractive effects in accretion environments, we demonstrate that the dilaton cloud dynamically alters the plasma frequency. Through systematic ray-tracing simulations covering a range of plasma densities and dilaton coupling strengths, we reveal a periodic distortion in the photon ring morphology, with the periodicity aligning with that of the dilaton-driven plasma frequency oscillations. We then assess the magnitude of this effect under the current angular resolution constraints of VLBI observations. Our analysis indicates that a comprehensive search for superradiant dilaton clouds based on the dilaton-electromagnetic coupling would necessitate radio interferometric baselines significantly exceeding the Earth's diameter to resolve the corresponding signatures.


[26] 2503.08391

On the Interference between Meson Exchange and One-Body Currents in Quasielastic Electron Scattering

In this work, we present a detailed analysis of the interference between meson exchange currents (MEC) and one-body currents in quasielastic electron scattering, with a focus on the sign of this interference in the transverse response for one-particle emission. We prove that the interference of both the Delta and pion-in-flight currents with the one-body current is negative, leading to a partial cancellation with the seagull current. This is mathematically demonstrated within the framework of the Fermi gas model. By comparing these interferences across various independent particle models, both relativistic and non-relativistic, our results indicate that all studied models display the same behavior. This consistency suggests that the interference is negative in models that do not incorporate tensor correlations in the nuclear wave function.


[27] 2503.08567

Density matrices in quantum field theory: Non-Markovianity, path integrals and master equations

Density matrices are powerful mathematical tools for the description of closed and open quantum systems. Recently, methods for the direct computation of density matrix elements in scalar quantum field theory were developed based on thermo field dynamics (TFD) and the Schwinger-Keldysh formalism. In this article, we provide a more detailed discussion of these methods and derive expressions for density matrix elements of closed and open systems. At first, we look at closed systems by discussing general solutions to the Schr\"odinger-like form of the quantum Liouville equations in TFD, showing that the dynamical map is indeed divisible, deriving a path integral-based expression for the density matrix elements in Fock space, and explaining why perturbation theory enables us to use the last even in situations where all initial states in Fock space are occupied. Subsequently, we discuss open systems in the same manner after tracing out environmental degrees of freedom from the solutions for closed systems. We find that, even in a general basis, the dynamical map is not divisible, which renders the dynamics of open systems non-Markovian. Finally, we show how the resulting expressions for open systems can be used to obtain quantum master equations, and comment on the artificiality of time integrals over density matrices that usually appear in many other master equations in the literature but are absent in ours.


[28] 2503.08671

Cosmic topology. Part IIIb. Eigenmodes and correlation matrices of spin-2 perturbations in orientable Euclidean manifolds

We study the eigenmodes of the spin-2 Laplacian in orientable Euclidean manifolds and their implications for the tensor-induced part of the cosmic microwave background (CMB) temperature and polarization anisotropies. We provide analytic expressions for the correlation matrices of Fourier-mode amplitudes and of spherical harmonic coefficients. We demonstrate that non-trivial spatial topology alters the statistical properties of CMB tensor anisotropies, inducing correlations between harmonic coefficients of differing $\ell$ and $m$ and across every possible pair of temperature and $E$- and $B$-modes of polarization. This includes normally forbidden $TB$ and $EB$ correlations. We compute the Kullback-Leibler (KL) divergence between the pure tensor-induced CMB fluctuations in the usual infinite covering space and those in each of the non-trivial manifolds under consideration, varying both the size of the manifolds and the location of the observer. We find that the amount of information about the topology of the Universe contained in tensor-induced anisotropies does not saturate as fast as its scalar counterpart; indeed, the KL divergence continues to grow with the inclusion of higher multipoles up to the largest $\ell$ we have computed. Our results suggest that CMB polarization measurements from upcoming experiments can provide new avenues for detecting signatures of cosmic topology, motivating a full analysis where scalar and tensor perturbations are combined and noise is included.