We analyze how nonrelativistic effective models for the magnetic coupling of a spin to the electromagnetic field (proportional to $\widehat{\mathit{\sigma }}·\mathit{B}$) emerge from a full quantum field theoretical description of charged fermionic fields with the quantum electromagnetic field. This allows us to keep track of relativistic corrections to the models commonly used in experimental spin physics. We discuss how this interaction compares to the usual simplified models used in relativistic quantum information.

Pulsar timing array experiments have reported evidence for a stochastic background of nanohertz gravitational waves consistent with the signal expected from a population of supermassive black hole binaries. Their analyses assume power-law spectra for intrinsic pulsar noise and for the background, as well as a Hellings-Downs cross-correlation pattern among the gravitational-wave-induced residuals across pulsars. These assumptions may not be realized in actuality. We test them in the NANOGrav 15 yr dataset using Bayesian posterior predictive checks. After fitting our fiducial model to real data, we generate a population of simulated dataset replications. We use the replications to assess whether the optimal statistic significance, interpulsar correlations, and spectral coefficients are extreme. We recover Hellings-Downs correlations in simulated datasets at significance levels consistent with the correlations measured in the NANOGrav 15 yr dataset. A similar test on spectral coefficients shows that their values in real data are not extreme compared to their distributions across replications. We also evaluate the evidence for the stochastic background using posterior predictive versions of the frequentist optimal statistic and of Bayesian model comparison and find comparable significance ($3.2\sigma$ and $3\sigma$ respectively) to what was previously reported for the standard statistics. We conclude with novel visualizations of the reconstructed gravitational waveforms that enter the residuals for each pulsar. Our analysis strengthens confidence in the identification and characterization of the gravitational-wave background.

With the advent of advanced machine learning techniques, boosted object tagging has witnessed significant progress. In this article, we take this field further by introducing novel architectural modifications compatible with a wide array of GNN architectures. Our approach advocates for integrating capsule layers, replacing the conventional decoding blocks in standard GNNs. These capsules are a group of neurons with vector activations. The orientation of these vectors represents important properties of the objects under study, with their magnitude characterizing whether the object under study belongs to the class represented by the capsule. Moreover, capsule networks incorporate a regularization by reconstruction mechanism, facilitating the seamless integration of expert-designed high-level features into the analysis. We have studied the usefulness of our architecture with the LorentzNet architecture for quark-gluon tagging. Here, we have replaced the decoding block of LorentzNet with a capsulated decoding block and have called the resulting architecture CapsLorentzNet. This new architecture improves LorentzNet’s performance by approximately 25% for quark-gluon tagging, establishing CapsLorentzNet as the state-of-the-art solution for this task.

$B$ meson rare decays play a crucial role in exploring new physics beyond the standard model. In this study, we explore the rare decay process $B_s^0\to {\mu }^{+}{\mu }^{-}$ in a flavor violating extension of the Minimal Supersymmetric Standard Model (MSSM), namely, the $\mu$-from-$\nu$ SSM ($\mu \nu \mathrm{SSM}$). Combined with the decay $\overline{B}\to X_s\gamma$, the numerical results indicate that the $\mu \nu \mathrm{SSM}$ can successfully accommodate the experimental data for $B_s^0\to {\mu }^{+}{\mu }^{-}$ and additionally narrow down the parameter space.

Leptophilic axionlike particles (ALPs) exhibit rich phenomenology, focusing exclusively on interactions between an ALP and Standard Model leptons. Through integration by parts, it is shown that both the three-point interaction, $a\overline{\ell }\ell$, and the four-point interaction, $a{\ell }^{-}\nu W^{+}$, play significant roles, making the flavor portal particularly compelling. For ALPs with masses ranging from $\mathcal{O}(1)\mathrm{MeV}$ to $\mathcal{O}(1)\mathrm{GeV}$, they can contribute to exotic hadron decays. Suppressed couplings naturally extend the ALP lifetime, presenting opportunities for detection at forward detectors. In this study, we explore ALPs with both electrophilic and muonphilic scenarios. We propose an inclusive search for various hadrons that undergo exotic decays at the LHC. In the electrophilic scenario, long-lived ALPs are searched in the Forward Search Experiment and its upgrading phase, Forward Search Experiment II. In the muonphilic scenario, where the ALP lifetime is significantly reduced due to its coupling to muons, we further investigate its detection potential at LHCb and its high-luminosity upgrade. Several benchmarks are analyzed, including electroweak-preserving, electroweak-violating, and left-right softly asymmetric models, to demonstrate possible experimental constraints.

The simplified connection between Standard Model (SM) particles and light dark matter (LDM) can be introduced via spin-0 and spin-1 lepton-specific mediators. Moreover, in a mediator mass range from sub-MeV to sub-GeV, fixed-target facilities such as $\mathrm{NA}64e$, LDMX, $\mathrm{NA}64\mu$, and ${\mathrm{M}}^3$ can potentially probe such particles of the hidden sector via missing energy signatures that are described by the bremsstrahlunglike process involving leptons. We compare the Weizsaker-Williams (WW) approximation and the exact tree-level (ETL) approach for the bremsstrahlunglike mediator production cross section by choosing various parameters of the fixed-target experiments. We show that the relative difference between the total cross sections calculated in the WW and ETL approximation varies from $\mathcal{O}(1)\%$ to $\mathcal{O}(10)\%$ for a muon mode and from $\mathcal{O}(-20)\%$ to $\mathcal{O}(80)\%$ for an electron mode. We argue that the main difference between two approaches for electron beam mode arises from peak forward region of the cross section. We also discuss the impact of parametrization of nuclear and atomic elastic form factors on the total cross section. In particular, we show that the employing different form-factor parametrization can lead to a uncertainty in the cross section at the level of $\lesssim \mathcal{O}(10)\%$. That study may be helpful for the lepton fixed-target experiments that examine the bremsstrahlunglike production of the DM mediators.

The string landscape statistical draw to large scalar soft masses leads to a mixed quasidegeneracy/decoupling solution to the supersymmetry (SUSY) flavor and $CP$ problems where first/second generation matter scalars lie in the 20–40 TeV range. With increasing first/second generation scalars, SUSY models actually become more natural due to two-loop renormalization group (RG) effects that suppress the corresponding third generation soft masses. This can also lead to substantial parameter space regions that are forbidden by the presence of charge and/or color breaking minima of the scalar potential. We outline the allowed SUSY parameter space for the gravity-mediated three extra-parameter-nonuniversal Higgs model NUHM3. The natural regions with $m_h\sim 125\mathrm{GeV}$, ${\mathrm{\Delta }}_{\mathrm{EW}}\lesssim 30$ and decoupled first/second generation scalar are characterized by rather heavy gluinos and EW gauginos, but with rather small $\mu$ and top squarks not far beyond LHC Run 2 limits. This scenario also explains why SUSY has so far eluded discovery at LHC in that the parameter space with small scalar and gaugino masses is all excluded by the presence of charge and/or color breaking minima.

We propose a new realization of light Dirac neutrino mass and dark matter (DM) within the framework of a non-Abelian discrete flavor symmetry based on $A_4$ group. In addition to $A_4$, we also consider a $Z_2$ and an unbroken global lepton number symmetry $U(1{)}_L$ to keep unwanted terms away while guaranteeing the Dirac nature of light neutrinos. The field content, their transformations, and flavon vacuum alignments are chosen in such a way that the type-I Dirac seesaw generates only one light Dirac neutrino mass while the other two masses arise from scotogenic contributions at one-loop. This leads to the Dirac scoto-seesaw framework, a generalization of the widely studied scoto-seesaw model to Dirac neutrinos. The symmetry breaking of $A_4$ leaves a remnant ${\mathcal{Z}}_2$ symmetry responsible for stabilizing DM. Dirac nature of light neutrinos introduces additional relativistic degrees of freedom $\mathrm{\Delta }{N}_{\mathrm{eff}}$ within reach of cosmic microwave background experiments.

A novel approach for estimating the lower end of the SU(3) conformal window is presented through the study of center vortex geometry and its dependence on the number of fermion flavors $N_f$. Values ranging from $N_f=2–8$ are utilized to infer an upper limit for vortex behavior in the low $N_f$ phase, which may inform the transition to the conformal window. The simulations are performed at a single lattice spacing and pion mass, both fixed for all $N_f$. Visualizations of the center vortex structure in three-dimensional slices of the lattice reveal a growing roughness in the vortex matter as a function of $N_f$, embodied by an increase in the density of vortex matter in the percolating cluster and a simultaneous reduction in secondary clusters disconnected from the percolating cluster in 3D slices. This is quantified by various bulk properties, including the vortex and branching point densities. A correlation of the vortex structure reveals a turning point near $N_f\simeq 5$ past which a randomness in the vortex field becomes the dominant aspect of its evolution with $N_f$. As a byproduct, extrapolations to the vortex content of a uniform-random gauge field provide a critical point at which there must be a drastic shift in vacuum field structure. A precise estimate for the critical value is extracted as $N_f^{*}=11.43(16)(17)$, close to various other estimates.

Some calculations of parton distributions from first principles only give access to a limited range of Fourier modes of the function to reconstruct. We present a physically motivated procedure to regularize the inverse integral problem using a Gaussian process as a Bayesian prior. We propose to fix the hyperparameters of the prior in a meaningful physical fashion, offering a simple implementation, great numerical efficiency, and allowing us to understand and keep control easily of the uncertainty of the reconstruction.

In the context of the AdS/CFT, it was recently proposed that the boundary partial entanglement entropy structure can be represented by the so-called partial entanglement entropy (PEE) threads in the AdS bulk, which are bulk geodesics with the density determined by the boundary PEE structure [J. High Energy Phys. 02 (2024) 191. and arXiv:2401.07471.]. In Poincaré anti–de Sitter (AdS) space, it was shown that the PEE threads cover the AdS space uniformly, such that the number of intersections between any bulk surface and the bulk PEE threads is always given by the area of the surface divided by $4G$. In this paper, we investigate the configurations of PEE threads when the boundary state is in the island phase. The island phase was studied in the context of the holographic Weyl transformed ${\mathrm{CFT}}_2$, which has been shown to capture all the main features of AdS/BCFT (Boundary Conformal Field Theory). Compared with ${\mathrm{AdS}}_3/{\mathrm{CFT}}_2$, in the island phase instead of modifying the distribution of the bulk PEE threads, we should replace the boundary points with the corresponding cutoff spheres. Then the two-point functions and the four-point functions of twist operators can be reproduced by identifying the bulk homologous surfaces anchored on the corresponding cutoff spheres that has the minimal number of intersections with the bulk PEE threads. This gives us a better understanding about the PEE structure in the island phase and reproduces the island formula for entanglement entropy by allowing homologous surfaces to anchor on any cutoff spheres. Furthermore, it gives a demonstration for the two basic proposals and a better understanding for the entanglement contribution that makes the foundation to compute the balanced partial entanglement entropy [SciPost Phys. 15, 227 (2023).], which reproduces the entanglement wedge cross section in the island phase.

In Nielsen’s geometric approach to quantum complexity, the introduction of a suitable geometrical space, based on the Lie group formed by fundamental operators, facilitates the identification of complexity through geodesic distance in the group manifold. Earlier work has shown that the computation of geodesic distance can be challenging for Lie groups relevant to harmonic oscillators. Here, this problem is approached by working to leading order in an expansion by the structure constants of the Lie group. An explicit formula for an upper bound on the quantum complexity of a harmonic oscillator Hamiltonian with time-dependent frequency is derived. Applied to a massless test scalar field on a cosmological de Sitter background, the upper bound on complexity as a function of the scale factor exhibits a logarithmic increase on super-Hubble scales. This result aligns with the gate complexity and earlier studies of de Sitter complexity. It demonstrates the consistent application of Nielsen complexity to quantum fields in cosmological backgrounds and paves the way for further applications.

We argue that dielectric haloscopes like MADMAX, originally designed for detecting axion dark matter, are also very promising gravitational wave detectors. Operated in resonant mode at frequencies around $\mathcal{O}(10\mathrm{GHz})$, these detectors benefit from enhanced gravitational wave to photon conversion at the surfaces of a stack of thin dielectric disks. Since the gravitational wave is relativistic, there is an additional enhancement of the signal compared to the axion case due to increased conversion probability of gravitational waves to photons in the vacuum between the disks. A gravitational wave search using a dielectric haloscope imposes stringent requirements on the disk thickness and placement, but relaxed requirements on the disk smoothness. An advantage is the possibility of a broadband or hybrid resonant/broadband operation mode, which extends the frequency range down to $\mathcal{O}(100\mathrm{MHz})$. We show that strain sensitivities down to ${10}^{-21}{\mathrm{Hz}}^{-1/2}\times (10\mathrm{GHz}/f)$ will be possible in the coming years for the broadband setup, while a resonant setup optimized for gravitational waves could even reach $3\times {10}^{-23}{\mathrm{Hz}}^{-1/2}\times (10\mathrm{GHz}/f)$ with current technology.

In Aguilar-Arevalo et al. [Phys. Rev. D 109, 095017 (2024)], we explored various effective field theories that could explain the MiniBooNE excess involving long-lived particles produced from charged meson decays and the sensitivity of the Coherent CAPTAIN Mills experiment to these models. In this addendum, we extend the analysis to project sensitivity of upcoming MicroBooNE data to the long-lived particle models considered in the previous work. We find that a dedicated MicroBooNE analysis of the single photon final state with longer exposure and improved signal efficiency will be sensitive to these new physics explanations of the MiniBooNE excess, and could rule them out with a null observation at the 95% confidence level.

We examine the possibility to detect new SM-neutral vector bosons ($Z^{\prime }$) that couple exclusively to leptons in the electron-positron mode of the Future Circular Collider (FCC-ee). Focusing on the $Z^{\prime }$ production with a radiated photon search channel, we show that the FCC-ee can significantly extend the unprobed parameter space by increasing the exclusion in the coupling by one to two orders of magnitude in the kinematically allowed mass range (from 10 to 365 GeV), with the leading sensitivity being driven by the muon channel. In doing so, it outperforms other proposed lepton collider options such as CLIC and ILC in this range of masses. Further, we discuss the possibility of improving the sensitivity of the FCC-ee to this model through the modification of the dilepton invariant mass resolution and the photon energy resolution. The impact of systematic uncertainties on the expected sensitivities is also studied.

The MiniBooNE low-energy excess stands as an unexplained anomaly in short-baseline neutrino oscillation experiments. It has been shown that it can be explained in the context of dark sector models. Here, we provide an overview of the possible new-physics solutions based on electron, photon, and dilepton final states. We systematically discuss the various production mechanisms for dark particles in neutrino-nucleus scattering. Our main result is a comprehensive fit to the MiniBooNE energy spectrum in the parameter space of dark neutrino models, where short-lived heavy neutral leptons are produced in neutrino interactions and decay to $e^{+}{e}^{-}$ pairs inside the detector. For the first time, other experiments will be able to directly confirm or rule out dark neutrino interpretations of the MiniBooNE low-energy excess.

A dark sink uses dark-sector interactions to siphon energy from dark matter to lighter dark degrees of freedom, i.e., dark radiation. Here, we extend dark matter models containing a dark sink to sub-MeV masses. We consider a dark sink model where the dark matter is charged under a light dark photon that has kinetic mixing with the Standard Model. For sub-MeV dark matter masses, plasmon decays are the dominant mechanism for transferring energy to the dark sector. Relative to a standard freeze-in cosmology, reproducing the observed dark matter density in a dark sink structure requires an increase in the dark matter couplings to the Standard Model, and hence increased direct detection cross sections. These models provide benchmarks for current and upcoming direct detection experiments. Accounting for plasmon effects, we derive the range of possible dark matter masses and cross sections for dark sink models in the sub-MeV regime. We make the freezein code available to reproduce our benchmarks; it may be of use for other freeze-in scenarios, including those where plasmon decays to the dark matter are important.

Current laboratory bounds imply that protons are extremely long-lived. However, this conclusion may not hold for all time and in all of space. We find that the proton lifetime can be $\sim 15$ orders of magnitude shorter in the relatively recent past on Earth or at the present time elsewhere in the Milky Way. A number of terrestrial and astrophysical constraints are examined and potential signals are outlined. We also sketch possible models that could lead to spatial or temporal variations in the proton lifetime. A positive signal could be compelling evidence for a new long range force of nature, with important implications for the limitations of fundamental inferences based solely on laboratory measurements.