Despite an intense theoretical and experimental effort over the past decade, observations of the extragalactic radio background at multiple frequencies below 10 GHz are not understood in terms of known radio sources and may represent a sign of new physics. In this paper, we identify a new class of dark sector models with feebly interacting particles, where dark photons oscillate into ordinary photons that contribute to the radio background. Our scenario can explain both the magnitude and the spectral index of the radio background, while being consistent with other cosmological and astrophysical constraints. These models predict new relativistic degrees of freedom and spectral distortions of the cosmic microwave background, which could be detected in the next generation of experiments.

We introduce a new search strategy for visibly decaying muonphilic particles using a proton beam spectrometer modeled after the SpinQuest experiment at Fermilab. In this setup, a $\sim 100\mathrm{GeV}$ primary proton beam impinges on a thick fixed target and yields a secondary muon beam. As these muons traverse the target material, they scatter off nuclei and can radiatively produce hypothetical muonphilic particles as initial- and final-state radiation. If such new states decay to dimuons, their combined invariant mass can be measured with a downstream spectrometer immersed in a Tesla-scale magnetic field. For a representative setup with $3\times {10}^{14}$ muons on target with typical energies of $\sim 20\mathrm{GeV}$, a 15% invariant mass resolution, and an effective 100 cm target length, this strategy can probe the entire parameter space for which $\sim 200\mathrm{MeV}-\mathrm{GeV}$ scalar particles resolve the muon $g-2$ anomaly. We present sensitivity to these scalar particles at the SpinQuest experiment where no additional hardware is needed and the search could be parasitically executed within the primary nuclear physics program. Future proton beam dump experiments with optimized beam and detector configurations could have even greater sensitivity.

In this work, a three-quark picture is constructed using a bottom-up approach for baryons in a light-front quark model. The shape parameters, which characterize the momentum distribution inside a baryon, are determined with the help of the pole residue of the baryon. The relation between the three-quark picture and the diquark picture is clarified. When building the model, we find that Lorentz boost plays a crucial role, and the bottom-up modeling approach can be generalized to multiquark states. Based on this, a unified theoretical framework for describing multiquark states may be established. As a by-product of model construction, we can easily obtain a newly improved definition of baryon interpolating current. The hadron interpolating currents are the starting point of lattice QCD and QCD sum rules, and therefore are of great importance.

In this work, we study the interaction strength among a neutral scalar boson and two massless vector bosons in the presence of an external magnetic field. Based on global symmetries, we build the general tensor structure amplitude ${\mathcal{M}}^{\mu \nu }$ for the process $V^{\mu }+V^{\nu }\to \varphi$ in terms of the vector boson polarization states. Then, we present a novel methodology to compute the one-loop amplitude contributions for a homogeneous magnetic field with arbitrary strength. With the obtained results expressed in terms of integrals over the Schwinger parameters, we explore its behavior in two regions widely used in the literature: the strong and weak field strength regions. The methodology presented in this work can be employed to compute an arbitrary process in the presence of an external magnetic field where the initial and final states are neutral.

Dark photon dark matter that has a kinetic mixing with the Standard Model photon can resonantly convert in environments where its mass $m_{A^{\prime }}$ coincides with the plasma frequency. We show that such conversion in neutron stars or accreting white dwarfs in the Galactic Center can lead to detectable radio signals. Depending on the dark matter spatial distribution, future radio telescopes could be sensitive to values of the kinetic mixing parameter that exceed current constraints by orders of magnitude for $m_{A^{\prime }}\in (6\times {10}^{-6},7\times {10}^{-4})\mathrm{eV}$.

Electroweak effects in the $e^{+}{e}^{-}\to t\overline{t}$ annihilation process are described by taking into account polarization of the initial and final particles. We investigate the effects of complete one-loop electroweak radiative corrections (RCs) and higher-order radiative effects to the total cross section and analyze different types of asymmetries for polarized initial and final states for typical energies and degrees of polarization of the ILC and CLIC projects. Numerical results are obtained with the help of Monte Carlo tools: the ReneSANCe event generator and the MCSANC integrator.

We present a new analysis of previously published SuperCDMS data using a profile likelihood framework to search for sub-GeV dark matter (DM) particles through two inelastic scattering channels: bremsstrahlung radiation and the Migdal effect. By considering these possible inelastic scattering channels, experimental sensitivity can be extended to DM masses that are undetectable through the DM-nucleon elastic scattering channel, given the energy threshold of current experiments. We exclude DM masses down to $220\mathrm{MeV}/c^2$ at $2.7\times {10}^{-30}{\mathrm{cm}}^2$ via the bremsstrahlung channel. The Migdal channel search provides overall considerably more stringent limits and excludes DM masses down to $30\mathrm{MeV}/c^2$ at $5.0\times {10}^{-30}{\mathrm{cm}}^2$.

The importance of the proper treatment of the wave function renormalization in the renormalization group analysis of quantum gravity is pointed out. The renormalization factor, sometimes called an inessential coupling, can be used to fix any one of the coupling constants, with the exception of the coupling constants that remain unchanged by the rescaling of the field. Choosing to fix the cosmological constant, we propose to use a new regulator to obtain the renormalization group equations for invariant couplings which tell us the flow of the Newton and $R^2$ couplings. We find that the Newton coupling reaches a nontrivial ultraviolet fixed point (FP) and becomes small in the low energy, but find only asymptotically free FP of the $R^2$ couplings for the higher-derivative gauge fixing and regulator. For the asymptotically free FP, we find that both of the two independent terms are relevant operators in the high energy. It is noted that the existence of nontrivial FPs may depend on the choice of the gauge and regulator.

We present a fermion model characterized by an anticommuting-parameter shift symmetry. The Hamiltonian formulation exhibits a combination of first-class and second-class constraints. We derive the well-known Dirac equation by fixing the gauge in a covariant manner, enabling the fields to propagate accordingly. Notably, the model inherently possesses invariance under reparametrizations of time. Consequently, the Hamiltonian vanishes, setting it apart from the conventional framework of Dirac’s theory. Furthermore, we establish a correspondence between these particles and the zero energy modes of the massless Rarita-Schwinger system, bringing forth the intriguing implication that they may describe a supergravity ground state.

Rapid progress in electromagnetic black-hole observation presents a theoretical challenge: how can the universal signatures of extreme gravitational lensing be distilled from stochastic astrophysical signals? With this motivation, the two-point correlation function of specific intensity fluctuations across image positions, times, and frequencies is here considered. The contribution of strongly deflected light rays, those which make up the photon ring, is analytically computed for a Kerr black hole illuminated by a simple geometric-statistical emission model. We subsequently integrate over the image to yield a spectrotemporal correlation function that is relevant for unresolved sources. Finally, some observational aspects are discussed and a preliminary assessment of detectability with current and upcoming missions is provided.

We use ray-tracing techniques to determine the evolution of the event horizon of a large black hole that “gobbles” a tiny, traversable wormhole. This calculation has physical meaning in the extreme mass ratio limit. Two setups are considered; a single-mouth wormhole connecting two otherwise independent universes, and a double-mouth zero-length wormhole within the same universe. In the first setting it turns out that, at early times, there exist two disconnected horizons, one in each universe, which then merge as the wormhole falls into the large black hole. In the second setup, we observe the appearance of an “island,” a region of spacetime that is spatially disconnected from the exterior of the black hole, but in causal contact with future null infinity. The island shrinks as time evolves and eventually disappears after sufficient time has elapsed, as compared to the distance between the two mouths. This provides a communication channel with the interior of the large black hole for a certain time interval. We compute numerically the lifetime of the island and verify that it depends linearly on the intermouth distance. Extending the analysis to wormholes with finite length, we show that the achronal averaged null energy condition prevents the appearance of islands.

The tangent vector of the light trajectory at future infinity and the angle of total light deflection in the gravitational field of an isolated axisymmetric body at rest with full set of mass multipoles and spin multipoles is determined in harmonic coordinates in the 1PN and 1.5PN approximation of the post-Newtonian (PN) scheme. It is found that the evaluation of the tangent vector and of the angle of total light deflection caused by mass multipoles and spin multipoles leads directly and in a compelling way to Chebyshev polynomials of the first and second kind, respectively. This fact allows one to determine the upper limits of the total light deflection, which are strictly valid in the 1PN and 1.5PN approximation. They represent a criterion to identify those multipoles which contribute significantly to the total light deflection for a given astrometric accuracy. These upper limits are used to determine the total light deflection in the gravitational field of the Sun and giant planets of the Solar System. It is found that the first few mass multipoles with $l\le 10$ and the first few spin multipoles with $l\le 3$ are sufficient for an accuracy on the nanoarcsecond level in astrometric angular measurements.

We investigate the role that the evaporation of light primordial black holes may have played in the production of the baryon asymmetry of the Universe through high-scale leptogenesis. In particular, for masses of primordial black holes in the range $[{10}^6–{10}^9]\mathrm{g}$, we find a dilution of thermally generated lepton asymmetry via entropy injection in the primordial plasma after the sphaleron freeze-out. As a consequence, we can put strong constraints on the primordial black hole parameters, showing the mutual exclusion limits between primordial black holes and high-scale leptogenesis. Remarkably, we point out an interplay between the upper bound on the initial abundance of primordial black holes and the active neutrino mass scale.

We use numerical relativity simulations to describe the spacetime evolution during nonlinear structure formation in $\mathrm{\Lambda }\mathrm{CDM}$ cosmology. Fully nonlinear initial conditions are set at an initial redshift $z\approx 300$, based directly on the gauge invariant comoving curvature perturbation ${\mathcal{R}}_c$ commonly used to model early-universe fluctuations. Assigning a simple 3-D sinusoidal structure to ${\mathcal{R}}_c$, we then have a lattice of quasispherical overdensities representing idealized dark matter halos connected through filaments and surrounded by voids. This structure is implemented in the synchronous-comoving gauge, using a pressureless perfect fluid (dust) description of CDM, and then it is fully evolved with the einstein toolkit code. With this, we look into whether the top-hat spherical and homogeneous collapse model provides a good description of the collapse of overdensities. We find that the top-hat is an excellent approximation for the evolution of peaks, where we observe that the shear is negligible and collapse takes place when the linear density contrast reaches the predicted critical value ${\delta }_C^{(1)}=1.69$. Additionally, we characterize the outward expansion of the turn-around boundary and show how it depends on the initial distribution of matter, finding that it is faster in denser directions, incorporating more and more matter in the infalling region. Using the EBWeyl code we look at the distribution of the electric and magnetic parts of the Weyl tensor, finding that they are stronger along and around the filaments, respectively. We introduce a method to dynamically classify the different regions of the simulation box in Petrov types. With this, we find that the spacetime is of Petrov type I everywhere, as expected, but we can identify the leading order type in each region and at different times. Along the filaments, the leading Petrov type is D, while the center of the overdensities remains conformally flat, type O, in line with the top-hat model. The surrounding region demonstrates a sort of peeling-off in action, with the spacetime transitioning between different Petrov types as nonlinearity grows, with production of gravitational waves.

The aim of this work is to improve models for the $\gamma$-ray discrete or small-scale structure related to ${\mathrm{H}}_2$ interstellar gas. Reliably identifying this contribution is important to disentangle $\gamma$-ray point sources from interstellar gas, and to better characterize extended $\gamma$-ray signals. Notably, the Fermi–LAT Galactic center (GC) excess, whose origin remains unclear, might be smooth or pointlike. If the data contain a pointlike contribution that is not adequately modeled, a smooth GC excess might be erroneously deemed to be pointlike. We improve models for the ${\mathrm{H}}_2$-related $\gamma$-ray discrete emission for a $50°\times 1°$ region along the Galactic plane via ${\mathrm{H}}_2$ proxies better suited to trace these features. We find that these are likely to contribute significantly to the $\gamma$-ray Fermi–LAT data in this region, and the brightest ones are likely associated with detected Fermi–LAT sources, a compelling validation of this methodology. We discuss prospects to extend this methodology to other regions of the sky and implications for the characterization of the GC excess.

We discuss the mechanism to produce electron-specific dark matter mediators of spin-0 and spin-2 in the electron fixed target experiments such as NA64 and LDMX. The secondary positrons induced by the electromagnetic shower can produce the mediators via annihilation on atomic electrons. That mechanism, for some selected kinematics, results in the enhanced sensitivity with respect to the bounds derived by the bremsstrahlunglike emission of the mediator in the specific parameter space. We derive the corresponding experimental reach of the NA64 and LDMX.

We calculate the color screening mass in thermalized and magnetized QCD matter in the frame of loop resummation theory without restriction to the magnetic field strength. Our full calculation covers the often-used approximations for a weak magnetic field at high temperature, and for a strong magnetic field at low temperature. We find that while the magnetic field created in heavy ion collisions at RHIC and LHC energies is probably the strongest one in nature, its effect on the QCD matter is still weaker in comparison with the high temperature of the fireball, and therefore can safely be treated as a perturbation.

We present a new parton distribution function analysis which includes new data for $W$ boson production in proton-proton collisions and lepton pair production in proton-proton and proton-deuteron collisions. The new data provide strong constraints on the light antiquark parton distribution functions in the proton. We identify an interesting correlation between the $d/u$ ratio and the $\overline{d}/\overline{u}$ ratio which leads to a modification of our previous results for the $d/u$ ratio as the parton momentum fraction $x\to 1$.

A primary goal of the upcoming Deep Underground Neutrino Experiment (DUNE) is to measure the $\mathcal{O}(10)\mathrm{MeV}$ neutrinos produced by a Galactic core-collapse supernova if one should occur during the lifetime of the experiment. The liquid-argon-based detectors planned for DUNE are expected to be uniquely sensitive to the ${\nu }_e$ component of the supernova flux, enabling a wide variety of physics and astrophysics measurements. A key requirement for a correct interpretation of these measurements is a good understanding of the energy-dependent total cross section $\sigma (E_{\nu })$ for charged-current ${\nu }_e$ absorption on argon. In the context of a simulated extraction of supernova ${\nu }_e$ spectral parameters from a toy analysis, we investigate the impact of $\sigma (E_{\nu })$ modeling uncertainties on DUNE’s supernova neutrino physics sensitivity for the first time. We find that the currently large theoretical uncertainties on $\sigma (E_{\nu })$ must be substantially reduced before the ${\nu }_e$ flux parameters can be extracted reliably; in the absence of external constraints, a measurement of the integrated neutrino luminosity with less than 10% bias with DUNE requires $\sigma (E_{\nu })$ to be known to about 5%. The neutrino spectral shape parameters can be known to better than 10% for a 20% uncertainty on the cross-section scale, although they will be sensitive to uncertainties on the shape of $\sigma (E_{\nu })$. A direct measurement of low-energy ${\nu }_e$-argon scattering would be invaluable for improving the theoretical precision to the needed level.

We propose a new algorithm for the identification of the production flavor of neutral $D$ mesons in the Belle II experiment. The algorithm exploits the correlation between the flavor of a reconstructed neutral $D$ meson (signal $D$ meson) and the electric charges of particles reconstructed in the rest of the $e^{+}{e}^{-}\to c\overline{c}$ event. These include those originating from the decay of the other charm hadron produced in the event, as well as those possibly produced in association with the signal $D$ meson. We develop the algorithm using simulation and calibrate it in data using decay modes that identify the flavor of the decaying neutral $D$ meson. We use a data sample of $e^{+}{e}^{-}$ collisions, corresponding to $362{\mathrm{fb}}^{-1}$ of integrated luminosity, collected by Belle II at center-of-mass energies near the $\mathrm{\Upsilon }(4S)$ mass. The effective tagging efficiency in data is $(47.91\pm 0.07(\mathrm{stat})\pm 0.51(\mathrm{syst}))\%$, independent of the neutral-$D$-meson decay mode. This charm flavor tagger will approximately double the effective sample size of many $CP$-violation and charm-mixing measurements that so far have exclusively relied on neutral $D$ mesons originating from $D^{*\pm }$ decays. While developed for Belle II, the basic principles underlying the charm flavor tagger can be used in other experiments, including those at hadron colliders.