We study the application of the background field method in the framework of the exact renormalization group (ERG). By considering the case of a scalar field theory, we provide a detailed discussion of the properties satisfied by a background dependent Wilson action. We show how the Ward identity associated with background field shifts for the Wilson action is related to that for the 1PI Wilson action, or effective average action. Moreover, we discuss the ERG equations in the dimensionless framework and emphasize the role of the Ward identity in this setting. We give two examples: the Gaussian fixed point for the real scalar theory and the large $N$ limit of the linear sigma model.

Recently, the “bootstrap” technique was applied in quantum mechanics to solve the eigenspectra of Hermitian Hamiltonians and extended to non-Hermitian parity-time (PT)-symmetric systems. However, its application has been limited to real spectra. In this work, we establish bootstrap conditions for the non-Hermitian system and generate eigenspectra for a generic complex polynomial potential, which includes PT-symmetric Hamiltonians as a special case. Additionally, we demonstrate the method’s ability to obtain eigenspectra under various boundary conditions imposed on the eigenfunction, including the notable application of capturing the PT-symmetric phase transition.

Strong-field gravity simulators are laboratory experiments that can investigate a wide range of both classical and quantum phenomena occurring in nature. In this work, we introduce an effective geometry that captures most of the characteristics of the strong-field regime of astrophysical, rotating black holes. This geometry can represent a vortex made from a variety of fluid and superfluid profiles with zero viscosity, making it a promising finite-temperature quantum-field-theory simulator for rotating curved spacetimes. Our geometry includes not only the typical radial flow which gives rise to an acoustic horizon, but also azimuthal circulation of the fluid. We compute the quasinormal modes, semianalytically, and the exact quasibound states of acoustic excitations interacting with this effective geometry. The resulting spectra can be identified for both corotating and counterrotating surface acoustic waves. In particular, the behavior of our acoustic geometry with circulation aligns with the phenomenology observed in recent experiments that include superfluids.

We prove the uniqueness theorem for static spherically symmetric traversable wormholes with two asymptotically flat ends constituting the solutions of the Einstein-phantom-electric-magnetic equations of motion. For the completeness of the results, we also consider the case of the phantom $U(1)$-gauge field. The key role in the proof is bounded with the conformal positive energy theorem.

The standard cosmological model, rooted in general relativity (GR), has achieved remarkable success, yet it still faces unresolved issues like the nature of dark matter, dark energy, and the Hubble tension. These challenges might imply the need for alternative gravitational theories. Teleparallel gravity offers a compelling framework by reformulating the gravitational interaction using torsion, rather than curvature, as its fundamental geometrical property. This paper delves into $f(T)$ gravity, an extension of the teleparallel equivalent of general relativity (TEGR), which introduces nonlinear modifications of the torsion scalar $T$. We focus on the role of spacetime-dependent Lorentz transformations in the vierbein formalism, examining their impact on both background solutions and perturbation dynamics. Special attention is given to the homogeneous and isotropic Friedmann-Lemaître-Robertson-Walker (FLRW) spacetime, as well as the anisotropic Bianchi I spacetime. Furthermore, the analysis of the propagating degrees of freedom on these spacetimes is performed. While it is well established that TEGR reproduces the same results as GR, the propagating degrees of freedom in its nonlinear extension, $f(T)$ gravity, is still debated in the literature. In this work, we find that only two fields propagate in the gravity sector, independent of the background spacetime considered, either FLRW or Bianchi I. Although not definitive, this paper provides fresh insights into the issue of the propagating degrees of freedom in $f(T)$ gravity, opening the door to intriguing new directions for further investigation.

It is commonly assumed that low-mass primordial black holes cannot constitute a significant fraction of the dark matter in our universe due to their predicted short lifetimes from the conventional Hawking radiation and evaporation process. Assuming physical black holes are nonsingular—likely due to quantum gravity or other high-energy physics—we demonstrate that a large class of nonsingular black holes have finite evaporation temperatures. This can lead to slowly evaporating low-mass black holes or to remnant mass states that circumvent traditional evaporation constraints. As a proof of concept, we explore the limiting curvature hypothesis and the evaporation process of a nonsingular black hole solution in two-dimensional dilaton gravity. We identify generic features of the radiation profile and compare them with known regular black holes, such as the Bardeen solution in four dimensions. Remnant masses are proportional to the fundamental length scale, and we argue that slowly evaporating low-mass nonsingular black holes, or remnants, are viable dark matter candidates.

Predicting the flavor composition of neutrinos from supernovae is a challenging task, primarily due to the high neutrino densities at their core. In such an environment, neutrino self-interactions give rise to collective effects that have dramatic yet poorly understood consequences for their flavor evolution. In this paper, however, we show that standard matter effects in the outer layers of supernovae can significantly constrain the flavor composition of the neutrino flux. We assume that, since a large number of neutrinos undergo different evolutions within the core, their state upon entering the Mikheyev–Smirnov–Wolfenstein-dominated region is affected by decoherence. This assumption simplifies the problem and suggests that the fraction of neutrinos with electron flavor reaching Earth, denoted as $f_{{\nu }_e}$, is constrained to be less than 0.5 for all energies throughout the emission phase in the case of normal mass ordering. In contrast, for inverted mass ordering, we anticipate neutrinos arriving in near flavor equipartition ($f_{{\nu }_e}\approx 1/3$). These predictions, and consequently their underlying assumptions, could be tested by future observations and may provide valuable insights into the properties of neutrino fluxes emerging from supernovae.

The direct observation of intermediate-mass black holes (IMBH) populations would not only strengthen the possible evolutionary link between stellar and supermassive black holes, but unveil the details of the pair-instability mechanism and elucidate their influence in galaxy formation. Conclusive observation of IMBHs remained elusive until the detection of gravitational-wave (GW) signal GW190521, which lies with high confidence in the mass gap predicted by the pair-instability mechanism. Despite falling in the sensitivity band of current GW detectors, IMBH searches are challenging due to their similarity to transient bursts of detector noise, known as glitches. In this proof-of-concept work, we combine a matched-filter algorithm with a machine learning (ML) method to differentiate IMBH signals from nontransient burst noise, known as glitches. In particular, we build a multilayer perceptron network to perform a multiclass classification of the output triggers of matched filter. In this way we are able to distinguish simulated GW IMBH signals from different classes of glitches that occurred during the third observing run (O3) in single detector data. We train, validate, and test our model on O3a data, reaching a true positive rate of over 90% for simulated IMBH signals. To test the generalization ability over the evolutionary observing run, we test on the unseen data of O3b, which yields a true positive rate of over 70%. We also combine data from multiple detectors to search for simulated IMBH signals in real detector noise, providing a significance measure for the output of our ML method.

In this work, we investigate the influence of neutron stars’ crusts on the nonradial $g$-mode oscillations and examine their correlations with nuclear matter properties fixed by adopting ten different relativistic density functionals. At subsaturation densities, neutron star matter takes nonuniform structures and form the crusts. We find that the Brunt-Väisälä (BV) frequency increases significantly at densities slightly above the neutron drip density (i.e., neutron stars’ inner crusts), which leads to crust $g$-mode oscillations with their frequencies insensitive to the adopted density functional. At larger densities, BV frequency increases as well due to the core-crust transitions and emergence of muons, which lead to core $g$-mode oscillations. It is found that the obtained core $g$-mode frequencies generally increase with the slope of nuclear symmetry energy $L$, which eventually intersect with that of the crust $g$-modes adopting large enough $L$. This leads to the avoid-crossing phenomenon for the global $g$-modes that encompass contributions from both the crust and core. For neutron stars with fixed masses, the frequency of the global $g_1$-mode generally increases linearly with $L$, where the Pearson correlation coefficient ranges from 0.7 to 0.9. The corresponding linear functions are then fixed by fitting to the $g_1$-mode frequencies predicted by the ten relativistic density functionals, which enables the possible measurements of $L$ based on gravitational wave observations. In our future study, the effects of the discontinuities in density or shear modulus should be considered, while the temperature, rotation, magnetic field, and superfluid neutron gas in neutron stars could also play important roles.

We investigate the singly and doubly charmful two-body ${\mathrm{\Omega }}_b^{-}$ decays using the light-front quark model. Our findings reveal that most branching fractions calculated in this study, such as $\mathcal{B}({\mathrm{\Omega }}_b^{-}\to {\mathrm{\Xi }}^{-}{D}^0,{\mathrm{\Xi }}^{-}{D}^{*0})$, can be ten to one hundred times larger than those reported in previous calculations. Additionally, we interpret the ratio $\mathcal{B}({\mathrm{\Omega }}_b^{-}\to {\mathrm{\Omega }}^{-}J/\psi )/\mathcal{B}({\mathrm{\Omega }}_b^{-}\to {\mathrm{\Omega }}^{-}{\eta }_c)\simeq 3.4$ within the helicity framework. While the decay involving external $W$-boson emission appears to be suppressed by the $b\to u\overline{c}s$ weak transition, it still yields a significant branching fraction. For instance, $\mathcal{B}({\mathrm{\Omega }}_b^{-}\to {\mathrm{\Xi }}^0{D}_s^{*-})=(5.9–14.2)\times {10}^{-5}$, $\mathcal{B}({\mathrm{\Omega }}_b^{-}\to {\mathrm{\Xi }}^{*0}{D}_s^{-})=(6.7–12.1)\times {10}^{-5}$, and $\mathcal{B}({\mathrm{\Omega }}_b^{-}\to {\mathrm{\Xi }}^{*0}{D}_s^{*-})=(12.8–26.7)\times {10}^{-5}$, with values reaching as large as ${10}^{-4}$. These predictions are well within the experimental reach of LHCb.

We explore a novel mechanism for dark matter production through the formation of light black holes from the collapse of dark baryons in confining SU(N) gauge theories in the large-$N$ limit. While glueballs and mesons cannot form black holes under physically reasonable conditions, we prove that for appropriate ranges of the confinement scale, quark masses, number of colors $N$, and dark sector temperature, dark baryons can produce Planck-scale black hole relics in the early Universe. Assuming the relics are stable, the abundance of both the dark baryon black hole population directly arising at confinement and that frozen in from dark glueball and meson pair annihilation are exponentially suppressed in $N$, leading to an upper limit $N\lesssim 100$ and of a few hundred Planck units in mass for models where the black hole relics are the entirety of the dark matter. We present a detailed numerical study of the parameter space where this scenario is realized.

We explore constraints on the parameter space of the alternative left-right model originating from the leptonic sector. Our analyses focuses on both lepton-flavor-conserving observables, particularly the anomalous magnetic moment of the muon, and lepton-flavor-violating processes like $\mu \to e\gamma$ decay and $\mu -e$ conversions in nuclei. While contributions to the anomalous magnetic moment fall below the measured values at $2\sigma$, current and future experimental sensitivities to flavor-violating branching rations of the Standard Model leptons are expected to impose lower bounds on the mass of the peculiar $SU(2{)}_R$ gauge boson of the model. This provides complementary constraints relative to existing limits, which are indirect and derived from collider bounds on the mass of the associated neutral gauge boson $Z^{\prime }$.

We discuss a model of neutrino mass based on the type I seesaw mechanism embedded in a spontaneously broken global lepton number framework with a $Z_2$ symmetry. We show that the resulting Majoron is a viable freeze-in dark matter candidate. Two right-handed neutrinos are assumed to have dominant off-diagonal masses suggesting resonant leptogenesis as the origin of baryon asymmetry of the Universe. Explicit higher dimensional lepton number violating operators are shown to play a crucial role in simultaneously controlling both the Majoron production in the early Universe and the right handed neutrino mass splitting relevant for resonant leptogenesis. We perform a combined analysis of Majoron dark matter and leptogenesis, discussing the relative importance of self-energy and vertex contributions to $CP$ asymmetry, and explore the parameter space, leading to an intricate relation between neutrino mass, dark matter, and baryon asymmetry.

The latest result from the ORGAN experiment, an axion haloscope, is presented. This iteration of the experiment operated at millikelvin temperatures using a flux-driven Josephson parametric amplifier for reduced noise, along with various other improvements over previous iterations. Covering the $25.45-26.27\mathrm{\mu }\mathrm{eV}$ (6.15–6.35 GHz) mass (frequency) range, this near-quantum-limited phase of ORGAN employs a conducting rod resonator and a 7-T solenoidal magnet to place the most sensitive exclusion limits on axion-photon coupling in the range to date, with $|g_{a\gamma \gamma }|\gtrsim 2.8\times {10}^{-13}$ at a 95% confidence level.

Reconstructing the internal three-dimensional quark and gluon structures of hadrons through generalized parton distributions (GPDs) from hard exclusive scattering processes is one of the most challenging tasks in nuclear and particle physics. In this paper, we introduce a new optimized reference frame that, for the first time, enables a unified view of all the reactions sensitive to GPDs and facilitates the interpretation of a variety of phase-space patterns that were previously hardly accessible and interpretable. Similarly to how the heliocentric description advanced our understanding of the solar system and gravitation, our new frame centers around a quasireal state, allows for a consistent separation of physical scales, and reveals a novel quantum interference mechanism.

We investigate the systematic uncertainties and potential biases arising from the inclusion of large-$x$ corrections to proton and deuteron deep inelastic scattering (DIS) data in global quantum chromodynamics (QCD) analyses. Using the CTEQ-JLab framework, we examine various approaches to implementing higher-twist corrections in nucleon structure functions and off-shell PDF modifications in deuteron targets. We analyze how these components interact and influence the determination of the $d$-quark PDF and the neutron structure function at large $x$. We find that it is very important to consider isospin-dependent higher-twist corrections in order to minimize implementation biases in the extracted quantities.

We study the potential to probe the origin of neutrino masses, by searching for long-lived right-handed neutrinos (RHNs) $N$ in the $B-L$ model and in the RHN-extended Standard Model (SM) effective field theory (EFT). Despite the small active-sterile mixing $|V_{\ell N}{|}^2$, RHNs are produced abundantly via SM and exotic Higgs production, as long as the Higgs mixing or EFT operator coefficient is sufficiently large. We reinterpret a search for displaced showers in the CMS muon system and we find that it is sensitive to parameter space at and below the seesaw floor, $|V_{\ell N}{|}^2\approx {10}^{-12}$ ($\ell =e$, $\tau$) for $m_N\approx 40\mathrm{GeV}$. With existing data constraining such well-motivated scenarios of neutrino mass generation, we determine the projected sensitivity at the HL-LHC, motivating dedicated searches for long-lived RHNs with decay lengths $\approx 10\mathrm{m}$.

We propose a geometric formulation of effective field theories via nonlinear supersymmetry. Nonsupersymmetric particles are embedded in constrained superfields governed by a nonlinear $\sigma$ model, and operators are collected into potentials on the target space. The use of chiral superfields standardizes the treatment of flavor across scalars and fermions, and the minimal jet bundle extension makes invariance under derivative field redefinitions manifest.

The nature of gravity can be tested by how gravitational waves (GWs) are emitted, detected, and propagate through the universe. Propagation tests are powerful, as small deviations compound over cosmological distances. However, GW propagation tests of theories beyond Einstein’s general relativity (GR) are limited by the high degree of symmetry of the average cosmological spacetime. Deviations from homogeneity, i.e. gravitational lenses, allow for new interactions, e.g. between standard GW polarization and new scalar or vector fields, with different spin. Therefore, GW lensing beyond GR offers novel tests of cosmological gravity. Here we present the theory of GW propagation beyond GR in the short-wave expansion, including corrections to the leading-order amplitude and phase for the first time. As an example, we compute the dispersive (frequency-dependent) corrections to all metric and scalar field perturbations in Brans-Dicke, the simplest modified theory exhibiting GW dispersion. GW lensing effects are too small to observe in Brans-Dicke theories compatible with solar system and binary pulsar limits. Nevertheless, our formalism opens the possibility of novel tests of gravity, including dark-energy theories and screening mechanisms.

It was recently suggested the quasinormal-mode spectrum of black holes is related to a class of four-dimensional $\mathcal{N}=2$ super Yang-Mills theories described by Seiberg-Witten curves, a proposal that has been tested for a number of black hole spacetimes. The aim of this study is to clarify the key ideas of this conjecture to a non-high-energy-physics audience and test it in a setting that has not yet been explored: the electromagnetic and gravitational perturbations of Kerr-Newman black holes in the Dudley-Finley approximation. In the parameter space we explore, we find numerical evidence that the conjecture is valid for subextremal black holes and its slowest damped quasinormal frequencies, thereby providing further support for the conjecture’s validity. In addition, we exploit the symmetries of the four-dimensional $\mathcal{N}=2$ super Yang-Mills theory to obtain a strikingly simple isospectral version of the radial Dudley-Finley equation.