We study minimal and nonminimal couplings of fermions to the Palatini action in $n$ dimensions ($n\ge 3$) from the Lagrangian and Hamiltonian viewpoints. The Lagrangian action considered is not, in general, equivalent to the Einstein-Dirac action principle. However, by choosing properly the coupling parameters, it is possible to give a first-order action fully equivalent to the Einstein-Dirac theory in a spacetime of dimension four. By using a suitable parametrization of the vielbein and the connection, the Hamiltonian analysis of the general Lagrangian is given, which involves manifestly Lorentz-covariant phase-space variables, a real noncanonical symplectic structure, and only first-class constraints. Additional Hamiltonian formulations are obtained via symplectomorphisms, one of them involving half-densitized fermions. To confront our results with previous approaches, the time gauge is imposed.

The detection of the stochastic gravitational wave background (SGWB) is essential for understanding black hole populations, especially for supermassive black hole binaries. The recent promising results from various pulsar timing array (PTA) collaborations allude to an imminent detection. In this paper, we investigate the relative astrometric gravitational wave detection method, which can contribute to SGWB studies in the microhertz range. We consider the Roman Space Telescope and Gaia as candidates and quantitatively discuss the survey sensitivity in both the frequency and spatial domains. We emphasize the importance of survey specific constraints on performance estimates by considering mean field of view (FoV) signal subtraction and angular power spectrum binning. We conclude that if the SGWB is at a similar level as in PTA estimates, both Roman and Gaia have the potential to detect this frequency-domain power excess. However, both Roman and Gaia are subject to FoV limitations, and are unlikely to be sensitive to the spatial pattern of the SGWB.

Axions provide a natural and well-motivated dark matter candidate, with the capability to convert directly to photons in the presence of an electromagnetic field. A particularly compelling observational target is the conversion of dark matter axions into photons in the magnetospheres of highly magnetised neutron stars, which is expected to produce a narrow spectral peak centerd at the frequency of the axion mass. We point the MeerKAT radio telescope towards the isolated neutron star $\mathrm{J}0806.4-4123$ for 10-hours of observation and obtain the radio spectra in the frequency range 769–1051 MHz. By modeling the conversion process of infalling axion dark matter (DM), we then compare these spectra to theoretical expectations for a given choice of axion parameters. Whilest finding no signal above $5\sigma$ in the data, we provide a unique constraint on the Primakoff coupling of axion DM, $g_{\mathrm{a}\gamma \gamma }\lesssim 9.3\times {10}^{-12}{\mathrm{GeV}}^{-1}$ at the 95% confidence level, in the mass range $3.18–4.35\mu \mathrm{eV}$. This result serves the strongest constraint in the axion mass range $4.20–4.35\mu \mathrm{eV}$.

Neutrinos can rapidly change flavor in the inner dense regions of core-collapse supernovae and neutron star mergers due to the neutrino fast flavor instability. If the amount of flavor transformation is significant, the fast flavor instability (FFI) could significantly affect how supernovae explode and how supernovae and mergers enrich the universe with heavy elements. Since many state of the art supernova and merger simulations rely on neutrino transport algorithms based on angular moments of the radiation field, there is incomplete information with which to determine if the distributions are unstable to the FFI. In this work we test the performance of several proposed moment-based instability tests in the literature. We perform time-independent general relativistic neutrino transport on a snapshot of a 3D neutron star merger simulation to generate reasonable neutrino distributions and check where each of these criteria correctly predict instability. In addition, we offer a new “maximum entropy” instability test that is somewhat more complex, but offers more detailed (though still approximate) estimates of electron lepton number crossing width and depth. We find that this maximum entropy test and the resonant trajectory test are particularly accurate at predicting instability in this snapshot, though all tests predict instability where significant flavor transformation is most likely.

It is often said that asymmetric dark matter is light compared to typical weakly interacting massive particles. Here we point out a simple scheme with a neutrino portal and $\mathcal{O}(60\mathrm{GeV})$ asymmetric dark matter which may be “added” to any standard electroweak baryogenesis scenario. The dark sector contains a copy of the Standard Model gauge group, as well as one matter family (at least), Higgs, and right-handed neutrino. After baryogenesis, some lepton asymmetry is transferred to the dark sector through the neutrino portal where dark sphalerons convert it into a dark baryon asymmetry. Dark hadrons form asymmetric dark matter and may be directly detected due to the vector portal. Surprisingly, even dark anti-neutrons may be directly detected if they have a sizeable electric dipole moment. The dark photons visibly decay in current and future experiments which probe complementary parameter space to dark matter direct detection searches. Exotic Higgs decays are excellent signals at future $e^{+}{e}^{-}$ Higgs factories.

We searched for proton decay via $p\to {\mu }^{+}{K}^0$ in $0.37\mathrm{Mton}·\mathrm{years}$ of data collected between 1996 and 2018 from the Super-Kamiokande water Cherenkov experiment. The selection criteria were defined separately for $K_S^0$ and $K_L^0$ channels. No significant event excess has been observed. As a result of this analysis, which extends the previous search by an additional $0.2\mathrm{Mton}·\mathrm{years}$ of exposure and uses an improved event reconstruction, we set a lower limit of $3.6\times {10}^{33}\mathrm{years}$ on the proton lifetime.

Using about $23\mathrm{f}{\mathrm{b}}^{-1}$ of data collected with the BESIII detector operating at the BEPCII storage ring, a precise measurement of the $e^{+}{e}^{-}\to {\pi }^{+}{\pi }^{-}J/\psi$ Born cross section is performed at center-of-mass energies from 3.7730 to 4.7008 GeV. Two structures, identified as the $Y(4220)$ and the $Y(4320)$ states, are observed in the energy-dependent cross section with a significance larger than $10\sigma$. The masses and widths of the two structures are determined to be ($M,\mathrm{\Gamma })=(4221.4\pm 1.5\pm 2.0\mathrm{MeV}/c^2,41.8\pm 2.9\pm 2.7\mathrm{MeV})$ and $(M,\mathrm{\Gamma })=(4298\pm 12\pm 26\mathrm{MeV}/c^2,127\pm 17\pm 10\mathrm{MeV})$, respectively. A small enhancement around 4.5 GeV with a significance about $3\sigma$, compatible with the $\psi (4415)$, might also indicate the presence of an additional resonance in the spectrum. The inclusion of this additional contribution in the fit to the cross section affects the resonance parameters of the $Y(4320)$ state.

We propose a prescription for describing correlation functions in higher-dimensional defect conformal field theories (DCFTs) by those in ancillary conformal field theories (CFTs) without defects, which is a vast generalization of the image method in two-dimensional boundary CFTs. A correlation function of $n$ operators inserted away from a defect in a DCFT is represented by a correlation function of $2n$ operators in the ancillary CFT, each pair of which is placed symmetrically with respect to the defect. We establish the correspondence by matching the constraints on correlation functions imposed by conformal symmetry on both sides. Our method has the potential to shed light on new aspects of DCFTs from the viewpoint of conventional CFTs.

We consider all 4D $\mathcal{N}=2$ theories of class $\mathcal{S}$ arising from the compactification of exceptional 6D (2, 0) SCFTs on a three-punctured sphere with a simple puncture. We find that each of these 4D theories has another origin as a 6D (1, 0) SCFT compactified on a torus, which we check by identifying and comparing the central charges and the flavor symmetry. Each 6D theory is identified with a complex structure deformation of $({\mathfrak{e}}_n,{\mathfrak{e}}_n)$ minimal conformal matter, which corresponds to a Higgs branch renormalization group flow. We find that this structure is precisely replicated by the partial closure of the punctures in the class $\mathcal{S}$ construction. We explain how the plurality of origins makes manifest some aspects of 4D SCFTs, including flavor symmetry enhancements and determining if it is a product SCFT. We further highlight the string theoretic basis for this identification of 4D theories from different origins via mirror symmetry.

We report the results of testing gravitational-wave birefringence using the largest population of gravitational-wave events currently available. Gravitational-wave birefringence, which can arise from the effective field theory extension of general relativity, occurs when the parity symmetry is broken, causing the left- and right-handed polarizations to propagate following different equations of motion. We perform Bayesian inference on the 94 events reported by the 4th-Open Gravitational-wave Catalog (4-OGC) using a parity-violating waveform. We find no evidence for a violation of general relativity in the vast majority of events. However, the most massive event, GW190521, and the second most massive event, GW191109, show intriguing nonzero results for gravitational-wave birefringence. We find that the probability of association between GW190521 and the possible electromagnetic (EM) counterpart reported by Zwicky Transient Facility (ZTF) is increased when assuming birefringence. Excluding GW190521 and GW191109, the parity-violating energy scale is constrained to $M_{\mathrm{PV}}>0.05\mathrm{GeV}$ at 90% credible interval, which is an improvement over previous results from twelve events by a factor of five. We discuss the implications of our results on modified gravity and possible alternative explanations such as waveform systematics. More detections of massive binary black hole mergers from the upcoming LIGO/Virgo/KAGRA run will shed light on the true origin of the apparent birefringence.

In this work, we obtain the shadow images of spherically symmetric scalar boson and Proca stars using analytical fittings of numerical solutions, when illuminated by a geometrically thin accretion disk. We chose a sample of four boson and four Proca stars with radii ranging from more compact configurations with $R\sim 9M$ to more dilute configurations with $R\sim 20M$, where $M$ is the total mass of the bosonic star. In these configurations, the absence of the light sphere (the locus of unstable bound geodesics) makes the optical appearance of these stars to be dominated by a single luminous ring enclosing a central brightness depression, and no further photon rings are available. We show that if one considers face-on observations and a disk model whose emission is truncated at some finite radius at which the luminosity attains its maximum value, both the size of the shadow, as well as the luminosity and depth of the bright region, are heavily influenced by the emission profile, with the choice of the type and parameters of the bosonic stars in our samples having a sub-dominant influence. These differences are nonetheless significantly magnified when one allows the accretion disk to extend close enough to the center of the star. Our results point out that even though bosonic stars are horizonless and do not have a photon sphere, some of them may be able to produce conventional black hole shadowlike images provided that their compactness is large enough, thus being potentially consistent with current and future observations.

Large-scale peculiar motions are commonplace in our universe. Nevertheless, their origin, evolution, and implications are still largely unknown. It is generally assumed that bulk motions are a relatively recent addition to the universal kinematics, triggered by the increasing inhomogeneity and anisotropy of the post-recombination epoch. In this work, we focus on the linear evolution of peculiar velocities prior to recombination, namely in the late radiation era and also during a phase of de Sitter inflation. We begin by showing/confirming that bulk motions are triggered and sustained by the nongravitational forces developed during structure formation. Since density and therefore peculiar-velocity perturbations cannot grow in the baryonic sector before recombination, we consider drift motions in nonbaryonic species, which can start growing in the late radiation era. Using relativistic linear cosmological perturbation theory, we find that peculiar motions in the low-energy dark component exhibit power-law growth, which increases further after equilibrium. Turning to the very early universe, we consider the evolution of linear peculiar velocities during de Sitter inflation. We find that typical slow-roll scenarios do not source peculiar motions. Moreover, even if the latter were to be present at the onset of the de Sitter phase, the subsequent exponential expansion should quickly wash away any traces of peculiar-velocity perturbations.

The spatial curvature (${\mathrm{\Omega }}_K$) of the Universe is one of the most fundamental quantities that could give a link to the early universe physics. In this paper we develop an approximate method to compute the nonlinear matter power spectrum, $P(k)$, for “nonflat” $\mathrm{\Lambda }\mathrm{CDM}$ models using the separate universe (SU) ansatz which states that the effect of the curvature on structure formation is equivalent to that of background density fluctuation (${\delta }_{\mathrm{b}}$) in a local volume in the “flat” $\mathrm{\Lambda }\mathrm{CDM}$ model, via the specific mapping between the background cosmological parameters and redshifts in the nonflat and flat models. By utilizing the fact that the normalized response of $P(k)$ to ${\delta }_{\mathrm{b}}$ (equivalently ${\mathrm{\Omega }}_K$), which describes how the nonzero ${\mathrm{\Omega }}_K$ alters $P(k)$ as a function of $k$, is well approximated by the response to the Hubble parameter $h$ within the flat model, our method allows one to generalize the prediction of $P(k)$ for flat cosmologies via fitting formulas or emulators to that for nonflat cosmologies. We use $N$-body simulations for the nonflat $\mathrm{\Lambda }\mathrm{CDM}$ models with $|{\mathrm{\Omega }}_K|\le 0.1$ to show that our method can predict $P(k)$ for nonflat models up to $k\simeq 6h{\mathrm{Mpc}}^{-1}$ in the redshift range $z\simeq [0,1.5]$, to the fractional accuracy within $\sim 1\%$ that roughly corresponds to requirements for weak lensing cosmology with upcoming surveys. We find that the emulators, those built for flat cosmologies such as EuclidEmulator, can predict the nonflat $P(k)$ with least degradation.

In the binary-driven hypernova (BdHN) scenario, long gamma-ray bursts (GRBs) originate in a cataclysmic event that occurs in a binary system composed of a carbon-oxygen (CO) star and a neutron star (NS) companion in close orbit. The collapse of the CO star generates at its center a newborn NS ($\nu \mathrm{NS}$), and a supernova (SN) explosion. Matter from the ejecta is accreted both onto the $\nu \mathrm{NS}$ because of fallback and onto the NS companion, leading to the collapse of the latter into a black hole (BH). Each of the ingredients of the above system leads to observable emission episodes in a GRB. In particular, the $\nu \mathrm{NS}$ is expected to show up (hereafter $\nu \mathrm{NS}\text{−}\mathrm{rise}$) in the early GRB emission, nearly contemporary or superimposed to the ultrarelativistic prompt emission (UPE) phase, but with a different spectral signature. Following the $\nu \mathrm{NS}\text{−}\mathrm{rise}$, the $\nu \mathrm{NS}$ powers the afterglow emission by injecting energy into the expanding ejecta leading to synchrotron radiation. We here show that the $\nu \mathrm{NS}\text{−}\mathrm{rise}$ and the subsequent afterglow emission in both systems, GRB 180720B and GRB 190114C, are powered by the release of rotational energy of a Maclaurin spheroid, starting from the bifurcation point to the Jacobi ellipsoid sequence. This implies that the $\nu \mathrm{NS}$ evolves from a triaxial Jacobi configuration, prior to the $\nu \mathrm{NS}\text{−}\mathrm{rise}$, into the axially symmetric Maclaurin configuration observed in the GRB. The triaxial $\nu \mathrm{NS}$ configuration is short-lived (less than a second) due to a copious emission of gravitational waves, before the GRB emission, and it could be in principle detected for sources located at distances closer than 100 Mpc. This appears to be a specific process of emission of gravitational waves in the BdHN I powering long GRBs.

Gravitational wave models are used to infer the properties of black holes in merging binaries from the observed gravitational wave signals through Bayesian inference. Although we have access to a large collection of signal models that are sufficiently accurate to infer the properties of black holes, for some signals, small discrepancies in the models lead to systematic differences in the inferred properties. In order to provide a single estimate for the properties of the black holes, it is preferable to marginalize over the model uncertainty. Bayesian model averaging is a commonly used technique to marginalize over multiple models, however, it is computationally expensive. An elegant solution is to simultaneously infer the model and model properties in a joint Bayesian analysis. In this work we demonstrate that a joint Bayesian analysis can not only accelerate but also account for model-dependent systematic differences in the inferred black hole properties. We verify this technique by analyzing 100 randomly chosen simulated signals and also the real gravitational wave signal GW200129_065458. We find that not only do we infer statistically identical properties as those obtained using Bayesian model averaging, but we can sample over a set of three models on average $2.5\times$ faster. In other words, a joint Bayesian analysis that marginalizes over three models takes on average only 20% more time than a single model analysis. We then demonstrate that this technique can be used to accurately and efficiently quantify the support for one model over another, thereby assisting in Bayesian model selection.

Recently, a hadronic state named ${\eta }_1(1855)$, about 1.86 GeV, was observed in the BESIII experiment. This finding has a peculiar interest due to its exotic quantum number $J^{\mathrm{PC}}=1^{-+}$. In this paper, we examine the tetraquark interpretation for the structure of ${\eta }_1(1855)$ in the configurations of $[1_c{]}_{\overline{s}s}\otimes [1_c{]}_{\overline{q}q}$ and $[1_c{]}_{\overline{s}q}\otimes [1_c{]}_{\overline{s}q}$, and perform a mass spectrum calculation in the framework of QCD sum rules. The results show that the observed ${\eta }_1(1855)$ could be embedded into the $[1_c{]}_{\overline{s}s}\otimes [1_c{]}_{\overline{q}q}$ configuration. The possible tetraquark and hybrid decay modes are analyzed, which are critical in decoding its inner structure. In the same way, we evaluate as well the $\overline{s}s\overline{s}s$ molecular state with $1^{-+}$ quantum number and find that there might exist two such ground states.

Mixing effects on the mass spectrum of light neutral pseudoscalar and vector mesons in the presence of an external uniform magnetic field $\overrightarrow{B}$ are studied in the framework of a two-flavor Nambu-Jona-Lasinio (NJL)-like model. The model includes isoscalar and isovector couplings both in the scalar-pseudoscalar and vector sectors, and also incorporates flavor mixing through a ’t Hooft-like term. Numerical results for the $B$ dependence of meson masses are compared with present lattice QCD results. In particular, it is shown that the mixing between pseudoscalar and vector meson states leads to a significant reduction of the mass of the lightest state. The role of chiral symmetry and the effect of the alignment of quark magnetic moments in the presence of the magnetic field are discussed.

The singly Cabibbo suppressed decay ${\mathrm{\Lambda }}_c^{+}\to p{\eta }^{\prime }$ is measured using $4.5{\mathrm{fb}}^{-1}$ of $e^{+}{e}^{-}$ collision data collected at center-of-mass energies between 4.600 and 4.699 GeV with the BESIII detector at BEPCII. Evidence for ${\mathrm{\Lambda }}_c^{+}\to p{\eta }^{\prime }$ with a statistical significance of $3.6\sigma$ is reported with a double-tag approach. The ${\mathrm{\Lambda }}_c^{+}\to p{\eta }^{\prime }$ absolute branching fraction is determined to be $(5.62_{-2.04}^{+2.46}\pm 0.26)\times {10}^{-4}$, where the first and second uncertainties are statistical and systematic, respectively. Our result is consistent with the branching fraction obtained by the Belle collaboration within the uncertainty of $1\sigma$.

The localization of gravity for ($5+1$)-dimensional intersecting thick braneworld models is thoroughly investigated. Departing from preliminary results for five independent proposals, from $I$ to $V$, gravity is shown to be localized in the brane. In particular, for models from $I$ to $III$, only the zero modes are analytically determined. On the other hand, for models $IV$ and $V$, massive modes are all obtained: a finite number of massive states is identified for model $IV$, while an infinite but discrete number of massive states bounded from below is exhibited by model $V$. Considering that the discreteness of the graviton modes implies that gravity does not propagate in the codimensions, the naked singularities of models $IV$ and $V$, at edges of space, are made harmless. To conclude, the phenomenological implications for sphere models, constructed out of models $III$ and $IV$, are also discussed. According to such an overall classification, if the internal space is a sphere, model $IV$ is shown to exhibit normalizable modes. More relevantly, for the sphere model assembled out of model $III$, the subtle property of reproducing a consistent Newtonian limit is identified.

In a recent paper, Raju showed that the essential features of the monogamy paradox for old flat space black holes could be modeled using a setup in empty anti–de Sitter, leading to a violation in the monogamy of entanglement there. A physically interesting question is whether such a violation in the monogamy of entanglement can be posed in empty flat space. The answer is not immediately clear since flat space gravity has an entirely different vacuum and infrared structure than the gapped and unique AdS vacuum, which was exploited in Raju’s toy model. We answer this question in the affirmative, with an explicit construction. We formulate the paradox in terms of monogamy of Clauser-Horne-Shimony-Holt correlations, which we use to quantify the monogamy of entanglement. Extending Raju’s analysis to empty flat space, within effective field theory, we show that the entanglement of approximately local bulk modes just outside a light cone with modes just inside the light cone as well as with modes situated far away at the past of future null infinity $({\mathcal{I}}_{-}^{+})$ gives rise to an O(1) violation in the monogamy of entanglement. This cannot be resolved by small corrections of O($\sqrt{G_N}$). The issues arising from the above-mentioned vacuum and infrared features unique to flat spacetime are dealt with by introducing a physically motivated boundary projector onto states below a given infrared cutoff, which allows us to construct suitable operators at $({\mathcal{I}}_{-}^{+})$ that give rise to the violation. We argue that the resolution of the paradox is that our spatially separated observables probe the same underlying degrees of freedom, i.e., such observables act on a nonfactorized Hilbert space arising from the Gauss constraint, thereby circumventing the conflict with monogamy of entanglement.