There is increasing interest in discrete or “pixelated” spacetime models as a foundation for a satisfactory theory of quantum gravity. If spacetime possesses a cellular structure, there should be observable consequences; for example, the vacuum becomes a dispersive medium. Of obvious interest are the implications for the thermodynamic properties of quantum black holes. As a first step to investigating that topic, we present here a calculation of the response of a uniformly accelerating particle detector in the (modified) quantum vacuum of a background pixelated spacetime, which is well known to mimic some features of the Hawking effect. To investigate the detector response we use the standard DeWitt’s treatment, with a two-point function modified to incorporate the dispersion. We use dispersion relations taken from the so-called doubly special relativity (DSR) and Hořava-Lifshitz gravity. We find that the correction terms retain the Planckian nature of particle detection, but only for propagation faster than the speed of light, a possibility that arises in this treatment because the dispersion relations violate Lorentz invariance. A fully Lorentz-invariant theory requires additional features; however, we believe the thermal response will be preserved in the more elaborate treatment.

The dynamics of classical field theories is usually governed by field equations, but when fields are constrained to bounded domains it is also dependent on its boundary conditions. Usually boundary conditions are constrained by the requirement of preserving the maximal symmetry of the system. In the case of charged particles the symmetry is $U(1)$, but there are many fields (e.g. electromagnetic fields) which are neutral and charge conservation does not constraint its boundary conditions. In this paper we explore the most general boundary conditions that preserve another symmetry that all relativistic field theories do preserve: space-time translations. In particular the families of boundary conditions of isolated systems which preserve energy for scalar, electromagnetic and Yang-Mills field theories. We point out the global properties of the space of all possible boundary conditions of confined systems in two special domains. We also explore the connection between energy preserving and charge preserving boundary conditions.

We investigate isotropic and homogeneous cosmological scenarios in the scalar-tensor theory of gravity with nonminimal derivative coupling of a scalar field to the curvature given by the term $(\zeta /H_0^2)G^{\mu \nu }{\nabla }_{\mu }\varphi {\nabla }_{\nu }\varphi$ in the Lagrangian. In general, a cosmological model is determined by six dimensionless parameters: the coupling parameter $\zeta$, and density parameters ${\mathrm{\Omega }}_0$ (cosmological constant), ${\mathrm{\Omega }}_2$ (spatial curvature term), ${\mathrm{\Omega }}_3$ (nonrelativistic matter), ${\mathrm{\Omega }}_4$ (radiation), ${\mathrm{\Omega }}_6$ (scalar field term), and the universe evolution is described by the modified Friedmann equation. In the case $\zeta =0$ (no nonminimal derivative coupling) and ${\mathrm{\Omega }}_6=0$ (no scalar field) one has the standard $\mathrm{\Lambda }\mathrm{CDM}$ model, while if ${\mathrm{\Omega }}_6\ne 0$, one has the $\mathrm{\Lambda }\mathrm{CDM}$ model with an ordinary scalar field. As is well-known, this model has an initial singularity, the same for all $k$ ($k=0,\pm 1$), while its global behavior depends on $k$. The universe expands eternally if $k=0$ (zero spatial curvature) or $k=-1$ (negative spatial curvature), while in the case $k=+1$ (positive spatial curvature) the universe expansion is changed to contraction, which is ended by a final singularity. The situation is crucially changed when the scalar field possesses nonminimal derivative coupling to the curvature, i.e., when $\zeta \ne 0$. Now, depending on model parameters: (i) There are three qualitatively different initial states of the universe: an eternal kinetic inflation, an initial singularity, and a bounce. The bounce is possible for all types of spatial geometry of the homogeneous universe. (ii) For all types of spatial geometry, the universe goes inevitably through the primary quasi–de Sitter (inflationary) epoch when $a(t)\propto e^{h_{\mathrm{dS}}(H_{0}t)}$ with the de Sitter parameter $h_{\mathrm{dS}}^2=1/9\zeta -8\zeta {\mathrm{\Omega }}_2^3/27{\mathrm{\Omega }}_6$. The mechanism of primary or kinetic inflation is provided by nonminimal derivative coupling and needs no fine-tuned potential. (iii) There are cyclic scenarios of the universe evolution with the nonsingular bounce at a minimal value of the scale factor, and a turning point at the maximal one. (iv) There is a natural mechanism providing a change of cosmological epochs.

Penrose limits are considered in spacetimes admitting two Abelian, spacelike Killing vectors in general nonvacuum as well as in particular in the presence of an electromagnetic field. This class of spacetimes includes inhomogeneous cosmologies as well as colliding plane gravitational and the corresponding field waves or matter. Following the work of Tod [Classical Quantum Gravity 37, 075021 (2020)] the conditions for diagonal Penrose limits are investigated in these backgrounds. The twistor equation is considered in these spacetimes, and solutions are given in the radial Penrose limit.

We formulate a biconnection theory of gravity whose gravitational action consists of a recently defined mutual curvature scalar. Namely, we build a gravitational theory consisting of one metric and two affine connections, in a metric-affine gravity setup. Consequently, coupling the two connections on an equal footing with matter, we show that the geometry of the resulting theory is, quite intriguingly, that of statistical manifolds. This ultimately indicates a remarkable mathematical correspondence between gravity and information geometry.

Infalling matter may destroy a black hole and expose the naked singularity. Thus, Penrose proposed the weak cosmic censorship conjecture to avoid such a possibility. On the other hand, if the black hole is not destroyed by infalling matter, from the second law of black hole thermodynamics, the black hole entropy should increase due to the information carried by the infalling matter. In this work, we demonstrate by examples of perturbative near-extremal black holes in higher derivative gravity theories that the second law implies weak cosmic censorship. We also compare our proposal to the one developed by Sorce and Wald based on the first law of black hole thermodynamics and show that the latter fails to yield weak cosmic censorship in such cases. Finally, we give proof of our proposal for generic gravity theories.

Cosmic string cusps are sources of short-lived, linearly polarized gravitational wave bursts which can be searched for in gravitational wave detectors. We assess the capability of LISA to detect these bursts using the latest LISA configuration and operational assumptions. For such short bursts, we verify that LISA can be considered as “frozen”, namely that one can neglect LISA’s orbital motion. We consider two models for the network of cosmic string loops, and estimate that LISA should be able to detect 4–30 bursts per year assuming a string tension $G\mu \approx {10}^{-10.6}–{10}^{-10.1}$ and detection threshold $\mathrm{SNR}\ge 20$. Nondetection of these bursts would constrain the string tension to $G\mu \lesssim {10}^{-11}$ for both models.

We present small-scale structure constraints on sterile dark matter produced from a heavy mediator particle, inspired by models of moduli decay. Dark matter particles produced through this mechanism can contribute to the entire dark matter energy density but the particles have a nonthermal phase-space distribution; however, we show that the resulting linear matter power spectra can be mapped to effective thermal-relic warm dark matter models. This production mechanism is therefore subject to warm dark matter constraints from small-scale structure as probed by ultrafaint dwarf galaxy abundances and strong gravitational lensing flux ratio statistics. We use the correspondence to thermal-relic models to derive a lower bound on the nonthermal particle mass of 107 keV, at 95% confidence limits. These are the most stringent constraints derived on sterile dark matter produced via the heavy mediator decay scenario we consider.

We argue that the reflection of relic neutrinos from the surface of the Earth results in a significant local $\nu -\overline{\nu }$ asymmetry, far exceeding the expected primordial lepton asymmetry. The net fractional electron neutrino number $\frac{n_{{\nu }_e}-n_{{\overline{\nu }}_e}}{n_{{\nu }_e}}$ is up to $\mathcal{O}({10}^5)\sqrt{\frac{m_{\nu }}{0.1\mathrm{eV}}}$ larger than that implied by the baryon asymmetry. This enhancement is due to the weak 4-Fermi repulsion of the ${\nu }_e$ from ordinary matter which slows down the ${\nu }_e$ near the Earth’s surface, and to the resulting evanescent neutrino wave that penetrates below the surface. This repulsion thus creates a net ${\nu }_e$ overdensity in a shell $\sim 7\text{meters}\sqrt{\frac{0.1\mathrm{eV}}{m_{\nu }}}$ thick around the Earth’s surface. Similarly the repulsion between ${\overline{\nu }}_{\mu }$ or ${\overline{\nu }}_{\tau }$ and ordinary matter creates an overdensity of ${\overline{\nu }}_{\mu ,\tau }$ of similar size. These local enhancements increase the size of $\mathcal{O}(G_F)$ torques of the $C\nu B$ on spin-polarized matter by a factor of order ${10}^5$. In addition, they create a gradient of the net neutrino density which naturally provides a way out of the forty-year-old “no-go” theorems on the vanishing of $\mathcal{O}(G_F)$ forces. The torque resulting from such a gradient force can be ${10}^8$ times larger than that of earlier proposals. Although the size of these effects is still far from current reach, they may point to new directions for $C\nu B$ detection.

As dense and hot bodies with a well-understood equation of state, white dwarfs offer a unique opportunity to investigate new physics. In this paper, we examine the role of dark sectors, which are extensions of the Standard Model of particle physics that are not directly observable, in the cooling process of white dwarfs. Specifically, we examine the role of a dark photon, within the framework of a three-portal model, in enhancing the neutrino emission during the cooling process of white dwarfs. We compare this scenario to the energy release predicted by the Standard Model. By analyzing the parameter space of dark sectors, our study aims to identify regions that could lead to significant deviations from the expected energy release of white dwarfs.

We present dark matter (DM)-only simulations of halo formation and evolution in scalar field dark matter (SFDM) cosmologies in the Thomas-Fermi regime, also known as “SFDM-TF,” where a strong repulsive two-particle self-interaction (SI) is included. This model is a valuable alternative to cold dark matter (CDM), with the potential to resolve the “cusp-core” problem of the latter. In general, SFDM behaves like a quantum fluid. Previous literature has presented fluid approximations for SFDM-TF in 1D and 3D, respectively, as well as numerical DM-only simulations of SFDM-TF halo formation, whose results are in agreement with earlier analytic expectations, that a core-envelope halo structure arises; a central region close to a ($n=1$)-polytropic core, surrounded by a CDM-like [i.e. Navarro–Frenk–White (NFW)-like] halo envelope. While those previous results are generally in mutual agreement, discrepancies have been also reported. Therefore, we perform dedicated 3D cosmological simulations of the halo infall problem for the SFDM-TF model, as well as for CDM and its corresponding CDM fluid approximation, where we implement both previous fluid approximations into the code ramses. We compare our findings with those previous simulations. Our results are very well in accordance with previous works and extend upon them, in that we can explain the reported discrepancies. They are not due to the different fluid approximations, nor the geometry, but rather a result of different simulation setups. Moreover, we find some interesting details, as follows. The evolution of both SFDM-TF and CDM halos follows a two-stage process. In the early stage, the central density in the halo rises, its profile becomes close to a ($n=1.5$)-polytropic core being dominated by an “effective” velocity-dispersion pressure $P_{\sigma }$ that stabilizes it against gravity. In fact, this pressure stems from random orbital motion in CDM, but from random wave motion in SFDM. Consecutively, for CDM halos, this core transitions into a steep central cusp whose slope is almost the same as the outer density slope, which is close to $\rho \propto r^{-3}$ as expected from Navarro–Frenk–White (NFW). Finally, however, the central profile makes another transition to a “shallower cusp,” very close to the NFW behavior of $\rho \propto r^{-1}$. On the other hand, in the formation of the SFDM-TF halo, the additional pressure $P_{\mathrm{SI}}$ due to SI determines the second stage of the evolution. At the end, $P_{\mathrm{SI}}$ dominates in the central region, whose density follows closely a ($n=1$)-polytropic core. This core is enshrouded by a nearly isothermal envelope, i.e. the outskirts are similar to CDM at this point. We also encounter a new effect in our simulations, namely a late-time expansion of both polytropic core plus envelope, because the size of the almost isothermal halo envelope is affected by the external pressure, which decreases with the expansion of the background universe. Hence, the core size of SFDM-TF halos is not necessarily determined only by the parameters of the model, as our simulations reveal that an initial primordial core of $\sim 100\mathrm{pc}$—demanded by power spectrum constraints—can evolve into a larger core of $\gtrsim 1\mathrm{kpc}$, after all, during halo evolution, even without feedback from baryons.

Rare decays of the Higgs boson into quarkonia pairs are studied within the framework of nonrelativistic QCD approach. The main decay mechanisms and their interference are studied in detail. One-loop corrections to the widths of these decays are taken into account for the first time.

Gravity’s quantum nature can be probed in a laboratory by witnessing the entanglement between the two quantum systems, which cannot be possible if gravity is a classical entity. In this paper, we will provide a simple example where we can probe the effects of higher dimensions, in particular the warped extra dimension of five-dimensional anti–de Sitter spacetime (${\mathrm{AdS}}_5$). We assume that the two quantum harmonic oscillators are kept at a distance $d$ on a 3-brane (our 4D world) embedded in ${\mathrm{AdS}}_5$, while gravity can propagate in all five dimensions. We will compute the effective potential due to the massless and massive gravitons propagating in the warped geometry. We will compute the entanglement between position and momentum states for both static and nonstatic cases. The entanglement enhances compared to the four-dimensional massless graviton, and it depends now on the ${\mathrm{AdS}}_5$ radius. We will also show that if we would prepare non-Gaussian superposition states, e.g., spatial superposition of masses of order ${10}^{-14}–{10}^{-15}\mathrm{kg}$ with a superposition size of $\mathcal{O}(20)$ micron, we can yield larger concurrence of order $\mathcal{O}(0.1)$.

We compute the electromagnetic properties of spin-$\frac{1}{2}$ doubly charmed baryons on ($2+1$)-flavor lattices that have a pion mass of $\sim 156\mathrm{MeV}$. The Tsukuba action is employed for the charm quark in addition to the standard isotropic Clover action to quantify the $\mathcal{O}(m_{q}a)$ effects. We calculate the electric and magnetic Sachs form factors and extract the magnetic moments and electric and magnetic-charge radii. We also investigate the individual quark-sector contributions to the charge radii and the magnetic moments. The results provide vital information to understand the size and shape of the doubly charmed baryons. We find that the two heavy-charm quarks drive the charge radii and the magnetic moments to smaller values than that of light baryons. The central values of the observables that are obtained using the relativistic action for the charm quark are 5% to 10% larger than those obtained using the Clover action. Utilizing the available lattice data, we reexamine the quark mass dependence of the observables.

In this work, we investigate the production of isovector scalar meson $a_0(1817)$ by the effective Lagrangian approach. Specifically, we employ the Reggeized $t$ channel Born term to calculate the total and differential cross sections for the reaction $K^{-}p\to a_0(1817)\mathrm{\Lambda }$. Our analysis reveals that the optimal energy range for detecting the $a_0(1817)$ meson lies between $W=3.4\mathrm{GeV}$ and $W=3.6\mathrm{GeV}$, where the predicted total cross section reaches a minimum value of 112 nb. Notably, the $t$ channel, as predicted by the Regge model, significantly enhances the differential cross sections, particularly at extreme forward angles. Furthermore, we investigate the Dalitz processes of $2\to 3$ and discuss the feasibility of detecting the $a_0(1817)$ meson in experiments like J-PARC.

Most antineutrinos produced in a nuclear reactor have energies below the inverse beta decay threshold and have not yet been detected. We show that a coherent elastic neutrino-nucleus scattering experiment with an ultralow energy threshold like NUCLEUS can measure the flux of reactor neutrinos below 1.8 MeV. Using a regularized unfolding procedure, we find that a meaningful upper bound can be placed on the low energy flux, but the existence of the neutron capture component cannot be established.

Using data corresponding to an integrated luminosity of $651{\mathrm{pb}}^{-1}$ accumulated at 22 center-of-mass energies from 2.00 to 3.08 GeV by the BESIII experiment, the process $e^{+}{e}^{-}\to \varphi {\pi }^{+}{\pi }^{-}$ is studied. The cross sections for $e^{+}{e}^{-}\to \varphi {\pi }^{+}{\pi }^{-}$ are consistent with previous results, but with improved precision. To measure the mass and width of the structure observed in the cross section line shape, a combine fit is performed after enhancing the contribution from $\varphi f_0(980)$. The fit reveals a structure with the mass of $M=2178\pm 20\pm 5\mathrm{MeV}/c^2$ and the width of $\mathrm{\Gamma }=140\pm 36\pm 16\mathrm{MeV}$, where the first uncertainties are statistical and the second ones are systematic.

We derive an algorithm for computing the total differentials of multiloop integrals expressed as onefold integrals of multiple polylogarithms, which can involve square roots of polynomials up to degree 4 and may evaluate to (elliptic) multiple polylogarithms [(e)MPLs]. This gives simple algebraic rules for computing the ($W-1$, 1) coproduct of the resulting weight-$W$ functions up to period terms, and iterating it gives the symbol without actually performing any integration. In particular, our algorithm generalizes existing MPL integration rules and sidesteps the complicated rationalization procedure in the presence of square roots. We apply our algorithm to conformal double-$D$-gon integrals in $D$ dimensions with generic kinematics and possibly massive circumferential propagators. We directly compute, for the first time, the total differential and symbol (up to period terms) of the $D=3$ double triangle and the $D=4$ double box, which in the special case with massless propagators represent the first appearance of eMPL functions in (two-loop) scattering amplitudes of Aharony-Bergman-Jafferis-Maldacena theory and $\mathcal{N}=4$ super-Yang-Mills theory, respectively.

The potential for mismodeling of ${\nu }_{\mu }/{\nu }_e$, ${\overline{\nu }}_{\mu }/{\overline{\nu }}_e$, and ${\nu }_e/{\overline{\nu }}_e$ cross-section ratios due to nuclear effects is quantified by considering model spread within the full kinematic phase space for charged-current quasielastic interactions. Its impact is then propagated to simulated experimental configurations based on the Hyper-K and $\mathrm{ESS}\nu \mathrm{SB}$ experiments. Although significant discrepancies between theoretical models is confirmed, it is found that these largely lie in regions of phase space that contribute only a very small portion of the flux-integrated cross sections. Overall, a systematic uncertainty on the oscillated flux-averaged ${\nu }_e/{\overline{\nu }}_e$ cross-section ratio is found to be $\sim 2$ and $\sim 4\%$ for Hyper-K and $\mathrm{ESS}\nu \mathrm{SB}$, respectively.

We calculate the holographic complexity of a family of hyperbolic black holes in an Einstein-Maxwell-dilaton system by applying the $\text{complexity}=\text{action}$ conjecture. While people previously studied spherical black holes in the same system, we show that hyperbolic black holes have intriguing features. We confirm that the complexity expression mainly depends on the spacetime causal structure despite the rich thermodynamics. The nontrivial neutral limit that exists only for hyperbolic black holes enables us to analytically obtain the complexity growth rate during phase transitions. We find that the dilaton accelerates the growth rate of complexity, and the Lloyd bound can be violated. This is in contrast to the spherical case where the dilation slows the complexity growth rate down, and the Lloyd bound is always satisfied. As a special case, we study the holographic complexity growth rate of the neutral hairy black holes and find that the Lloyd bound is always violated.