Measurements of gravitational lensing of the cosmic microwave background (CMB) hold the promise of yielding unique insights into cosmology at high redshift. Uncertainties due to baryonic effects associated with galaxy formation and evolution, including gas cooling, star formation, and feedback from active galactic nuclei (AGN) and supernovae, have typically been neglected when forecasting the sensitivity of future CMB surveys. In this paper, we determine the impact of these effects using four suites of hydrodynamical simulations which incorporate various prescriptions for baryonic processes, namely OWLS, BAHAMAS, Horizon, and IllustrisTNG. Our analysis shows characteristic power suppressions of several percent in CMB lensing due to baryonic effects, compared to dark-matter only simulations, at experimentally observable angular scales. We investigate the associated bias in the inferred neutrino mass for experiments like the upcoming Simons Observatory and CMB-S4. Depending on the experimental precision and the strength of the baryonic feedback within the simulations, biases in the neutrino mass sum show significant dispersion, ranging from very small to an overestimation by $1.1\sigma$. We conclude that baryonic effects will likely be non-negligible for a detection of neutrino mass using CMB lensing.

We investigate a particle physics model for cosmic inflation based on the following assumptions: (i) there are at least two complex scalar fields; (ii) the scalar potential is bounded from below and remains perturbative up to the Planck scale; (iii) we assume slow-roll inflation with maximally correlated adiabatic and entropy fluctuations 50–60 e-folds before the end of inflation. The energy scale of the inflation is set automatically by the model. Assuming also at least one massive right-handed neutrino, we explore the allowed parameter space of the scalar potential as a function of the Yukawa coupling of this neutrino.

Light dark photons are subject to various plasma effects, such as Debye screening and resonant oscillations, which can lead to a more complex cosmological evolution than is experienced by conventional cold dark matter candidates. Maintaining a consistent history of dark photon dark matter requires ensuring that the superthermal abundance present in the early Universe (i) does not deviate significantly after the formation of the cosmic microwave background (CMB), and (ii) does not excessively leak into the Standard Model plasma after big band nucleosynthesis (BBN). We point out that the role of nonresonant absorption, which has previously been neglected in cosmological studies of this dark matter candidate, produces strong constraints on dark photon dark matter with mass as low as ${10}^{-22}\mathrm{eV}$. Furthermore, we show that resonant conversion of dark photons after recombination can produce excessive heating of the intergalactic medium (IGM) which is capable of prematurely reionizing hydrogen and helium, leaving a distinct imprint on both the Ly-$\alpha$ forest and the integrated optical depth of the CMB. Our constraints surpass existing cosmological bounds by more than 5 orders of magnitude across a wide range of dark photon masses.

Assuming that the differential rotation of the massive neutron star (NS) formed in the double NS (DNS) mergers has been effectively terminated by the magnetic braking and a uniform rotation has been subsequently established (i.e., a supramassive NS is formed), we analytically derive in this work an approximated expression for the critical total gravitational mass ($M_{\mathrm{tot},\mathrm{c}}$) to form supramassive NS (SMNS) in the DNS mergers, benefited from some equation of state (EoS) insensitive relationships. The maximum gravitational mass of the nonrotating NSs ($M_{\mathrm{TOV}}$) as well as the dimensionless angular momentum of the remnant ($j$) play the dominant roles in modifying $M_{\mathrm{tot},\mathrm{c}}$, while the radius and mass differences of the premerger NSs do not. The GW170817/GRB 170817A/AT2017gfo observations have provided so far the best opportunity to quantitatively evaluate $M_{\mathrm{TOV}}$. Supposing the central engine for GRB 170817A is a black hole quickly formed in the collapse of an SMNS, we find $M_{\mathrm{TOV}}=2.13_{-0.08}^{+0.09}{M}_{\odot }$ (68.3% credibility interval, including also the uncertainties of the EoS insensitive relationships), which is consistent with the constraints set by current NS mass measurements.

According to the Kubo formulas, we employ the ($3+1$)-d parton cascade, Boltzmann approach of multiparton scatterings to calculate the anisotropic transport coefficients (shear viscosity and electric conductivity) for an ultrarelativistic Boltzmann gas in the presence of a magnetic field. The results are compared with those recently obtained by using the Grad’s approximation. We find good agreements between both results, which confirms the general use of the derived Kubo formulas for calculating the anisotropic transport coefficients of quark-gluon plasma in a magnetic field.

We develop a general formalism for multiple moduli and their associated modular symmetries. We apply this formalism to an example based on three moduli with finite modular symmetries $S_4^A$, $S_4^B$, and $S_4^C$, associated with two right-handed neutrinos and the charged lepton sector, respectively. The symmetry is broken by two bitriplet scalars to the diagonal $S_4$ subgroup. The low energy effective theory involves the three independent moduli fields ${\tau }_A$, ${\tau }_B$, and ${\tau }_C$, which preserve the residual modular subgroups $Z_3^A$, $Z_2^B$, and $Z_3^C$, in their respective sectors, leading to trimaximal ${\mathrm{TM}}_1$ lepton mixing, consistent with current data, without flavons.

The diquark is a strongly correlated quark pair that plays an important role in hadrons and hadronic matter. In order to treat the diquark as a building block of hadrons, we formulate an effective theory of diquark fields with $SU(3{)}_R\times SU(3{)}_L$ chiral symmetry. We concentrate on the scalar ($0^{+}$) and pseudoscalar ($0^{-}$) diquarks and construct a linear-sigma-model Lagrangian. It is found that the effective Lagrangian contains a new type of chirally symmetric meson-diquark-diquark coupling that breaks axial $U_A(1)$ symmetry. We discuss consequences of the $U_A(1)$ anomaly term to the diquark masses as well as to the singly heavy baryon spectrum, which is directly related to the diquark spectrum. We find an inverse mass ordering between strange and nonstrange diquarks. The parameters of the effective theory can be determined by the help of lattice QCD calculations of diquarks and also from the mass spectrum of the singly heavy baryons. We determine the strength of the $U_A(1)$ anomaly term, which is found to give a significant portion of the diquark masses.

A recently observed spectrum of $P_c$ states exhibits a strong link to ${\mathrm{\Sigma }}_c{\overline{D}}^{(*)}$ thresholds. In spite of successful molecular interpretations, we still push forward to wonder whether there exist finer structures. Utilizing the effecitve Lagrangians respecting heavy quark symmetry and chiral symmetry, as well as instantaneous Bethe-Salpeter equations, we investigate the ${\mathrm{\Sigma }}_c{\overline{D}}^{(*)}$ interactions and three $P_c$ states. We confirm that $P_c(4312)$ and $P_c(4440)$ are good candidates of ${\mathrm{\Sigma }}_c\overline{D}$ and ${\mathrm{\Sigma }}_c{\overline{D}}^{*}$ molecules with spin-$\frac{1}{2}$, respectively. Unlike other molecular calculations, our results indicate the $P_c(4457)$ signal might be a mixture of spin-$\frac{3}{2}$ and spin-$\frac{1}{2}$ ${\mathrm{\Sigma }}_c{\overline{D}}^{*}$ molecules, where the latter one appears to be an excitation of $P_c(4440)$. Therefore we conclude that, confronting three LHCb $P_c$ signals, there may exist not three, but four molecular states.

The quantum null energy condition (QNEC) is a quantum generalization of the null energy condition, which gives a lower bound on the null energy in terms of the second derivative of the von Neumann entropy or entanglement entropy of some region with respect to a null direction. The QNEC states that $⟨T_{kk}{⟩}_p\ge {\lim }_{A\to 0}(\frac{\hslash }{2\pi A}{S}_{\mathrm{out}}^{\prime \prime })$, where $S_{\mathrm{out}}$ is the entanglement entropy restricted to one side of a codimension-2 surface $\mathrm{\Sigma }$, which is deformed in the null direction about a neighborhood of point $p$ with area $A$. A proof of QNEC has been given before, which applies to free and super-renormalizable bosonic field theories, and to any points that lie on a stationary null surface. Using similar assumptions and methods, we prove the QNEC for fermionic field theories.

We examine the holographic complexity conjectures in the context of holographic theories of Friedmann-Robertson-Walker (FRW) spacetimes. Analyzing first the complexity-action conjecture for a flat FRW universe with one component, we find that the complexity grows as $t^2$, regardless of the value of $w$. In addition, we examine the holographic complexity for a flat universe sourced by a scalar field that is undergoing a transition. We find that the complexity decreases when the holographic entanglement entropy decreases for this universe. Moreover, the calculations show that, while the entanglement entropy decreases only slightly, the magnitudes of the corresponding fractional decreases in complexity are much larger. This presumably reflects the fact that entanglement is computationally expensive. Interestingly, we find that the gravitational action behaves like a complexity, while the total action is negative, and is thus ill suited as a measure of complexity, in contrast to the conjectures in AdS settings. Finally, the implications of the complexity-volume conjecture are examined. The results are qualitatively similar to the complexity-action conjecture.

This article sheds new light on the problem of cosmological reduction in loop quantum gravity. We critically analyze quantum reduced loop gravity—an attempt to extract the cosmological sector of the full theory. We reconsider the reduction procedure applied to the states of the kinematical Hilbert space, developing a comparative analysis with previous efforts in the literature. We show that the constraints of the model were formerly instantiated in an inconsistent fashion, leading to an overconstrained dynamics and an ill-defined Hilbert space. We then scrutinize alternative implementations of symmetry reduction. While remaining unaffected by the shortcomings encountered in quantum reduced loop gravity, these latter procedures bridge the gap between the full theory and former endeavors in loop quantum cosmology.

Motivated by the study of conserved Aretakis charges for a scalar field on the horizon of an extremal black hole, we construct the metrics for certain classes of four-dimensional and five-dimensional extremal rotating black holes in Gaussian null coordinates. We obtain these as expansions in powers of the radial coordinate, up to sufficient order to be able to compute the Aretakis charges. The metrics we consider are for 4-charge black holes in four-dimensional STU supergravity ($N=2$ supergravity coupled to three vector multiplets) (including the Kerr-Newman black hole in the equal-charge case) and the general 3-charge black holes in five-dimensional STU supergravity. We also investigate the circumstances under which the Aretakis charges of an extremal black hole can be mapped by conformal inversion of the metric into Newman-Penrose charges at null infinity. We show that while this works for four-dimensional static black holes, a simple radial inversion fails in rotating cases because a necessary conformal symmetry of the massless scalar equation breaks down. We also discuss that a massless scalar field in dimensions higher than four does not have any conserved Newman-Penrose charge, even in a static asymptotically flat spacetime.

In the case of a spherically symmetric nonlinear scalar field (SF) in flat space, besides singularity at the center, spherical singularities can occur for nonzero values of radial variable $r>0$. We show that in the general relativity the gravitational field suppresses the occurrence of the spherical singularities under some generic conditions. Our consideration deals with asymptotically flat space-times around static spherically symmetric configurations in the presence of $N$ nonlinear SFs, which are minimally coupled to gravity. Constraints are imposed on the SF potentials, which guarantee a monotonicity of the fields as functions of $r$; also the potentials are assumed to be exponentially bounded. We give direct proof that solutions of the joint system of Einstein-SF equations satisfying the conditions of asymptotic flatness are regular for all values of $r$, except for naked singularities in the center $r=0$ in the Schwarzschild (curvature) coordinates. Asymptotic relations for SF and a metric near the center are derived, which appear to be remarkably similar to the Fisher solution for free SF. These relations determine two main types of the corresponding geodesic structure when photons can be captured by the singularity or not. To illustrate, the case of one SF with monomial potential is analyzed in detail numerically. We show that the image of the accretion disk around the singularity, observed from infinity, can take the form of a bright ring with a dark spot in the center, like an ordinary black hole.

We provide more evidence of not quite black holes at LIGO. We update and streamline our previous search strategy and apply it to the ten black hole merger events and the one neutron star merger event. The strategy is aimed at the evenly spaced resonance spectrum expected from not quite black holes, given that at low frequencies the radial wave equation describes the modes of a stretched 1D cavity. We describe various indications of the self-consistency of the apparent signals across all events in the context of a simple theoretical model. The merger with the largest final mass, spin and redshift, GW170729, provides additional interesting support.

A deformed relativistic kinematics can be understood within a geometrical framework through a maximally symmetric momentum space. However, when considering this kind of approach, usually one works in a flat spacetime and in a curved momentum space. In this paper, we will discuss a possible generalization to take into account both curvatures and some possible observable effects. We will first explain how to construct a metric in the cotangent bundle in order to have a curved spacetime with a nontrivial geometry in momentum space and the relationship with an action in phase space characterized by a deformed Casimir. Then, we will study within this proposal two different space-time geometries. In the Friedmann-Robertson-Walker universe, we will see the modifications in the geodesics (redshift, luminosity distance, and geodesic expansion) due to a momentum dependence of the metric in the cotangent bundle. Also, we will see that when the spacetime considered is a Schwarzschild black hole, one still has a common horizon for particles with different energies, differently from a Lorentz invariance violation case. However, the surface gravity computed as the peeling off of null geodesics is energy dependent.

We derive the equations of motion for scalar metric perturbations in a particular nonsingular bouncing cosmology, where the big bang singularity is replaced by a spacetime defect with a degenerate metric. The adiabatic perturbation solution is obtained for nonrelativistic hydrodynamic matter. We get the same result by working with conformal coordinates. This last method is also valid for vector and tensor metric perturbations, and selected results are presented. We, finally, discuss several new effects from the linear perturbations of this nonsingular bouncing cosmology, such as across-bounce information transfer and the possible imprint on cosmological perturbations from a new phase responsible for the effective spacetime defect.

An idealized “test” object in general relativity moves along a geodesic. However, if the object has a finite mass, this will create additional curvature in the spacetime, causing it to deviate from geodesic motion. If the mass is nonetheless sufficiently small, such an effect is usually treated perturbatively and is known as the gravitational self-force due to the object. This issue is still an open problem in gravitational physics today, motivated not only by basic foundational interest, but also by the need for its direct application in gravitational wave astronomy. In particular, the observation of extreme-mass-ratio inspirals by the future space-based detector LISA will rely crucially on an accurate modeling of the self-force driving the orbital evolution and gravitational wave emission of such systems. In this paper, we present a novel derivation, based on conservation laws, of the basic equations of motion for this problem. They are formulated with the use of a quasilocal (rather than matter) stress-energy-momentum tensor—in particular, the Brown-York tensor—so as to capture gravitational effects in the momentum flux of the object, including the self-force. Our formulation and resulting equations of motion are independent of the choice of the perturbative gauge. We show that, in addition to the usual gravitational self-force term, they also lead to an additional “self-pressure” force not found in previous analyses, and also that our results correctly recover known formulas under appropriate conditions. Our approach thus offers a fresh geometrical picture from which to understand the self-force fundamentally, and potentially useful new avenues for computing it practically.

We study the core mass-halo mass relation of bosonic dark matter halos, in the form of self-gravitating Bose-Einstein condensates, harboring a supermassive black hole. We use the “velocity dispersion tracing” relation according to which the velocity dispersion in the core $v_c^2\sim G{M}_c/R_c$ is of the same order as the velocity dispersion in the halo $v_h^2\sim G{M}_h/r_h$ (this relation can be justified from thermodynamical arguments) and the approximate analytical mass-radius relation of the quantum core in the presence of a central black hole obtained in our previous paper [P.H. Chavanis, Eur. Phys. J. Plus 134, 352 (2019)]. For a given minimum halo mass $(M_h{)}_{\min }\sim {10}^8{M}_{\odot }$ determined by the observations, the only free parameter of our model is the scattering length $a_s$ of the bosons (their mass $m$ is then determined in order to match the characteristics of the minimum halo). For noninteracting bosons and for bosons with a repulsive self-interaction, we find that the core mass $M_c$ increases with the halo mass $M_h$ and achieves a maximum value $(M_c{)}_{\max }$ at some halo mass $(M_h{)}_{*}$ before decreasing. The whole series of equilibria is stable. For bosons with an attractive self-interaction, we find that the core mass achieves a maximum value $(M_c{)}_{\max }$ at some halo mass $(M_h{)}_{*}$ before decreasing. The series of equilibria becomes unstable above a maximum halo mass $(M_h{)}_{\max }\ge (M_h{)}_{*}$. In the absence of black hole $(M_h{)}_{\max }=(M_h{)}_{*}$. At that point, the quantum core (similar to a dilute axion star) collapses. We perform a similar study for fermionic dark matter halos. We find that they behave similarly to bosonic dark matter halos with a repulsive self-interaction, the Pauli exclusion principle for fermions playing the role of the repulsive self-interaction for bosons.

We propose a new dark energy model for solving the cosmological fine-tuning and coincidence problems. A default assumption is that the fine-tuning problem disappears if we do not interpret dark energy as vacuum energy. The key idea to solving the coincidence problem is that the Universe may have several acceleration phases across the whole cosmic history. The specific example we study is a quintessence model with approximately repeated double exponential potential, which only introduces one Planck scale parameter and three dimensionless parameters of order unity. The cosmological background evolution equations can be recast into a four-dimensional dynamical system and its main properties are discussed in details. Preliminary calculations show that our model is able to explain the observed cosmic late-time acceleration.