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We have investigated the electromagnetic decays of the antitriplet and sextet charmed baryon systems with JP = 1+/2, 3+/2 in the framework of the heavy baryon chiral perturbation theory. We first construct the chiral Lagrangians at 0(p²) and 0(p³). Then we calculate the electromagnetic (EM) decay amplitudes of the charmed baryon systems up to 0(p³). With the help of the quark model, we estimate the low energy constants. The numerical results of the EM decay widths show good convergence of the chiral expansion. We notice that the two neutral EM decay processes Ξ'c0 → γ + Ξc0 and Ξ*c0 → γ Ξc0 are strongly suppressed by the SU(3) U-spin flavor symmetry. With the same formalism, we also estimate the EM decay widths of the bottomed baryons. The EM decay widths of the heavy baryons may be measured at facilities such as LHCb and JPARC. The explicit chiral structures of the heavy baryon decay amplitudes derived in this work may be useful to the possible chiral extrapolations of the future lattice simulations of these EM decay amplitudes. [ABSTRACT FROM AUTHOR]

We obtain bounds on the stability of various self-gravitating astrophysical objects using a new measure of shape complexity known as configurational entropy. We apply the method to Newtonian polytropes, neutron stars with an Oppenheimer-Volkoff equation of state, and to self-gravitating configurations of complex scalar field (boson stars) with different self couplings, showing that the critical stability region of these stellar configurations obtained from traditional perturbation methods correlates well with critical points of the configurational entropy with accuracy of a few percent or better. [ABSTRACT FROM AUTHOR]

We investigate the antitriplet and sextet heavy baryon systems with JP =1/2 +, 3/2+ in the framework of the heavy baryon chiral perturbation theory. We first calculate the chiral corrections to the heavy baryon mass from the SU(3) flavor breaking effect up to O(p³). Then we extend the same formalism to calculate the chiral corrections to the axial charges of the heavy baryons in the isospin symmetry limit. [ABSTRACT FROM AUTHOR]

Gravitational-wave sources can serve as standard sirens to probe cosmology by measuring their luminosity distance and redshift. Such standard sirens are also useful to probe theories beyond general relativity with a modified gravitational-wave propagation. Many of previous studies on the latter assume multimessenger observations so that the luminosity distance can be measured with gravitational waves while the redshift is obtained by identifying sources' host galaxies from electromagnetic counterparts. Given that gravitational-wave events of binary neutron star coalescences with associated electromagnetic counterpart detections are expected to be rather rare, it is important to examine the possibility of using standard sirens with gravitational-wave observations alone to probe gravity. In this paper, we achieve this by extracting the redshift from the tidal measurement of binary neutron stars that was originally proposed within the context of gravitational-wave cosmology (another approach is to correlate "dark sirens" with galaxy catalogs that we do not consider here). We consider not only observations with ground-based detectors (e.g., Einstein Telescope) but also multiband observations between ground-based and space-based (e.g., DECIGO) interferometers. We find that such multiband observations with the tidal information can constrain a parametric non-Einsteinian deviation in the luminosity distance (due to the modified friction in the gravitational wave evolution) more stringently than the case with electromagnetic counterparts by a factor of a few. We also map the above-projected constraints on the parametric deviation to those on specific theories and phenomenological models beyond general relativity to put the former into context. [ABSTRACT FROM AUTHOR]

Recent observations of neutron stars with radio, x rays, and gravitational waves have begun to constrain the equation of state for nuclear matter beyond the nuclear saturation density. To one's surprise, there exist approximate universal relations connecting certain bulk properties of neutron stars that are insensitive to the underlying equation of state and having important applications on probing fundamental physics including nuclear and gravitational physics. To date, analytic works on universal relations for realistic neutron stars are lacking, which may lead to a better understanding of the origin of the universality. Here, we focus on the universal relations between the compactness (C), the moment of inertia (I), and the tidal deformability (related to the Love number) and derive analytic, approximate I-Love-C relations. To achieve this, we construct slowly rotating and tidally deformed neutron star solutions analytically starting from an extended Tolman VII model that accurately describes nonrotating realistic neutron stars, which allows us to extract the moment of inertia and the tidal deformability on top of the compactness. We solve the field equations analytically by expanding them about the Newtonian limit and keeping up to sixth order in the stellar compactness. Based on these analytic solutions, we can mathematically demonstrate the O (10%) equation-of-state variation in the I-C and Love-C relations and the O (1%) variation in the I-Love relation that have previously been found numerically. Our new analytic relations agree more accurately with numerical results for realistic neutron stars (especially the I-C and Love-C ones) than the analytic relations for constant-density stars derived in previous work. Based on these analytic findings, we attribute a possible origin of the universality for the I-C and Love-C relations to the fact that the energy density of realistic neutron stars can be approximated as a quadratic function, as is the case for the Tolman VII solution. [ABSTRACT FROM AUTHOR]

Studies of neutron stars are extremely timely, given the recent detection of gravitational waves from a binary neutron star merger GW170817 and the International Space Station payload NICER currently in operation that aims to determine radii of neutron stars to a precision better than 5%. In many cases, neutron star solutions are constructed numerically due to the complexity of the field equations with realistic equations of state. However, to relate observables like the neutron star mass and radius to interior quantities like central density and pressure, it would be useful to provide an accurate, analytic modeling of a neutron star interior. One such solution for static and isolated neutron stars is the Tolman VII solution characterized only by two parameters (e.g., mass and radius), though its agreement with numerical solutions is not perfect. We introduce here an improved analytic model based on the Tolman VII solution by introducing an additional parameter to make the analytic density profile agree better with the numerically obtained one. This additional parameter can be fitted in terms of the stellar mass, radius, and central density in an equation of state-insensitive way. In most cases, we find that the new model more accurately describes realistic profiles than the original Tolman VII solution by a factor of 2-5. Our results are first-step calculations towards constructing analytic interior solutions for more realistic neutron stars under rotation or tidal deformation. [ABSTRACT FROM AUTHOR]