Holographic Soliton Crystals for Dense Nuclear Matter and Neutron Stars

Researchers have developed a new equation of state (EOS) for dense nuclear matter, using a holographic QCD model that represents baryons as solitons. This approach, which goes beyond previous homogeneous approximations, constructs dense baryonic matter more directly from the solitonic description of holographic baryons. The team assembled an infinite face-centered cubic (FCC) crystal, using the two-baryon interaction potential derived from linearized soliton tails in a curved background, thus approximating a quantum liquid of baryons. The symmetric-matter EOS was calibrated by fixing the 't Hooft coupling (λ) and the Witten-Sakai-Sugimoto scale (M_KK) to saturation-density and onset-chemical-potential properties. Additionally, a quark-mass term was included to reproduce the physical pion mass (m_π = 135 MeV). This fit proved to be consistent with the parameters of the vacuum meson sector and with Brown-Rho scaling in a dense medium. The incompressibility obtained at saturation density is of the correct order of magnitude, which significantly contrasts with previous homogeneous approximations. The study was extended to beta-equilibrated matter, incorporating phenomenological input for the symmetry energy. This allowed for the derivation of hybrid EOS and neutron-star observables that are compatible with constraints from NICER observations. This advancement provides a more precise description of dense nuclear matter, with significant implications for understanding neutron stars and nuclear physics at high densities.

Positive Mass Theorem Proven for Spacetime with Corners

Researchers have demonstrated a positive mass theorem for asymptotically flat initial data featuring "corners" along a hypersurface Σ. This advance is significant in general relativity, as it extends the validity of a fundamental theorem that relates the energy and momentum of an isolated system to the curvature of spacetime. The result is applicable to dimensions n ≥ 3 and establishes that the energy E must be greater than or equal to the magnitude of the momentum |P| in the exterior end of spacetime, provided certain conditions are met. The positive mass theorem is a cornerstone in gravitational physics, ensuring that the total mass-energy of an isolated system is non-negative. The novelty of this work lies in its ability to address spacetime configurations that are not smooth but exhibit discontinuities or "corners." To achieve this, a strict dominant energy deformation theorem has been developed that preserves a specific corner condition on the Bartnik data across Σ. This approach allows for the analysis of more complex and realistic gravitational systems. The proof relies on the dominant energy condition, which must hold on each side of the hypersurface Σ, and on the Bartnik data satisfying the corner condition. These data are crucial for describing the geometry and gravitational field at the boundary of a region. The ability to handle these geometric singularities opens new avenues for studying the stability and energetic properties of exotic gravitational configurations, with implications for understanding black holes and other compact objects.