Topology change, emergent symmetries and compact star matter

Topology effects have being extensively studied and confirmed in strongly correlated condensed matter physics. In the limit of large number of colors, baryons can be regarded as topological objects—skyrmions—and the baryonic matter can be regarded as a skyrmion matter. We review in this paper the generalized effective field theory for dense compact-star matter constructed with the robust inputs obtained from the skyrmion approach to dense nuclear matter, relying on possible “emergent” scale and local flavor symmetries at high density. All nuclear matter properties from the saturation density n0 up to several times n0 can be fairly well described. A uniquely novel—and unorthdox—feature of this theory is the precocious appearance of the pseudo-conformal sound velocity $v^{2}_{s}/c^{2} \approx 1/3$ v s 2 / c 2 ≈ 1 / 3 , with the non-vanishing trace of the energy momentum tensor of the system. The topology change encoded in the density scaling of low energy constants is interpreted as the quark-hadron continuity in the sense of Cheshire Cat Principle (CCP) at density $\gtrsim 2n_{0}$ ≳ 2 n 0 in accessing massive compact stars. We confront the approach with the data from GW170817 and GW190425.

Small Angle Neutron Scattering Studies of Skyrmion Lattices

Skyrmion lattices in chiral magnets can be regarded as macroscopic lattices formed by topological entities with particle like properties where the particle-like character of the Skyrmions is reflected in the integer winding number of their magnetization [1]. Caused by their topology, Skyrmions cannot be destroyed or created by a smooth deformation of a trivial spin texture. Skyrmion lines can be seen as magnetic whirls – sharing strong similarities with vortices of type II superconductors. Analogous to the large variety of different phases of superconducting vortex matter, Skyrmion lattice melting transitions, Skyrmion liquids and Skyrmion glass phases are expected to exist in the various B20 materials. The structure of Skyrmion matter thereby sensitively reflects the underlying physical properties of the material carrying the Skyrmions. Moreover, due to their topology, Skyrmion lattices in chiral magnets provide an excellent showcase for the investigation of topological stability and phase conversion [2]. A further consequence of the special topological properties of Skyrmions is called emergent electrodynamics: While moving through the Skyrmion lattice, conduction electrons collect a Berry´s phase in real space which leads to a very efficient coupling of transport current and magnetic structure. This leads to considerable spin transfer torque effects at current densities as low as 10^6 A/m2 [3]. Small angle neutron scattering (SANS) has played a central role in the investigation of Skyrmion lattices. We show how SANS can be used for a detailed investigation of the structure, stability, transport properties and topological decay of Skyrmion lattices in B20 compounds. *Work in collaboration with: T. Adams, A. Bauer, H. Berger, P. Böni, S. Buhrandt, A. Chacon, S. Dunsiger, L. Eng, K. Everschor-Sitte, M. Garst, R. Georgii, M. Janoschek, F. Jonietz, J. Kindervater, P. Milde, A. Neubauer, C. Pfleiderer, A. Rosch, C. Schütte, J. Seidel, J. Waizner, W. Wünzer

VECTOR MESONS AND DENSE SKYRMION MATTER

We describe a problem associated with the role the ω meson at short distance in applying the Skyrme model to the dense matter: the ω coupling to the baryon density prevents the scale-anomaly dilaton field from developing a vanishing vacuum expectation value at the chiral restoration, which is at variance with standard scenario of QCD at the phase transition. We suggest a possible phenomenological solution to this puzzle and discuss its physical consequences.