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Register a new userScale-Invariant Hidden Local Symmetry, Topology Change and Dense Baryonic Matter II
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Exploiting certain robust topological inputs from the skyrmion description of compressed baryonic matter with a scale-chiral symmetric Lagrangian, we predict the equation of state that is consistent with the properties of nuclear matter at the equilibrium density, supports the maximum mass of massive compact star $sim 2 M_odot$ and surprisingly gives the sound velocity close to the conformal velocity $1/sqrt{3}$ at densities $gtrsim 3 n_0$. At the core of this result is the observation that parity-doubling occurs in the nucleon structure as density goes above $sim 2n_0$ with a chiral-singlet mass $m_0 sim (0.6-0.9) m_N$, hinting at a possible up-to-date unsuspected source of proton mass and an emergence at high density of scale symmetry and flavor local symmetry, both hidden in the QCD vacuum.
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When scale symmetry is implemented into hidden local symmetry in low-energy strong interactions to arrive at a scale-invariant hidden local symmetric (HLS) theory, the scalar $f_0(500)$ may be interpreted as pseudo-Nambu-Goldstone (pNG) boson, i.e., dilaton, of spontaneously broken scale invariance, joining the pseudo-scalar pNG bosons $pi$ and the matter fields $V=(rho,omega)$ as relevant degrees of freedom. Implementing the skyrmion-half-skyrmion transition predicted at large $N_c$ in QCD at a density roughly twice the nuclear matter density found in the crystal simulation of dense skyrmion matter, we determine the intrinsically density-dependent (IDD) bare parameters of the scale-invariant HLS Lagrangian matched to QCD at a matching scale $Lambda_M$. The resulting effective Lagrangian, with the parameters scaling with the density of the system, is applied to nuclear matter and dense baryonic matter relevant to massive compact stars by means of the double-decimation renormalization-group $V_{lowk}$ formalism. We satisfactorily post-dict the properties of normal nuclear matter and more significantly {it predict} the EoS of dense compact-star matter that quantitatively accounts for the presently available data coming from both the terrestrial and space laboratories. We interpret the resulting structure of compact-star matter as revealing how the combination of hidden-scale symmetry and hidden local symmetry manifests itself in compressed baryonic matter.
Topology effects have being extensively studied and confirmed in strongly correlated condensed matter physics. In the large color number limit of QCD, 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 to possible ``emergent scale and local flavor symmetries at high density. All nuclear matter properties from the saturation density $n_0$ up to several times $n_0$ can be fairly well described. A uniquely novel -- and unorthdox -- feature of this theory is the precocious appearance of the pseudo-conformal sound velocity $v^2_{s}/c^2 approx 1/3$, 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 $gsim 2n_0$ in accessing massive compact stars. We confront the approach with the data from GW170817 and GW190425.
We investigate the properties of baryonic matter within the framework of the in-medium modified chiral soliton model by taking into account the effects of surrounding baryonic environment on the properties of in-medium baryons. The internal parameters of the model are determined based on nuclear phenomenology at nonstrange sector and fitted by reproducing nuclear matter properties near the saturation point. We discuss the equations of state in different nuclear environments such as symmetric nuclear matter, neutron and strange matters. We show that the results for the equations of state are in good agreement with the phenomenology of nuclear matter. We also discuss how the SU(3) baryons masses undergo changes in these various types of nuclear matter.
We study the weak interaction processes taking place within a combustion flame that converts dense hadronic matter into quark matter in a compact star. Using the Boltzmann equation we follow the evolution of a small element of just deconfined quark matter all along the flame interior until it reaches chemical equilibrium at the back boundary of the flame. We obtain the reaction rates and neutrino emissivities of all the relevant weak interaction processes without making any assumption about the neutrino degeneracy. We analyse systematically the role the initial conditions of unburnt hadronic matter, such as density, temperature, neutrino trapping and composition, focusing on typical astrophysical scenarios such as cold neutron stars, protoneutron stars, and post merger compact objects. We find that the temperature within the flame rises significantly in a timescale of 1 nanosecond. The increase in $T$ strongly depends on the initial strangeness of hadronic matter and tends to be more drastic at larger densities. Typical final values range between $20$ and $60 , mathrm{MeV}$. The nonleptonic process $u + d rightarrow u + s$ is always dominant in cold stars, but in hot objects the process $u + e^{-} leftrightarrow d + { u_e}$ becomes relevant, and in some cases dominant, near chemical equilibrium. The rates for the other processes are orders of magnitude smaller. We find that the neutrino emissivity per baryon is very large, leading to a total energy release per baryon of $2-60 , mathrm{MeV}$ in the form of neutrinos along the flame. We discuss some astrophysical consequences of the results.
The recent announcement of the PREX-II measurement of the neutron skin of $^{208}$Pb that suggests a stiff symmetry energy near nuclear matter density $n_0$ and its impact on the EoS of massive compact stars raise the issue as to whether the widely accepted lore in nuclear astrophysics that the EoS determined at $n_0$ necessarily gives a stringent ``constraint at high densities relevant to massive compact stars. We present the argument that the ``cusp structure in the symmetry energy at $n_{1/2}gsim 2 n_0$ predicted by a topology change in dense matter could obstruct the validity of the lore. The topology change, encoding the emergence of QCD degrees of freedom in terms of hidden local and scale symmetries, predicts an EoS that is soft below and stiff above $ngsim n_{1/2}$, involving no low-order phase transitions, and yields the macrophysical properties of neutron stars overall consistent with the astrophysical observations including the maximum mass $ 2.0lsim M/ M_odotlsim 2.2$ as well as the GW data. Furthermore it describes the interior core of the massive stars constituted of baryon-charge-fractionalized quasi-fermions, that are neither baryonic nor quarkonic, with the ``pseudo-conformal sound speed $v^2_{pcs}/c^2approx 1/3$ converged from below at $n_{1/2}$ with a nonzero trace of energy-momentum tensor. { In the renormalization-group approach to interacting fermions dubbed $Gn$EFT, the strangeness degrees of freedom play no role in the density regime relevant to the massive stars considered.}
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