A Way of Approach to Ultra Dense Matter and Neutron Stars with Quark Matter Core T. Takatsuka (Iwate Univ.) In collaboration with T. Hatsuda (Univ. Tokyo/ RIKEN) and K. Masuda (Univ. Tokyo) Int. Workshop on “Formation of Compact Stars” (March 7-9, 2012, Waseda Univ.) □ Motivation □ Dramatic effects of hyperons □ Strategy to hybrid star EOS □ Possibility of Hybrid Stars

□ Motivation ○ Obs. of 2M_{solar}-NS[1] → stringent cond. on NS-EOS (stiffer) ○ Various new-phases proposed → tend to soften EOS (→ significant) ○ Especially, hyperon (Y)-mixing → Dramatic Softening, contradict NS-mass observations (even for 1.44 M_{solar}) ○ This serious problem can be solved if we introduce the universal 3-body force repulsion (not only for NN part, but also YN and YY parts) [2] ○ Even 2M_{solar}-NS is possible[3] [1] P.B. Demorest, et al., Nature, 467 (2010) [2] T. Takatsuka, Prog. Theor. Phys. Suppl. No 156 (2004) 84. [3] T. Takatsuka, S. Nishizki and R. Tamagaki, Proc. Int. Symp. “FM50” (AIP Conference proceedings, 2008) 209.

□ Hyperon Mixing in NS cores → Hyperon (Y) surely participate in Neutron Star (NS) Cores → Standard picture for NS constituens: Old (n, p, e^-, μ^-) → Now (n, p, Y, e^-, μ^-)

□ Our approach [1] 1) G-matrix-based effective interactions V applicable to {N+Y}-matter 2) 3-body force U(TNI; phenomenological one of Illinoi’s type, expressed as an effective 2-body force) 3) Parameters in TNI are determined so that the EOS from V+U satisfies the saturation property, symmetry energy and nuclear incompressibility κ: κ=250(300)MeV for TNI2(TNI3) [1] T. Takatsuka, Prog. Theor. Phys. Suppl. No. 156 (2004) 84

Dramatic softening of EOS Necessity of “Extra Repulsion” TNI3 TNI3u: Universal inclusion of TNI3 repulsion

L-Vidana et al, P.R. C62 (2000) M. Baldo et al, P.R. C61 (2000)

○ Hyperons are always present → profound consequence for NS-mass H. Dapo, B-J. Schaefer and J. Wambach, Phys. Rev. C81 (2010)

2πΔ （ Fujita-Miyazawa)-Type 3-body Force Extended to N+Δ space B* B*=(Δ, Σ^-, Σ^0)

(a)2B come in short distance (b)Deformation (resistance) (c)Fusion into 6-quark state (by R. Tamagaki) Repulsion from SJM (string-junction quark model) -----flavor independent (universal) Prog. Theor. Phys. 119 (2008) 965.

Mass v.s. Central Density NS-mass from 2-body force + ”universal” 3-body force (2πΔ- type + SJM). M_{max} >2M_{solar} is possible. How about NSs With Q-Matt.core?  Our motivation

○ Massive NS → means that the central density (ρ_c) would be very high → hadrons begin to overlap,quarks tend to be deconfined and eventually realize q-matter core → 2-solar mass NS (hybrid) is made possible or not ? → Some works say “YES” and Some works say “NO”, Why? ○ Our aim here is to discuss the problem by a new strategy.

A way of approach H-phase H-Q trans. Q-phase ? uncertain □ H: point particle + interaction → G-Matrix, Variational □ Q: q-matter + asymptotic freedom □ HQ Phase transition Cross point (Maxwell, Gibbs) → not necessarily reliable □ Matching Conditions ○ p increasing with ρ ○ thermodynamics (e, p) ○ coincide at x_H and x_Q

□ Hadron Matter phase ○ Matter composed of N (n, p), Y(Λ, Σ^-) and Leptons (e^-, μ^-) ○ effective interaction approach based on G-matrix calculations, (effective int. V for NN, NY, YY) Introduction of 3-body force U (TNI, phenomenological Illinoi-type, expressed as effective 2-body force) ○ V+U satisfy the saturation property and symmetry energy at nuclear density ○ (hard, soft) is classified by the incompressibility κ TNI3u → κ=300MeV, TNI2u → κ=250MeV

□ Quark Matter phase ○ Flavor symmetric (u, d, s)-quark gass, by a simple MIT-Bag model ○ η= effective parameter (deviation from asymptotic freedom) η=1 ← free q-gass η<1 ← + OGE correction η>1 ← + some repulsive effects (assumed) ○ EOS for H-phase would be reliable up to (3-6)ρ_0 → x_H=(3-6)ρ_0 ○ q-matter would come into existence beyond x_Q ≃ (8 ～ 10) c.f. ρ ～ 8.4 (11.2)ρ_0 for r_0=0.55 (0.50)fm

Matching X=ρ/ρ _ o

Some results (preliminary) CASE η B**(1/4) x_H x_Q M_{max} R ρ_c ① ② ③ ④ ⑤ B**(1/4) in MeV, x_H=ρ_H/ρ_0, x_Q=ρ_Q/ρ=0 M_{max} in M_{solar}, R in km ρ_c in ρ_0 (= nuclear density; 0.17/fm^3)

□ To summarize ; Hyperon effects should be taken into account. The maximum mass of hybrid star strongly depends on the Q-matter EOS, as well as the stiffnes of H-matter EOS. The mass exceeding 2-solar mass would be possible only when the EOS of Q-matter is stiffer than that of free quark gass. Further study is in progress, by using more detailed quark matter EOS (by NJL-model ;[ ４ ] ) and more refined matching procedure, i.e., “superposition” of hadron and quark phases in the H-Q region [ ４ ] T. Hatsuda and T. Kunihiro, Phys. Reports 247 (1994) 221.

Appendix

Pressure v.s. Baryon Number Density HH-QQ

Energy (Mass) Density v.s. Baryon Number Density HH-QQ

Results (Linear Interpolation for HQ-Phase) CASE H-EOS Q-EOS HQ-PHASE NS MODEL Cq B**1/4 ρ_{H} ρ_{Q} M_{max} R ρ_{C} 1-1 TNI3u １ TNI3u TNI3u TNI3u TNI3u TNI3u TNI3u TNI3u TNI3u TNI2u TNI2u TNI2u TNI2u TNI2u TNI2u TNI2u TNI2u TNI2u TNI TNI TNI TNI TNI TNI TNI TNI TNI ＊ B**1/4 in MeV, ρ_{H} and ρ_{Q} in ρ_0, M_{max} in M_{solar}, R in κ_{m}, ρ_{C} in ρ_0

□Some remarks (at the present stage) ○ Maximum Mass M_{max} of NSs with quark matter core depends strongly on the stiffness of EOS and the pertion of hadron phase included and is larger for higher Q-H transition density. In this sense, M_{max} is mainly controlled by the EOS of hadron phase. ○ In the matching procedure, special care should be taken for the thermo-dynamic relation between e and p. Otherwise, in some case, we encounter a class of “ unusual” NS models with dM/dR >0 (dρ_c/dR >0). The stability condition to satisfy average Γ>4/3 for these NSs is under investigation. ○ Our study is in progress, by using more detailed quark matter EOS (by NJL-model;[6]) and more refined matching procedure, i.e., “superposition” of hadron and quark phases at H-Q region, instead of “linear interpolation” used here. [6] T. Hatsuda and T. Kunihiro, Phys. Reports 247 (1994) 221.