2000 Fiscal Year Final Research Report Summary
Realistic Calculations of Hyperon-Mixed Phase and Neutron Stars at Birth and at Evolved Stage
| Project/Area Number |
11640245
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| Research Category |
Grant-in-Aid for Scientific Research (C)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
素粒子・核・宇宙線
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| Research Institution | Iwate University |
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Principal Investigator |
TAKATSUKA Tatsuyuki Faculty of Humanities and Social Sciences, Iwate University Professor, 人文社会科学部, 教授 (50043427)
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| Co-Investigator(Kenkyū-buntansha) |
YAMAMOTO Yasuo Physica Section, Tsuru University, Professor, 文学部, 教授 (80124866)
NISHIZAKI Shigeru Faculty of Humanities and Social Sciences, Iwate University Associate Professor, 人文社会科学部, 助教授 (60198455)
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| Project Period (FY) |
1999 – 2000
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| Keywords | Hyperon-Mixing / Effective YN and YY interactions / Neutron Stars / Hyperon Superfluidity / Neutron-Star Mass / Equation of State |
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| Research Abstract |
(A) The effective ΛN and ΛΛ interactions applicable to the Y-mixing problem are constructed from the G-matrix calculations by paying particular attention to the use of YN and YY interactions compatible with hypernuclear data. Similarly, the effective Σ^-N and Σ^-Σ^- interactions are constructed.
(B) The Y-mixing problem in neutron star cores is investigated by an efffective interaction approach based on (A). It is found that ∧ and Σ^- begin to mix in neutron star matter at the total baryon density ρ〜3ρ_0 (ρ_0 being the nuclear density) and the mixing ratio y_Y increases with ρ, with hyperons becoming components comparable to nucleons (N) (e.g., y_Λ〜20%, y_Σ-〜15%, y_p〜15%, y_n〜50% at ρ=6ρ_0). Of particular interest is the fact that the Y-mixing effects soften the EOS dramatically and thereby the maximum mass M_<max> sustained by the EOS cannot exceed the observed mass M_<obs>=1.44M_<【of sun】> for PSR1913+16, leading to a serious problem contradicting observations. The mechanism of such a dramatic softening is analyzed, showing up the characterisics of Y-mixing effects.
(C) It is stressed that M_<max><M_<obs> is of special interest, suggesting the necessity of "Extra Repulsion" in hypernuclear systems. It is pointed out that such a repulsion as in the three- body force currently introduced in nuclear systems could be one of the candidates for "Extra Repulsion".
(D) The existence of Λ- and Σ^-- superfluids (and also Ξ^--superfluid) in neutron star cores is shown by using three kinds of YY interaction models. The limited density region for Λ-superfluid interestingly restricts the mass of neutron stars with the "hyperon cooling".
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