Motoi Tachibana (Saga Univ.)

Dark matter capture in neutron stars -stellar constraints on dark matter-

Oct. 25, 2013 ＠ NS matter symposium, Kyoto

Dark matter capture in neutron stars with exotic phases

Why their connections?

Possibly constraining WIMP-DM properties via NS

For a typical neutron star,

Way below the CDMS limit!

CDMSII, 1304.4279

Impacts of dark matter on NS

• NS mass-radius relation with dark matter EOS

• NS heating via dark matter annihilation　　　 　　　　　　　：

cf) This is not so a new idea. People have considered the DM capture by Sun and the Earth since 80’s.

W. Press and D. Spergel (1984)

• Dark matter capture in NS and formation of black-hole to collapse host neutron stars

cosmion

DM capture in NS

*based on paper by McDermott-Yu-Zurek (2012)

*

(1)Accretion of DM

(2)Thermalization of DM (energy loss)

(3)BH formation and destruction of host NS

condition of self-gravitation

Capturable number of DMs in NS

Capture rate via DM-neutron scattering

Capture rate via DM-DM self-interaction

DM pair annihilation rate

(1) DM capture rate

The accretion rate (A. Gould, 1987)

neutron-DM elastic cross section

Capture efficiency factor ξ

(i) If momentum transfer δp is less than p , only neutrons with momentum larger than p -δp can participate in

(ii) If not, all neutrons can join

F

F

In NS, neutrons are highly degenerated

(2) Thermalization of DM

After the capture, DMs lose energy via scattering with neutrons and eventually get thermalized

DM mass ≦ 1GeV,

DM mass ≧ 1GeV,

(3) Self–gravitation & BH formation

If the DM density gets larger than the baryon density within thermal radius, DM particles be self-gravitating.This is the on-set of the gravitational collapse and black-hole formation (cf. the Chandrasekhar limit)

BH formation is the dynamical issueand not so trivial to deal with

Condition

Observational constraints

For the case of the pulsar B1620-26:

McDermott-Yu-Zurek (2012)

So far people have been mainly studyingthe issue from particle physics side.

However, hadrons in NS are in EXTREME, and exotic matter states could appear.

NS as Landau’s gigantic nucleus

(e.g.) neutron superfluidity Bose condensation of mesons superconductivity of quarks

What if those effects are incorporated?

Possible effects

① Modification of capture efficiency via energy gap

② Modification of low-energy effective theory

We are on the way of the calculations

(e.g.) neutron superfluidity dominant d.o.f. is a superfluid phonon.

Cirigliano, Reddy, Sharma (2011)

(e.g.) color-flavor-locked(CFL) quark matter

sizable effect?

Bertoni, Nelson and Reddy, 1309.1721[hep-ph]

Summary

Stellar constraints on dark matter properties

Dark matter capture in neutron stars--Accretion, thermalization and on-set of BH formation—

Models for DM, but not considering NS seriously

Proposal of medium effects for hadrons in NS--modified vacuum structures and collective modes--

This is OUR problem

Thank you