Motoi Tachibana (Saga Univ.)

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

Oct. 20, 2014 ＠ QCS2014, KIAA, Beijin

Dark matter capture in neutron stars with exotic phases

What/Why dark matter (DM) ?

Undoubtedly exists, but properties unknownInteracting with other particles very weaklyProposed by Zwicky as missing mass (1934)

What/Why neutron star (NS) ?

Landau’s gigantic nucleusGood market selling ultimate

environments

Proposed by Baade and Zwicky as a remnant after supernova explosion (1934)

Why the connection between

DM and NS?

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• NS seismology 　　　 　　　　　　　 ：

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

Cooling curves of Neutron Star

t

T

C. Kouvaris (‘10)

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

Capture rate due to DM-neutron scattering

Self-capture rate due to DM-DM scattering

DM self-annihilation rate

Capturable number of DMs in NS

(A) (no self-capture)

Reaches the steady state value ,

within time .

(B) (no self-annihilation)

Linearly grows until , and then

exponentially grows until the geometric

limit is reached.

(C) (no self-capture/annihilation)

Just linearly grows and is the growth rate.

Realized when DM carries a conserved charge,

analogous to baryon number?

Below we consider the case (C)

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

Thermalization of DM

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

DM mass ≦ 1GeV,

DM mass ≧ 1GeV,

Then, the DM gets self-gravitating once the total number of DM particles is larger than a critical one

If this condition is met, for the wide range of theDM mass, gravitational collapse takes place, i.e.,Nself exceeds the Chandrasekhar limit.

Condition

Observational constraints

For the case of the pulsar B1620-26:

McDermott-Yu-Zurek (2012)

But…Neutron star is Landau’s gigantic nucleus!

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.

(e.g.) neutron superfluidity meson condensation 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 still struggling…

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

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

sizable effect?

M. Ruggieri and M.T. (2013)

Bertoni, Nelson and Reddy, Phys. Rev. D88 (2013)

• Asymmetric • Complex scalar• M_DM ~ 1 keV – 5 GeV• Couples to regular matter via heavy vector boson

• Pauli blocking• Kinematic constraints• Superfluidity/Superconductivity

Significantly affects thermalization time!

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--

Study of dark matter from neutron stars!