chris kouvaris- can neutron stars constrain dark matter?

8/3/2019 Chris Kouvaris- Can Neutron Stars Constrain Dark matter?

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Can Neutron Stars Constrain

Dark matter?

Chris Kouvaris

Universit Libre de Bruxelles


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Mass 2010, CP3-Origins

The Missing Mass ProblemZwicky 1933: Virial Theorem

applied on Coma cluster

Zwicky took 5*1015 cm2s-2 as the value for the time and mass averaged squared velocity and 2

million light-years for the radius of the cluster. The total cluster mass is then about 7*1013 solar

masses. Since the cluster contains about 1000 galaxies, this yields an average galactic mass of

7*1010 solar masses. However, the average galactic luminosity in the Coma cluster is found to be

only 8.5*107 solar luminosities. Thus, the average mass to light ratio, in solar units, of the galaxies

in the Coma cluster is approximately 800.


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Rotation CurvesVera Rubin 70s: Rotatoion

curves of Andromeda are notfalling as Newtons law

predicts!

Velocity should drop as rv /1

However v roughly constant rM2

/1 r


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MOND???

Tully-Fisher

Milgrom

Mond explains well theTully-Fisher relation and

the rotation curves

but fails in clusters ofgalaxies


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Fluctuations of the Microwave Background Radiation


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Bullet Cluster

The galaxy cluster 1E 0657-56, known as the "bullet cluster. A mere 3.4 billion light-years away, the bullet cluster'sindividual galaxies are seen in the optical image data, but their total mass adds up to far less than the mass of thecluster's two clouds of hot x-ray emitting gas shown in red. Representing even more mass than the optical galaxies and x-ray gas combined, the blue hues show the distribution of dark matter in the cluster. Otherwise invisible to telescopicviews, the dark matter was mapped by observations of gravitational lensing of background galaxies. In a text bookexample of a shock front, the bullet-shaped cloud of gas at the right was distorted during the titanic collision between twogalaxy clusters that created the larger bullet cluster itself. But the dark matter present has not interacted with the clustergas except by gravity. The clear separation of dark matter and gas clouds is considered direct evidence that dark matterexists.


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What Dark Matter is Not

Baryons obviously!!!! MaCHO (Massive Compact Halo Objects): Ruled out

NeutrinoseV

mh i i

94

2

Light neutrinos: are problematic in small scale structurem>500 eV (Tremaine-Gunn) otherwise neutrinos violate Pauli

blocking in dwarf galaxies. But for m>500 eV gives too muchdark matter

Heavy Neutrinos: m> 2 GeV (Lee-Weinberg)

excluded by direct dark matter search experiments unlessthe mass is huge

ChaMP (Charged Massive Particles)SIMP (Strongly Interacting Massive Particles)Ruled out by searches of Hydrogen anomalous isotope in water*

by microlensing observations

m


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Direct Dark Matter Candidates

Supersymmetric (neutralino, gravitino etc)Hidden SectorsTechnicolor CandidatesKaluza KleinAxions and many other

Candidates can have:Spin independent cross section

Spin Dependent cross sectionInelastic Scattering

Self-Interacting cross section

Thermal annihilation cross section

Non-thermal annihilation cross section


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Direct Dark Matter Search Experiments I

Joachim Kopp, Thomas Schwetz, Jure Zupan: arXiv 0912.4264


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Direct Dark Matter Search Experiments II


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Can Stars impose constraints on Dark Matter?

Neutrino production from WIMP annihilationIceCube & Super-Kamiokande can impose

constraints on the WIMP-nucleon cross section

WIMP accumulation and formation of Black Holes

In neutron stars at rich dark matter regions, WIMPs cancause gravitational collapse (Goldman, Nussinov 89, CKTinyakov 10)

WIMP annihilation and cooling of starsWIMP annihilation as a heating mechanismfor neutron stars (CK 07, CK, P. Tinyakov, Lavallaz, Fairbairn 10)

for white dwarfs (Bertone, Fairbairn 07, McCullough 10)


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Why look at compact stars?

Example: Sun

WIMP mean free pathinside the sun

,1

n

23

3108

)3/4(

nsolar

solar

mR

Mn

3/cmparticles

Even if currentlimit of CDMS

,10241

cm

,1017cm 610

solarR

Only one out of a million WIMPs scatters!

The number of accumulated WIMPs is even smallerbecause not all the scattered WIMPs get trapped.

Condition: The energy loss in the collision

should be larger than the asymptotic kineticenergy of the WIMP far out of the star.

Advantage: The sun is close!!!


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White Dwarfs

When the Fermi pressure of the

electrons acts against gravitationalcollapse


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Same Exercise for a White Dwarf

30

3107.1

)3/4(

nWD

WD

mR

Mn

,solarWD MM kmRWD 55003

/cmparticles

If we want onecollisions per WIMPpassing the crosssection

23910 cmcritical

However still abovethe CDMS limit!!!

This is an improvement!!!

Since for the sun235

10 cmcritical

Could Coherent Scattering help???

,5.0 solarWD MM kmRWD 10000If239

107 cmcritical


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Coherent Scattering WIMP-Nucleus

Dirac (non-Majorana) type of candidates can interactcoherently with the whole nucleus

This effect is taken into account in earth based experiments,where WIMPs are passing through with velocities 220 km/sputting tight constraints on these candidates.

However loss of coherence occurs when

Helm factor


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Studies so far were assuming coherence in the scatteringbetween WIMP-nucleus in the White Dwarfs.

but this not true (CK, Tinyakov 10) because the potentialenergy is much larger than the asymptotic kinetic energy ofthe WIMP. WIMPs are almost relativistic while entering theWhit Dwarf.

0E

R

GM

The de Broglie wavelength is much shorter than the size ofthe nuclei and the form factor kills the enhancement of thecross section due to the coherence.


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Neutron Stars

even more compact objects! Fermi pressure of neutronsand/or quark matter??? balances gravity.

For a typical neutron star ,4.1 solarNS MM kmR 10

246105 cmcritical

CK 07 Way below the CDMS

limit!!!

WIMPs are relativistic while entering the NS, and therefore also herecoherence is lost, but this is not important since for cross sections largerthan the critical one, every WIMP passing the NS will scatter at least once

on average.

Neutron Stars seem to be the objects with the best efficiency incapturing WIMPs!


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furthermore

since

the two cross sections become almost identical for a NS andtherefore the same constraints apply

Inelastic Dark Matter


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and

Self-Interacting Dark Matter

Strong WIMP-WIMP cross section

For a Neutron star as long as the WIMP-nucleon cross section isabove the critical value, self-interactions make no difference in

the accretion and capture of the the WIMPs

Bound on the cross sectionGeVcm

m

2

2410


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Capture of WIMPs in Neutron Stars

CK 07

For a

typical

NS

Thermalization


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Thermalization is so fast that allows extremely

small annihilation cross sections


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Neutron Stars as Giant Detectors!

CDMS NSDensity 5 g/cm^3 10^14g/cm^31% Light production 100% Light ProductionLocal dark matter density0.3 GeV/cm^3 up to 10^10!? GeV/cm^3


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Annihilation of WIMPs inside the Neutron Stars

EnergyRelease

We must compare it with the otherheating/cooling mechanisms


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Basics of Neutron Star Cooling

Urca Process

Direct Urca eepn

enep

Energy release through

escaping neutrinos

However for nuclear matter triangleinequalities are not satisfied

Modified Urcapresence ofbystander

eepnnn

ennnep

For quark matter itholds!

Emissivity: 6T

Emissivity:8

T

Photon Emission Emissivity: 4T


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more cooling mechanisms

Nucleon Pair Bremsstrahlung nnnn

pnpn

Neutrino Pair Bremsstrahlung ),(),( ZAeZAe

Pionic Reactions

Superfluidity

Color Superconductivity


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Cooling Equation


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Cooling Curves

CK 07


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Galactic Center

CK , Tinyakov 10


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Globular Clusters

NFW for M4

Baryonic contraction might reduce the temperature up to 30%

Examples: X7 in 47 Tuc1620-26 in M4 both have temperatures roughly

610 K

Observed temperatures smaller than the ones predicted, excludesthe dark matter candidate.


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Isolated Neutron Stars

maybe the best candidates for the constraints

No accretion from bystander white dwarf or other star

Probably better knowledge of the local dark matter candidate

Examples: J0437-4715 temperature 10^5 KJ0108-1431 temperature 9 x 10^4 K

Both of them are old only problem their distance from the earth is 130-140 pcThe local dark matter density should be small (or maybe not)Other heating mechanisms can take place

Reisenegger 94 (chemical energy converted to thermal),Alford, CK, Kundu, Rajagopal 04 (color superconducting matter)


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Can A Progenitor change the picture??

A supermassive star cancollapse to a neutron star viaa Supernova II explosion

The pre-existence of the starincreases the local dark matterdensity in the vicinity of thenewly born neutron star

The effect in principle can be large!

Total number of accumulatedparticles

Same order of magnitude as for a neutron star!Compactness and small WIMP mean free path iscounterbalanced by huge mass and radius


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After the explosion

The mean free path of the WIMPs is too large for them to becarried away from the shock wave, however the WIMPs aresucked inside the neutron star very fast (exponentially)

Neutron star kicks up to several thousands of km/s do not alter the picture.WIMPs remain gravitationally bound to the neutron star within the thermalradius of the last stage of the star (silicon).

still the annihilation cannot compete with the Urca process


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however

Non-thermally produced WIMPs can have extremely small annihilationcross section (supersummetry etc.)

In that case:

It can change the temperature estimate by 50%


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Black Hole formation

Neutron Stars close to the galactic center might accrete to many WIMPs,and gravitational collapse might occur

For fermionic WIMPs there is a Chandrasekhar limit by setting

Fermi momentum

For gravitational collapse, it takes

If the dark matter density issmaller than 37 /10 cmGeV

The time needed for collapse exceeds the age of the universe!

C


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Mass 2010 CP3 Origins

Conclusions

Neutron Stars are the only objects that have efficient accretionof WIMPs for WIMP-nucleon cross section below the current

experimental limits.

The constraints apply to thermally and non-thermally produced

WIMPs with extremely small annihilation cross section.Although observing neutron stars at the galactic center is an

extremely difficult task, globular clusters or isolated neutronstars can impose constraints.

We set lower bounds on the surface temperature of a NS. If a

NS is observed with a temperature lower than what we predict,

a huge class of candidates is ruled out!

chris kouvaris- can neutron stars constrain dark matter?

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