Interacting relic neutrinos and free streaming

G. ManganoG. Mangano NOW 2006NOW 2006 11

Interacting relic neutrinos Interacting relic neutrinos and free streaming and free streaming

Gianpiero ManganoGianpiero Mangano

INFN, Sezione di NapoliINFN, Sezione di Napoli

ItalyItaly

22G. ManganoG. Mangano NOW 2006NOW 2006


rimo exponitur usitatam neutrinorum naturam. Considerandum est utrum neutrinos habeant insolitum vel novum novorum entium commercium . Et circa hoc quaeruntur tres:Primo utrum entes in neutrinis defluant postquam neutrini segregati sunt ab electronibusSecundo utrum mundum sine neutrinis sint

Tertio utrum novorum entium commercio obscurae etiam levis materiae dispositionem mutetur

P


Pseudo-thermal distribution: T = 1.95 K

Number density ( v + v ): 112 cm-3 /flavor

Mean kinetic energy: 10-7(eV/m) eV

Direct searches:

GF2me Ev 10-50 (Ev/eV) cm2 hopeless ?

Standard picture

Indirect searches: cosmological observables

neutrino influence weak + gravity (T> 1 MeV)

gravity (T< 1 MeV)

Primo exponitur usitatam neutrinorum naturam


Neutrinos and CMB

Neff affects the radiation-matter equality point

ISW: Integrated Sachs-Wolfe Effect on acoustic peaks

The large number of cosmological parameters does not allow for a stringent limit


Neutrinos and Large Scale Structuresneutrinos suppress inhomogeneities which grow for gravitational instability until they become nonrelativistic

mv=1.2 eVmv=2.3 eV

mv=4.6 eV

mv=6.9 eV

Key parameters:

Mpchm

eVl

eV

mh

vv

nr

v

1

5.38

1.94

12

2/1

02


How strong are present (and future) bounds

on exotic features in v distribution?

General parametrization

nnanya yPa

e

yyf )(

1)(

2

Pn orthogonal polynomials with respect to Fermi-Dirac distribution

an in one to one correspondence with moments of distribution Qn

dyyyfQ nn 2)(41

3

2

3002

4

11

7

120

4

11058.0

TQN

TQeV

mh

eff

v

Articulus IPrimo utrum entes in neutrinis defluant postquam neutrini segregati sunt ab electronibus


A model Cuoco, Lesgourgues, G.M. and Pastor 2005

Extra neutrinos from out of equilibrium decay of scalars after neutrino decoupling

In the instantaneous decay limit at TD )( DTH

22* 2/)(

2

22

21

1)(

yy

ya eA

eyyf

Non thermal features in neutrino distributions

Effects seen in CMB and LSS


*2

202

7

12099.0104.3

)3(3

299.01

2.93

AyN

AeV

mh

eff

v

Bounds from BBN

particles (decoupled) should not contribute too much to the expansion rate H

A < 0.1 at 95% C.L.


Present constraints from CMB (WMAP+ACBAR+VSA+CBI) and LSS (2dFGRS+SDSS) + SNIa data (Riess et al.)

Model: standard CDM + nonthermal v’s

Cl and P(k) computed using CAMB code (Lewis and Challinor 2002)

Likelihoods (using COSMOMC Lewis and Bridle 2002))


Forecast:

“conservative”: Planck+ SDSS

“ambitious”: CMBPOL+ 40 h-3 Gpc survey with kmax=0.1 h Mpc-1

m0 and vh2 (q) large degeneracy

=vh2(93.2eV/m0)


Articulus II

A neutrinoless Universe?

Models where v’s interact with light (pseudo)scalar particles

vv

chvvgvvhL jiijjiij ..

Beacom, Bell and Dodelson 2004

For the tightly coupled regime

v density strongly reduced, v’s play no role in LSS

Delay in matter domination epoch, different content in relativistic species after v decays (Neff=6.6 after decays)

Secundo utrum mundum sine neutrinis sint

couplings < 10-5 from several data (meson decay, 0, SN)


Beacom, Bell and Dodelson 2004


Including CMB in the analysis:

•No free streaming (no anisotropic stress) leads to

smaller effects on LSS (for massive v’s)

change of sub-horizon perturbations at CMB epoch

•Change of sound speed and equation of state of the the titghly coupled v - fluid

•v decays

larger Neff i.e. larger ISW effect for CMB

smaller effects on LSS (no v left at LSS formation epoch

Bell, Pierpaoli and Sigurdson 2005

Hannestad 2005


Massless interacting Massive decaying


Massive decaying


Articulus IIITertio utrum novorum entium commercio obscurae etiam levis materiae dispositionem mutetur

Usual picture of Dark Matter: cold collisionless massive particles which decoupled around the weak scale for freeze-out of annihilation processes

Ex: neutralino in MSSM with mass of O(100 GeV)

Difficulties:

Excess of small scale structures

Far more satellite galaxies in the Milky Way than observed (from numerical simulation)

DM in the MeV range: SPI spectrometer on the INTEGRAL satellite observed a bright 511 KeV gamma line from the galactic bulge

Boehm, Fayet and Silk 2003 ee


Framework: light (MeV) DM interacting with neutrinos

Several options for lagrangian density

Effects on cosmological scales: if DM - v’s scatterings at work during LSS formation we expect an oscillating behavior in the power spectrum (analogous to baryon – photon fluid during CMB epoch)

G.M., Melchiorri, Serra, Cooray and Kamionkowski 2006


Constraints

from BBN: if DM annihilate with a picobarn cross section (correct relic density) then its mass cannot be too large or it would distrub light nuclide formation

from SNII: if DM also inteacts more than weakly with nucleons neutrinos woulb be kept in equilibrium inside a SN down to a lower temperature neutrinosphere

Serpico and Raffelt 2004

Fayet, Hooper and Sigl 2006

mDM > 10 MeV


Effects on LSS•DM is not collisionless

•v’s are not free streaming

Scattering cross section depends upon the model

Ex. Scalar DM

2

4

222

24

1

3

4

3

4

DM

DMDM

vsc

DMF

DMDM

vsc

mhn

mm

Thn

mF mDM

mF = mDM

Scatterings leave an imprint only if efficient at very late times. Is this compatible with a picobarn DM annihilation cross section into neutrinos?


NOT AT ALL !

mF mDM

mF = mDM

If annihilations freeze-out around mDM (order MeV), also scatterings do so!

DM relic abundance produced rather than e.g. an asymmetry in particle/antiparticle (as baryons, electrons…)


Equation for velocity perturbations

Effect depends upon the parameter Q

mF mDM

mF = mDM


Bounds on differential opacity Q from SDSS data

mDM mF scenario almost ruled out. Requires coupling of order one

mDM = mF still viable


Very small effect on CMB sub-horizon scales


Astrophysical bounds1. Neutrinos from SN 1987A from LMC were not disturbed by

scatterings with DM, since their spectrum at earth is in agreement with SN model

2. Scattering length for high energy neutrinos emitted by astrophysical sources:


Conclusions

Worth studying exotic properties of v’s as a tool to explore physics beyond standard model

Keeping in mind Occam razor……


Degeneracies:

DM, Neff and m0

Neff >4 not forbidden

by BBN !

Future perspectives:

can we remove the

degeneracy?


If we add extra relativistic particles the situation gets even more involved

For each non thermal model there is a “twin” model with extra thermal relativistic particles, sharing the same value of Neff, vh2 but a different value of the neutrino mass scale.

Way to solve the degeneracy:

independent information on the absolute neutrino mass scale (beta decay experiments)

*2

202

7

12099.0104.3

)3(3

299.01

2.93

AyN

AeV

mh

eff

v

NNeV

mh

eff

v

04.3 2.93

'02

Mpchm

eVl v

vnr

15.38

12

2/1


If neutrino interacts during LSS formation the picture can be quite different even for massless v’s!

Interacting relic neutrinos and free streaming

Documents

Transcript of Interacting relic neutrinos and free streaming