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Alexander Kusenko (UCLA/Kavli IPMU) PHENO-2014
Astroparticle physics news
• The mystery of distant blazars ⇒ secondary gamma rays
and PeV neutrinos
• IceCube neutrinos: astrophysical or dark matter?
• X-ray line at 3.5 keV? If it’s real, what it implies.
(...more or less, in the order from “astro” to “particle”.)
1
Alexander Kusenko (UCLA/Kavli IPMU) PHENO-2014
Active galactic nuclei: blazars
when AGN jet points at Earth, called blazar
2
Alexander Kusenko (UCLA/Kavli IPMU) PHENO-2014
3
Alexander Kusenko (UCLA/Kavli IPMU) PHENO-2014
Atmospheric Cherenkov Telescopes
4
Alexander Kusenko (UCLA/Kavli IPMU) PHENO-2014
5
Alexander Kusenko (UCLA/Kavli IPMU) PHENO-2014
Gamma-ray observations of distant blazars:1ES 0229+200 (z = 0.14) and 3C66A (z = 0.44)
Energy [ TeV ]1 10
]-1
TeV
-1 s
-2dN
/dE
[ c
m
-1610
-1510
-1410
-1310
-1210
100 200 500 1000 2000 5000
10−17
10−16
10−15
10−14
10−13
10−12
E(GeV)
dN/d
E (
GeV
cm
s )−2
−1−1
HESS (black), MAGIC (blue) and VERITAS (red) data points
6
Alexander Kusenko (UCLA/Kavli IPMU) PHENO-2014
Gamma-ray observations of distant blazars:1ES 0229+200 (z = 0.14) and 3C66A (z = 0.44)
Energy [ TeV ]1 10
]-1
TeV
-1 s
-2dN
/dE
[ c
m
-1610
-1510
-1410
-1310
-1210
100 200 500 1000 2000 5000
10−17
10−16
10−15
10−14
10−13
10−12
E(GeV)
dN/d
E (
GeV
cm
s )−2
−1−1
HESS (black), MAGIC (blue) and VERITAS (red) data points
Theory, e.g., Stecker, et al. (1992): ...“we predict a sharp cutoff between 0.1 and 1 TeV”
6
Alexander Kusenko (UCLA/Kavli IPMU) PHENO-2014
Gamma-ray observations of distant blazars:1ES 0229+200 (z = 0.14) and 3C66A (z = 0.44)
Energy [ TeV ]1 10
]-1
TeV
-1 s
-2dN
/dE
[ c
m
-1610
-1510
-1410
-1310
-1210
100 200 500 1000 2000 5000
10−17
10−16
10−15
10−14
10−13
10−12
E(GeV)
dN/d
E (
GeV
cm
s )−2
−1−1
HESS (black), MAGIC (blue) and VERITAS (red) data points
Theory, e.g., Stecker, et al. (1992): ...“we predict a sharp cutoff between 0.1 and 1 TeV”
The data: no signs of absorption due to γγEBL → e+e−
6
Alexander Kusenko (UCLA/Kavli IPMU) PHENO-2014
Extragalactic background light (EBL)(direct and processed starlight)
• intimately connected with star formation history and with dust content of the galaxies
• models uncertain, but robust lower limits exist from star counts, especially for UV EBL
0.1
1
10
100
0.1 1 10 100 1000 10000
λ[µm]
νIν
[nW
/m2 /s
r]
Madau & Pozzetti ’00 (HST)Elbaz et al. ’02 (ISO)
Papovich et al. ’04 (Spitzer)Fazio et al. ’04 (Spitzer)Xu et al. ’05 (GALEX)Dole et al. ’06 (Spitzer)
Frayer et al. ’06 (Spitzer)Gardner et al. ’00 (HST)
Berta et al. ’11 (Hershel/PEP)Wright & Reese ’00 (DIRBE)
Wright ’04 (DIRBE)Levenson et al. ’07 (DIRBE)
Levenson & Wright ’08 (DIRBE)Bernstein ’07 (HST)
Matsuoka et al. ’11 (Pioneer)Matsumoto et al. ’11 (IRTS)Matsuura et al. ’11 (AKARI)Cambrésy et al. ’01 (DIRBE)Dwek & Arendt ’98 (DIRBE)
Gorijian et al ’00 (DIRBE)Finkbeiner et al ’00 (DIRBE)
Hauser et al ’98 (DIRBE)Lagache et al ’00 (DIRBE)
Edelstein et al ’00 (Voyger)Brown et al ’00 (HST/STIS)
Albert et al ’08 (MAGIC)
Baseline ModelKneikse et al. ’04Stecker et al. ’06
Franceschini et al. ’08Gilmore et al. ’09
Finke et al. ’10Kneiske & Dole ’10
Gilmore et al. ’12
γγEBL → e+e− should degrade
the energy of TeV photons
7
Alexander Kusenko (UCLA/Kavli IPMU) PHENO-2014
Distant blazars have implausibly hard spectra
E [TeV]
-110 1 10
/s]
2 d
N/d
E [e
rg/c
m2
E
-1310
-1210
-1110
-1010
-910
-810
-710
-610
-510 1ES 0229+200(scaled)
1ES 1218+30.4(scaled)
1ES 1101+232
= 2.40 Γ
= 1.30 Γ
= 1.28 Γ
Absorption-corrected spectra are
extremely hard, Γ < 1.5, for distant
blazars. [Aharonian et al.]
8
Alexander Kusenko (UCLA/Kavli IPMU) PHENO-2014
Blazar spectra
E [TeV]0.05 0.1 0.2 1 2 3 4 5 6 10 20 30
]-1 s
-2 d
N/d
E [T
eV c
m2
E-1410
-1310
-1210
-1110
-1010
RGB_J0152+0173C_66A1ES_0229+2001ES_0347-121PKS_0548-322RGB_J0710+591S5_0716+7141ES_0806+5241ES_1011+4961ES_1101-232Markarian_421Markarian_1801ES_1218+304W_ComaePKS_1424+240H_1426+428PG_1553+113Markarian_5011ES_1959+650PKS_2005-489PKS_2155-304BL_Lacertae1ES_2344+514H_2356-309
RGB_J0152+0173C_66A1ES_0229+2001ES_0347-121PKS_0548-322RGB_J0710+591S5_0716+7141ES_0806+5241ES_1011+4961ES_1101-232Markarian_421Markarian_1801ES_1218+304W_ComaePKS_1424+240H_1426+428PG_1553+113Markarian_5011ES_1959+650PKS_2005-489PKS_2155-304BL_Lacertae1ES_2344+514H_2356-309
RGB_J0152+0173C_66A1ES_0229+2001ES_0347-121PKS_0548-322RGB_J0710+591S5_0716+7141ES_0806+5241ES_1011+4961ES_1101-232Markarian_421Markarian_1801ES_1218+304W_ComaePKS_1424+240H_1426+428PG_1553+113Markarian_5011ES_1959+650PKS_2005-489PKS_2155-304BL_Lacertae1ES_2344+514H_2356-309
RGB_J0152+0173C_66A1ES_0229+2001ES_0347-121PKS_0548-322RGB_J0710+591S5_0716+7141ES_0806+5241ES_1011+4961ES_1101-232Markarian_421Markarian_1801ES_1218+304W_ComaePKS_1424+240H_1426+428PG_1553+113Markarian_5011ES_1959+650PKS_2005-489PKS_2155-304BL_Lacertae1ES_2344+514H_2356-309
RGB_J0152+0173C_66A1ES_0229+2001ES_0347-121PKS_0548-322RGB_J0710+591S5_0716+7141ES_0806+5241ES_1011+4961ES_1101-232Markarian_421Markarian_1801ES_1218+304W_ComaePKS_1424+240H_1426+428PG_1553+113Markarian_5011ES_1959+650PKS_2005-489PKS_2155-304BL_Lacertae1ES_2344+514H_2356-309
RGB_J0152+0173C_66A1ES_0229+2001ES_0347-121PKS_0548-322RGB_J0710+591S5_0716+7141ES_0806+5241ES_1011+4961ES_1101-232Markarian_421Markarian_1801ES_1218+304W_ComaePKS_1424+240H_1426+428PG_1553+113Markarian_5011ES_1959+650PKS_2005-489PKS_2155-304BL_Lacertae1ES_2344+514H_2356-309
RGB_J0152+0173C_66A1ES_0229+2001ES_0347-121PKS_0548-322RGB_J0710+591S5_0716+7141ES_0806+5241ES_1011+4961ES_1101-232Markarian_421Markarian_1801ES_1218+304W_ComaePKS_1424+240H_1426+428PG_1553+113Markarian_5011ES_1959+650PKS_2005-489PKS_2155-304BL_Lacertae1ES_2344+514H_2356-309
RGB_J0152+0173C_66A1ES_0229+2001ES_0347-121PKS_0548-322RGB_J0710+591S5_0716+7141ES_0806+5241ES_1011+4961ES_1101-232Markarian_421Markarian_1801ES_1218+304W_ComaePKS_1424+240H_1426+428PG_1553+113Markarian_5011ES_1959+650PKS_2005-489PKS_2155-304BL_Lacertae1ES_2344+514H_2356-309
RGB_J0152+0173C_66A1ES_0229+2001ES_0347-121PKS_0548-322RGB_J0710+591S5_0716+7141ES_0806+5241ES_1011+4961ES_1101-232Markarian_421Markarian_1801ES_1218+304W_ComaePKS_1424+240H_1426+428PG_1553+113Markarian_5011ES_1959+650PKS_2005-489PKS_2155-304BL_Lacertae1ES_2344+514H_2356-309
RGB_J0152+0173C_66A1ES_0229+2001ES_0347-121PKS_0548-322RGB_J0710+591S5_0716+7141ES_0806+5241ES_1011+4961ES_1101-232Markarian_421Markarian_1801ES_1218+304W_ComaePKS_1424+240H_1426+428PG_1553+113Markarian_5011ES_1959+650PKS_2005-489PKS_2155-304BL_Lacertae1ES_2344+514H_2356-309
RGB_J0152+0173C_66A1ES_0229+2001ES_0347-121PKS_0548-322RGB_J0710+591S5_0716+7141ES_0806+5241ES_1011+4961ES_1101-232Markarian_421Markarian_1801ES_1218+304W_ComaePKS_1424+240H_1426+428PG_1553+113Markarian_5011ES_1959+650PKS_2005-489PKS_2155-304BL_Lacertae1ES_2344+514H_2356-309
RGB_J0152+0173C_66A1ES_0229+2001ES_0347-121PKS_0548-322RGB_J0710+591S5_0716+7141ES_0806+5241ES_1011+4961ES_1101-232Markarian_421Markarian_1801ES_1218+304W_ComaePKS_1424+240H_1426+428PG_1553+113Markarian_5011ES_1959+650PKS_2005-489PKS_2155-304BL_Lacertae1ES_2344+514H_2356-309
RGB_J0152+0173C_66A1ES_0229+2001ES_0347-121PKS_0548-322RGB_J0710+591S5_0716+7141ES_0806+5241ES_1011+4961ES_1101-232Markarian_421Markarian_1801ES_1218+304W_ComaePKS_1424+240H_1426+428PG_1553+113Markarian_5011ES_1959+650PKS_2005-489PKS_2155-304BL_Lacertae1ES_2344+514H_2356-309
RGB_J0152+0173C_66A1ES_0229+2001ES_0347-121PKS_0548-322RGB_J0710+591S5_0716+7141ES_0806+5241ES_1011+4961ES_1101-232Markarian_421Markarian_1801ES_1218+304W_ComaePKS_1424+240H_1426+428PG_1553+113Markarian_5011ES_1959+650PKS_2005-489PKS_2155-304BL_Lacertae1ES_2344+514H_2356-309
RGB_J0152+0173C_66A1ES_0229+2001ES_0347-121PKS_0548-322RGB_J0710+591S5_0716+7141ES_0806+5241ES_1011+4961ES_1101-232Markarian_421Markarian_1801ES_1218+304W_ComaePKS_1424+240H_1426+428PG_1553+113Markarian_5011ES_1959+650PKS_2005-489PKS_2155-304BL_Lacertae1ES_2344+514H_2356-309
RGB_J0152+0173C_66A1ES_0229+2001ES_0347-121PKS_0548-322RGB_J0710+591S5_0716+7141ES_0806+5241ES_1011+4961ES_1101-232Markarian_421Markarian_1801ES_1218+304W_ComaePKS_1424+240H_1426+428PG_1553+113Markarian_5011ES_1959+650PKS_2005-489PKS_2155-304BL_Lacertae1ES_2344+514H_2356-309
RGB_J0152+0173C_66A1ES_0229+2001ES_0347-121PKS_0548-322RGB_J0710+591S5_0716+7141ES_0806+5241ES_1011+4961ES_1101-232Markarian_421Markarian_1801ES_1218+304W_ComaePKS_1424+240H_1426+428PG_1553+113Markarian_5011ES_1959+650PKS_2005-489PKS_2155-304BL_Lacertae1ES_2344+514H_2356-309
RGB_J0152+0173C_66A1ES_0229+2001ES_0347-121PKS_0548-322RGB_J0710+591S5_0716+7141ES_0806+5241ES_1011+4961ES_1101-232Markarian_421Markarian_1801ES_1218+304W_ComaePKS_1424+240H_1426+428PG_1553+113Markarian_5011ES_1959+650PKS_2005-489PKS_2155-304BL_Lacertae1ES_2344+514H_2356-309
RGB_J0152+0173C_66A1ES_0229+2001ES_0347-121PKS_0548-322RGB_J0710+591S5_0716+7141ES_0806+5241ES_1011+4961ES_1101-232Markarian_421Markarian_1801ES_1218+304W_ComaePKS_1424+240H_1426+428PG_1553+113Markarian_5011ES_1959+650PKS_2005-489PKS_2155-304BL_Lacertae1ES_2344+514H_2356-309
RGB_J0152+0173C_66A1ES_0229+2001ES_0347-121PKS_0548-322RGB_J0710+591S5_0716+7141ES_0806+5241ES_1011+4961ES_1101-232Markarian_421Markarian_1801ES_1218+304W_ComaePKS_1424+240H_1426+428PG_1553+113Markarian_5011ES_1959+650PKS_2005-489PKS_2155-304BL_Lacertae1ES_2344+514H_2356-309
RGB_J0152+0173C_66A1ES_0229+2001ES_0347-121PKS_0548-322RGB_J0710+591S5_0716+7141ES_0806+5241ES_1011+4961ES_1101-232Markarian_421Markarian_1801ES_1218+304W_ComaePKS_1424+240H_1426+428PG_1553+113Markarian_5011ES_1959+650PKS_2005-489PKS_2155-304BL_Lacertae1ES_2344+514H_2356-309
RGB_J0152+0173C_66A1ES_0229+2001ES_0347-121PKS_0548-322RGB_J0710+591S5_0716+7141ES_0806+5241ES_1011+4961ES_1101-232Markarian_421Markarian_1801ES_1218+304W_ComaePKS_1424+240H_1426+428PG_1553+113Markarian_5011ES_1959+650PKS_2005-489PKS_2155-304BL_Lacertae1ES_2344+514H_2356-309
RGB_J0152+0173C_66A1ES_0229+2001ES_0347-121PKS_0548-322RGB_J0710+591S5_0716+7141ES_0806+5241ES_1011+4961ES_1101-232Markarian_421Markarian_1801ES_1218+304W_ComaePKS_1424+240H_1426+428PG_1553+113Markarian_5011ES_1959+650PKS_2005-489PKS_2155-304BL_Lacertae1ES_2344+514H_2356-309
RGB_J0152+0173C_66A1ES_0229+2001ES_0347-121PKS_0548-322RGB_J0710+591S5_0716+7141ES_0806+5241ES_1011+4961ES_1101-232Markarian_421Markarian_1801ES_1218+304W_ComaePKS_1424+240H_1426+428PG_1553+113Markarian_5011ES_1959+650PKS_2005-489PKS_2155-304BL_Lacertae1ES_2344+514H_2356-309
Measured Spectra
E [TeV]0.05 0.1 0.2 1 2 3 4 5 6 10 20 30
]-1 s
-2 d
N/d
E [T
eV c
m2
E
-1410
-1310
-1210
-1110
-1010
Measured Spectra
E [TeV]0.05 0.1 0.2 1 2 3 4 5 10 20 30
]-1 s
-2 d
N/d
E [T
eV c
m2
E
-1410
-1310
-1210
-1110
-1010
EBL corrected spectrum
M. Errando
measured spectra naive EBL−corrected spectra
9
Alexander Kusenko (UCLA/Kavli IPMU) PHENO-2014
Softening of the spectrum as a function of the redshift
0.00 0.05 0.10 0.15 0.20 0.25 0.30-1
0
1
2
3
Redshift z
DG
∆Γ = ΓGeV − ΓTeV [Stecker, Scully]
10
Alexander Kusenko (UCLA/Kavli IPMU) PHENO-2014
Distant blazars are different:
0
0.5
1
1.5
2
2.5
3
0 0.1 0.2 0.3 0.4 0.5 0.6z
Stecker−ScullyΓδ
δΓ = ΓGeV − ΓTeV [Stecker, Scully]
11
Alexander Kusenko (UCLA/Kavli IPMU) PHENO-2014
Proposed “new physics” solutions:
The lack of absorption prompted some exotic solutions:
• photons may convert into some hypothetical axion-like particles that convert back
into photons in the galactic magnetic fields
[Hooper et al.; de Angelis et al.; Simet et al.]
• Lorentz invariance violation for high-velocity particles may prevent pair production
[Protheroe et al.]
Is there a more conventional explanation?
12
Alexander Kusenko (UCLA/Kavli IPMU) PHENO-2014
AGN produce both cosmic rays and gamma rays
EBL
ee−
+
CMB+EBL CMB+EBL
pB
primary γsecondary gamma rays
13
Alexander Kusenko (UCLA/Kavli IPMU) PHENO-2014
Cosmic rays from AGN
• No significant attenuation below GZK cutoff.
Propagate cosmological distances for E <∼ 1018 eV.
• Rectilinear propagation affected only by IGMFs.
Clusters of galaxies (size R, density n) cause large deflections, but the mean free path
of a proton
Λ ∼ 1/(πR2n) ∼ 3 × 103Mpc
The mean MFP for linear propagation is of the order of the size of the observed
universe.
• IGMFs are not known:
– upper limits: B < 10−9 G from non-observation of Faraday rotations
– lower limits: B > 10−30 G if one believes the galactic fields are seed fields
amplified by dynamo.
For magnetic fields B < 10−14 G, deflections are smaller than the angular resolution
of ACTs.
14
Alexander Kusenko (UCLA/Kavli IPMU) PHENO-2014
Secondary gamma rays from cosmic rays along the line of sight?
Gamma-rays produced at the source can attenuate via pair production on EBL for TeV
energies: expect attenuation of TeV γ rays.
Protons below GZK cutoff interact with EBL, CMB and produce γ rays via
pγ → pe+e−, pγ → pπ0: expect regeneration of TeV γ rays
Photon backgrounds provide opacity/sink for the former, source for the latter.
What is the scaling of these effects with distance?
15
Alexander Kusenko (UCLA/Kavli IPMU) PHENO-2014
Different scaling
Fprimary,γ(d) ∝1
d2exp−d/λγ (1)
Fsecondary,γ(d) =pλγ
4πd2
[
1 − e−d/λγ
]
∝
1/d, for d ≪ λγ,
1/d2, for d ≫ λγ.(2)
Fsecondary,ν(d) ∝ (Fprotons × d) ∝1
d. (3)
16
Alexander Kusenko (UCLA/Kavli IPMU) PHENO-2014
Different scaling
Fprimary,γ(d) ∝1
d2exp−d/λγ (1)
Fsecondary,γ(d) =pλγ
4πd2
[
1 − e−d/λγ
]
∝
1/d, for d ≪ λγ,
1/d2, for d ≫ λγ.(2)
Fsecondary,ν(d) ∝ (Fprotons × d) ∝1
d. (3)
For distant sources, secondary signals win
16
Alexander Kusenko (UCLA/Kavli IPMU) PHENO-2014
Secondary photons and neutrinos from 1ES0229+200 (z = 0.14)
10 −6
10 −5
10 −4
10 −3
10 −2
10 −1
10 0
10 1
10 2
1010 1011 1012 1013 1014 1015 1016 1017 1018 1019 10 1020 21
E2 d
N/d
E, e
V c
m−
2s−
1
E, eV
10
10
1020
17
19eV
eV
eVgamma rays
neutrinos
p, maxE =
[Essey, Kalashev, AK, Beacom, PRL 104, 141102 (2010)]
17
Alexander Kusenko (UCLA/Kavli IPMU) PHENO-2014
Robust spectral shapes explain the observed universality
10 −6
10 −5
10 −4
10 −3
10 −2
10 −1
10 0
10 1
10 2
1010 1011 1012 1013 1014 1015 1016 1017 1018 1019 10 1020 21
E2 d
N/d
E, e
V c
m−
2s−
1
E, eV
10
10
1020
17
19eV
eV
eVgamma rays
neutrinos
p, maxE =
E [TeV]0.05 0.1 0.2 1 2 3 4 5 6 10 20 30
]-1 s
-2 d
N/d
E [T
eV c
m2
E
-1410
-1310
-1210
-1110
-1010
Measured Spectra
18
Alexander Kusenko (UCLA/Kavli IPMU) PHENO-2014
IceCube detector
19
Alexander Kusenko (UCLA/Kavli IPMU) PHENO-2014
PeV neutrinos discovered by IceCube
20
Alexander Kusenko (UCLA/Kavli IPMU) PHENO-2014
PeV neutrinos discovered by IceCube consistent withsecondary spectrum
10−1
100
101
102
103
104
105
106
107
1010 1012 1014 1016 1018
jE2 , e
V c
m−2 s
−1 s
r−1
E, eV
pγν
[Kalashev, Kusenko, Essey, Phys.Rev.Lett. 111 (2013) 041103]
21
Alexander Kusenko (UCLA/Kavli IPMU) PHENO-2014
Can the IceCube neutrinos come from decays of heavy dark matter?
Possible types of DM particles: gravitino with R-partity violation; hidden sector gauge
boson; a singlet fermion in an extra dimension; a heavy right-handed neutrino.
[Feldstein, AK, Matsumoto, Yanagida (2013)]
22
Alexander Kusenko (UCLA/Kavli IPMU) PHENO-2014
Sterile neutrinos, moduli, and dark matter with a keV mass.
• Dark matter candidates at a keV scale: sterile neutrinos, string/supersymmetry moduli
• Warm or cold, depending on the production scenario
• Particle physics models
• – Sterile neutrinos and an SU(2) singlet Higgs boson
– Sterile neutrinos and the Split Seesaw
– String/supersymmetry moduli
• Detection strategy: the search for a keV line
23
Alexander Kusenko (UCLA/Kavli IPMU) PHENO-2014
Unidentified line from Bulbul et al.; Boyarsky et al.
24
Alexander Kusenko (UCLA/Kavli IPMU) PHENO-2014
Unidentified line from Bulbul et al.; Boyarsky et al.
25
Alexander Kusenko (UCLA/Kavli IPMU) PHENO-2014
Neutrino masses and light sterile neutrinos
Discovery of the neutrino masses implies a plausible existence of right-handed (sterile)
neutrinos. Most models of neutrino masses introduce sterile states
νe, νµ, ντ ,νs,1, νs,2, ..., νs,N
and consider the following Lagrangian:
L = LSM + νs,a
(
i∂µγµ)
νs,a − yαaH Lανs,a −Mab
2ν
cs,aνs,b + h.c. ,
where H is the Higgs boson and Lα (α = e, µ, τ ) are the lepton doublets. The mass
matrix:
M =
(
0 D3×N
DTN×3 MN×N
)
What is the natural scale of M?
26
Alexander Kusenko (UCLA/Kavli IPMU) PHENO-2014
Seesaw mechanism
In the Standard Model, the matrix D arises from the Higgs mechanism:
Dij = yij〈H〉
Smallness of neutrino masses does not imply the smallness of Yukawa couplings. For large
M ,
mν ∼y2〈H〉2
MOne can understand the smallness of neutrino masses even if the Yukawa couplings are
y ∼ 1 [Gell-Mann, Ramond, Slansky; Yanagida; Glashow; Mohapatra, Senjanovic].
27
Alexander Kusenko (UCLA/Kavli IPMU) PHENO-2014
Seesaw mechanism
0.1 eVy=1
M GUT scale
28
Alexander Kusenko (UCLA/Kavli IPMU) PHENO-2014
Seesaw mechanism
0.1 eVy<<1
keV scaleM
(dark matter)(pulsar kicks)
GUT scale
29
Alexander Kusenko (UCLA/Kavli IPMU) PHENO-2014
Various approaches to small Majorana masses
• Just write them down.
– One sterile keV sterile neutrino, the dark matter candidate [Dodelson, Widrow].
– Three sterile neutrinos, one with a several keV mass (dark matter) and two degenerate
with GeV masses and a keV splitting, νMSM [Shaposhnikov et al.].
• Use lepton number conservation as the reason for a small mass [de Gouvea].
• Use flavor symmetries, new gauge symmetries [Lindner et al.]
• Singlet Higgs (discussed below) at the electroweak scale can generate the Majorana
mass. Added bonuses:
– production from S → NN at the electroweak scale generates the right amount of
dark matter.
– production from S → NN at the electroweak scale generates colder dark matter.
A “miracle”: EW scale and mass at the keV scale (for stability)
⇒ correct DM abundance. [AK; AK, Petraki]
• Split seesaw (discussed below) makes the scale separation natural. Dark matter cooled
by various effects. ⇒ democracy of scales
30
Alexander Kusenko (UCLA/Kavli IPMU) PHENO-2014
Sterile neutrinos as dark matter: production scenarios
Production color coded by “warmness” vs “coldness”:
31
Alexander Kusenko (UCLA/Kavli IPMU) PHENO-2014
Sterile neutrinos as dark matter: production scenarios
Production color coded by “warmness” vs “coldness”:
• Neutrino oscillations off resonance [Dodelson, Widrow] No prerequisites; production
determined by the mixing angle alone; no way to turn off this channel, except for
low-reheat scenarios [Gelmini et al.]
31
Alexander Kusenko (UCLA/Kavli IPMU) PHENO-2014
Sterile neutrinos as dark matter: production scenarios
Production color coded by “warmness” vs “coldness”:
• Neutrino oscillations off resonance [Dodelson, Widrow] No prerequisites; production
determined by the mixing angle alone; no way to turn off this channel, except for
low-reheat scenarios [Gelmini et al.]
• MSW resonance in νa → νs oscillations [Shi, Fuller] Pre-requisite: sizable lepton
asymmetry of the universe. The latter may be generated by the decay of heavier sterile
neutrinos [Laine, Shaposhnikov]
31
Alexander Kusenko (UCLA/Kavli IPMU) PHENO-2014
Sterile neutrinos as dark matter: production scenarios
Production color coded by “warmness” vs “coldness”:
• Neutrino oscillations off resonance [Dodelson, Widrow] No prerequisites; production
determined by the mixing angle alone; no way to turn off this channel, except for
low-reheat scenarios [Gelmini et al.]
• MSW resonance in νa → νs oscillations [Shi, Fuller] Pre-requisite: sizable lepton
asymmetry of the universe. The latter may be generated by the decay of heavier sterile
neutrinos [Laine, Shaposhnikov]
• Higgs decays [AK, Petraki] Assumes the Majorana mass is due to Higgs mechanism.
Sterile miracle: abundance a “natural” consequence of singlet at the electroweak
scale. Advantage: “natural” dark matter abundance
31
Alexander Kusenko (UCLA/Kavli IPMU) PHENO-2014
Sterile neutrinos as dark matter: production scenarios
Production color coded by “warmness” vs “coldness”:
• Neutrino oscillations off resonance [Dodelson, Widrow] No prerequisites; production
determined by the mixing angle alone; no way to turn off this channel, except for
low-reheat scenarios [Gelmini et al.]
• MSW resonance in νa → νs oscillations [Shi, Fuller] Pre-requisite: sizable lepton
asymmetry of the universe. The latter may be generated by the decay of heavier sterile
neutrinos [Laine, Shaposhnikov]
• Higgs decays [AK, Petraki] Assumes the Majorana mass is due to Higgs mechanism.
Sterile miracle: abundance a “natural” consequence of singlet at the electroweak
scale. Advantage: “natural” dark matter abundance
• Split seesaw: [AK, Takahashi, Yanagida]
Two production mechanisms, cold and even colder.
Advantage: “naturally” low mass scale
31
Alexander Kusenko (UCLA/Kavli IPMU) PHENO-2014
Lyman-α bounds on Dodelson-Widrow production
1 keV/m s
F WD
M
0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45 0.50
0.2
0.4
0.6
0.8
1
m =
5 k
eVDW fractionallowed
(e.g. Higgs decays)mechanismanother production
or a different candidate
[Boyarsky, Lesgourgues, Ruchayskiy, Viel]
Free-streaming properties: [Boyanovsky; Petraki]
32
Alexander Kusenko (UCLA/Kavli IPMU) PHENO-2014
New scale or new Higgs physics?
L = LSM + Na (i∂µγµ)Na − yαaH LαNa − Ma
2Nc
aNa + h.c. ,
To explain the pulsar kicks and dark matter, one needs M ∼ keV. Is this a new
fundamental scale? Perhaps. Alternatively, it could arise from the Higgs mechanism:
L = LSM + Na (i∂µγµ)Na − yαaH LαNa − ha S Nc
aNa + V (H,S)
M = h〈S〉
Now S → NN decays can produce sterile neutrinos.
33
Alexander Kusenko (UCLA/Kavli IPMU) PHENO-2014
For small h, the sterile neutrinos are out of equilibrium in the early universe, but S is in
equilibrium. There is a new mechanism to produce sterile dark matter at T ∼ mS from
decays S → NN :
Ωs = 0.2
(
33
ξ
)(
h
1.4 × 10−8
)3(
〈S〉
mS
)
Here ξ is the dilution factor due to the change in effective numbers of degrees of freedom.
〈S〉 ∼ 102 GeV (EW scale)
Ms ∼ keV (for stability) ⇒ h ∼ 10−8
⇒ Ω ≈ 0.2
The sterile neutrino momenta are red-shifted by factor ξ1/3 > 3.2. [AK, Petraki]
34
Alexander Kusenko (UCLA/Kavli IPMU) PHENO-2014
Cooling changes the clustering properties
1´10-11 2´10-11 5´10-11 1´10-10 2´10-10 5´10-10 1´10-91.0
10.0
5.0
2.0
20.0
3.0
1.5
15.0
7.0
excluded region
m(k
eV)
2sin θ
pulsar kick via MSW
no MSW(allowed)
pulsar kick
dark matter (allowed, subject tosome model−dependent constraints)
[AK, PRL 97:241301 (2006); Petraki, AK, PRD 77, 065014 (2008); Petraki, PRD 77, 105004 (2008)]
35
Alexander Kusenko (UCLA/Kavli IPMU) PHENO-2014
Implications for the EW phase transition and the LHC
One may be able to discover the singlet Higgs at the LHC [Profumo, Ramsey-Musolf, G.
Shaughnessy; Davoudiasl et al.; O’Connell et al.; Ramsey-Musolf, Wise]
The presence of S in the Higgs sector changes the nature of the electroweak phase
transition [AK, Petraki]
0 50 100 150 200Η
-200
0
200
400
Σ
T>>Tc
0 50 100 150 200 250 300Η
-300
-200
-100
0
100
200
300
Σ
T=Tc
0 50 100 150 200 250 300Η
-300
-200
-100
0
100
200
300
Σ
T=0
First-order transition, CP in the Higgs sector =⇒ electroweak baryogenesis
36
Alexander Kusenko (UCLA/Kavli IPMU) PHENO-2014
Split seesaw
N1
2,3N
Standard Model
37
Alexander Kusenko (UCLA/Kavli IPMU) PHENO-2014
Split seesaw
N1
2,3N
Standard Model
38
Alexander Kusenko (UCLA/Kavli IPMU) PHENO-2014
N1
2,3N
Standard Model
Standard Model on z = 0 brane. A Dirac
fermion with a bulk mass m:
S =
∫
d4x dzM
(
iΨΓA∂AΨ +mΨΨ
)
,
The zero mode: (iΓ5∂5 + m)Ψ(0) = 0.
behaves as ∼ exp(±mz). The 4D fermion:
Ψ(0)R (z, x) =
√
2m
e2mℓ − 1
1√Memzψ
(4D)R (x).
Also, a U(1)(B−L) gauge boson in the bulk,
(B − L) = −2 Higgs φ on the SM
brane. The VEV 〈φ〉 ∼ 1015GeV gives
right-handed neutrinos heavy Majorana masses.
[AK, Takahashi, Yanagida]
39
Alexander Kusenko (UCLA/Kavli IPMU) PHENO-2014
Split seesaw
N1
2,3N
Standard Model
Effective Yukawa coupling and the mass are
suppressed:
M(R)d=4 = M
(R)d=5
(
2mi
M(e2miℓ − 1)
)
,
yd=4 = yd=5
√
2mi
M(e2miℓ − 1)
successful seesaw relation unchanged:
mν ∼y2d=4〈H〉2
M(R)d=4
=y2d=5〈H〉2
M(R)d=5
[AK, Takahashi, Yanagida]
40
Alexander Kusenko (UCLA/Kavli IPMU) PHENO-2014
Split seesaw: economical, natural extension of SM
N1
2,3N
Standard Model
• Democracy of scales: small difference in the
bulk massesmi results in exponentially large
splitting between the sterile neutrino masses.
• An rather minimal model: SM augmented
by three right-handed singlets can explain
– observed neutrino masses
– baryon asymmetry (via leptogenesis)
– dark matter
if, for example
M1 = 5 keV or M1 = 17 keV, and
M2,3 ∼ 1015GeV
[AK, Takahashi, Yanagida]
41
Alexander Kusenko (UCLA/Kavli IPMU) PHENO-2014
An alternative DM at a keV scale: string/supersymmetry moduli
• Expansion of the universe breaks supersymmetry: the effective potential acquires terms
of the form −cH2φ2, where c is of order one
• on average, each degree of freedom carries a non-zero energy in the de Sitter universe.
U( )
inflH
φ
φ
1. the minimum of the effective potential during inflation is displaced, for a light field, by
a large amount (∼ MPl)
2. at the end of inflation, the field is not necessarily in the minimum of either de Sitter or
flat effective potential
42
Alexander Kusenko (UCLA/Kavli IPMU) PHENO-2014
Moduli problem
Oscillating scalar field is a cosmological equivalent of matter. The field starts oscillating
when H ∼ mφ, and the temperature is
Tφ ∼ (90/π2g∗)1/4√
MPlmφ.
The density to entropy ratio is
ρφ
s∼
m2φφ
20/2
(2π2/45)g∗T 3φ
∼ 105GeV
(
mφ
keV
)1/2( φ0
MPl
)2
.
...to be compared with dark matter:
ρDM
s= 0.2
ρc
s= 3 × 10
−10GeV,
bad discrepancy. Moreover, the universe with so much dark matter forms only one form of
structures: black holes.
43
Alexander Kusenko (UCLA/Kavli IPMU) PHENO-2014
The density to entropy ratio is can be small enough in those (superhorion-size) patches
that have φ0 ≪ MPl:
ρφ
s∼
m2φφ
20/2
(2π2/45)g∗T 3φ
∼ 10−9
GeV
(
mφ
keV
)1/2( φ0
10−7MPl
)2
.
44
Alexander Kusenko (UCLA/Kavli IPMU) PHENO-2014
The density to entropy ratio is can be small enough in those (superhorion-size) patches
that have φ0 ≪ MPl:
ρφ
s∼
m2φφ
20/2
(2π2/45)g∗T 3φ
∼ 10−9
GeV
(
mφ
keV
)1/2( φ0
10−7MPl
)2
.
Can life exist in those parts of the universe where ΩDM/Ωbaryon ≫ 1?
44
Alexander Kusenko (UCLA/Kavli IPMU) PHENO-2014
The density to entropy ratio is can be small enough in those (superhorion-size) patches
that have φ0 ≪ MPl:
ρφ
s∼
m2φφ
20/2
(2π2/45)g∗T 3φ
∼ 10−9
GeV
(
mφ
keV
)1/2( φ0
10−7MPl
)2
.
Can life exist in those parts of the universe where ΩDM/Ωbaryon ≫ 1?
Structures start forming at Teq ∼ 105 GeV(
mφkeV
)1/2 (φ0MG
)2
. and only black holes
emerge, unless ΩDM/Ωbaryon < 10. [Tegmark, Aguirre, Rees, Wilczek]
44
Alexander Kusenko (UCLA/Kavli IPMU) PHENO-2014
The density to entropy ratio is can be small enough in those (superhorion-size) patches
that have φ0 ≪ MPl:
ρφ
s∼
m2φφ
20/2
(2π2/45)g∗T 3φ
∼ 10−9
GeV
(
mφ
keV
)1/2( φ0
10−7MPl
)2
.
Can life exist in those parts of the universe where ΩDM/Ωbaryon ≫ 1?
Structures start forming at Teq ∼ 105 GeV(
mφkeV
)1/2 (φ0MG
)2
. and only black holes
emerge, unless ΩDM/Ωbaryon < 10. [Tegmark, Aguirre, Rees, Wilczek]
Anthropic selection favors the maximal allowed value φ0, which corresponds to dark matter
density close to the observed ΩDM/Ωbaryon.
44
Alexander Kusenko (UCLA/Kavli IPMU) PHENO-2014
The density to entropy ratio is can be small enough in those (superhorion-size) patches
that have φ0 ≪ MPl:
ρφ
s∼
m2φφ
20/2
(2π2/45)g∗T 3φ
∼ 10−9
GeV
(
mφ
keV
)1/2( φ0
10−7MPl
)2
.
Can life exist in those parts of the universe where ΩDM/Ωbaryon ≫ 1?
Structures start forming at Teq ∼ 105 GeV(
mφkeV
)1/2 (φ0MG
)2
. and only black holes
emerge, unless ΩDM/Ωbaryon < 10. [Tegmark, Aguirre, Rees, Wilczek]
Anthropic selection favors the maximal allowed value φ0, which corresponds to dark matter
density close to the observed ΩDM/Ωbaryon.
Anthropic solution to moduli problem ⇒ correct amount of dark matter.
[AK, Loewenstein, Yanagida]
44
Alexander Kusenko (UCLA/Kavli IPMU) PHENO-2014
Radiative decays of sterile neutrinos and moduli
Sterile neutrino in the mass range of interest have lifetimes longer than the age of the
universe, but they do decay:
γ
νν ννs s e
e
γ
γ
φγ
W
W
Photons have energies m/2: X-rays. Concentrations of dark matter emit X-rays.
[Abazajian, Fuller, Tucker; Loewenstein et al., others]
Can one distiguish between sterile neutrinos and moduli? Not from the spectrum.
However, moduli make a very cold dark matter, while
sterile neutrios can have a measurable free-streaming length.
45
Alexander Kusenko (UCLA/Kavli IPMU) PHENO-2014
Conclusions: many exciting news
• The IceCube discovery of PeV neutrinos may be able to
confirm our understanding of secondary particle production
from blazars.
• It can also point to decays of heavy dark matter particles!
• Dark matter at a keV mass scale is viable, well-motivated,
and hinted by the recent X-ray data.
46
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