Neutrinos and Big Bang Nucleosynthesis · variations ( neutrino oscillations). • Baksan, Kamioka,...
Transcript of Neutrinos and Big Bang Nucleosynthesis · variations ( neutrino oscillations). • Baksan, Kamioka,...
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Neutrinos and Big BangNucleosynthesis
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Expansion of the Universe
Edwin Hubble
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From WMAP
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Expansion of the Universe
Universe remains homogeneous and isotropic during expansion
Any length scale
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Hubble’s constant
units
1 pc = 3.09 1013 km 3.26 light years
Observations
H-1 = 9.78 109 years h = H/100 km s-1 Mpc-1
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r
m
Enclosed mass:
H2
E < 0 the mass m is bound and cannot escape to infinity
E > 0 expansion can continue
E = 0 critical density, c
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Planck Mass:
mp = 2.17 10-5 g mpc2 = 1.2 1019 GeV
Hence if > c the universe will begin to contract
cc2 = 9.45 10-9 ergs/cm3
Planck time
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= / c = + + baryon + dark-matter + vacuum 1
0.3 0.65
For a flat universe, k=0
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From WMAP
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Elementary Statistical Mechanics
Particle Number
Energy
Ep = ( p2 + m2)1/2
μ: Chemical potential
g: Spin degrees of freedom
+ fermions
- bosons
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Relativistic Limit ( T>>μ, T>>m)
Energy density:
Number density:
sEffective energy density:
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Cosmic microwave background photons (CMBR)
Number density: N/V = (2/ 2) 1.202 T3 ~ 398 photons/cm3
Temperature: T=2.7oK, g=2, two polarization components
Energy density: E/V = 2 ( 2/30) T4 ~ 5 x 10-13 ergs/cm3
= ( / c) ~ 10-4 , does not close the universe
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Recall that H2 ~
Small R, Radiation-dominated universe(very early Universe)
H2 ~ R-4 R ~ t1/2
Large R, Matter-dominated universe(later Universe)
H2 ~ R-3 R ~ t2/3
Species will remain in thermal equilibrium as long as their interactionrate exceeds the expansion rate
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H = 1.66 (gs)1/2 T2/mp
~ GF2 E2 ~ GF
2 T2
n ~ T3
~ GF2 T5
Freeze-out when Freeze-out when = H= H
T3 freeze-out =1.66 (gs)1/2
mp GF2
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205/4, e, μ, , e±, μ±,u, u, d, d, g
msc2
69/4, e, μ, , e±, μ±,±, 0
QCD
57/4, e, μ, , e±, μ± m c2
43/4 , e, μ, , e± mμc2
11/2 , e± mec2
2 1 eV
gsParticles inequilibrium
kT
less than
Thermal history of the Universe
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4He equilibrium abundance
Y =2 (N2 (Nnn/N/Npp))
NNn n + N+ Np
(N(Nnn/N/Npp) =) = exp(- m/T)
neutron--proton massdifference
freeze-out temperatureT~ 0.8 MeV
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From PDG
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Tfreeze-out =1.66 (gs)1/2
mp GF2
Recall that
Y depends on Tfreeze-out which in turn depends on gs
Neutrino counting !Neutrino counting !
Y gs N
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Neutrino decoupling
dS = dE/T entropy per unit volume ~ gs T3
Before e+e- annihilation:
After e+e- annihilation:
gs(b) = 2 + (7/8) x 4 = 11/2
gs(a) = 2
Entropy conservation: gbefore T3before = gafter T3
after
Tafter = (11/4)1/3 Tbefore
T = 2.7 oK T = 1.9 oK
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Probing the Cosmic Microwave Background Radiation (CMBR)
CMBR is anisotropic, its temperature variesslightly at different locations
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Dark Blue = -200 μK Red = +200 μK
WMAP results:
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WMAP results
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In the matter-dominated epoch massive neutrinos cluster on verylarge scales, but free-stream out of smaller scale fluctuations.
This suppresses the amplitude of the fluctuations.
Combination of several experiments: h2 < 0.0072 (95% C.L.)
~m
92 eV
T
2.75 K
3
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neutrino masses: 0.048 < m1+m2+m3 < 6.6 eV
Cosmological Implications
Atmospheric neutrinos: m232 2.0 10-3 eV2
One neutrino mass > 0.04 eV
SNO + KamLAND: m122 7.1 x 10-5 eV2
One neutrino mass > 0.008 eV
Limits on “ e mass” give: m( 1,2,3) < 2.2 eV
0.001 < < 0.13
Stay tuned…
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Summary of Methods to Obtain Neutrino Masses
Observed~ 0.1 eV
miCosmology
Observed~ 10-5 eV2
m2 = m12 - m2
2Neutrinooscillations
Sensitivity0.01 eV
m = | mi |Uei|2 i|
i = Majoranaphases
Double betadecay
Sensitivity0.2 eV
mi2 |Uei|2Single beta
decay
Only double beta decay is sensitive to Majorana nature.
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Where do we stand?
A perspective
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Fundamental discoveries are recentlymade
• SNO, 2002: Discovery of the non-electron neutrinocomponent of the solar flux ( neutrino oscillations);measurement of the total solar neutrino flux.
• SuperK, 1998:Discovery of atmospheric neutrino fluxvariations ( neutrino oscillations).
• Baksan, Kamioka, IMB, 1987: Detection of neutrinos fromSupernova 1987A (neutrino flux consistent with neutron starbinding energy, cooling time is near that expected).
• Irvine, 1987: Detection of two-neutrino double-beta decay.• MSW, 1986: Recognition that matter enhances neutrino
oscillations.
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..that broadly impact physics,astronomy, and cosmology
• Massive neutrinos: Beyond the Standard Model ofelementary particles.
• Neutrino mixing angles are close to maximal: Impacts onleptogenesis; explosion mechanism and nucleosynthesis incore-collapse supernovae.
• Total solar neutrino flux is measured: The theory of mainsequence stellar evolution is verified.
• Direct neutrino mass measurements:
Neutrino component of dark matter.
WMAP put significant limits on
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Backup slides
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Applications of -nucleus interactions
Theory and applications of Detector Response:Detectors for solar, atmospheric, accelerator, andreactor neutrinos.
Input into astrophysics: Neutrino reactions in core-collapse supernovae, supernova nucleosynthesis,gamma-ray burst nucleosynthesis.
Tests of nuclear structure calculations: Shell Model,effective field theories.
Fundamental physics at low energies: Determiningproton strange form factors.
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Neutrino-nucleus cross-sections
Atmospheric ’s,neutrinos from pointsourcesIcecube, Antares
Deep-inelasticscattering, partonicd.o.f., x-scaling
High Energy(~200 GeV < E < EeV)
AtmosphericneutrinosMINERVA,SciBooNE, etc.
Relativistic; hadronic partonic d.o.f,
superscaling ideas;quasielastic andresonance regime
Intermediate E(~200 MeV < E <~200 GeV)
Solar, reactor, andsupernova neutrinos;beam-stops
Non-relativisticmany-body theories(Shell Model, RPA);effective field theory
Low Energy(0 < E <~200 MeV)
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0 100 200 300 400 500
Neutrino Energy (MeV)
Solar
Reactor
Supernova
Atmospheric
Neut
rino
type
We need to know the response of the nucleusto neutrinos with a wide range of energies.
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What happens when a 50 MeVneutrino hits a nucleus? Where is
the strength? What is gA/gV?
As the incoming neutrino energyincreases, the contribution of thestates which are not well-known
increase, including first- and evensecond-forbidden transitions.
At the lowest energies ShellModel is the best approach.Gamow-Teller strength is
quenched in the Shell Model:
Beta-decay rates from Nowacki
At higher energies where therate is sensitive to totalstrength and the energy ofgiant resonances there is atendency to use RPA.
However…
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Using Shell Model to calculate neutrino-nucleus cross-sectionsone needs to use effective operators when one employseffective Hamiltonians. However in most calculations thesystematics of BE(2) transitions are characterized byeffective charges and Gamow-Teller distributions byquenching. Different calculations disagree by as much as 30%from from one another. To understand neutrino-nucleuscollisions at energies up to 60 MeV we need 1) A moreconsistent treatment of the Shell Model in a bigger basisspaces; and 2) More data. We should also be careful with theQRPA calculations.
We should also question the effective interactions utilized.For example, Otsuka, et al. find that inclusion of a tensorforce in the Shell Model may increase the Gamow-Tellerstrength distribution at higher energies.
This is bread and butter nuclear structure physics!
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A.B. Balantekin and H. Yuksel
Effective Field theory Approach to low-energy neutrino-deuteron scattering Butler, Chen
Below the pion threshold 3S1 3S0 transition dominates and oneonly needs the coefficient of the two-body counter term, L1A
(isovector two-body axial current)
L1A can be obtained bycomparing the cross section
(E) = 0(E) + L1A 1(E) withcross-section calculatedusing other approaches ormeasured experimentally
Not easy to studythree-body systems
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Note that anobservation of 0double beta decay doesnot necessarily implythe existence of a lightMajorana neutrino!AL ~ mAH ~ MW
4 / 5
for ~ 1 TeV bothmechanisms maycontribute equally.
Lepton Flavor violationinvolving chargedleptons may provide a“diagnostic tool” forestablishing themechanism of 0decay
Ramsey-Musolf & Vogel
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In QRPA the dependence of the 0 matrix element on s.p. states is
reduced if the coupling strength gppis adjusted to the 2 rate:
F.Simkovic
There is a big spread in thematrix elements calculated
using QRPA
Most of this spread can be traced to different choices of the initialand final states, choice of the value of the parameter gpp, and
corrections for the short-range nuclear repulsion.