Lumely Castle, County Durham July 15-19, 2013 Neutrino oscillations, N eff and cosmological constraints: role of the sterile ν Ninetta Saviano II Institut für Theoretische Physik, Universität Hamburg, Dipartimento di Scienze Fisiche, Università di Napoli Federico II in collaboration with: E. Borriello, C. Giunti, G. Mangano, G. Miele, A. Mirizzi, O. Pisanti and P.D. Serpico
Experimental anomalies & sterile ν interpretation Some experimental data in tension with the standard 3 ν scenario + oscillations (…and sometimes in tension among themselves….) ν e appearance signals Kopp at al., 2013 1. excess of ν e originated by initial ν µ : LSND/ MiniBooNE • A. Aguilar et al., 2001 A. Aguilar et al., 2010 2. ν e and ν e disappearance signals • deficit in the ν e fluxes from nuclear reactors (at short distance) Mention’s talk Mention et al.2011 Acero, Giunti and Lavder, 2008 reduced solar ν e event rate in Gallium experiments • Giunti and Lavder, 2011 Kopp, et al. 2011 All these anomalies, if interpreted as oscillation signals, point towards the possible existence of 1 (or more) sterile neutrino with Δ m 2 ~ O (eV 2 ) and θ s ~ O ( θ 13 ) Many analysis have been performed 3+1 , 3+2 schemes Sterile neutrino : does not have weak interactions and does not contribute to the number of active neutrinos determined by LEP Ninetta Saviano Invisibles13, 19 July 2013 1
Radiation Content in the Universe At T < m e , the radiation content of the Universe is ε R = ε γ + ε ν + ε x The non-e.m. energy density is parameterized by the effective numbers of neutrino species N eff π 2 π 2 ε ν + ε x = 7 ν N e ff = 7 15 T 4 15 T 4 ν ( N SM e ff + ∆ N ) 8 8 N SM due to non-instantaneous neutrino decoupling e ff = 3 . 046 Mangano et al. 2005 (+ oscillations) At T~ m e , e + e - pairs annihilate heating photons. Since T dec ( ν ) is close to m e , neutrinos share a small part of the entropy release ∆ N = Extra Radiation: axions and axion-like particles, sterile neutrinos (totally or partially thermalized), neutrinos in very low-energy reheating scenarios, relativistic decay products of heavy particles... For a recent review on Cosmic Dark radiation and ν see M. Archidiacono et al., 2013 Ninetta Saviano Invisibles13, 19 July 2013 2
v and Big Bang Nucleosynthesis Big Bang Nucleosynthesis (BBN) is the epoch of the Early Universe ( T ~ 1- 0.01 MeV ) when the primordial abundances of light elements were produced, in particular 2 H, 3 He, 4 He, 7 Li. When Γ n ⟷ p < H ➜ freezes out fixing the primordial yields n n = n p = e − ∆ m/T n p 2 n/p ⤷ !1/7 ! including !neutron !decays Y p = 1 + n/p Helium mass fraction Ninetta Saviano Invisibles13, 19 July 2013 3
v and Big Bang Nucleosynthesis Big Bang Nucleosynthesis (BBN) is the epoch of the Early Universe ( T ~ 1- 0.01 MeV ) when the primordial abundances of light elements were produced, in particular 2 H, 3 He, 4 He, 7 Li. When Γ n ⟷ p < H ➜ freezes out fixing the primordial yields n n = n p = e − ∆ m/T n p 2 n/p ⤷ !1/7 ! including !neutron !decays Y p = 1 + n/p Helium mass fraction Cosmological ν influence the production of primordial light elements in two ways: 1) ν e , ν e participate in the CC weak interactions which rule the n ⟷ p interconversion any change in the their energy spectra can shift the n/p ratio ν e + n → e − + p freeze out temperature ➪ modification in the primordial yields ν e + p → e + + n e − + ν e + p → n i.e. ν e - ν e asymmetry (chemical potential ξ e ) ➝ n p = e ( − ∆ m/T − ξ e ) Ninetta Saviano Invisibles13, 19 July 2013 3
v and Big Bang Nucleosynthesis Big Bang Nucleosynthesis (BBN) is the epoch of the Early Universe ( T ~ 1- 0.01 MeV ) when the primordial abundances of light elements were produced, in particular 2 H, 3 He, 4 He, 7 Li. When Γ n ⟷ p < H ➜ freezes out fixing the primordial yields n n = n p = e − ∆ m/T n p 2 n/p ⤷ !1/7 ! including !neutron !decays Y p = 1 + n/p Helium mass fraction Cosmological ν influence the production of primordial light elements in two ways: 1) ν e , ν e participate in the CC weak interactions which rule the n ⟷ p interconversion any change in the their energy spectra can shift the n/p ratio ν e + n → e − + p freeze out temperature ➪ modification in the primordial yields ν e + p → e + + n e − + ν e + p → n i.e. ν e - ν e asymmetry (chemical potential ξ e ) ➝ n p = e ( − ∆ m/T − ξ e ) 2) ν α contribute to the radiation energy density that governs the expansion rate of the Universe before and during BBN epoch and then the n/p ratio. Changing the H would alter the n/p ratio at the onset r a 8 ⇡ G N ✏ R H = ˙ a = ( γ , e, ν , x) of BBN and hence the light element abundances 3 ↳ ∝ N eff Ninetta Saviano Invisibles13, 19 July 2013 3
Extra radiation impact on BBN and constraints Light element abundances are sensitive to extra radiation: N eff H early freeze out n/p 4 He (T d ↑ ) Upper limit on N eff from constrains on primordial yields of D and 4 He Mangano and Serpico. 2012 B Adapted from Cyburt et al, 2002 Δ N eff ≤ 1 1.0 2 H+ 4 He ω b + 2 H low + 4 He ω b + 2 H+ 4 He (at 95% C.L) Same results from analysis on sterile neutrino : likelihood CMB + 2 H+ 4 He ω b +Y no strong indication for N s > 0 from BBN alone 0.5 Hamann et al, 2011 From a measurement of D in a particle astrophysical system: 0.0 0.0 1.0 2.0 3.0 4.0 5.0 N eff N eff = 3.0 ± 0.5 Pettini and Cooke, 2012 4
Extra radiation impact on BBN and constraints Light element abundances are sensitive to extra radiation: N eff H early freeze out n/p 4 He (T d ↑ ) Upper limit on N eff from constrains on primordial yields of D and 4 He Mangano and Serpico. 2012 B Adapted from Cyburt et al, 2002 Δ N eff ≤ 1 1.0 2 H+ 4 He ω b + 2 H low + 4 He ω b + 2 H+ 4 He (at 95% C.L) Same results from analysis on sterile neutrino : likelihood CMB + 2 H+ 4 He ω b +Y no strong indication for N s > 0 from BBN alone 0.5 Hamann et al, 2011 From a measurement of D in a particle astrophysical system: 0.0 0.0 1.0 2.0 3.0 4.0 5.0 N eff N eff = 3.0 ± 0.5 Pettini and Cooke, 2012 4
Extra radiation impact on BBN and constraints Light element abundances are sensitive to extra radiation: N eff H early freeze out n/p 4 He (T d ↑ ) Upper limit on N eff from constrains on primordial yields of D and 4 He Mangano and Serpico. 2012 B Adapted from Cyburt et al, 2002 Δ N eff ≤ 1 1.0 2 H+ 4 He ω b + 2 H low + 4 He ω b + 2 H+ 4 He (at 95% C.L) Same results from analysis on sterile neutrino : likelihood CMB + 2 H+ 4 He ω b +Y no strong indication for N s > 0 from BBN alone 0.5 Hamann et al, 2011 From a measurement of D in a single astrophysical system: 0.0 0.0 1.0 2.0 3.0 4.0 5.0 N eff N eff = 3.0 ± 0.5 Pettini and Cooke, 2012 4
v and CMB and LSS v’s and their masses effect the PS of temperature fluctuations of CMB (T < eV) and the matter PS of the LSS inferred by the galaxy surveys. N eff and m ν affect the time of matter-radiation equality ➟ consequences on the amplitude of the first peak and on the peak locations Lesgourgues’s talk 1.05 1 k NR 0.95 0.9 m ν ( Σ ) P(k) f ν /P(k) 0 0.85 i ncreases 0.8 0.75 0.7 Taken from m ν = 0.05, 0.1, 0.15, ..., 0.50 eV 0.65 Lesgourgues, Mangano, Miele and Pastor “Neutrino Cosmology”, 2013 0.6 10 -3 10 -2 10 -1 10 0 10 1 k (h/Mpc) Ninetta Saviano Invisibles13, 19 July 2013 5
v and CMB and LSS v’s and their masses effect the PS of temperature fluctuations of CMB (T < eV) and the matter PS of the LSS inferred by the galaxy surveys. The small-scale matter power spectrum P(k > knr) is reduced in presence of massive ν : ✓ free-streaming neutrinos do not cluster ✓ slower growth rate of CDM (baryon) perturbations 1.05 1 k NR 0.95 0.9 m ν ( Σ ) P(k) f ν /P(k) 0 0.85 i ncreases 0.8 0.75 0.7 Taken from m ν = 0.05, 0.1, 0.15, ..., 0.50 eV 0.65 Lesgourgues, Mangano, Miele and Pastor “Neutrino Cosmology”, 2013 0.6 10 -3 10 -2 10 -1 10 0 10 1 k (h/Mpc) Ninetta Saviano Invisibles13, 19 July 2013 5
Extra radiation impact on CMB If additional degrees of freedom are still relativistic at the time of CMB formation, they impact the CMB anisotropies. Constraints N eff from the CMB Spectrum (peaks height and position, anisotropic stress (l~ 200), damping tail (l >1000)) Adapted from Y.YY Wong Ninetta Saviano Invisibles13, 19 July 2013 6
Extra radiation impact on CMB If additional degrees of freedom are still relativistic at the time of CMB formation, they impact the CMB anisotropies. Constraints N eff from the CMB Spectrum (peaks height and position, anisotropic stress (l~ 200), damping tail (l >1000)) Same data used to measure Adapted from Y.YY Wong other cosmological parameters basic parameters of Λ CDM: ( Ω b h 2 , Ω c h 2 , 100 θ MC , n s , A s , τ ) + derived parameters X ( H 0 , Ω k , Ω Λ , N e ff , σ 8 , m ν , z re , Y p , w, Ω m z LS ... ) degeneracies necessary to combine with other cosmological probes Ninetta Saviano Invisibles13, 19 July 2013 6
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