Damping of neutrino flavor conversion in the wake of the supernova shock wave

1. Damping of neutrino flavor conversion in the wake of the supernova shock wave • by G.L. Fogli, E. Lisi, D. Montanino, A. Mirizzi Based onhep-ph/0603033: Damping of supernova neutrino transitions in stochastic shock-wave density profiles

2. n • Core collapse SN’s is one of the most energetic event in nature. It corresponds to the terminal phase of a massive star which becomes instable at the end of its life. It collapses and ejects its outer mantle in a shock wave driven explosion. • ENERGY SCALES: 99% of the released energy available in the core collapse (~1053 erg) is emitted by (anti)neutrinos of all flavors with energies of order of a tenth of MeVs. • TIME SCALE: The duration of the burst lasts ~10s • EXPECTED RATE: 1-3 SN/century in our galaxy (dO(10) kpc).

3.  cooling     RPN102km Rc104km “Hot” PN star    Stellar core Shock wave Schirato & Fuller astro-ph/0205390  T. Totani et al., Astrophys. J. 496, 216 (1998).

4. i InvertedHierarchy (IH) Normal Hierarchy (NH) 2 m122 3 1 m132 kH>0 kH<0 2 not known but from solar & KamLAND m122 3 1 not relevant for SNe from solar & KamLAND from atmospheric & K2K  transitions The flavor evolution in matter is described by the MSW equation: where: Neutrino potential in matter

5. Behind this phenomenology and neglecting Earth matter crossing, the (relevant) survival probability PeeP(ee) can be decomposed into two effective “high” (H) and “low” (L) 2 subsystems, up to small terms of the order of O(m122/m132, sin213): [see, e.g., G.L. Fogli et al.,PRD68 (2003) 033005, Dighe and Smirnov, PRD62, (2000) 033007] where the only dependence on the matter effect is encoded in terms of P2,Hee. Clearly, a time dependent potential V=V(t) induced by the passage of the shock modulates the survival probability P2,Hee and thus leaves an “imprint” on the time spectrum of the neutrino burst.

6. Our parameterization of the shock profile Livermore group (Schirato & Fuller), astro-ph/0205390 Tokio group (Kawagoe et al.), unpublished Forward shock Forward shock Garching group (Tomàs et al.), astro-ph/0205390 Forward shock No reverse shock Reverse shock Models of shock NOT A SIMULATION!

8. 

9. t=20s t=10s t=4s 0 5 10 15 X 109cm Kifonidis (PhD thesis)

11. We will consider only “small” scale fluctuations, i.e., fluctuations whose correlation length is smaller than the typical oscillation wavelength in matter at resonance: Stochastic scale density fluctuation of various magnitudes and correlation lengths may reasonably arise in the wake of a shock front (i.e., for r<rshock). A SN neutrino “beam” traveling to the Earth might thus experience stochastic matter effects while traversing the stellar envelope. We shall assume L0=10km. With this hypothesis the density fluctuations can be considered “-correlated”, i.e.: with

12. represents the “r.m.s” of the amplitude of the stochastic fluctuations and, in principle, =(r). Unfortunately, there is not an ab initio theory of small scale fluctuation, so we make the simplifying assumption that fluctuation arise only after the passage of the shock wave: We conservatively assume that 4%.

13. Evolution in fluctuating potentials Suppose that a system is described by an Hamiltonian which is composed by one “deterministic” and one “stochastic” component: where (t) is random fluctuating -correlated function: In this case Schrödinger equation is no longer adequate to describe the evolution of the system: [see, e.g., Balantekin et al., Burgess et al.]

14. In our case Q=|ee|. The previous modified “Liouville” equation can be written as a “Bloch” equation in term of the polarization vector with , and the probability of observing an electron neutrino at distance r can be calculated as standard term (leading) “damping” term (perturbation for  up to ~10%) Application to SN ’s

15. We suppose that the fluctuations are sufficiently small to affect only the “High” subsector. After some calculations, the probability P2,Hee in presence of random noise can be recast as with where is the effective “13” mixing angle in matter. The effect of noise is thus to suppress the MSW effect into the stellar medium. In the limit of large fluctuations, one gets P2,Hee1/2, which correspond to a sort of complete “flavor depolarization” for the effective  states in the H subsystem.

17. Conclusions • The observation of a modulation in the survival probability caused by the passage of the shock wave inside the exploding supernova can give us valuable information on the unknown oscillation parameters (mass hierarchy, 13) as well as on the internal structure of the exploding star • But small-scale fluctuations can partially hide this effect and cause a dangerous confusion scenario (no prompt shock? “wrong” hierarchy? too small 13?) • For this reason, a better theoretical understanding of stochastic density fluctuationsbehind the shock front would be of great benefit for future interpretation of SN neutrino events

18. ADVERTISEMENT NOW 2006 Neutrino Oscillation Workshop Conca Specchiulla (Otranto, Italy) September 9-16, 2006 www.ba.infn.it/~now2006 (only by invitation)

19. Bonus slides

20.  () in inverse (direct) hierarchy

23. Analytical vs Runge Kutta

24. 3 2 1 0 1 2 3 X 108cm Evolution of entropy in SN explosion Kifonidis et al., Astrophys. J. Lett., 531, L123 (2000)