Relic Neutrinos as a Source of Dark Energy

1. What does dark energy have to do with anything? What does dark energy have to do with us? Relic Neutrinos as a Source of Dark Energy R.Fardon, D.B.Kaplan, A.E.Nelson, NW Neal Weiner New York University IDM04

2. Theories of Dark Energy • Cosmological Constant • Good: Easy to write down, easy to calculate • Bad: Hard to understand, harder to test (e.g. false vacuum) • Slow-roll quintessence • Good: Easy to write down, seems to have happened once already (inflation), potentially testable (w ≠ -1) • Bad: Requires 10-33eV mass scalar field • IR modification of gravity (e.g., DGP model) • Good: Profound (rethink spacetime symmetries and scales), testable (w~0.7) • Bad: w~0.7 - unless you add CC then w<-1 (Lue&Starkman), origin of hierarchy • Interacting dark matter (negative pressure “stuff”) • Good: Strong evidence for dark matter, similar scales • Bad: Get acceleration messes up structure, getting structure messes up acceleration

3. Cosmological tests: CMB, SNIa, lensing, structure formation… Cosmological tests: CMB, SNIa, lensing, structure formation… Direct detection experiments (axions, WIMPs) Indirect detection experiments (positrons, gamma rays, neutrinos…) Testing the dark sector Dark Matter Dark Energy Does Dark Energy have anything to do with us?

4. rCDM new scales of physics Energy density at (10-2.5 eV)4 rL Typically new energy scales are associated with new particles (e.g., weak scale, QCD scale) 1+z Natural to consideral new particles with mass parameters near this scale Program: start with fermions (n) and scalars (A), dynamics at 10-3eV, study general properties and interactions with SM

5. General interactions Q: What is “leading” interaction with SM? A: Leading means: i) dimension four operator ii) large effect compared with SM Not immediately obvious significance, but already interesting

6. just seesaw mass, but A undetermined = mn dynamical Relic neutrinos = system at finite density Simplify: assume mD< mn(A) = l A, then Neutrinos “source” homogeneous A-field (mA< 10-4eV for mean-field) Neutrino mass determined by environment Total energy (neutrino+scalar) can redshift slowly

7. Effective scalar potential Minimize wrt A Example: Observations: • Neutrino mass is not constant in time (Mass Varying Neutrinos - MaVaNs), independent of DE scenario • Total energy can be much larger than neutrino energy alone • SM particles integral component of dark energy

8. Equation of state - model independent Mean-field means any parameterization ok Energy minimization yields: E.O.S. is

9. More interactions with SM Planckian effects can yield NR operators with quarks mB = baryon mass, lB is strength relative to gravity Tested via short distance modifications of gravity => lB < 1/30

10. Effects on neutrino propagation Neutrino mass sensitive to weakest known physics (e.g., seesaw mechanism) Must consider new force, even if sub-Planckian Neutrino mass shifts in matter New matter effects (e.g., discrepancies between experiments in matter/air) would be strong evidence for new neutrino-scalar and baryon-scalar interactions

11. Summary • DE discovered, now we want to study it • Important to ask how SM can interact with DE sector • Neutrinos and neutrino mass ideal probes • SM particles integral component of DE • mn varies over cosmological times, significant changes to neutrino cosmology • Does not require 10-33eV mass fields • Opportunities for tests on Earth: • short distance modifications of gravity • new matter effects in neutrino oscillations • others, e.g., flavor violation in HE astrophysical neutrino sources (Hung & Pas)