Relic Neutrinos as a Source of Dark Energy

Neal Weiner

New York University

IDM04

R.Fardon, D.B.Kaplan, A.E.Nelson, NW

What does dark energy have to do with anything?

What does dark energy have to do with us?

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

Testing the dark sector

• 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…)

Dark Energy Dark Matter

Does Dark Energy have anything to do with us?

new scales of physics

CDM

1+z

Energy density at (10-2.5 eV)4

Typically new energy scalesare associated with new particles(e.g., weak scale, QCD scale)

Natural to consideral new particles with mass parameters near thisscale

Program: start with fermions (n) and scalars (A), dynamics at 10-3eV, study general properties and interactions

with SM

General interactions

Q: What is “leading” interaction with SM?

A:

Leading means: i) dimension four operatorii) large effect compared with SM

Not immediately obvious significance, but already interesting

Relic neutrinos = system at finite density

Simplify: assume mD< mn(A) = A, then

Neutrinos “source” homogeneous A-field (mA< 10-4eV for mean-field)

Total energy (neutrino+scalar) canredshift slowly

just seesaw mass, but Aundetermined = m dynamical

Neutrino mass determined byenvironment

Example:

Effective scalar potential

Minimize wrt A

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

Equation of state - model independent

Mean-field means any parameterization ok

Energy minimization yields:

E.O.S. is

More interactions with SMPlanckian effects can yield NR operators with quarks

mB = baryon mass, B is strength relative to gravity

Tested via short distance modifications of gravity => B < 1/30

Effects on neutrino propagationNeutrino 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

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– m 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)