UMICH-2015:Neutrino and Light Relativisic Species Summary
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- 1 Wiki navigation
- 2 Neff
- 2.1 Very sensitive probe of the thermal history. Forecasts at a very exciting level
- 2.2 How do we make the most of the measurement?
- 2.3 Things to do
- 3 Neutrino Masses
- 4 Action Items
- Forecasts for CMB Stage IV
- Planck 2015 versus CMB S4
Very sensitive probe of the thermal history. Forecasts at a very exciting level
- E.g. a field in thermal equilibrium that decouples above 100 GeV :
- Real scalar - ΔNeff = 0.027
- Weyl fermion - ΔNeff = 0.047 (Dirac - 0.094)
- Vector field - ΔNeff = 0.054
- Sensitive to lots of exciting ideas in BSM physics
- axions, gravitinos, dark radiation, etc.
- Can test our thermal history by comparing with BBN
- e.g. time evolution of Neff
- BBN and the CMB test different things!
- E.g. we can test interacting (Nfluid versus non-interacting dark radiation
How do we make the most of the measurement?
- Most optimistic measurements use lmax > 3000
- Need to understand foregrounds for E-modes at small scales
- Delensing E-modes improves the constraints
- What are our requirements from optimizing Neff measurement
But a lot of information is coming from the phase shift, which is less sensitive to lmax
- What do we gain from relic abundances and BBN
- D/H measurements will also be very good. How does this impact CMB S4?
- Do we need lab measurements to help with BBN predictions?
- Standard model prediction of Neff is still uncertain at 0.01 level. Do we need to improve this?
Things to do
CMB S4 is very sensitive -- do we need a broader parameterization of BSM physics?
- Sterile neutrinos, non-thermal relics in general
- are there good targets
Can we really achieve this sensitivity ?
- How realistic are these forecasts? What is the impact of foregrounds
- Will we be able to use the high l modes?
- What is the tradeoff between lmax and sensitivity?
- We don't see the shape in lensing
Neutrino masses signature can be spoiled by degeneracy with τ
- Need a good measurement of τ to achieve forecasts
- Unrealistic to get this from the ground
- How do we get around this issue?
Relation to Lab Experiments
- Lab experiments are complimentary
- measure different parameters
- BSM physics can hide in any disagreement between lab based and cosmology based measurements
- Non-standard energy density / thermal history / laws of physics will alter cosmology and lab measurements differently
What needs to be done?
- How do non-linearities, baryonic effects enter lensing power spectrum
- How is lensing reconstruction affected by foregrounds
- Are estimators bias by foregrounds?
- We are assuming that only lensing + BAO are the observables. Would be believe constraints from RSD, clustering, etc.?
- Opportunities with other observables (e.g. clusters) and cross-correlation (e.g. LSST, DESI, Euclid)
- How would we confirm the signature (checks for robustness) ?
- Is there a good parameterization of BSM physics that is captured by cosmological neutrino mass constraints (versus lab constraints)?
- More realistic forecasts
- how do things depend on lmin?
- How sensitive are we to foregrounds?
- Can we reach ΔNeff=0.01-0.02?
- How do we deal with the tau degeneracy for mν?
- What is the right space of models? Are we missing opportunities?
- e.g. non-thermal relics
- BSM physics associated with neutrinos
- What more can we learn from CMB lensing?
- Are models computed to the necessary accuracy
- neutrinos in the CMB
- Neff from the Standard model
- Can we leverage improvements in relic abundance measurements