Please enable JavaScript.
Coggle requires JavaScript to display documents.
Blake D. Sherwin- Fundamental physics from CMB lensing: new data and new…
Blake D. Sherwin- Fundamental physics from CMB lensing: new data and new approaches
Galaxies trace large amounts of underlying dark matter (80% of matter)
want to probe distribution in detail, as contains clean information on open questions in cosmology and physics
What is the physics of inflation and the early universe
what is dark energy
is standard cosmology correct
what are the properties/masses of neutrinos
Gravitational lensing
Distribution of dark matter deflects CMB light that passes through
CMB: leftover radiation from the hot primodrdial plasma-most distant observable source of light
distribution of matter deflects light that passes through
Dark matter causes lensing magnification feature in CMB
Can infer magnification and lensing from "stretchin" of the local CMB power spectrum
Outline
Part 1: ACT and Simons Observatory: Lensing and neutrino mass constraints
Part 2: New approaches to small scale CMB lensing - are our current lensing estimators good enough
Part 3: delensing Simons Observatory: new methods for revealing inflationary signal
Example-lensing can tell us about neutrinos
Don't know absolute mass, order of neutrino masses (2light 1 heavy or 1 light 2 heavy), Dirac/Majorana?
look for extra neutrinos
Neutrinos affect how cosmic structure grows
The more massive neutrinos are, the more small scale dark matter structure is suppressed
suppression also visible in lensing map- want to measure (and compare with primordial CMB amplitude)
Key observable: CMB lensing power spectrum
y axis: how much lensing
xaxis for a lens of this angular scale
Progress
Precise probe
Simons
ACT (atacama cosmology telescope)
CMB lensing becomes increasingly powerful
New power spectra
Simons
0.6% precise lensing
combines ACT POLARBEAR collaborations
will have highest sensitivity
will determine unknown neutrino mass in any scenario
Lensing Systematics:main concern
Forground biases from SZ cluster, CIB, contamination
When nothing is done, few % effect. Multifrequency or geometric cleaning can reduce further
Lots of work required to make upcoming measurements robust
Improved CMB lensing Foreground Cleaning
New combination of frequency-cleaned and uncleaned fields:
Cleaned and uncleaned have very similar error bars
Small scale:
Quadratic estimator noise gets large - seemingly cannot probe tiny CMB lenses/scales
With low noise, can read off tiny lenses from small-scale power spectrum. Is there better estimator out there
Simulation: Novel lensing maps and spectra
Simulated lensing reconstruction with new method (L>4000)
GI reconstruction appears to do ok, especially on large gradients
Some diagrams
Improvements on signal to noise ratio at L>4000
caveat: scatter from foregrounds (but not bias)
Next steps and future work
Detailed foreground and poarisation analysis
Same physics in maximum likelihood algorithms
Can this improve constraints on e.g. cross-correlations, dark matter, axion physics
Measure lens power on much smaller scales
Delensing - new methods for revealing inflationary signals
Many simple) models make inflationary gravity waves
Probe physics at ultra-high energy (at the doorstep of the planck scale)
The strength of the waves - tensor to scalar ratio r - tells us about the energy at which inflation happened
Leaves characteristic pattern in the CMB polarization
CMB polarization basics
Any polarization map can be decomposed ino E and B mode fields
B-mode : contains signnals from inflation, if there
CMB B-polarization with small inflationary signal
See signal clearly as there is no background
B-modes are a null channel
Gravitation lensing converts E to B polarization
Lensing B-mode noise obscured any inflationary B signal, lensing adds additional error (cosmic varience)
Lensing removal
Know lensing, so can estimate lensing B modes and subtract
To delense, need to measure good maps of CMB lensing - How?
CMB lensing is a probe of the projected mass distribution
Standard internal case: reconstruct lensing d from changes in background CMB
Delensing for Simons
SO is significantly limited by lensing B-modes
Problem : SO lensing reconstruction, while powerful, is still too noisy to allow large improvements from internal lensing
Only 20% improvement expected internally
Estimate lensing from large scale structure tracers of lensing e.g. CIM galaxies.
Multi-Tracer delensing for simons
Can co-add SO lensing map with different large scale structure tracers to delens
multitracer delelnsing can greatly improve delensing performance: now coadd SO lensing + DES/LSST + CIB
Why this might work
LSS modeling required
Tracer calibration and delensing residual depend only on measureable spectra
Cross-spectra (assuming isotropy) can have high S/N
Can calibrate low noise LSS map, modelling often not needed
Demonstration of LSS delensing in data
Theory prediction for delensed - lensed CMB temperature power agrees well
New SO delensing pipeline applied to simulations
Polarization simulation: multitracer delensing demonstration with SO (preliminary)
Might not work:
Lensing foreground correlated with B fregrounds can give biases to delensing process
foregrounds in B, E and d all could matter investigation in progress, also of other challenges
Significant improvements possible for SO
With multitracer delensing methods