Axion Cosmology and the Lightest Possible Dark Matter
Axion Cosmology and the Lightest Possible Dark Matter Candidate David J. E. Marsh Phys. Rep. 643, 1 (2016)
David J. E. Marsh
The Principle of Plenitude: “This best of all possible worlds will contain all possibilities, with our finite experience of eternity giving no reason to dispute nature’s perfection. ” Gottfried Leibniz (1646 -1716), in Theodicee Quoted in “String Axiverse” Pangloss sometimes said to Candide: “There is a concatenation of events in this best of all possible worlds: for if you had not been kicked out of a magnificent castle for love of Miss Cune gonde–if you had not come under the Inquisition–if you had not walked over America–if you had not stabbed the Baron–if you had not lost all your sheep from the fine country of El Dorado– why, then, you would not be here, eating preserved citrons and pistachio-nuts. ” “All that is very well, ” answered Candide, “but let us cultivate our garden. ”
Initial Conditions and Relic Density David J. E. Marsh
Symmetry Breaking and Inflation Cold condensate from SSB. The axion is born: David J. E. Marsh
Vacuum Realignment Axion acquires mass*, evolves according to Klein. Gordon: Axion is “frozen” by Hubble friction term. Light axions are “DElike” David J. E. Marsh (* I am ignoring Tdependence and
Vacuum Realignment Axion acquires mass*, evolves according to Klein. Gordon: Field oscillates & damps. WKB (or exact) Osc. scalar ~ matter David J. E. Marsh (* I am ignoring Tdependence and
David J. E. Marsh
Relic Density of Cold Axions CMB B-pol BICEP/Planck (2014) Ultralight axions: • Relic abundance natural for GUT scale decay constants! • SSB occurs before/during inflation. Universe is one q patch. David J. E. Marsh >1 % DM
Scales of Interest Non-thermal compare mass to Hubble (not T). Linear perts: LSS and Galaxy “Fuzzy DM”, UV the CMB v. non-linear. formation, physics? halo Solitons in Non-thermal model. galaxies. epoch? “DM-like” “DE/n-like” “WDMn<<1 Hz Miniclusters like” ? Rough DM Precision DM cosmology lower bound Physi BBN cs: Hubble: [e. V] Size of d. Sph Nonlinea r David J. E. Marsh Equalit y Field frozen : behav e as L Today
Precision Cosmology: Perturbations and Linear Observables CMB download: github. com/dgrin 1/axion. CAMB Cosmosis module coming soon…
Axion DM is “Fuzzy” Clustering suppressed relative to CDM on small scales. Heuristically: de Broglie wavelength from Hubble Uncertainty in flow. position: Recession veocity: Q: how far away does cosmic DM have to be for r>l? Parametrically, this is borne out in cosmological PT… David J. E. Marsh
The Axion Jeans Scale Gradient energy scalar DM has effective sound speed: pressure gravity WKB approx, e. g. Park et al (2012) Exact solutions possible in axion-dominated e. g. DJEM (2016) Universe. Fits for “transfer function” relative to CDM. Hu et al (2000) David J. E. Marsh
The Axion Jeans Scale Numerical solution* in Boltzmann code axion. CAMB. (*un-normalized) David J. E. Marsh Fig. Hlozek, DJEM et al (2014)
CMB Temperature Power Physics: early w=-1 evolution changes expansion rate. DM-like axions change DE-like axions change during rad. dom. epoch angular scale and acoustic peak evolution of F. SW David J. E. Marsh Hlozek, DJEM effect. et al (2014) heights.
Constraints from Planck TT Marginalised constraints via nested sampling with Multi. Nest. David J. E. Marsh Hlozek, DJEM et al (2014)
Constraints from Planck TT Interpretation as constraints on decay constant if fi~fa. David J. E. Marsh Hlozek, DJEM et al (2014)
The Future: CMB-S 4 Science Book Axion DM Fraction Array of ground based telescopes for ~2020*. Advantage over Planck for DM: high-l lensing power. Improve lower bound on DM particle mass by 102. Allow detection of 1% departures from CDM at 5 s. S 4 can do precision tests of the CDM paradigm! Planck Wa~fa 2 improve fa“forecast” bound. Challenge: modelling effects of non-linear David J. E. Marsh (*near term also “Simons clustering. array”) S 4 forecast Hlozek, DJEM et al (2016)
Non-Linear Scales and Galaxy Formation Overview: Hui et al (2016) Fig: Schive et al (2014) Fig: Schwabe et al (2016) Halo Model download:
The Halo Mass Function Physics: pressure/ld. B suppresses galaxy formation. Methodology: Press-Schechter and/or N-body sims. David J. E. Marsh DJEM & Silk (2013), et al Corasaniti, DJEM et al. Du (2016)
High-z Galaxy Formation Abundance matching: HMF UV luminosity. Less clustering later halo formation, fewer high-z galaxies. Different techniques 50% (matching, SFR, HMF), 100 different data JWS % (observations, redshifts, No CDMT binning) all reach the fainter -22 10 e. V same conclusions: galaxies -23 10 e. V 50% Bright HUDF cumulative luminosity. Data: Bouwens et al Faint is consistent with the data. David J. E. Marsh Bozek, DJEM et al (2015); Schive et al (2015); Corasaniti, DJEM et al
Reionization and CMB t High-z galaxies reionize the Universe optical depth. Fewer galaxies later reionization lower t Planck. tension CDM 1022 e. V 1021 e. V Ionized fraction inc. astro. CMB uncertain. But will uncertainties. Integrate… improve with better EE & David J. E. Marsh Bozek, DJEM et al k. SZ.
“Axion Stars” and Galaxy Cores ULAs gravitationally condense on small scales inside David J. E. Marsh Schive et al (2014+), Schwabe et al halos.
“Axion Stars” and Galaxy Cores • Cores are local ground state soliton soln. • Cores size shrinks with increasing density. • Scaling relationship: • Large scale incoherence NFW. • Parameterise density profile with transition. simulation results… R>ld. B NFW Soliton core David J. E. Marsh Schive et al (2014+), Schwabe et al
The Cusp-Core Problem? Pure cusp excluded >99% (e. g. ) Slopes of Fornax & Sculptor density profiles: Velocity dispersion at half-light measures enclosed mass. David J. E. Marsh slope of DMWalker & Penarrubia Two populations constrain halo.
Constraints From Cores David J. E. Marsh High-z galaxies 0. 4 x 10 -22 e. V Slopes Use of mock method data + improved shows that estimator Jeans analysis is unbiased. is biased and cannot discriminate between models (b • degeneracy). All evidence Jeans points to cores. Slope • BUT axions (just) s too light c. f. WDM. New • Assume negligible baryonic feedback. • Testable in future via (non)universality. Gonzalez-Morales, DJEM et al (2016)
Extra Topics David J. E. Marsh
Let’s take a break. . . m~10 -22 e. V appears special: Limit of our ignorance for DM. Possible source of d. Sph cores. Can we ever detect such an axion? David J. E. Marsh
Detecting ULAs with n. EDM: Paving the Way for CASPEr Fig: Harris (2007) David J. E. Marsh
The neutron EDM Experiment Ultracold neutrons spinning “in a jar” in E and B fields. Ran at RAL/ILL from 1998 giving best static n. EDM limit: Measures energy splitting relative to Larmour freq. of Hg: Sensitive to tiny energy shifts: Cycles: 130 s; E-flips: hourly; “Run” measures dn every Q: canday. we use the time series to search for axions? David J. E. Marsh Baker et al (2006); Pendlebury et al (2015)
Axions and n. EDM Graham & Rajendran: assumed no signal on cycle scales, and averaged. Published data not available for this. For m-1>run, ILL limit ~ 10 times worse than published: (unpublished) cycle level PSI data + 4 years ILL: David J. E. Marsh Graham & Rajendran (2013) Ayres, Rawlik, DJEM et al (in prep. )
Nicholas Ayres and Michal Rawlik for n. EDM: n. EDM (blinded) n. EDM also sensitive to “axion wind”, but cannot beat David J. E. Marsh SNe…
Numerical GR for Axion Stars Fig: Helfer, DJEM et al (2016) David J. E. Marsh
GRChombo, Clough et al (2015) (3+1) numerical GR with a scalar cosine potential (any V!). Katy Clough Thomas Helfer David J. E. Marsh
Stability Solution Space David J. E. Marsh
Core Collapse I: BHs • Above critical MADM and fa axion stars collapse to BHs. • Appears hard to realise for axion stars from DM structure. • Mergers and BH formation signals? David J. E. Marsh Helfer, DJEM et al (2016)
Core Collapse II: Axion Emission • Below critical fa, quartic interactions axion emission. • Destabilise galaxy cores for fa<1015 Ge. V. CDM HDM? David J. E. Marsh Helfer, DJEM et al (2016)
ULA Endgame: Can We -22 Exclude 10 e. V? David J. E. Marsh
-18 10 ULA Endgame: 21 cm and DM-baryon relative v modulates large scale 21 cm e. V 21 cm Power Spectrum z=20 power. Effect can be measured by e. g. LOFAR. CDM w/ vel CDM no vel Sensitivity early LW Scale Mpc-1 David J. E. Marsh Fig. Visbal et al (2012) Tseliakhovich & Hirata (2010) Visbal et al (2012)
-18 10 ULA Endgame: 21 cm and Large e. V scale 21 cm power from baryon v coherence. 21 cm Power Spectrum z=20 Originates from small-scale P(k) effect absent for ULAs. CDM m<10 -18 e. V Sensitivity early LW Scale Mpc-1 David J. E. Marsh Problem: need to understan d SFR! Fig. Visbal et al (2012) DJEM (2015)
Caveats & Work in Progress Anharmonic potentials: • Relic density lower fa. In prep w/ Diez. Tejedor. • axion. CAMB: modified perts. In prep Leung. Iscourvature: precision CMB in prep w/ w/ Hlozek. Multiple axions? “Predicted” by string/M-theory. Can we do precision cosmology? In prep w/ Stott. “Miniclusters”. Beyond the QCD axion microlensing constraints. In prep w/ Quevillon. Simulations with m~10 -22 e. V. More community input! detection: can it ever work at ultra-low Direct frequency? Lyman-alpha forest: WTF? In prep w/ Bozek et al. David J. E. Marsh
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