Probing the early Universe and inflation with indirect detection

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1 Probing the early Universe and inflation with indirect detection Pat Scott Department of Physics, McGill University With: Yashar Akrami, Torsten Bringmann, Jenni Adams, Richard Easther Based on PS, Adams, Bringmann & Easther, in prep. Bringmann, PS, Akrami, arxiv: Slides available from patscott

2 Background Question What is an ultracompact minihalo (UCMH)?

3 Background Question What is an ultracompact minihalo (UCMH)? Answer A DM halo that collapses shortly after matter-radiation equality

4 Background Question What is an ultracompact minihalo (UCMH)? Answer A DM halo that collapses shortly after matter-radiation equality Shortly means z collapse is O(100) or more = isolated collapse = formation by radial infall = very steep density profile ρ r 9/4 = excellent indirect detection targets Also good lensing prospects (Ricotti & Gould 2009; Li et al. 2012) (Scott & Sivertsson 2009 Lacki & Beacom 2010)

5 Background Question How would UCMHs be created?

6 Background Question How would UCMHs be created? Answer Small-scale, large amplitude density perturbations in the early Universe Small-scale power in primordial perturbation spectrum (e.g. features in the inflaton potential) Phase transitions Other seeds (e.g. cosmic strings)

7 UCMH formation Conditions for formation Seeded well before matter-radiation equality Requires δ O(10 3 ) (compare with normal inflationary perturbations δ 10 5 ) much more likely than PBH formation (δ 0.3) Usefulness UCMH mass is set by horizon scale at time of horizon entry = specific UCMH mass specific cosmological scale = limit on abundance of specific mass halo limit on power on specific scale k

8 Limits on present-day UCMH abundance with Fermi 1-year, 95% CL upper limits Based on public Fermi point source sensitivity Proper statistical treatment of observable limit Rather conservative assumptions: - 100% b b - σv = cm 3 s 1 - m χ = 1 TeV - no DM minihalo detected fmax M 0 UCMH (M ) k (Mpc 1 ) Galactic sources extragalactic sources Galactic diffuse

9 Scale-free (power law) spectrum ( ) k n 1 σχ,h 2 (R) δ2 H (t k 0 ) k M 0 UCMH (M ) This work (gamma rays, Fermi-LAT) Improved σχ,h 2 using top hat window function Explicit calculation of δ min (Solution to linear growth eqs; δ = during matter domination in linear approximation = δ in non-linear regime) Early-time (z 800) contribution of UCMHs to reionisation is constrained by WMAP τ (Zhang 2010) nmax(k) This work (reionisation, WMAP5 τe) Simple σχ,h 2, δmin χ k (Mpc 1 ) = 10 3 (Fermi-LAT)

10 Spectrum with a step } δh 2 (k) δ2 H {θ (k) (k s k) + p 2 θ (k k s ) (1) pmax(ks) gamma rays (Fermi-LAT), n = ± reionisation (WMAP5 τe), n = ± k s (Mpc 1 )

11 General spectrum and curvature perturbation limits Limits on P R from UCMHs 5 orders better than from PBHs = strong limits on inflationary models Pδ(k) WIMP kinetic decoupling k (Mpc 1 ) Allowed regions Ultracompact minihalos (gamma rays, Fermi-LAT) Ultracompact minihalos (reionisation, WMAP5 τe) Primordial black holes CMB, Lyman-α, LSS and other cosmological probes PR(k)

12 Tension with inflationary models α Allowed Scott, Adams, Bringmann & Easther 2012 Slow roll WMAP5 (Peiris & Easther 2008) Excluded 10 GeV, BF = 0, b b, Fermi-LAT 1 TeV, BF = 500, µ + µ, Fermi-LAT 1 TeV, BF = 500, µ + µ, Dark Matter Array n s With z c = 200 (vs 1000 in previous limits) Excludes much of slow-roll inflationary parameter space = detection soon if z c = 200 is reasonable Otherwise, slow-roll or WIMPs need to go...

13 Summary Ultracompact minihalos are promising indirect detection targets Could be visible by Fermi/VERITAS/HESS/CTA/Gaia Assuming DM annihilates, non-observation places limits on primordial perturbations at small scales Derived limits are much tighter than existing ones from primordial black holes Significant tension already exists with slow-roll inflationary models

14 Backup Slides UCMH density profiles Initially single UCMH per horizon, minimal initial angular momentum = UCMHs form via radial infall = Very steep radial density profile ρ χ (r) = 3f χm UCMH 16πR 3 4 UCMH r 9 4, (2) Truncated at self-annihilation radius r SA, and radius r AM where gas angular momentum violates radial infall approx. ρ(r SA ) = m χ σv (t t i ), r AM = σ 8 7 DM R 11 7 UCMH G 4 7 M 4 7 UCMH (3)

15 Backup Slides UCMH relic density calculation For some distribution of perturbations pdf(δ) ( ) 1 + δpbh zeq f UCMH = pdf(δ) dδ (4) 1 + z stop δ min For Gaussian perturbations, pdf(δ) = ) 1 ( 2πσ 2 χ,h (z X, R) exp δ 2 2σχ,H 2 (z X, R) 2 (5) Improved σ 2 χ,h using top hat window function Explicit calculation of δ min

16 Backup Slides Implications of kinetic decoupling for step spectrum α 2 χ 0 { ( ) ( x n+2 Tχ 2 (x) WTH(x)/T 2 χ 2 ks (1) θ k x + p 2 θ x k )} s dx k Halo mass at kinetic decoupling M i,min (M ) pmax(ks) gamma rays (Fermi-LAT), n = ± reionisation (WMAP5 τe), n = ± pmax(ks = 10 4 Mpc 1 ) gamma rays (Fermi-LAT), n = ± reionisation (WMAP5 τe), n = ± k s (Mpc 1 ) Wavenumber at kinetic decoupling k max (Mpc 1 )

Primordial Black Holes in Cosmology. Lectures 1 & 2 : What are PBHs? Do they exist? Massimo Ricotti (University of Maryland, USA)

Primordial Black Holes in Cosmology Lectures 1 & 2 : What are PBHs? Do they exist? Massimo Ricotti (University of Maryland, USA) Institute of Cosmos Sciences, University of Barcelona 23/10/2017 What are