detec%ng(gravitaonal/wave( … · 2015-06-19 · astrophysical(backgrounds:((bns(example(3 n bns...
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Detec%ng gravita%onal-‐wave backgrounds with advanced detectors:
Opportuni%es and challenges
Eric Thrane (Monash University)
DCC G1500532
Stochas%c backgrounds
• Superposi%on of GW sources. • Astrophysical sources – AMer radia%on-‐dominated era – Binaries, rota%ng neutron stars, the first stars – Cosmic strings, exo%ca
• Cosmological sources: created during radia%on era. – Phase transi%ons, prehea%ng.
• Primordial sources: from infla%on
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Astrophysical backgrounds: BNS example
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NBNS=26
NBNS=260
E. Thrane and J. D. Romano, Phys. Rev. D, 88 124032 (2013) With results from Wu, Mandic, & Regimbau, Phys. Rev. D, 85 104024 (2012)
Ini%al LIGO GW
Cosmological sources
• For most cosmological models (e.g., phase transi%ons, prehea%ng), numerical studies predict ΩGW<10-‐11. – ~50x too weak to detect.
• What is the common physics that sets this scale?
• Assume a radia%on-‐era source with Gaussian T(k) with characteris%c wave number scale k* and some width σ…
4 Giblin & Thrane, Phys. Rev. D, 90 107502 (2014)
A “rule-‐of-‐thumb” cosmological source
• Frac%on of energy density available for source: ρs = αρ.
• How quadrupolar is source: β = |STT|2/|T|2. • Equa%on of state parameter: w ≈ 1/3. • Numerical studies: k*/H>100 (causality) and σ/k*>1/2 (the process has non-‐zero width).
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See: P. Binétruy, A. Bohé, C. Caprini, and J.-‐F. Dufaux, JCAP 06, 027 (2012). J. F. Dufaux, Phys. Rev. Len. 103, 041301 (2009). C. Caprini, R. Durrer, and G. Servant, Phys. Rev. D 77, 124015 (2008).
STT = the transverse-‐traceless projec%on of the anisotropic stress tensor
Observa%onal Implica%ons
6 Giblin & Thrane, Phys. Rev. D, 90 107502 (2014)
Excep%ons
• Signals from phase transi%on during non-‐minimal infla%on are “frozen in.”
• Non-‐standard equa%on of state. • Massive gravitons.
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Interpreta%on
• The rule of thumb uses simple scaling arguments to explain why many cosmological backgrounds fall below ΩGW <10-‐11.
• If a model predicts, ΩGW >>10-‐10, it is interes%ng to ask: what rule-‐of-‐thumb assump%on is evaded in order to facilitate this?
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Final results from ini%al LIGO/Virgo: No detec%ons
9 hnp://journals.aps.org/prl/abstract/10.1103/PhysRevLen.113.231101 hnp://journals.aps.org/prd/abstract/10.1103/PhysRevD.91.022003
Correlated noise from Schumann resonances
10 Thrane, Christensen, Schofield, Phys. Rev. D 87 123009 (2013)
Advanced LIGO Projec%ons (2014)
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SNR = 24–470
Thrane, Christensen, Schofield, Effler, Phys. Rev. D 90 023013 (2014)
Advanced LIGO Measurements (2015)
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SNRM = 0.4–3.7
With Effler, Schofield, Christensen and Biscoveanu
Mi%ga%on through Wiener subtrac%on
• Given sufficiently sensi%ve magnetometers placed in sufficiently quiet loca%ons (~0.1 pT/rHz), it should be possible to subtract correlated noise.
13 Thrane, Christensen, Schofield, Effler, Phys. Rev. D 90 023013 (2014)
Opportuni%es and challenges
• Astrophysical detec%on may be within reach. – Possible sensi%vity improvements through data analysis innova%on.
• Not easy to concoct cosmological model detectable with 2nd-‐genera%on detectors, but detec%on would have profound implica%ons.
• Correlated noise budgets are essen%al to make confident detec%on; contamina%on may be less than ini%ally feared.
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Extra slides
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Communica%on measurements: power-‐law integrated curves
• Measure
• Assume power law.
• Predicted spectra that do not intersect the PI curve are not detectable.
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Power-‐law integrated curve: Advanced LIGO: HL, one year, design sensi%vity
E. Thrane and J. D. Romano, Phys. Rev. D, 88 124032 (2013)
Thrane & Romano
not detectable
2014 Length Coupling
17 Effler, Schofield, Christensen, Thrane
2014 Angular Coupling
18 Effler, Schofield, Christensen, Thrane
2015 Coupling
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Effler, Schofield, Christensen, Thrane, Biscoveanu
Hand-‐waving deriva%on • Strain perturba%ons obey sourced Klein-‐Gordon equa%on:
• S = anisotropic stress tensor (depends on T). • Assume a parameterised form of T:
• Calculate ΩGW(k) from source and relate it to ΩGW,0 today…
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characteris%c scale
width amplitude
Es%mate β from simula%on
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Chose six random phases for T, project T onto S.
op?mis?c
realis?c
pessimis?c
Rule of thumb anecdote
• “Gravita%onal Waves from Fragmenta%on of a Primordial Scalar Condensate into Q Balls”
• Contacted by author. • Not a model I was familiar with, but the assump%ons appear to obey the rule of thumb assump%ons:
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Energy budget
23 Mandic, Thrane, Giampanis, & Regimbau, PRL 109, 171102 (2012)
Parameter es)ma)on in searches for the stochas)c gravita)onal-‐wave background
Example two: Galac%c neutron stars
24 Talukder, Thrane, Bose, Regimbau, Phys. Rev. D, 89 123008 (2014)
ellip?city
Con%ngency plan: Op%mal weigh%ng
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