Gravitational Waves from Inspiralling Compact Binaries in ... - LUTH

Gravitational Waves from Inspiralling Compact Binaries in ... - LUTH Gravitational Waves from Inspiralling Compact Binaries in ... - LUTH

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Gauge Invariant Variables Memmesheimer, Gopakumar and Schäfer (2004) stress use of gauge invariant variables in the elliptical orbit case Damour and Schäfer (1988) showed that the functional form of n and Φ as functions of gauge invariant variables like E and h is the same in different coordinate systems (gauges). From the explicit expressions for n and Φ in the ADM and modified harmonic coordinates the gauge invariance of these two parameters is explicit at 3PN. MGS04 suggest the use of variables xMGS = (Gmn/c 3 ) 2/3 and k ′ = (Φ − 2π)/6π as gauge invariant variables in the general orbit case. We propose a variant of the former: x = (Gmn Φ/2πc 3 ) 2/3 = (Gmn Kc 3 ) 2/3 = (Gmn (1 + k)c 3 ) 2/3 . Our choice is the obvious generalisation of gauge invariant variable x in the circular orbit case and thus facilitates the straightforward reading out of the circular orbit limit. BRI-IHP06-I – p.43/??

Orbital average - Energy flux -MHar To average the energy flux over an orbit requires use of 3PN GQKR → Modified Harmonic coords Involves evaluation of the the integral, 〈 ˙ E〉 = 1 P P 0 E(t) ˙ dt = 1 2 π 2 π 0 dl du ˙ E(u)du . Using GQKR, transform the expression for the energy flux ˙ E (r, ˙r 2 , v2 ) or more exactly (dl/du × ˙ E)(r, ˙r 2 , v2 ) to (dl/du × ˙ E)(x, et, u). Choices: GI97 uses Gm/ar and er. DGI04 employs Gmn/c 3 and et. ABIQ06 uses et and x = (GmnΦ/2πc 3 ) 2/3 Recall: 3PN flux contains log terms; convenient to rewrite the expression as dl du ˙ E = 11 N=3 αN (et) 1 (1 − et cos u) N + βN (et) Non-vanishing αN ’s, βN ’s and γN ’s are too long to be listed. βN ’s correspond to all the 2.5PN terms. γN represent the log terms at order 3PN. sin u (1 − et cos u) N + γN (et) ln(1 − et cos u) (1 − et cos u) N BRI-IHP06-I – p.44/??

Orbital average - Energy flux -MHar<br />

To average the energy flux over an orbit requires use of 3PN GQKR →<br />

Modified Harmonic coords<br />

Involves evaluation of the the <strong>in</strong>tegral,<br />

〈 ˙<br />

E〉 = 1<br />

P<br />

P<br />

0<br />

E(t) ˙ dt = 1<br />

2 π<br />

2 π<br />

0<br />

dl<br />

du<br />

˙<br />

E(u)du .<br />

Us<strong>in</strong>g GQKR, transform the expression for the energy flux ˙ E (r, ˙r 2 , v2 ) or more<br />

exactly (dl/du × ˙ E)(r, ˙r 2 , v2 ) to (dl/du × ˙ E)(x, et, u).<br />

Choices: GI97 uses Gm/ar and er. DGI04 employs Gmn/c 3 and et.<br />

ABIQ06 uses et and x = (GmnΦ/2πc 3 ) 2/3<br />

Recall: 3PN flux conta<strong>in</strong>s log terms; convenient to rewrite the expression as<br />

dl<br />

du<br />

˙<br />

E =<br />

11<br />

N=3<br />

<br />

αN (et)<br />

1<br />

(1 − et cos u) N + βN (et)<br />

Non-vanish<strong>in</strong>g αN ’s, βN ’s and γN ’s are too long to be listed.<br />

βN ’s correspond to all the 2.5PN terms.<br />

γN represent the log terms at order 3PN.<br />

s<strong>in</strong> u<br />

(1 − et cos u) N + γN (et) ln(1 − et cos u)<br />

(1 − et cos u) N<br />

<br />

BRI-IHP06-I – p.44/??

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