Lensing in McVittie metric - · 2019. 5. 10. · avoid a detectable correction to the Mercury...
Transcript of Lensing in McVittie metric - · 2019. 5. 10. · avoid a detectable correction to the Mercury...
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Lensing and Λ Criticisms McVittie metric Conclusions
Lensing in McVittie metrichttp://arxiv.org/abs/1508.04763
Oliver F. Piattella
Universidade Federal do Espırito Santo, Vitoria, Brazil
ICG theory group seminarSeptember 2, 2015
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Lensing and Λ Criticisms McVittie metric Conclusions
Outline
Lensing and Λ
Criticisms
McVittie metric
Conclusions
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Lensing and Λ Criticisms McVittie metric Conclusions
References
• G. McVittie, Mon. Not. Roy. Astron. Soc. 93, 325 (1933).
• S. M. Kopeikin, Phys. Rev. D86, 064004 (2012).
• K. Lake and M. Abdelqader, Phys. Rev. D84, 044045(2011).
• M. E. Aghili, B. Bolen, and L. Bombelli, (2014),arXiv:1408.0786 [gr-qc].
• F. Kottler, Annalen der Physik 361, 401 (1918).
• J. Islam, Physics Letters A 97, 239 (1983).
• W. Rindler and M. Ishak, Phys. Rev. D76, 043006 (2007).
• M. Ishak, W. Rindler, and J. Dossett, Mon. Not. Roy.Astron. Soc. 403, 2152 (2010).
• T. Schucker, Gen.Rel.Grav. 41, 67 (2009).
• M. Park, Phys.Rev. D78, 023014 (2008).
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Lensing and Λ Criticisms McVittie metric Conclusions
Non-cosmological manifestation of Λ
• Eddington, 1923. Upper limit Λ . 10−42 cm−2 in order toavoid a detectable correction to the Mercury perihelionprecession.
• Pioneer anomaly, 1970. Now agreed to be a thermal recoilforce effect (Turyshev, 2012).
• Islam, 1983. No influence of Λ on the bending of lightbecause Λ does not enter the orbital equation for photons.
• Ishak and Rindler, 2007. Λ does influence the bending oflight via the metric, which has to be used for computingthe bending angle.
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Lensing and Λ Criticisms McVittie metric Conclusions
Effect of Λ on the bending of lightIshak and Rindler, 2007 (2010)
Kottler metric, 1918.
ds2 = f(r)dt2 − f(r)−1dr2 − r2dΩ2 ,
where
f(r) ≡ 1− 2m
r− Λr2
3.
This metric has two horizons, r ≈ 2m and r ≈√
3/Λ, and it isnot asymptotically flat.
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Lensing and Λ Criticisms McVittie metric Conclusions
Geometry of Kottler solution
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Lensing and Λ Criticisms McVittie metric Conclusions
Orbital equation for photons
For θ = π/2 and at first-order in m/r:
1
r=
sinφ
R+
3m
2R2
(1 +
1
3cos 2φ
),
where, for φ = π/2:1
r0=
1
R+m
R2,
and r0 is the closest approach distance and R is the distance ofthe zeroth-order solution (a straight line) from the centre.
The above equations hold true both for Schwarzschild andKottler metrics. No Λ appears.
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Lensing and Λ Criticisms McVittie metric Conclusions
Trajectory of photons
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Lensing and Λ Criticisms McVittie metric Conclusions
Calculating the bending angle
In Schwarzschild metric, one takes r →∞ and, since the spaceis asymptotically flat, the coordinate angle φ is also themeasured angle.
The same is not true for Kottler space. Ishak and Rindlerpropose then to use:
cosψ =gijδ
idj
(gijδiδj)1/2(gijdidj)1/2.
This is where Λ comes into play. Another form:
tanψ =
√gφφ√grr
∣∣∣∣dφdr∣∣∣∣ = r
√f(r)
∣∣∣∣dφdr∣∣∣∣ .
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Lensing and Λ Criticisms McVittie metric Conclusions
Results
Assuming small angles and 2m/R 1 and Λr2 1.For a generic lens system:
ψ = φ+2m
R− ΛR3
6(2m+ φR).
For an Einstein’s ring (φ = 0):
ψ =2m
R− ΛR3
12m.
The total bending angle is:
δ = 2(ψ − φ) .
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Lensing and Λ Criticisms McVittie metric Conclusions
Other results
• Schucker, 2009. He uses a self-contained method, avoidingthe lens equation. Analysing the lensing cluster of SDSSJ1004+4112, he finds:
Λ = (2.1± 1.5)× 10−52 m−2 ;
• Biressa and Pacheco, 2011. They find for the bendingangle:
δ ' 4M
b−Mb
(1
r2S
+1
r2obs
)+
2MbΛ
3− bΛ
6(rS + robs) ,
and determine corrections of 2% in the mass estimates.Masses are slightly lower if a cored density profile is usedand slightly higher if an isothermal density profile isadopted.
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Lensing and Λ Criticisms McVittie metric Conclusions
CriticismsPark, 2008
The main criticism is that the results presented above are basedon Kottler metric, which is static, and therefore does not takeinto account the relative motion of source, lens and observer.
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Lensing and Λ Criticisms McVittie metric Conclusions
Result found by Park
Park found for the following lens equation:
θ = β +2mdSL
βdSdL
[1 +O(H3) +O(β2)
]+O(m2) ,
in contradiction with the results based on Kottler metric, whichassert that there should be a O(Λ) ∼ O(H2) correction to theconventional lensing analysis.
Ishak, Rindler and Dossett, 2010, questioned the final result ofPark since other terms including H2 = Λ/3 terms wereapparently dropped out the calculation at some point, leadingto the conclusion that Λ does not contribute to lensing exceptvia the angular diameter distances.
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Lensing and Λ Criticisms McVittie metric Conclusions
McVittie metricMcVittie, 1933
McVittie metric has the following form:
ds2 = −(
1− µ1 + µ
)2
dt2 + (1 + µ)4a(t)2(dρ2 + ρ2dΩ2) ,
where a(t) is the scale factor and
µ ≡ M
2a(t)ρ,
where M is the mass of the point-like lens. When µ 1,McVittie metric can be approximated as
ds2 = − (1− 4µ) dt2 + (1 + 4µ)a(t)2(dρ2 + ρ2dΩ2) ,
which is the usual perturbed FLRW metric in the Newtoniangauge; 2µ is the gravitational potential.
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Lensing and Λ Criticisms McVittie metric Conclusions
Scheme of lensing
b
Us
Lens
Source
χSχL
χ(t)
The relation between χ and the background expansion is theusual one for the FLRW metric:
dχ
dt= −1
a,
and the comoving distances of the source and of the lens, χSand χL respectively, do not change.
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Lensing and Λ Criticisms McVittie metric Conclusions
Null geodesics equations
For the transversal displacement li:
a
p
1− µ1 + µ
d
dχ
(p
a
1 + µ
1− µdli
dχ
)=
2(1− µ)
(1 + µ)7δil∂lµ
+2Ha
[1 +
2∂tµ
(1 + µ)H
]dli
dχ
− 2
1 + µ
(δij∂kµ+ δik∂jµ− δjkδil∂lµ
) dljdχ
dlk
dχ,
The equation describing the evolution of the proper momentump is the following:
1
p
dp
dt= −H − 2
1 + µ∂tµ+ 2
P i∂iµ
p(1 + µ)2.
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Lensing and Λ Criticisms McVittie metric Conclusions
ApproximationsWe consider µ 1 and small displacements li χ.
d2li
dχ2= 4∂iµ .
Using µ ≡M/2aρ in the equation above, one gets:
d2l
dχ2= − 2Ml
a(χ) [(χ− χL)2 + l2]3/2.
With the following definitions:
x ≡ χ/χL , α ≡ 2M/χL , y ≡ l/χL ,
the displacement equation becomes:
d2y
dx2= −α y
a(x) [(x− 1)2 + y2]3/2.
Note that a vanishing α implies that a(x) has no effect on thetrajectory.
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Lensing and Λ Criticisms McVittie metric Conclusions
Solving the equation
Considering small α:
y = y(0) + αy(1) + α2y(2) + . . . ,
and initial conditions:
y(xS) = yS , y(0) = 0 ,
the zero-order solution is a straight line:
y(0) = C1x+ C2 . (1)
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Lensing and Λ Criticisms McVittie metric Conclusions
Zeroth-order solution
UsLens
Source
xSxL
y(0)
yS
We choose the two integration constants so that y(0) = yS , i.e.the trajectory is a straight, horizontal line.
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Lensing and Λ Criticisms McVittie metric Conclusions
First-order equationThe first-order equation is the following:
d2y(1)
dx2= − yS
a(x)[(x− 1)2 + y2
S
]3/2 ,for which we must choose the following initial conditions:
y(1)(xS) = 0 , y(1)(0) = −yS/α .
For a constant Hubble factor H = H0:
χ =
∫ z
0
dz′
H(z′)=
z
H0≡ 1
H0
(1
a− 1
),
so that:d2y(1)
dx2= − yS (1 +H0χLx)[
(x− 1)2 + y2S
]3/2 .20 / 29
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Lensing and Λ Criticisms McVittie metric Conclusions
The bending angle
In the limit yS 1 the deviation angle
δ ≡ dy
dx
∣∣∣∣x=0
− dy
dx
∣∣∣∣x=xS
,
is the following:
δ =2α(1 + χLH0)
yS+O(yS) .
Recalling that α ≡ 2M/χL and yS = b/χL:
δ =4M(1 + χLH0)
b+O(b/χL) .
The mass has been increased by a relative amount ofH0χL = zL, the redshift of the lens.
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Lensing and Λ Criticisms McVittie metric Conclusions
Einstein’s ring systems
UsLensSource θS
xSxL
x
The zeroth-order trajectory is now:
y(0) = θS(xS − x) ,
where θS 1. In order for the trajectory to reach us, we mustchoose the initial condition y(1)(0) = −θSxS/α.Computing again the deflection angle, we get:
δ =4M(1 + χLH0)
θS(χS − χL)+
χL2(χS − χL)
+O(θS) .
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Lensing and Λ Criticisms McVittie metric Conclusions
Einstein radius
Introducing the angular diameter distance one has:
θS(χS − χL) = θSDLSaLaS
= θEDL1 + zS1 + zL
.
From the lens equation, one has for the Einstein radius:
θE =
√4M
(1 + zL)2
1 + zS
DLS
DLDS.
Writing the angular diameter distances as functions of theredshift:
θE =
√4MH0
(1 + zL)4(zS − zL)
(1 + zS)zSzL.
In the above formula, the new contribution is one of the fourpowers of 1 + zL in the square root.
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Lensing and Λ Criticisms McVittie metric Conclusions
Mass estimatesWe apply our formula to some Einstein ring systems observedby the CASTLES Survey,1 assuming H0 = 70 km s−1 Mpc−1.
Object zS zL θE M/M (1 + zL)−1
Q0047-2808 3.60 0.48 1.35 5.0× 1011 0.68
PMNJ0134-0931 2.216 0.77 0.365 2.7× 1010 0.56
B0218+357 0.96 0.68 0.17 8.6× 109 0.60
CFRS03.1077 2.941 0.938 1.05 2.2× 1011 0.52
MG0751+2716 3.20 0.35 0.35 3.2× 1010 0.74
HST15433+5352 2.092 0.497 0.59 7.2× 1010 0.67
MG1549+3047 1.17 0.11 0.9 7.3× 1010 0.90
MG1654+1346 1.74 0.25 1.05 1.9× 1011 0.80
PKS1830-211 2.51 0.89 0.5 4.9× 1010 0.53
B1938+666 2.059 0.881 0.5 4.8× 1010 0.53
1https://www.cfa.harvard.edu/castles/24 / 29
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Lensing and Λ Criticisms McVittie metric Conclusions
Caveat
Considering the standard ΛCDM model Friedmann equation
H2
H20
= ΩΛ + Ωm(1 + z)3 ,
H is approximately constant only as long as ΩΛ Ωm(1 + z)3.
Using the observed values for the density parameters,approximately ΩΛ = 0.7 and Ωm = 0.3, the above conditionamounts to state that zL 0.3. Therefore, a reliable correctionon the bending angle is at most of 30%.
For the mass estimate, (1 + zL)−1 0.77.
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Lensing and Λ Criticisms McVittie metric Conclusions
Conclusions and perspectives
Adopting McVittie metric as description of the geometry of apoint-like lens in the expanding universe:
1. There is an important 1 + zL contribution to the bendingangle:
M →M(1 + zL) ,
i.e. a new 1/(1 + zL) correction to the mass;
2. This contribution has been calculated assuming a constantH = H0;
3. We have to consider the standard ΛCDM model:
H2
H20
= ΩΛ + Ωm(1 + z)3
4. Calculation of the delay time;
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Lensing and Λ Criticisms McVittie metric Conclusions
http://www.cosmo-ufes.org
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Lensing and Λ Criticisms McVittie metric Conclusions
http://www.cosmo-ufes.org
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Lensing and Λ Criticisms McVittie metric Conclusions
Thank you!http://www.cosmo-ufes.org
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