CAMB: A question regarding DE perturbations and crossing of w=-1

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Savvas Nesseris
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Affiliation: UAM/IFT
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CAMB: A question regarding DE perturbations and crossing of

Post by Savvas Nesseris » May 17 2006

Hi,
I have modified CAMB to include a varying equation of state of the form [tex]w(a)=w_0+w_1(1-a)[/tex], where [tex]a [/tex] is the scale factor. Obviously, when we have DE perturbations, for some parameters [tex](w_0,w_1)[/tex], [tex]w(a)[/tex] crosses -1 and the code crashes.

I would like to know if there is a consistent way to deal with this problem, within the CAMB code, and if anyone knows of any paper that has done this so as to crosscheck my results.

Thanks for any pointers/advice,

Savas Nesseris

Antony Lewis
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Re: CAMB: A question regarding DE perturbations and crossing

Post by Antony Lewis » May 17 2006

I think you can do almost anything and the result will look quite similar. For a consistent two-field approach see astro-ph/0410680.

Savvas Nesseris
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CAMB: A question regarding DE perturbations and crossing of

Post by Savvas Nesseris » May 17 2006

My question however is a bit more technical. For this model, [tex]w(a)=w_0+ w_1(1-a)[/tex], lets say that I use the set of parameters [tex](w_0,w_1)=(-0.5,-1.5)[/tex] then the EoS crosses -1 and the code crashes.

The point is, how should I modify CAMB so that it doesn't crash for any set of parameters and without neglecting the DE perturbations?

Thanks in advance

Savas Nesseris

Ben Gold
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CAMB: A question regarding DE perturbations and crossing of

Post by Ben Gold » May 18 2006

The trouble is that there's not really a general answer. You need a model for dark energy to calculate perturbations; the model CAMB uses breaks down as [tex]w\to -1[/tex]. If you want to calculate perturbations through [tex]w=-1[/tex] then you either need to use a different model and totally replace the dark energy perturbation code, or you "patch" the existing one in some way that may or may not be terribly physical.

The two-field stuff is the first approach, and there are other models that also allow some "effective" [tex]w[/tex] to pass through -1. For the second approach, I've seen some researchers (I forget who, I really should look up the reference) who put in code that just sets [tex]\dot \delta[/tex] and [tex]\dot\theta[/tex] to zero for dark energy whenever [tex]w[/tex] gets too close to -1.

gongbo zhao
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CAMB: A question regarding DE perturbations and crossing of

Post by gongbo zhao » May 24 2006

Dear colleagues,
I have just seen the post here which is related to our work. In Astro-ph/0507482 we did a thorough investigation of the dark energy perturbation in the case of the equation of state crossing -1 based on quintom dark energy model proposed in Astro-ph/0404224.
Further, in Astro-ph/0511625 we did a MCMC analysis to determine the cosmological parameters using the method in Astro-ph/0507482. Most of the contours, especially for the dark energy parameters, get enlarged.
I regret many aspects in the literature regarding the fact that the credit of getting across -1 scenario has not been properly given and shall I list the relevant papers below from our group as follows.


Cheers,
Gong-Bo Zhao

Dark energy constraints from the cosmic age and supernova.
Bo Feng (Beijing, Inst. High Energy Phys.) , Xiu-Lian Wang (Beijing, Inst.
Theor. Phys.) , Xin-Min Zhang (Beijing, Inst. High Energy Phys.) . Apr 2004.
5pp.
Published in Phys.Lett.B607:35-41,2005
e-Print Archive: astro-ph/0404224

Oscillating quintom and the recurrent universe.
Bo Feng, Mingzhe Li (Beijing, Inst. High Energy Phys.) , Yun-Song Piao
(Beijing, Inst. High Energy Phys. & ICTS, Beijing) , Xinmin Zhang (Beijing,
Inst. High Energy Phys.) . Jul 2004. 4pp.
Published in Phys.Lett.B634:101-105,2006
e-Print Archive: astro-ph/0407432

Constraints on oscillating quintom from supernova, microwave background and
galaxy clustering.
Jun-Qing Xia, Bo Feng, Xin-Min Zhang (Beijing, Inst. High Energy Phys.) .
Nov 2004. 4pp.
Published in Mod.Phys.Lett.A20:2409,2005
e-Print Archive: astro-ph/0411501

A Single scalar field model of dark energy with equation of state
crossing -1.
Ming-zhe Li (Heidelberg U.) , Bo Feng, Xin-min Zhang (Beijing, Inst. High
Energy Phys.) . Mar 2005. 4pp.
Published in JCAP 0512:002,2005
e-Print Archive: hep-ph/0503268

Perturbations of the quintom models of dark energy and the effects on
observations.
Gong-Bo Zhao, Jun-Qing Xia (Beijing, Inst. High Energy Phys.) , Mingzhe Li
(Heidelberg U.) , Bo Feng, Xinmin Zhang (Beijing, Inst. High Energy Phys.) .
Jul 2005. 20pp.
Published in Phys.Rev.D72:123515,2005
e-Print Archive: astro-ph/0507482

Supernova constraints on models of neutrino dark energy.
Hong Li (Beijing, Inst. High Energy Phys.) , Bo Feng (Beijing Observ.) ,
Jun-Qing Xia, Xinmin Zhang (Beijing, Inst. High Energy Phys.) . Sep 2005.
7pp.
Published in Phys.Rev.D73:103503,2006
e-Print Archive: astro-ph/0509272

Dark energy and its interactions with neutrinos.
Xin-min Zhang (Beijing, Inst. High Energy Phys.) . Oct 2005. 7pp.
Plenary talk at 11th International Symposium on Particles, Strings and Cosmology (PASCOS 2005), Gyeongju, Korea, 30 May - 4 Jun 2005.
Published in AIP Conf.Proc.805:3-9,2006 Also in *Gyeongju 2005, Particles, strings and cosmology* 3-9
e-Print Archive: hep-ph/0510072

Observing dark energy dynamics with supernova, microwave background and
galaxy clustering.
Jun-Qing Xia, Gong-Bo Zhao (Beijing, Inst. High Energy Phys.) , Bo Feng
(Tokyo U., RESCEU) , Hong Li, Xinmin Zhang (Beijing, Inst. High Energy
Phys.) . Nov 2005. 6pp.
Published in Phys.Rev.D73:063521,2006
e-Print Archive: astro-ph/0511625

Detecting dark energy in long baseline neutrino oscillations.
Pei-Hong Gu, Xiao-Jun Bi (Beijing, Inst. High Energy Phys.) , Bo Feng
(Beijing Observ. & Tokyo U., RESCEU) , Bing-Lin Young (Iowa State U.) ,
Xinmin Zhang (Beijing, Inst. High Energy Phys.) . BIHEP-TH-2005-16, Dec
2005. 9pp.
e-Print Archive: hep-ph/0512076

The quintom model of dark energy.
Bo Feng (Beijing Observ. & Tokyo U., RESCEU) . Feb 2006. 4pp.
To appear in the proceedings of 15th Workshop on General Relativity and Gravitation (JGRG 15), Tokyo, Japan, 28 Nov - 2 Dec 2005.
e-Print Archive: astro-ph/0602156

Probing inflation and dark energy with current cosmological observations.
Jun-Qing Xia, Gong-Bo Zhao (Beijing, Inst. High Energy Phys.) , Bo Feng
(Tokyo U., RESCEU) , Xinmin Zhang (Beijing, Inst. High Energy Phys.) . Mar
2006. 7pp.
Submitted to JCAP
e-Print Archive: astro-ph/0603393

Probing dynamics of dark energy with supernova, galaxy clustering and the
three-year wilkinson microwave anisotropy probe (wmap) observations.
Gong-Bo Zhao, Jun-Qing Xia (Beijing, Inst. High Energy Phys.) , Bo Feng
(Tokyo U., RESCEU) , Xinmin Zhang (Beijing, Inst. High Energy Phys.) . Mar
2006. 7pp.
e-Print Archive: astro-ph/0603621


Cosmological evolution of quintom dark energy model of a single scalar field
with higher derivative.
Xiao-Fei Zhang, Taotao Qiu (Beijing, Inst. High Energy Phys.) . Mar 2006.
6pp.
e-Print Archive: astro-ph/0603824

Features in Dark Energy Equation of State and Modulations in the Hubble
Diagram.
Jun-Qing Xia, Gong-Bo Zhao, Hong Li, Bo Feng, Xinmin Zhang . May 2006. 14pp.
** Temporary entry **
e-Print Archive: astro-ph/0605366

Cosmological evolution of a quintom model of dark energy.
Zong-Kuan Guo (Beijing, Inst. Theor. Phys.) , Yun-Song Piao (ICTS, Beijing)
, Xin-Min Zhang (Beijing, Inst. High Energy Phys.) , Yuan-Zhong Zhang (CCAST
World Lab, Beijing & Beijing, Inst. Theor. Phys.) . Oct 2004. 9pp.
Published in Phys.Lett.B608:177-182,2005
e-Print Archive: astro-ph/0410654

Two-field models of dark energy with equation of state across -1.
Xiao-Fei Zhang, Hong Li (Beijing, Inst. High Energy Phys.) , Yun-Song Piao
(Beijing, Inst. High Energy Phys. & ICTS, Beijing) , Xin-Min Zhang (Beijing,
Inst. High Energy Phys.) . Jan 2005. 5pp.
Published in Mod.Phys.Lett.A21:231-242,2006
e-Print Archive: astro-ph/0501652

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