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

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CAMB: A question regarding DE perturbations and crossing of
Hi,
I have modified CAMB to include a varying equation of state of the form [tex]w(a)=w_0+w_1(1a)[/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
I have modified CAMB to include a varying equation of state of the form [tex]w(a)=w_0+w_1(1a)[/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

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 Joined: September 23 2004
 Affiliation: University of Sussex
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Re: CAMB: A question regarding DE perturbations and crossing
I think you can do almost anything and the result will look quite similar. For a consistent twofield approach see astroph/0410680.

 Posts: 70
 Joined: April 05 2005
 Affiliation: UAM/IFT
 Contact:
CAMB: A question regarding DE perturbations and crossing of
My question however is a bit more technical. For this model, [tex]w(a)=w_0+ w_1(1a)[/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
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
CAMB: A question regarding DE perturbations and crossing of
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 twofield 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.
The twofield 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.

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 Joined: January 04 2005
 Affiliation: ICG, Portsmouth
 Contact:
CAMB: A question regarding DE perturbations and crossing of
Dear colleagues,
I have just seen the post here which is related to our work. In Astroph/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 Astroph/0404224.
Further, in Astroph/0511625 we did a MCMC analysis to determine the cosmological parameters using the method in Astroph/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,
GongBo Zhao
Dark energy constraints from the cosmic age and supernova.
Bo Feng (Beijing, Inst. High Energy Phys.) , XiuLian Wang (Beijing, Inst.
Theor. Phys.) , XinMin Zhang (Beijing, Inst. High Energy Phys.) . Apr 2004.
5pp.
Published in Phys.Lett.B607:3541,2005
ePrint Archive: astroph/0404224
Oscillating quintom and the recurrent universe.
Bo Feng, Mingzhe Li (Beijing, Inst. High Energy Phys.) , YunSong Piao
(Beijing, Inst. High Energy Phys. & ICTS, Beijing) , Xinmin Zhang (Beijing,
Inst. High Energy Phys.) . Jul 2004. 4pp.
Published in Phys.Lett.B634:101105,2006
ePrint Archive: astroph/0407432
Constraints on oscillating quintom from supernova, microwave background and
galaxy clustering.
JunQing Xia, Bo Feng, XinMin Zhang (Beijing, Inst. High Energy Phys.) .
Nov 2004. 4pp.
Published in Mod.Phys.Lett.A20:2409,2005
ePrint Archive: astroph/0411501
A Single scalar field model of dark energy with equation of state
crossing 1.
Mingzhe Li (Heidelberg U.) , Bo Feng, Xinmin Zhang (Beijing, Inst. High
Energy Phys.) . Mar 2005. 4pp.
Published in JCAP 0512:002,2005
ePrint Archive: hepph/0503268
Perturbations of the quintom models of dark energy and the effects on
observations.
GongBo Zhao, JunQing 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
ePrint Archive: astroph/0507482
Supernova constraints on models of neutrino dark energy.
Hong Li (Beijing, Inst. High Energy Phys.) , Bo Feng (Beijing Observ.) ,
JunQing Xia, Xinmin Zhang (Beijing, Inst. High Energy Phys.) . Sep 2005.
7pp.
Published in Phys.Rev.D73:103503,2006
ePrint Archive: astroph/0509272
Dark energy and its interactions with neutrinos.
Xinmin 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.805:39,2006 Also in *Gyeongju 2005, Particles, strings and cosmology* 39
ePrint Archive: hepph/0510072
Observing dark energy dynamics with supernova, microwave background and
galaxy clustering.
JunQing Xia, GongBo 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
ePrint Archive: astroph/0511625
Detecting dark energy in long baseline neutrino oscillations.
PeiHong Gu, XiaoJun Bi (Beijing, Inst. High Energy Phys.) , Bo Feng
(Beijing Observ. & Tokyo U., RESCEU) , BingLin Young (Iowa State U.) ,
Xinmin Zhang (Beijing, Inst. High Energy Phys.) . BIHEPTH200516, Dec
2005. 9pp.
ePrint Archive: hepph/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.
ePrint Archive: astroph/0602156
Probing inflation and dark energy with current cosmological observations.
JunQing Xia, GongBo Zhao (Beijing, Inst. High Energy Phys.) , Bo Feng
(Tokyo U., RESCEU) , Xinmin Zhang (Beijing, Inst. High Energy Phys.) . Mar
2006. 7pp.
Submitted to JCAP
ePrint Archive: astroph/0603393
Probing dynamics of dark energy with supernova, galaxy clustering and the
threeyear wilkinson microwave anisotropy probe (wmap) observations.
GongBo Zhao, JunQing Xia (Beijing, Inst. High Energy Phys.) , Bo Feng
(Tokyo U., RESCEU) , Xinmin Zhang (Beijing, Inst. High Energy Phys.) . Mar
2006. 7pp.
ePrint Archive: astroph/0603621
Cosmological evolution of quintom dark energy model of a single scalar field
with higher derivative.
XiaoFei Zhang, Taotao Qiu (Beijing, Inst. High Energy Phys.) . Mar 2006.
6pp.
ePrint Archive: astroph/0603824
Features in Dark Energy Equation of State and Modulations in the Hubble
Diagram.
JunQing Xia, GongBo Zhao, Hong Li, Bo Feng, Xinmin Zhang . May 2006. 14pp.
** Temporary entry **
ePrint Archive: astroph/0605366
Cosmological evolution of a quintom model of dark energy.
ZongKuan Guo (Beijing, Inst. Theor. Phys.) , YunSong Piao (ICTS, Beijing)
, XinMin Zhang (Beijing, Inst. High Energy Phys.) , YuanZhong Zhang (CCAST
World Lab, Beijing & Beijing, Inst. Theor. Phys.) . Oct 2004. 9pp.
Published in Phys.Lett.B608:177182,2005
ePrint Archive: astroph/0410654
Twofield models of dark energy with equation of state across 1.
XiaoFei Zhang, Hong Li (Beijing, Inst. High Energy Phys.) , YunSong Piao
(Beijing, Inst. High Energy Phys. & ICTS, Beijing) , XinMin Zhang (Beijing,
Inst. High Energy Phys.) . Jan 2005. 5pp.
Published in Mod.Phys.Lett.A21:231242,2006
ePrint Archive: astroph/0501652
I have just seen the post here which is related to our work. In Astroph/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 Astroph/0404224.
Further, in Astroph/0511625 we did a MCMC analysis to determine the cosmological parameters using the method in Astroph/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,
GongBo Zhao
Dark energy constraints from the cosmic age and supernova.
Bo Feng (Beijing, Inst. High Energy Phys.) , XiuLian Wang (Beijing, Inst.
Theor. Phys.) , XinMin Zhang (Beijing, Inst. High Energy Phys.) . Apr 2004.
5pp.
Published in Phys.Lett.B607:3541,2005
ePrint Archive: astroph/0404224
Oscillating quintom and the recurrent universe.
Bo Feng, Mingzhe Li (Beijing, Inst. High Energy Phys.) , YunSong Piao
(Beijing, Inst. High Energy Phys. & ICTS, Beijing) , Xinmin Zhang (Beijing,
Inst. High Energy Phys.) . Jul 2004. 4pp.
Published in Phys.Lett.B634:101105,2006
ePrint Archive: astroph/0407432
Constraints on oscillating quintom from supernova, microwave background and
galaxy clustering.
JunQing Xia, Bo Feng, XinMin Zhang (Beijing, Inst. High Energy Phys.) .
Nov 2004. 4pp.
Published in Mod.Phys.Lett.A20:2409,2005
ePrint Archive: astroph/0411501
A Single scalar field model of dark energy with equation of state
crossing 1.
Mingzhe Li (Heidelberg U.) , Bo Feng, Xinmin Zhang (Beijing, Inst. High
Energy Phys.) . Mar 2005. 4pp.
Published in JCAP 0512:002,2005
ePrint Archive: hepph/0503268
Perturbations of the quintom models of dark energy and the effects on
observations.
GongBo Zhao, JunQing 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
ePrint Archive: astroph/0507482
Supernova constraints on models of neutrino dark energy.
Hong Li (Beijing, Inst. High Energy Phys.) , Bo Feng (Beijing Observ.) ,
JunQing Xia, Xinmin Zhang (Beijing, Inst. High Energy Phys.) . Sep 2005.
7pp.
Published in Phys.Rev.D73:103503,2006
ePrint Archive: astroph/0509272
Dark energy and its interactions with neutrinos.
Xinmin 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.805:39,2006 Also in *Gyeongju 2005, Particles, strings and cosmology* 39
ePrint Archive: hepph/0510072
Observing dark energy dynamics with supernova, microwave background and
galaxy clustering.
JunQing Xia, GongBo 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
ePrint Archive: astroph/0511625
Detecting dark energy in long baseline neutrino oscillations.
PeiHong Gu, XiaoJun Bi (Beijing, Inst. High Energy Phys.) , Bo Feng
(Beijing Observ. & Tokyo U., RESCEU) , BingLin Young (Iowa State U.) ,
Xinmin Zhang (Beijing, Inst. High Energy Phys.) . BIHEPTH200516, Dec
2005. 9pp.
ePrint Archive: hepph/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.
ePrint Archive: astroph/0602156
Probing inflation and dark energy with current cosmological observations.
JunQing Xia, GongBo Zhao (Beijing, Inst. High Energy Phys.) , Bo Feng
(Tokyo U., RESCEU) , Xinmin Zhang (Beijing, Inst. High Energy Phys.) . Mar
2006. 7pp.
Submitted to JCAP
ePrint Archive: astroph/0603393
Probing dynamics of dark energy with supernova, galaxy clustering and the
threeyear wilkinson microwave anisotropy probe (wmap) observations.
GongBo Zhao, JunQing Xia (Beijing, Inst. High Energy Phys.) , Bo Feng
(Tokyo U., RESCEU) , Xinmin Zhang (Beijing, Inst. High Energy Phys.) . Mar
2006. 7pp.
ePrint Archive: astroph/0603621
Cosmological evolution of quintom dark energy model of a single scalar field
with higher derivative.
XiaoFei Zhang, Taotao Qiu (Beijing, Inst. High Energy Phys.) . Mar 2006.
6pp.
ePrint Archive: astroph/0603824
Features in Dark Energy Equation of State and Modulations in the Hubble
Diagram.
JunQing Xia, GongBo Zhao, Hong Li, Bo Feng, Xinmin Zhang . May 2006. 14pp.
** Temporary entry **
ePrint Archive: astroph/0605366
Cosmological evolution of a quintom model of dark energy.
ZongKuan Guo (Beijing, Inst. Theor. Phys.) , YunSong Piao (ICTS, Beijing)
, XinMin Zhang (Beijing, Inst. High Energy Phys.) , YuanZhong Zhang (CCAST
World Lab, Beijing & Beijing, Inst. Theor. Phys.) . Oct 2004. 9pp.
Published in Phys.Lett.B608:177182,2005
ePrint Archive: astroph/0410654
Twofield models of dark energy with equation of state across 1.
XiaoFei Zhang, Hong Li (Beijing, Inst. High Energy Phys.) , YunSong Piao
(Beijing, Inst. High Energy Phys. & ICTS, Beijing) , XinMin Zhang (Beijing,
Inst. High Energy Phys.) . Jan 2005. 5pp.
Published in Mod.Phys.Lett.A21:231242,2006
ePrint Archive: astroph/0501652