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Bhaskar Shukla
Mar 20
Simplifying the gauge field equation
I am trying to vary the Born-Infeld action. I get accurate results for the Einstein field and the dilaton field equation. I have a simple question
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Simplifying the gauge field equation
I am trying to vary the Born-Infeld action. I get accurate results for the Einstein field and the dilaton field equation. I have a simple question
Mar 20
Bhaskar Shukla
, …
Armando Roque
5
Mar 18
Varying Einstein-Hilbert action through xAct
Dear Shukla, I checked your notebook and the error is that you used DefParameter to define the constant symbols. In this case, you need to use
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Varying Einstein-Hilbert action through xAct
Dear Shukla, I checked your notebook and the error is that you used DefParameter to define the constant symbols. In this case, you need to use
Mar 18
Claire
,
Jose
2
Mar 18
Equations of motion for a given chart
Hello all, I have some equations of motion that I would like to write for a given chart. In order to substitute the particular metric and fields into
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Equations of motion for a given chart
Hello all, I have some equations of motion that I would like to write for a given chart. In order to substitute the particular metric and fields into
Mar 18
Debojyoti Mondal
,
Jose
3
Mar 1
Black hole in f(Q,T) gravity
Thank you for the reply and the edits you made. Ptensor, Qtensor and SE are P[-a,-b,-c], Q[-a,-b,-c] and stress energy tensor respectively, as
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Black hole in f(Q,T) gravity
Thank you for the reply and the edits you made. Ptensor, Qtensor and SE are P[-a,-b,-c], Q[-a,-b,-c] and stress energy tensor respectively, as
Mar 1
Debojyoti Mondal
Feb 16
f(Q,T) gravity
Hi, I am trying to define weyl cartan connection and non metricity tensor and trace of stress energy tensor as mentioned in eq 10-18,25-27 in arXiv:
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f(Q,T) gravity
Hi, I am trying to define weyl cartan connection and non metricity tensor and trace of stress energy tensor as mentioned in eq 10-18,25-27 in arXiv:
Feb 16
Madhu Mishra
,
Jose
2
12/28/23
Notations not appearing in the output
Hi all, I am very new to xAct. I tried running example files on my mac after installing xAct but the output does not come as shown in example file. For
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Notations not appearing in the output
Hi all, I am very new to xAct. I tried running example files on my mac after installing xAct but the output does not come as shown in example file. For
12/28/23
Jing Ma
,
Leo Stein
3
11/2/23
Issue with xAct/xCoba performance on Maxwell-Chern-Simons
Hi there, I'm developing a notebook aimed at: (1) deriving the 5D Einstein-Maxwell-Chern-Simons equations with a negative cosmological constant and
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Issue with xAct/xCoba performance on Maxwell-Chern-Simons
Hi there, I'm developing a notebook aimed at: (1) deriving the 5D Einstein-Maxwell-Chern-Simons equations with a negative cosmological constant and
11/2/23
Ashim
,
Jose
3
8/11/23
Setting specific terms to 0 in perturbation expressions
Hi Jose, Thanks a lot for your reply. Embarrassingly, I don't appear to understand how to use either of these methods. I must be misunderstanding
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Setting specific terms to 0 in perturbation expressions
Hi Jose, Thanks a lot for your reply. Embarrassingly, I don't appear to understand how to use either of these methods. I must be misunderstanding
8/11/23
Roxane Theriault
,
magma
2
7/1/23
Finding the equations of motion in a given coordinate chart
xPert and
VarD
" notebook in the xAct examples folder https://github.com/xAct-contrib/examples/blob/master/README.md There is a scalar-tensor Lagrangian too Cheers
unread,
Finding the equations of motion in a given coordinate chart
xPert and
VarD
" notebook in the xAct examples folder https://github.com/xAct-contrib/examples/blob/master/README.md There is a scalar-tensor Lagrangian too Cheers
7/1/23
Nitol Attar
,
Sergi Sirera-Lahoz
2
2/24/23
Integration by parts using VarD
to use
VarD
to integrate by parts and discard total derivtives but for that I use a simple rule like the following: IBPrule1 = XX_*h[LI[1], aa_, bb_] CD[cc_]@CD[dd_]@h[LI[1], ee_,
unread,
Integration by parts using VarD
to use
VarD
to integrate by parts and discard total derivtives but for that I use a simple rule like the following: IBPrule1 = XX_*h[LI[1], aa_, bb_] CD[cc_]@CD[dd_]@h[LI[1], ee_,
2/24/23
Dong-han Yeom (염동한)
,
Markus B. Fröb
2
12/30/22
[FieldX] Inserting ansatz with vector bundle
Dear all, I would like to compute Einstein-Yang-Mills system with a metric and field ansatz. The attached one is my trial. Using the first and second
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[FieldX] Inserting ansatz with vector bundle
Dear all, I would like to compute Einstein-Yang-Mills system with a metric and field ansatz. The attached one is my trial. Using the first and second
12/30/22
Zakaria
, …
Jose
7
2/8/23
components of equations of motion using an ansatz ( for the metric and for Electromagnetic field) ( xTensor, xCoba)
It just requires adding one more rule for the Ricci scalar. You need a rule per object to be replaced. Notebook reattached. Cheers, Jose. On Tuesday,
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components of equations of motion using an ansatz ( for the metric and for Electromagnetic field) ( xTensor, xCoba)
It just requires adding one more rule for the Ricci scalar. You need a rule per object to be replaced. Notebook reattached. Cheers, Jose. On Tuesday,
2/8/23
K.S. Dhruva
10/20/22
Diffeomorphism invariance of a four graviton amplitude
Hi everyone. I have attempted to compute a four point flat space graviton amplitude with one vertex coming from the EH term and the other one from a
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Diffeomorphism invariance of a four graviton amplitude
Hi everyone. I have attempted to compute a four point flat space graviton amplitude with one vertex coming from the EH term and the other one from a
10/20/22
Zaki
10/4/22
xCoba : Equations of motion of in spherical symmetric components
Hi to all, I have a problem getting the equations of motions of the theory of Einstein scalar Gauss Bonnet gravity in spherical components, many terms
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xCoba : Equations of motion of in spherical symmetric components
Hi to all, I have a problem getting the equations of motions of the theory of Einstein scalar Gauss Bonnet gravity in spherical components, many terms
10/4/22
Nitol Attar
,
Thomas Bäckdahl
2
8/13/22
Error Validate:Found inhomogeneous indices
Hi all, While running the attached script, I am having the following error Validate::inhom: Found inhomogeneous indices: {IndexList[-\[Rho], -\[Sigma]]
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Error Validate:Found inhomogeneous indices
Hi all, While running the attached script, I am having the following error Validate::inhom: Found inhomogeneous indices: {IndexList[-\[Rho], -\[Sigma]]
8/13/22
Shubham Kumar Sinha
,
Thomas Bäckdahl
4
6/27/22
xTensor: how to define one tensor in terms of another
==
VarD
[\[Phi][i]][v[-j]] > wRule = ToRule[wDef, MetricOn -> All, ContractMetrics -> True] > AutomaticRules[w, wRule] > Solve[\[Gamma]1[-i, -j] \[Phi][i] \
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xTensor: how to define one tensor in terms of another
==
VarD
[\[Phi][i]][v[-j]] > wRule = ToRule[wDef, MetricOn -> All, ContractMetrics -> True] > AutomaticRules[w, wRule] > Solve[\[Gamma]1[-i, -j] \[Phi][i] \
6/27/22
NotoGrav
,
Thomas Bäckdahl
3
6/2/22
rule error
Hello all, Could you please take a look into the notebook attached here? I am having this error of validate: inhomogeneous indices after implementing
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rule error
Hello all, Could you please take a look into the notebook attached here? I am having this error of validate: inhomogeneous indices after implementing
6/2/22
seyeong
,
Jose
4
5/3/22
command recognition problem
As shown in the attached figure, the result is the same even if you code from ln1 to ln3 in order. What I originally wanted to do was to follow the
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command recognition problem
As shown in the attached figure, the result is the same even if you code from ln1 to ln3 in order. What I originally wanted to do was to follow the
5/3/22
NotoGrav
,
Jose
6
3/1/22
Renaming tensors!
Hello Jose, Thanks for the suggestions. After making it simplified, and syntactic errors-free, I am having a follow up question. Could you please take
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Renaming tensors!
Hello Jose, Thanks for the suggestions. After making it simplified, and syntactic errors-free, I am having a follow up question. Could you please take
3/1/22
NotoGrav
2/16/22
VarD errors!
to take
VarD
of an expression Lflat2 (please see the attached notebook). I converted g to eta metric for finding this expression. The
VarD
rules I have set as well. Here are the errors
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VarD errors!
to take
VarD
of an expression Lflat2 (please see the attached notebook). I converted g to eta metric for finding this expression. The
VarD
rules I have set as well. Here are the errors
2/16/22
NotoGrav
,
Thomas Bäckdahl
3
2/11/22
Removing terms of a definite order?
Hello Folks, Here is attached a file where I am trying to implement perturbation for a Lagrangian. In the last term Lflat1, how can I get rid of all
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Removing terms of a definite order?
Hello Folks, Here is attached a file where I am trying to implement perturbation for a Lagrangian. In the last term Lflat1, how can I get rid of all
2/11/22
kold...@gmail.com
12/8/21
VarD versus VarL
seeing between
VarD
and VarL, so I have not attached an MWE, which I hope is okay. From the documentation (http://www.xact.es/xtras/documentation/tutorial/MetricVariations
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VarD versus VarL
seeing between
VarD
and VarL, so I have not attached an MWE, which I hope is okay. From the documentation (http://www.xact.es/xtras/documentation/tutorial/MetricVariations
12/8/21
Sergi Sirera-Lahoz
,
Jose
3
11/15/21
Varying an action in components xCoba
by construction
VarD
only works on scalars. Indeed, the simplest way to bypass this is to contract anything else with some arbitrary vector field(s) and then remove (somehow) this
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Varying an action in components xCoba
by construction
VarD
only works on scalars. Indeed, the simplest way to bypass this is to contract anything else with some arbitrary vector field(s) and then remove (somehow) this
11/15/21
Amanda Fajardo
,
Jose
2
11/15/21
Questions about xTensor and xSVT
Related with xTensor: I attach a part of my work. I've tried to write the superpotential (Written as P) in terms of the metric (which I accomplish)
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Questions about xTensor and xSVT
Related with xTensor: I attach a part of my work. I've tried to write the superpotential (Written as P) in terms of the metric (which I accomplish)
11/15/21
Pawan Kumar Gupta
,
Jose
2
10/24/21
VarD in case of 3+1 decomposition
m afraid
VarD
does not handle it at the moment. xTensor implicitly assumes that you will first take variations and then perform a 3+1 decomposition, rather than viceversa. We should
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VarD in case of 3+1 decomposition
m afraid
VarD
does not handle it at the moment. xTensor implicitly assumes that you will first take variations and then perform a 3+1 decomposition, rather than viceversa. We should
10/24/21
Soham Bhattacharyya
,
Jose
4
10/23/21
Variational derivative of metric determinant
with the
VarD
command is >>> turning out to be positive. >>> >>> I have attached the example with this message. Hope to hear from you >>> soon
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Variational derivative of metric determinant
with the
VarD
command is >>> turning out to be positive. >>> >>> I have attached the example with this message. Hope to hear from you >>> soon
10/23/21
Jose
9/22/21
Re: Variation of Generalized Proca Action and equation of motion
commands using
VarD
(from xTensor) and VarL (from xTras) to get you started with this type of computation. There is documentation in xTensorDoc, in xTras, in xAct-contrib and in this
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Re: Variation of Generalized Proca Action and equation of motion
commands using
VarD
(from xTensor) and VarL (from xTras) to get you started with this type of computation. There is documentation in xTensorDoc, in xTras, in xAct-contrib and in this
9/22/21
kold...@gmail.com
,
Jose
5
9/1/21
ADM equations of motion (and xTensor bug?)
method and
VarD
got stuck in the > commutation of parametric and covariant derivatives. I'm not sure what's > the right thing to do in this variational context. >
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ADM equations of motion (and xTensor bug?)
method and
VarD
got stuck in the > commutation of parametric and covariant derivatives. I'm not sure what's > the right thing to do in this variational context. >
9/1/21
TLa
5/25/21
Variation including Tetrads
use the
VarD
function in that regard. This has been working greatly so far for "normal tensors" defined with DefTensor. However, I would also like to compute derivatives
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Variation including Tetrads
use the
VarD
function in that regard. This has been working greatly so far for "normal tensors" defined with DefTensor. However, I would also like to compute derivatives
5/25/21
Mahesh KNB
, …
Mahesh K N B
5
4/25/21
Modifying the VarD
> >
VarD
[v[a_], PD][P[LI[x_], LI[y_]], rest_] := rest (w[-a] P[LI[x], LI[y + > 1]] - v[-a] Scalar[w[b] w[-b]] P[LI[x - 1], LI[y + 1]]) >
VarD
[w[a_], PD][P[LI[x_], LI[
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Modifying the VarD
> >
VarD
[v[a_], PD][P[LI[x_], LI[y_]], rest_] := rest (w[-a] P[LI[x], LI[y + > 1]] - v[-a] Scalar[w[b] w[-b]] P[LI[x - 1], LI[y + 1]]) >
VarD
[w[a_], PD][P[LI[x_], LI[
4/25/21