{ "cells": [ { "cell_type": "markdown", "metadata": {}, "source": [ "# Kerr-Newman spacetime\n", "\n", "This worksheet demonstrates a few capabilities of SageManifolds (version 1.0, as included in SageMath 7.5) in computations regarding Kerr-Newman spacetime.\n", "\n", "Click [here](https://raw.githubusercontent.com/sagemanifolds/SageManifolds/master/Worksheets/v1.0/SM_Kerr_Newman.ipynb) to download the worksheet file (ipynb format). To run it, you must start SageMath within the Jupyter notebook, via the command `sage -n jupyter`" ] }, { "cell_type": "markdown", "metadata": {}, "source": [ "*NB:* a version of SageMath at least equal to 7.5 is required to run this worksheet:" ] }, { "cell_type": "code", "execution_count": 1, "metadata": { "collapsed": false }, "outputs": [ { "data": { "text/plain": [ "'SageMath version 7.5, Release Date: 2017-01-11'" ] }, "execution_count": 1, "metadata": {}, "output_type": "execute_result" } ], "source": [ "version()" ] }, { "cell_type": "markdown", "metadata": {}, "source": [ "First we set up the notebook to display mathematical objects using LaTeX rendering:" ] }, { "cell_type": "code", "execution_count": 2, "metadata": { "collapsed": true }, "outputs": [], "source": [ "%display latex" ] }, { "cell_type": "markdown", "metadata": {}, "source": [ "We also define a viewer for 3D plots (use `'threejs'` or `'jmol'` for interactive 3D graphics):" ] }, { "cell_type": "code", "execution_count": 3, "metadata": { "collapsed": true }, "outputs": [], "source": [ "viewer3D = 'threejs' # must be 'threejs', jmol', 'tachyon' or None (default)" ] }, { "cell_type": "markdown", "metadata": {}, "source": [ "Since some computations are quite long, we ask for running them in parallel on 8 cores:" ] }, { "cell_type": "code", "execution_count": 4, "metadata": { "collapsed": true }, "outputs": [], "source": [ "Parallelism().set(nproc=8)" ] }, { "cell_type": "markdown", "metadata": {}, "source": [ "## Spacetime manifold\n", "\n", "We declare the Kerr-Newman spacetime as a 4-dimensional diffentiable manifold:" ] }, { "cell_type": "code", "execution_count": 5, "metadata": { "collapsed": false }, "outputs": [], "source": [ "M = Manifold(4, 'M', r'\\mathcal{M}')" ] }, { "cell_type": "markdown", "metadata": {}, "source": [ "

Let us use the standard Boyer-Lindquist coordinates on it, by first introducing the part $\\mathcal{M}_0$ covered by these coordinates

" ] }, { "cell_type": "code", "execution_count": 6, "metadata": { "collapsed": false }, "outputs": [ { "name": "stdout", "output_type": "stream", "text": [ "Chart (M0, (t, r, th, ph))\n" ] }, { "data": { "text/html": [ "" ], "text/plain": [ "Chart (M0, (t, r, th, ph))" ] }, "execution_count": 6, "metadata": {}, "output_type": "execute_result" } ], "source": [ "M0 = M.open_subset('M0', r'\\mathcal{M}_0')\n", "# BL = Boyer-Lindquist\n", "BL. = M0.chart(r't r:(0,+oo) th:(0,pi):\\theta ph:(0,2*pi):\\phi') \n", "print(BL) ; BL" ] }, { "cell_type": "markdown", "metadata": {}, "source": [ "

Metric tensor

\n", "

The 3 parameters $m$, $a$ and $q$ of the Kerr-Newman spacetime are declared as symbolic variables:

" ] }, { "cell_type": "code", "execution_count": 7, "metadata": { "collapsed": false }, "outputs": [ { "data": { "text/html": [ "" ], "text/plain": [ "(m, a, q)" ] }, "execution_count": 7, "metadata": {}, "output_type": "execute_result" } ], "source": [ "var('m a q')" ] }, { "cell_type": "markdown", "metadata": {}, "source": [ "

Let us introduce the spacetime metric:

" ] }, { "cell_type": "code", "execution_count": 8, "metadata": { "collapsed": false }, "outputs": [], "source": [ "g = M.lorentzian_metric('g')" ] }, { "cell_type": "markdown", "metadata": {}, "source": [ "

The metric is defined by its components in the coordinate frame associated with Boyer-Lindquist coordinates, which is the current manifold's default frame:

" ] }, { "cell_type": "code", "execution_count": 9, "metadata": { "collapsed": false }, "outputs": [ { "data": { "text/html": [ "" ], "text/plain": [ "g = (-(q^2 - 2*m*r)/(a^2*cos(th)^2 + r^2) - 1) dt*dt + (q^2 - 2*m*r)*a*sin(th)^2/(a^2*cos(th)^2 + r^2) dt*dph + (a^2*cos(th)^2 + r^2)/(a^2 + q^2 - 2*m*r + r^2) dr*dr + (a^2*cos(th)^2 + r^2) dth*dth + (q^2 - 2*m*r)*a*sin(th)^2/(a^2*cos(th)^2 + r^2) dph*dt - ((q^2 - 2*m*r)*a^2*sin(th)^2/(a^2*cos(th)^2 + r^2) - a^2 - r^2)*sin(th)^2 dph*dph" ] }, "execution_count": 9, "metadata": {}, "output_type": "execute_result" } ], "source": [ "rho2 = r^2 + (a*cos(th))^2\n", "Delta = r^2 -2*m*r + a^2 + q^2\n", "g[0,0] = -1 + (2*m*r-q^2)/rho2\n", "g[0,3] = -a*sin(th)^2*(2*m*r-q^2)/rho2\n", "g[1,1], g[2,2] = rho2/Delta, rho2\n", "g[3,3] = (r^2 + a^2 + (2*m*r-q^2)*(a*sin(th))^2/rho2)*sin(th)^2\n", "g.display()" ] }, { "cell_type": "markdown", "metadata": {}, "source": [ "

The list of the non-vanishing components:

" ] }, { "cell_type": "code", "execution_count": 10, "metadata": { "collapsed": false }, "outputs": [ { "data": { "text/html": [ "" ], "text/plain": [ "g_t,t = -(q^2 - 2*m*r)/(a^2*cos(th)^2 + r^2) - 1 \n", "g_t,ph = (q^2 - 2*m*r)*a*sin(th)^2/(a^2*cos(th)^2 + r^2) \n", "g_r,r = (a^2*cos(th)^2 + r^2)/(a^2 + q^2 - 2*m*r + r^2) \n", "g_th,th = a^2*cos(th)^2 + r^2 \n", "g_ph,t = (q^2 - 2*m*r)*a*sin(th)^2/(a^2*cos(th)^2 + r^2) \n", "g_ph,ph = -((q^2 - 2*m*r)*a^2*sin(th)^2/(a^2*cos(th)^2 + r^2) - a^2 - r^2)*sin(th)^2 " ] }, "execution_count": 10, "metadata": {}, "output_type": "execute_result" } ], "source": [ "g.display_comp()" ] }, { "cell_type": "markdown", "metadata": {}, "source": [ "

The component $g^{tt}$ of the inverse metric:

" ] }, { "cell_type": "code", "execution_count": 11, "metadata": { "collapsed": false }, "outputs": [ { "data": { "text/html": [ "" ], "text/plain": [ "(a^4 + 2*a^2*r^2 + r^4 - (a^4 + a^2*q^2 - 2*a^2*m*r + a^2*r^2)*sin(th)^2)/(2*m*r^3 - r^4 - (a^2 + q^2)*r^2 - (a^4 + a^2*q^2 - 2*a^2*m*r + a^2*r^2)*cos(th)^2)" ] }, "execution_count": 11, "metadata": {}, "output_type": "execute_result" } ], "source": [ "g.inverse()[0,0]" ] }, { "cell_type": "markdown", "metadata": {}, "source": [ "

The lapse function:

" ] }, { "cell_type": "code", "execution_count": 12, "metadata": { "collapsed": false }, "outputs": [ { "data": { "text/html": [ "" ], "text/plain": [ "Scalar field on the Open subset M0 of the 4-dimensional differentiable manifold M" ] }, "execution_count": 12, "metadata": {}, "output_type": "execute_result" } ], "source": [ "N = 1/sqrt(-(g.inverse()[[0,0]])) ; N" ] }, { "cell_type": "code", "execution_count": 13, "metadata": { "collapsed": false }, "outputs": [ { "data": { "text/html": [ "" ], "text/plain": [ "M0 --> R\n", "(t, r, th, ph) |--> sqrt(a^2*cos(th)^2 + r^2)*sqrt(a^2 + q^2 - 2*m*r + r^2)/sqrt(a^4 + 2*a^2*r^2 + r^4 - (a^4 + a^2*q^2 - 2*a^2*m*r + a^2*r^2)*sin(th)^2)" ] }, "execution_count": 13, "metadata": {}, "output_type": "execute_result" } ], "source": [ "N.display()" ] }, { "cell_type": "markdown", "metadata": {}, "source": [ "

Electromagnetic field tensor

\n", "

Let us first introduce the 1-form basis associated with Boyer-Lindquist coordinates:

" ] }, { "cell_type": "code", "execution_count": 14, "metadata": { "collapsed": false }, "outputs": [ { "data": { "text/html": [ "" ], "text/plain": [ "Coordinate coframe (M0, (dt,dr,dth,dph))" ] }, "execution_count": 14, "metadata": {}, "output_type": "execute_result" } ], "source": [ "dBL = BL.coframe() ; dBL" ] }, { "cell_type": "markdown", "metadata": {}, "source": [ "

The electromagnetic field tensor $F$ is formed as [cf. e.g. Eq. (33.5) of Misner, Thorne & Wheeler (1973)]

" ] }, { "cell_type": "code", "execution_count": 15, "metadata": { "collapsed": false }, "outputs": [ { "data": { "text/html": [ "" ], "text/plain": [ "F = (a^2*q*cos(th)^2 - q*r^2)/(a^4*cos(th)^4 + 2*a^2*r^2*cos(th)^2 + r^4) dt/\\dr + 2*a^2*q*r*cos(th)*sin(th)/(a^4*cos(th)^4 + 2*a^2*r^2*cos(th)^2 + r^4) dt/\\dth + (a^3*q*cos(th)^2 - a*q*r^2)*sin(th)^2/(a^4*cos(th)^4 + 2*a^2*r^2*cos(th)^2 + r^4) dr/\\dph + 2*(a^3*q*r + a*q*r^3)*cos(th)*sin(th)/(a^4*cos(th)^4 + 2*a^2*r^2*cos(th)^2 + r^4) dth/\\dph" ] }, "execution_count": 15, "metadata": {}, "output_type": "execute_result" } ], "source": [ "F = M.diff_form(2, name='F')\n", "F.set_restriction( q/rho2^2 * (r^2-a^2*cos(th)^2)* dBL[1].wedge( dBL[0] - a*sin(th)^2* dBL[3] ) + \\\n", " 2*q/rho2^2 * a*r*cos(th)*sin(th)* dBL[2].wedge( (r^2+a^2)* dBL[3] - a* dBL[0] ) )\n", "F.display()" ] }, { "cell_type": "markdown", "metadata": {}, "source": [ "

The list of non-vanishing components:

" ] }, { "cell_type": "code", "execution_count": 16, "metadata": { "collapsed": false }, "outputs": [ { "data": { "text/html": [ "" ], "text/plain": [ "F_t,r = (a^2*q*cos(th)^2 - q*r^2)/(a^4*cos(th)^4 + 2*a^2*r^2*cos(th)^2 + r^4) \n", "F_t,th = 2*a^2*q*r*cos(th)*sin(th)/(a^4*cos(th)^4 + 2*a^2*r^2*cos(th)^2 + r^4) \n", "F_r,t = -(a^2*q*cos(th)^2 - q*r^2)/(a^4*cos(th)^4 + 2*a^2*r^2*cos(th)^2 + r^4) \n", "F_r,ph = (a^3*q*cos(th)^2 - a*q*r^2)*sin(th)^2/(a^4*cos(th)^4 + 2*a^2*r^2*cos(th)^2 + r^4) \n", "F_th,t = -2*a^2*q*r*cos(th)*sin(th)/(a^4*cos(th)^4 + 2*a^2*r^2*cos(th)^2 + r^4) \n", "F_th,ph = 2*(a^3*q*r + a*q*r^3)*cos(th)*sin(th)/(a^4*cos(th)^4 + 2*a^2*r^2*cos(th)^2 + r^4) \n", "F_ph,r = -(a^3*q*cos(th)^2 - a*q*r^2)*sin(th)^2/(a^4*cos(th)^4 + 2*a^2*r^2*cos(th)^2 + r^4) \n", "F_ph,th = -2*(a^3*q*r + a*q*r^3)*cos(th)*sin(th)/(a^4*cos(th)^4 + 2*a^2*r^2*cos(th)^2 + r^4) " ] }, "execution_count": 16, "metadata": {}, "output_type": "execute_result" } ], "source": [ "F.display_comp()" ] }, { "cell_type": "markdown", "metadata": {}, "source": [ "

The Hodge dual of $F$:

" ] }, { "cell_type": "code", "execution_count": 17, "metadata": { "collapsed": false }, "outputs": [ { "data": { "text/html": [ "" ], "text/plain": [ "*F = 2*a*q*r*cos(th)/(a^4*cos(th)^4 + 2*a^2*r^2*cos(th)^2 + r^4) dt/\\dr - (a^3*q*cos(th)^2 - a*q*r^2)*sin(th)/(a^4*cos(th)^4 + 2*a^2*r^2*cos(th)^2 + r^4) dt/\\dth - 2*(a^4*q*r*cos(th)*sin(th)^4 - (a^4*q*r + a^2*q*r^3)*cos(th)*sin(th)^2)/(a^6*cos(th)^6 + 3*a^4*r^2*cos(th)^4 + 3*a^2*r^4*cos(th)^2 + r^6) dr/\\dph + ((a^4*q + a^2*q*r^2)*sin(th)^3 - (a^4*q - q*r^4)*sin(th))/(a^4*cos(th)^4 + 2*a^2*r^2*cos(th)^2 + r^4) dth/\\dph" ] }, "execution_count": 17, "metadata": {}, "output_type": "execute_result" } ], "source": [ "star_F = F.hodge_dual(g) ; star_F.display()" ] }, { "cell_type": "markdown", "metadata": {}, "source": [ "

Maxwell equations

\n", "\n", "

Let us check that $F$ obeys the two (source-free) Maxwell equations:

" ] }, { "cell_type": "code", "execution_count": 18, "metadata": { "collapsed": false }, "outputs": [ { "data": { "text/html": [ "" ], "text/plain": [ "dF = 0" ] }, "execution_count": 18, "metadata": {}, "output_type": "execute_result" } ], "source": [ "F.exterior_derivative().display()" ] }, { "cell_type": "code", "execution_count": 19, "metadata": { "collapsed": false }, "outputs": [ { "data": { "text/html": [ "" ], "text/plain": [ "d*F = 0" ] }, "execution_count": 19, "metadata": {}, "output_type": "execute_result" } ], "source": [ "star_F.exterior_derivative().display()" ] }, { "cell_type": "markdown", "metadata": {}, "source": [ "

Levi-Civita Connection

\n", "\n", "

The Levi-Civita connection $\\nabla$ associated with $g$:

" ] }, { "cell_type": "code", "execution_count": 20, "metadata": { "collapsed": false }, "outputs": [ { "name": "stdout", "output_type": "stream", "text": [ "Levi-Civita connection nabla_g associated with the Lorentzian metric g on the 4-dimensional differentiable manifold M\n" ] } ], "source": [ "nab = g.connection() ; print(nab)" ] }, { "cell_type": "markdown", "metadata": {}, "source": [ "

Let us verify that the covariant derivative of $g$ with respect to $\\nabla$ vanishes identically:

" ] }, { "cell_type": "code", "execution_count": 21, "metadata": { "collapsed": false }, "outputs": [ { "data": { "text/html": [ "" ], "text/plain": [ "True" ] }, "execution_count": 21, "metadata": {}, "output_type": "execute_result" } ], "source": [ "nab(g) == 0" ] }, { "cell_type": "markdown", "metadata": {}, "source": [ "

Another view of the above property:

" ] }, { "cell_type": "code", "execution_count": 22, "metadata": { "collapsed": false }, "outputs": [ { "data": { "text/html": [ "" ], "text/plain": [ "nabla_g(g) = 0" ] }, "execution_count": 22, "metadata": {}, "output_type": "execute_result" } ], "source": [ "nab(g).display()" ] }, { "cell_type": "markdown", "metadata": {}, "source": [ "

The nonzero Christoffel symbols (skipping those that can be deduced by symmetry of the last two indices):

" ] }, { "cell_type": "code", "execution_count": 23, "metadata": { "collapsed": false }, "outputs": [ { "data": { "text/html": [ "" ], "text/plain": [ "Gam^t_t,r = (a^4*m + a^2*q^2*r + q^2*r^3 - m*r^4 - (a^4*m + a^2*m*r^2)*sin(th)^2)/(2*m*r^5 - r^6 - (a^2 + q^2)*r^4 - (a^6 + a^4*q^2 - 2*a^4*m*r + a^4*r^2)*cos(th)^4 + 2*(2*a^2*m*r^3 - a^2*r^4 - (a^4 + a^2*q^2)*r^2)*cos(th)^2) \n", "Gam^t_t,th = (a^2*q^2 - 2*a^2*m*r)*cos(th)*sin(th)/(a^4*cos(th)^4 + 2*a^2*r^2*cos(th)^2 + r^4) \n", "Gam^t_r,ph = -(a^3*q^2*r - a^3*m*r^2 + 2*a*q^2*r^3 - 3*a*m*r^4 - (a^5*m + a^3*q^2*r - a^3*m*r^2)*cos(th)^4 + (a^5*m - 2*a*q^2*r^3 + 3*a*m*r^4)*cos(th)^2)/(2*m*r^5 - r^6 - (a^2 + q^2)*r^4 - (a^6 + a^4*q^2 - 2*a^4*m*r + a^4*r^2)*cos(th)^4 + 2*(2*a^2*m*r^3 - a^2*r^4 - (a^4 + a^2*q^2)*r^2)*cos(th)^2) \n", "Gam^t_th,ph = ((a^5*q^2 - 2*a^5*m*r)*cos(th)*sin(th)^5 - (a^5*q^2 - 2*a^5*m*r + a^3*q^2*r^2 - 2*a^3*m*r^3)*cos(th)*sin(th)^3)/(a^6*cos(th)^6 + 3*a^4*r^2*cos(th)^4 + 3*a^2*r^4*cos(th)^2 + r^6) \n", "Gam^r_t,t = (m*r^4 - (2*m^2 + q^2)*r^3 + (a^2*m + 3*m*q^2)*r^2 - (a^4*m + a^2*m*q^2 - 2*a^2*m^2*r + a^2*m*r^2)*cos(th)^2 - (a^2*q^2 + q^4)*r)/(a^6*cos(th)^6 + 3*a^4*r^2*cos(th)^4 + 3*a^2*r^4*cos(th)^2 + r^6) \n", "Gam^r_t,ph = -(a*m*r^4 - (2*a*m^2 + a*q^2)*r^3 + (a^3*m + 3*a*m*q^2)*r^2 - (a^5*m + a^3*m*q^2 - 2*a^3*m^2*r + a^3*m*r^2)*cos(th)^2 - (a^3*q^2 + a*q^4)*r)*sin(th)^2/(a^6*cos(th)^6 + 3*a^4*r^2*cos(th)^4 + 3*a^2*r^4*cos(th)^2 + r^6) \n", "Gam^r_r,r = -(a^2*m + q^2*r - m*r^2 - (a^2*m - a^2*r)*sin(th)^2)/(2*m*r^3 - r^4 - (a^2 + q^2)*r^2 - (a^4 + a^2*q^2 - 2*a^2*m*r + a^2*r^2)*cos(th)^2) \n", "Gam^r_r,th = -a^2*cos(th)*sin(th)/(a^2*cos(th)^2 + r^2) \n", "Gam^r_th,th = (2*m*r^2 - r^3 - (a^2 + q^2)*r)/(a^2*cos(th)^2 + r^2) \n", "Gam^r_ph,ph = ((a^2*m*r^4 - (2*a^2*m^2 + a^2*q^2)*r^3 + (a^4*m + 3*a^2*m*q^2)*r^2 - (a^6*m + a^4*m*q^2 - 2*a^4*m^2*r + a^4*m*r^2)*cos(th)^2 - (a^4*q^2 + a^2*q^4)*r)*sin(th)^4 + (2*m*r^6 - r^7 - (a^2 + q^2)*r^5 + (2*a^4*m*r^2 - a^4*r^3 - (a^6 + a^4*q^2)*r)*cos(th)^4 + 2*(2*a^2*m*r^4 - a^2*r^5 - (a^4 + a^2*q^2)*r^3)*cos(th)^2)*sin(th)^2)/(a^6*cos(th)^6 + 3*a^4*r^2*cos(th)^4 + 3*a^2*r^4*cos(th)^2 + r^6) \n", "Gam^th_t,t = (a^2*q^2 - 2*a^2*m*r)*cos(th)*sin(th)/(a^6*cos(th)^6 + 3*a^4*r^2*cos(th)^4 + 3*a^2*r^4*cos(th)^2 + r^6) \n", "Gam^th_t,ph = -(a^3*q^2 - 2*a^3*m*r + a*q^2*r^2 - 2*a*m*r^3)*cos(th)*sin(th)/(a^6*cos(th)^6 + 3*a^4*r^2*cos(th)^4 + 3*a^2*r^4*cos(th)^2 + r^6) \n", "Gam^th_r,r = -a^2*cos(th)*sin(th)/(2*m*r^3 - r^4 - (a^2 + q^2)*r^2 - (a^4 + a^2*q^2 - 2*a^2*m*r + a^2*r^2)*cos(th)^2) \n", "Gam^th_r,th = r/(a^2*cos(th)^2 + r^2) \n", "Gam^th_th,th = -a^2*cos(th)*sin(th)/(a^2*cos(th)^2 + r^2) \n", "Gam^th_ph,ph = -((a^6 + a^4*q^2 - 2*a^4*m*r + a^4*r^2)*cos(th)^5 - 2*(2*a^2*m*r^3 - a^2*r^4 - (a^4 + a^2*q^2)*r^2)*cos(th)^3 - (a^4*q^2 - 2*a^4*m*r + 2*a^2*q^2*r^2 - 4*a^2*m*r^3 - a^2*r^4 - r^6)*cos(th))*sin(th)/(a^6*cos(th)^6 + 3*a^4*r^2*cos(th)^4 + 3*a^2*r^4*cos(th)^2 + r^6) \n", "Gam^ph_t,r = (a^3*m*cos(th)^2 + a*q^2*r - a*m*r^2)/(2*m*r^5 - r^6 - (a^2 + q^2)*r^4 - (a^6 + a^4*q^2 - 2*a^4*m*r + a^4*r^2)*cos(th)^4 + 2*(2*a^2*m*r^3 - a^2*r^4 - (a^4 + a^2*q^2)*r^2)*cos(th)^2) \n", "Gam^ph_t,th = (a*q^2 - 2*a*m*r)*cos(th)/((a^4*cos(th)^4 + 2*a^2*r^2*cos(th)^2 + r^4)*sin(th)) \n", "Gam^ph_r,ph = -(a^2*q^2*r - a^2*m*r^2 + q^2*r^3 - 2*m*r^4 + r^5 - (a^4*m - a^4*r)*cos(th)^4 + (a^4*m - a^2*m*r^2 + 2*a^2*r^3)*cos(th)^2)/(2*m*r^5 - r^6 - (a^2 + q^2)*r^4 - (a^6 + a^4*q^2 - 2*a^4*m*r + a^4*r^2)*cos(th)^4 + 2*(2*a^2*m*r^3 - a^2*r^4 - (a^4 + a^2*q^2)*r^2)*cos(th)^2) \n", "Gam^ph_th,ph = (a^4*cos(th)*sin(th)^4 - (2*a^4 + a^2*q^2 - 2*a^2*m*r + 2*a^2*r^2)*cos(th)*sin(th)^2 + (a^4 + 2*a^2*r^2 + r^4)*cos(th))/((a^4*cos(th)^4 + 2*a^2*r^2*cos(th)^2 + r^4)*sin(th)) " ] }, "execution_count": 23, "metadata": {}, "output_type": "execute_result" } ], "source": [ "g.christoffel_symbols_display()" ] }, { "cell_type": "markdown", "metadata": {}, "source": [ "

Killing vectors

\n", "

The default vector frame on the spacetime manifold is the coordinate basis associated with Boyer-Lindquist coordinates:

" ] }, { "cell_type": "code", "execution_count": 24, "metadata": { "collapsed": false }, "outputs": [ { "data": { "text/html": [ "" ], "text/plain": [ "True" ] }, "execution_count": 24, "metadata": {}, "output_type": "execute_result" } ], "source": [ "M.default_frame() is BL.frame()" ] }, { "cell_type": "code", "execution_count": 25, "metadata": { "collapsed": false }, "outputs": [ { "data": { "text/html": [ "" ], "text/plain": [ "Coordinate frame (M0, (d/dt,d/dr,d/dth,d/dph))" ] }, "execution_count": 25, "metadata": {}, "output_type": "execute_result" } ], "source": [ "BL.frame()" ] }, { "cell_type": "markdown", "metadata": {}, "source": [ "

Let us consider the first vector field of this frame:

" ] }, { "cell_type": "code", "execution_count": 26, "metadata": { "collapsed": false }, "outputs": [ { "data": { "text/html": [ "" ], "text/plain": [ "Vector field d/dt on the Open subset M0 of the 4-dimensional differentiable manifold M" ] }, "execution_count": 26, "metadata": {}, "output_type": "execute_result" } ], "source": [ "xi = BL.frame()[0] ; xi" ] }, { "cell_type": "code", "execution_count": 27, "metadata": { "collapsed": false }, "outputs": [ { "name": "stdout", "output_type": "stream", "text": [ "Vector field d/dt on the Open subset M0 of the 4-dimensional differentiable manifold M\n" ] } ], "source": [ "print(xi)" ] }, { "cell_type": "markdown", "metadata": {}, "source": [ "

The 1-form associated to it by metric duality is

" ] }, { "cell_type": "code", "execution_count": 28, "metadata": { "collapsed": false }, "outputs": [ { "data": { "text/html": [ "" ], "text/plain": [ "-(a^2*cos(th)^2 + q^2 - 2*m*r + r^2)/(a^2*cos(th)^2 + r^2) dt + (a*q^2 - 2*a*m*r)*sin(th)^2/(a^2*cos(th)^2 + r^2) dph" ] }, "execution_count": 28, "metadata": {}, "output_type": "execute_result" } ], "source": [ "xi_form = xi.down(g) ; xi_form.display()" ] }, { "cell_type": "markdown", "metadata": {}, "source": [ "

Its covariant derivative is

" ] }, { "cell_type": "code", "execution_count": 29, "metadata": { "collapsed": false }, "outputs": [ { "name": "stdout", "output_type": "stream", "text": [ "Tensor field of type (0,2) on the Open subset M0 of the 4-dimensional differentiable manifold M\n" ] }, { "data": { "text/html": [ "" ], "text/plain": [ "(m*r^4 - (2*m^2 + q^2)*r^3 + (a^2*m + 3*m*q^2)*r^2 - (a^4*m + a^2*m*q^2 - 2*a^2*m^2*r + a^2*m*r^2)*cos(th)^2 - (a^2*q^2 + q^4)*r)/(2*m*r^5 - r^6 - (a^2 + q^2)*r^4 - (a^6 + a^4*q^2 - 2*a^4*m*r + a^4*r^2)*cos(th)^4 + 2*(2*a^2*m*r^3 - a^2*r^4 - (a^4 + a^2*q^2)*r^2)*cos(th)^2) dt*dr - (a^2*q^2 - 2*a^2*m*r)*cos(th)*sin(th)/(a^4*cos(th)^4 + 2*a^2*r^2*cos(th)^2 + r^4) dt*dth - (m*r^4 - (2*m^2 + q^2)*r^3 + (a^2*m + 3*m*q^2)*r^2 - (a^4*m + a^2*m*q^2 - 2*a^2*m^2*r + a^2*m*r^2)*cos(th)^2 - (a^2*q^2 + q^4)*r)/(2*m*r^5 - r^6 - (a^2 + q^2)*r^4 - (a^6 + a^4*q^2 - 2*a^4*m*r + a^4*r^2)*cos(th)^4 + 2*(2*a^2*m*r^3 - a^2*r^4 - (a^4 + a^2*q^2)*r^2)*cos(th)^2) dr*dt - (a^3*m*cos(th)^4 - a*q^2*r + a*m*r^2 - (a^3*m - a*q^2*r + a*m*r^2)*cos(th)^2)/(a^4*cos(th)^4 + 2*a^2*r^2*cos(th)^2 + r^4) dr*dph + (a^2*q^2 - 2*a^2*m*r)*cos(th)*sin(th)/(a^4*cos(th)^4 + 2*a^2*r^2*cos(th)^2 + r^4) dth*dt - (a^3*q^2 - 2*a^3*m*r + a*q^2*r^2 - 2*a*m*r^3)*cos(th)*sin(th)/(a^4*cos(th)^4 + 2*a^2*r^2*cos(th)^2 + r^4) dth*dph + (a^3*m*sin(th)^4 - (a^3*m + a*q^2*r - a*m*r^2)*sin(th)^2)/(a^4*cos(th)^4 + 2*a^2*r^2*cos(th)^2 + r^4) dph*dr + (a^3*q^2 - 2*a^3*m*r + a*q^2*r^2 - 2*a*m*r^3)*cos(th)*sin(th)/(a^4*cos(th)^4 + 2*a^2*r^2*cos(th)^2 + r^4) dph*dth" ] }, "execution_count": 29, "metadata": {}, "output_type": "execute_result" } ], "source": [ "nab_xi = nab(xi_form) ; print(nab_xi) ; nab_xi.display()" ] }, { "cell_type": "markdown", "metadata": {}, "source": [ "

Let us check that the vector field $\\xi=\\frac{\\partial}{\\partial t}$ obeys Killing equation:

" ] }, { "cell_type": "code", "execution_count": 30, "metadata": { "collapsed": false }, "outputs": [ { "data": { "text/html": [ "" ], "text/plain": [ "True" ] }, "execution_count": 30, "metadata": {}, "output_type": "execute_result" } ], "source": [ "nab_xi.symmetrize() == 0" ] }, { "cell_type": "markdown", "metadata": {}, "source": [ "

Similarly, let us check that $\\chi := \\frac{\\partial}{\\partial\\phi}$ is a Killing vector:

" ] }, { "cell_type": "code", "execution_count": 31, "metadata": { "collapsed": false }, "outputs": [ { "data": { "text/html": [ "" ], "text/plain": [ "Vector field d/dph on the Open subset M0 of the 4-dimensional differentiable manifold M" ] }, "execution_count": 31, "metadata": {}, "output_type": "execute_result" } ], "source": [ "chi = BL.frame()[3] ; chi" ] }, { "cell_type": "code", "execution_count": 32, "metadata": { "collapsed": false }, "outputs": [ { "data": { "text/html": [ "" ], "text/plain": [ "True" ] }, "execution_count": 32, "metadata": {}, "output_type": "execute_result" } ], "source": [ "nab(chi.down(g)).symmetrize() == 0" ] }, { "cell_type": "markdown", "metadata": {}, "source": [ "

Another way to check that $\\xi$ and $\\chi$ are Killing vectors is the vanishing of the Lie derivative of the metric tensor along them:

" ] }, { "cell_type": "code", "execution_count": 33, "metadata": { "collapsed": false }, "outputs": [ { "data": { "text/html": [ "" ], "text/plain": [ "True" ] }, "execution_count": 33, "metadata": {}, "output_type": "execute_result" } ], "source": [ "g.lie_derivative(xi) == 0" ] }, { "cell_type": "code", "execution_count": 34, "metadata": { "collapsed": false }, "outputs": [ { "data": { "text/html": [ "" ], "text/plain": [ "True" ] }, "execution_count": 34, "metadata": {}, "output_type": "execute_result" } ], "source": [ "g.lie_derivative(chi) == 0" ] }, { "cell_type": "markdown", "metadata": {}, "source": [ "

Curvature

\n", "\n", "

The Ricci tensor associated with $g$:

" ] }, { "cell_type": "code", "execution_count": 35, "metadata": { "collapsed": false }, "outputs": [ { "name": "stdout", "output_type": "stream", "text": [ "Field of symmetric bilinear forms Ric(g) on the 4-dimensional differentiable manifold M\n" ] } ], "source": [ "Ric = g.ricci() ; print(Ric)" ] }, { "cell_type": "code", "execution_count": 36, "metadata": { "collapsed": false }, "outputs": [ { "data": { "text/html": [ "" ], "text/plain": [ "Ric(g) = -(a^2*q^2*cos(th)^2 - 2*a^2*q^2 - q^4 + 2*m*q^2*r - q^2*r^2)/(a^6*cos(th)^6 + 3*a^4*r^2*cos(th)^4 + 3*a^2*r^4*cos(th)^2 + r^6) dt*dt - (2*a^3*q^2 + a*q^4 - 2*a*m*q^2*r + 2*a*q^2*r^2 - (2*a^3*q^2 + a*q^4 - 2*a*m*q^2*r + 2*a*q^2*r^2)*cos(th)^2)/(a^6*cos(th)^6 + 3*a^4*r^2*cos(th)^4 + 3*a^2*r^4*cos(th)^2 + r^6) dt*dph + q^2/(2*m*r^3 - r^4 - (a^2 + q^2)*r^2 - (a^4 + a^2*q^2 - 2*a^2*m*r + a^2*r^2)*cos(th)^2) dr*dr + q^2/(a^2*cos(th)^2 + r^2) dth*dth - (2*a^3*q^2 + a*q^4 - 2*a*m*q^2*r + 2*a*q^2*r^2 - (2*a^3*q^2 + a*q^4 - 2*a*m*q^2*r + 2*a*q^2*r^2)*cos(th)^2)/(a^6*cos(th)^6 + 3*a^4*r^2*cos(th)^4 + 3*a^2*r^4*cos(th)^2 + r^6) dph*dt - ((a^6*q^2 + a^4*q^4 - 2*a^4*m*q^2*r + a^4*q^2*r^2)*sin(th)^6 - (a^4*q^4 - 2*a^4*m*q^2*r + a^2*q^4*r^2 - 2*a^2*m*q^2*r^3)*sin(th)^4 - (a^6*q^2 + 3*a^4*q^2*r^2 + 3*a^2*q^2*r^4 + q^2*r^6)*sin(th)^2)/(a^8*cos(th)^8 + 4*a^6*r^2*cos(th)^6 + 6*a^4*r^4*cos(th)^4 + 4*a^2*r^6*cos(th)^2 + r^8) dph*dph" ] }, "execution_count": 36, "metadata": {}, "output_type": "execute_result" } ], "source": [ "Ric.display()" ] }, { "cell_type": "code", "execution_count": 37, "metadata": { "collapsed": false }, "outputs": [ { "data": { "text/html": [ "" ], "text/plain": [ "[ -(a^2*q^2*cos(th)^2 - 2*a^2*q^2 - q^4 + 2*m*q^2*r - q^2*r^2)/(a^6*cos(th)^6 + 3*a^4*r^2*cos(th)^4 + 3*a^2*r^4*cos(th)^2 + r^6) 0 0 -(2*a^3*q^2 + a*q^4 - 2*a*m*q^2*r + 2*a*q^2*r^2 - (2*a^3*q^2 + a*q^4 - 2*a*m*q^2*r + 2*a*q^2*r^2)*cos(th)^2)/(a^6*cos(th)^6 + 3*a^4*r^2*cos(th)^4 + 3*a^2*r^4*cos(th)^2 + r^6)]\n", "[ 0 q^2/(2*m*r^3 - r^4 - (a^2 + q^2)*r^2 - (a^4 + a^2*q^2 - 2*a^2*m*r + a^2*r^2)*cos(th)^2) 0 0]\n", "[ 0 0 q^2/(a^2*cos(th)^2 + r^2) 0]\n", "[ -(2*a^3*q^2 + a*q^4 - 2*a*m*q^2*r + 2*a*q^2*r^2 - (2*a^3*q^2 + a*q^4 - 2*a*m*q^2*r + 2*a*q^2*r^2)*cos(th)^2)/(a^6*cos(th)^6 + 3*a^4*r^2*cos(th)^4 + 3*a^2*r^4*cos(th)^2 + r^6) 0 0 -((a^6*q^2 + a^4*q^4 - 2*a^4*m*q^2*r + a^4*q^2*r^2)*sin(th)^6 - (a^4*q^4 - 2*a^4*m*q^2*r + a^2*q^4*r^2 - 2*a^2*m*q^2*r^3)*sin(th)^4 - (a^6*q^2 + 3*a^4*q^2*r^2 + 3*a^2*q^2*r^4 + q^2*r^6)*sin(th)^2)/(a^8*cos(th)^8 + 4*a^6*r^2*cos(th)^6 + 6*a^4*r^4*cos(th)^4 + 4*a^2*r^6*cos(th)^2 + r^8)]" ] }, "execution_count": 37, "metadata": {}, "output_type": "execute_result" } ], "source": [ "Ric[:]" ] }, { "cell_type": "markdown", "metadata": {}, "source": [ "

Let us check that in the Kerr case, i.e. when $q=0$, the Ricci tensor is zero:

" ] }, { "cell_type": "code", "execution_count": 38, "metadata": { "collapsed": false }, "outputs": [ { "data": { "text/html": [ "" ], "text/plain": [ "[0 0 0 0]\n", "[0 0 0 0]\n", "[0 0 0 0]\n", "[0 0 0 0]" ] }, "execution_count": 38, "metadata": {}, "output_type": "execute_result" } ], "source": [ "Ric[:].subs(q=0)" ] }, { "cell_type": "markdown", "metadata": {}, "source": [ "

The Riemann curvature tensor associated with $g$:

" ] }, { "cell_type": "code", "execution_count": 39, "metadata": { "collapsed": false }, "outputs": [ { "name": "stdout", "output_type": "stream", "text": [ "Tensor field Riem(g) of type (1,3) on the 4-dimensional differentiable manifold M\n" ] } ], "source": [ "R = g.riemann() ; print(R)" ] }, { "cell_type": "markdown", "metadata": {}, "source": [ "

The component $R^0_{\\ \\, 101}$ of the Riemann tensor is

" ] }, { "cell_type": "code", "execution_count": 40, "metadata": { "collapsed": false }, "outputs": [ { "data": { "text/html": [ "" ], "text/plain": [ "(4*a^2*q^2*r^2 - 3*a^2*m*r^3 + 3*q^2*r^4 - 2*m*r^5 + (a^4*q^2 - 3*a^4*m*r)*cos(th)^4 - (2*a^4*q^2 - 9*a^4*m*r + 2*a^2*q^2*r^2 - 7*a^2*m*r^3)*cos(th)^2)/(2*m*r^7 - r^8 - (a^2 + q^2)*r^6 - (a^8 + a^6*q^2 - 2*a^6*m*r + a^6*r^2)*cos(th)^6 + 3*(2*a^4*m*r^3 - a^4*r^4 - (a^6 + a^4*q^2)*r^2)*cos(th)^4 + 3*(2*a^2*m*r^5 - a^2*r^6 - (a^4 + a^2*q^2)*r^4)*cos(th)^2)" ] }, "execution_count": 40, "metadata": {}, "output_type": "execute_result" } ], "source": [ "R[0,1,0,1]" ] }, { "cell_type": "markdown", "metadata": {}, "source": [ "

The expression in the uncharged limit (Kerr spacetime) is

" ] }, { "cell_type": "code", "execution_count": 41, "metadata": { "collapsed": false }, "outputs": [ { "data": { "text/html": [ "" ], "text/plain": [ "(3*a^4*m*r*cos(th)^4 + 3*a^2*m*r^3 + 2*m*r^5 - (9*a^4*m*r + 7*a^2*m*r^3)*cos(th)^2)/(a^2*r^6 - 2*m*r^7 + r^8 + (a^8 - 2*a^6*m*r + a^6*r^2)*cos(th)^6 + 3*(a^6*r^2 - 2*a^4*m*r^3 + a^4*r^4)*cos(th)^4 + 3*(a^4*r^4 - 2*a^2*m*r^5 + a^2*r^6)*cos(th)^2)" ] }, "execution_count": 41, "metadata": {}, "output_type": "execute_result" } ], "source": [ "R[0,1,0,1].expr().subs(q=0).simplify_rational()" ] }, { "cell_type": "markdown", "metadata": {}, "source": [ "

while in the non-rotating limit (Reissner-Nordström spacetime), it is

" ] }, { "cell_type": "code", "execution_count": 42, "metadata": { "collapsed": false }, "outputs": [ { "data": { "text/html": [ "" ], "text/plain": [ "-(3*q^2 - 2*m*r)/(q^2*r^2 - 2*m*r^3 + r^4)" ] }, "execution_count": 42, "metadata": {}, "output_type": "execute_result" } ], "source": [ "R[0,1,0,1].expr().subs(a=0).simplify_rational()" ] }, { "cell_type": "markdown", "metadata": {}, "source": [ "

In the Schwarzschild limit, it reduces to

" ] }, { "cell_type": "code", "execution_count": 43, "metadata": { "collapsed": false }, "outputs": [ { "data": { "text/html": [ "" ], "text/plain": [ "-2*m/(2*m*r^2 - r^3)" ] }, "execution_count": 43, "metadata": {}, "output_type": "execute_result" } ], "source": [ "R[0,1,0,1].expr().subs(a=0, q=0).simplify_rational()" ] }, { "cell_type": "markdown", "metadata": {}, "source": [ "

Obviously, it vanishes in the flat space limit:

" ] }, { "cell_type": "code", "execution_count": 44, "metadata": { "collapsed": false }, "outputs": [ { "data": { "text/html": [ "" ], "text/plain": [ "0" ] }, "execution_count": 44, "metadata": {}, "output_type": "execute_result" } ], "source": [ "R[0,1,0,1].expr().subs(m=0, a=0, q=0)" ] }, { "cell_type": "markdown", "metadata": {}, "source": [ "

Bianchi identity

\n", "\n", "

Let us check the Bianchi identity $\\nabla_p R^i_{\\ \\, j kl} + \\nabla_k R^i_{\\ \\, jlp} + \\nabla_l R^i_{\\ \\, jpk} = 0$:

" ] }, { "cell_type": "code", "execution_count": 45, "metadata": { "collapsed": false }, "outputs": [ { "name": "stdout", "output_type": "stream", "text": [ "Tensor field nabla_g(Riem(g)) of type (1,4) on the 4-dimensional differentiable manifold M\n" ] } ], "source": [ "DR = nab(R) ; print(DR) #long (takes a while)" ] }, { "cell_type": "code", "execution_count": 46, "metadata": { "collapsed": false }, "outputs": [ { "name": "stdout", "output_type": "stream", "text": [ "0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0\n" ] } ], "source": [ "for i in M.irange():\n", " for j in M.irange():\n", " for k in M.irange():\n", " for l in M.irange():\n", " for p in M.irange():\n", " print DR[i,j,k,l,p] + DR[i,j,l,p,k] + DR[i,j,p,k,l] ," ] }, { "cell_type": "markdown", "metadata": {}, "source": [ "

If the last sign in the Bianchi identity is changed to minus, the identity does no longer hold:

" ] }, { "cell_type": "code", "execution_count": 47, "metadata": { "collapsed": false }, "outputs": [ { "data": { "text/html": [ "" ], "text/plain": [ "0" ] }, "execution_count": 47, "metadata": {}, "output_type": "execute_result" } ], "source": [ "DR[0,1,2,3,1] + DR[0,1,3,1,2] + DR[0,1,1,2,3] # should be zero (Bianchi identity)" ] }, { "cell_type": "code", "execution_count": 48, "metadata": { "collapsed": false }, "outputs": [ { "data": { "text/html": [ "" ], "text/plain": [ "-4*((a^5*q^2 - 6*a^5*m*r + a^3*q^2*r^2 - 6*a^3*m*r^3)*cos(th)^3 - (5*a^3*q^2*r^2 - 6*a^3*m*r^3 + 5*a*q^2*r^4 - 6*a*m*r^5)*cos(th))*sin(th)/(2*m*r^7 - r^8 - (a^2 + q^2)*r^6 - (a^8 + a^6*q^2 - 2*a^6*m*r + a^6*r^2)*cos(th)^6 + 3*(2*a^4*m*r^3 - a^4*r^4 - (a^6 + a^4*q^2)*r^2)*cos(th)^4 + 3*(2*a^2*m*r^5 - a^2*r^6 - (a^4 + a^2*q^2)*r^4)*cos(th)^2)" ] }, "execution_count": 48, "metadata": {}, "output_type": "execute_result" } ], "source": [ "DR[0,1,2,3,1] + DR[0,1,3,1,2] - DR[0,1,1,2,3] # note the change of the second + to -" ] }, { "cell_type": "markdown", "metadata": {}, "source": [ "### Ricci scalar\n", "\n", "The Ricci scalar $R = g^{ab} R_{ab}$ of the Kerr-Newman spacetime vanishes identically:" ] }, { "cell_type": "code", "execution_count": 49, "metadata": { "collapsed": false }, "outputs": [ { "data": { "text/html": [ "" ], "text/plain": [ "r(g): M --> R\n", "on M0: (t, r, th, ph) |--> 0" ] }, "execution_count": 49, "metadata": {}, "output_type": "execute_result" } ], "source": [ "g.ricci_scalar().display()" ] }, { "cell_type": "markdown", "metadata": {}, "source": [ "

Einstein equation

\n", "

The Einstein tensor is

" ] }, { "cell_type": "code", "execution_count": 50, "metadata": { "collapsed": false }, "outputs": [ { "name": "stdout", "output_type": "stream", "text": [ "Field of symmetric bilinear forms +Ric(g) on the 4-dimensional differentiable manifold M\n" ] } ], "source": [ "G = Ric - 1/2*g.ricci_scalar()*g ; print(G)" ] }, { "cell_type": "markdown", "metadata": {}, "source": [ "

Since the Ricci scalar is zero, the Einstein tensor reduces to the Ricci tensor:

" ] }, { "cell_type": "code", "execution_count": 51, "metadata": { "collapsed": false }, "outputs": [ { "data": { "text/html": [ "" ], "text/plain": [ "True" ] }, "execution_count": 51, "metadata": {}, "output_type": "execute_result" } ], "source": [ "G == Ric" ] }, { "cell_type": "markdown", "metadata": {}, "source": [ "The invariant $F_{ab} F^{ab}$ of the electromagnetic field:" ] }, { "cell_type": "code", "execution_count": 52, "metadata": { "collapsed": false }, "outputs": [ { "name": "stdout", "output_type": "stream", "text": [ "Scalar field on the 4-dimensional differentiable manifold M\n" ] } ], "source": [ "Fuu = F.up(g)\n", "F2 = F['_ab']*Fuu['^ab'] ; print(F2)" ] }, { "cell_type": "code", "execution_count": 53, "metadata": { "collapsed": false }, "outputs": [ { "data": { "text/html": [ "" ], "text/plain": [ "M --> R\n", "on M0: (t, r, th, ph) |--> -2*(a^4*q^2*cos(th)^4 - 6*a^2*q^2*r^2*cos(th)^2 + q^2*r^4)/(a^8*cos(th)^8 + 4*a^6*r^2*cos(th)^6 + 6*a^4*r^4*cos(th)^4 + 4*a^2*r^6*cos(th)^2 + r^8)" ] }, "execution_count": 53, "metadata": {}, "output_type": "execute_result" } ], "source": [ "F2.display()" ] }, { "cell_type": "markdown", "metadata": {}, "source": [ "

The energy-momentum tensor of the electromagnetic field:

" ] }, { "cell_type": "code", "execution_count": 54, "metadata": { "collapsed": false }, "outputs": [ { "name": "stdout", "output_type": "stream", "text": [ "Tensor field of type (0,2) on the 4-dimensional differentiable manifold M\n" ] } ], "source": [ "Fud = F.up(g,0)\n", "T = 1/(4*pi)*( F['_k.']*Fud['^k_.'] - 1/4*F2 * g ); print(T)" ] }, { "cell_type": "code", "execution_count": 55, "metadata": { "collapsed": false }, "outputs": [ { "data": { "text/html": [ "" ], "text/plain": [ "[ -1/8*(a^2*q^2*cos(th)^2 - 2*a^2*q^2 - q^4 + 2*m*q^2*r - q^2*r^2)/(pi*a^6*cos(th)^6 + 3*pi*a^4*r^2*cos(th)^4 + 3*pi*a^2*r^4*cos(th)^2 + pi*r^6) 0 0 -1/8*(2*a^3*q^2 + a*q^4 - 2*a*m*q^2*r + 2*a*q^2*r^2)*sin(th)^2/(pi*a^6*cos(th)^6 + 3*pi*a^4*r^2*cos(th)^4 + 3*pi*a^2*r^4*cos(th)^2 + pi*r^6)]\n", "[ 0 1/8*q^2/(2*pi*m*r^3 - pi*r^4 - (pi*a^2 + pi*q^2)*r^2 - (pi*a^4 + pi*a^2*q^2 - 2*pi*a^2*m*r + pi*a^2*r^2)*cos(th)^2) 0 0]\n", "[ 0 0 1/8*q^2/(pi*a^2*cos(th)^2 + pi*r^2) 0]\n", "[ -1/8*(2*a^3*q^2 + a*q^4 - 2*a*m*q^2*r + 2*a*q^2*r^2)*sin(th)^2/(pi*a^6*cos(th)^6 + 3*pi*a^4*r^2*cos(th)^4 + 3*pi*a^2*r^4*cos(th)^2 + pi*r^6) 0 0 -1/8*((2*a^2*m*q^2*r^5 - 2*a^2*q^2*r^6 - (2*a^4*q^2 + a^2*q^4)*r^4 - (2*a^8*q^2 + a^6*q^4 - 2*a^6*m*q^2*r + 2*a^6*q^2*r^2)*cos(th)^4 + 2*(2*a^4*m*q^2*r^3 + 2*a^4*q^2*r^4 + (2*a^6*q^2 - a^4*q^4)*r^2)*cos(th)^2)*sin(th)^4 - (a^2*q^2*r^6 + q^2*r^8 + (a^8*q^2 + a^6*q^2*r^2)*cos(th)^6 - 5*(a^6*q^2*r^2 + a^4*q^2*r^4)*cos(th)^4 + (8*a^6*q^2*r^2 + 11*a^4*q^2*r^4 + 3*a^2*q^2*r^6)*cos(th)^2)*sin(th)^2)/(pi*a^10*cos(th)^10 + 5*pi*a^8*r^2*cos(th)^8 + 10*pi*a^6*r^4*cos(th)^6 + 10*pi*a^4*r^6*cos(th)^4 + 5*pi*a^2*r^8*cos(th)^2 + pi*r^10)]" ] }, "execution_count": 55, "metadata": {}, "output_type": "execute_result" } ], "source": [ "T[:]" ] }, { "cell_type": "markdown", "metadata": {}, "source": [ "

Check of the Einstein equation:

" ] }, { "cell_type": "code", "execution_count": 56, "metadata": { "collapsed": false }, "outputs": [ { "data": { "text/html": [ "" ], "text/plain": [ "True" ] }, "execution_count": 56, "metadata": {}, "output_type": "execute_result" } ], "source": [ "G == 8*pi*T" ] }, { "cell_type": "markdown", "metadata": {}, "source": [ "### Kretschmann scalar\n", "\n", "The tensor $R^\\flat$, of components $R_{abcd} = g_{am} R^m_{\\ \\, bcd}$:" ] }, { "cell_type": "code", "execution_count": 57, "metadata": { "collapsed": false }, "outputs": [ { "name": "stdout", "output_type": "stream", "text": [ "Tensor field of type (0,4) on the 4-dimensional differentiable manifold M\n" ] } ], "source": [ "dR = R.down(g) ; print(dR)" ] }, { "cell_type": "markdown", "metadata": {}, "source": [ "The tensor $R^\\sharp$, of components $R^{abcd} = g^{bp} g^{cq} g^{dr} R^a_{\\ \\, pqr}$:" ] }, { "cell_type": "code", "execution_count": 58, "metadata": { "collapsed": false }, "outputs": [ { "name": "stdout", "output_type": "stream", "text": [ "Tensor field of type (4,0) on the 4-dimensional differentiable manifold M\n" ] } ], "source": [ "uR = R.up(g) ; print(uR)" ] }, { "cell_type": "markdown", "metadata": {}, "source": [ "The Kretschmann scalar $K := R^{abcd} R_{abcd}$:" ] }, { "cell_type": "code", "execution_count": 59, "metadata": { "collapsed": false }, "outputs": [ { "data": { "text/html": [ "" ], "text/plain": [ "M --> R\n", "on M0: (t, r, th, ph) |--> -8*(6*m^2*r^8 - 12*(m^3 + m*q^2)*r^7 + (6*a^2*m^2 + 30*m^2*q^2 + 7*q^4)*r^6 - 6*(a^8*m^2 + a^6*m^2*q^2 - 2*a^6*m^3*r + a^6*m^2*r^2)*cos(th)^6 - 2*(6*a^2*m*q^2 + 13*m*q^4)*r^5 + 7*(a^2*q^4 + q^6)*r^4 + (7*a^6*q^4 + 7*a^4*q^6 + 90*a^4*m^2*r^4 - 60*(3*a^4*m^3 + a^4*m*q^2)*r^3 + (90*a^6*m^2 + 210*a^4*m^2*q^2 + 7*a^4*q^4)*r^2 - 2*(30*a^6*m*q^2 + 37*a^4*m*q^4)*r)*cos(th)^4 - 2*(45*a^2*m^2*r^6 - 30*(3*a^2*m^3 + 2*a^2*m*q^2)*r^5 + (45*a^4*m^2 + 165*a^2*m^2*q^2 + 17*a^2*q^4)*r^4 - 2*(30*a^4*m*q^2 + 47*a^2*m*q^4)*r^3 + 17*(a^4*q^4 + a^2*q^6)*r^2)*cos(th)^2)/(2*m*r^13 - r^14 - (a^2 + q^2)*r^12 - (a^14 + a^12*q^2 - 2*a^12*m*r + a^12*r^2)*cos(th)^12 + 6*(2*a^10*m*r^3 - a^10*r^4 - (a^12 + a^10*q^2)*r^2)*cos(th)^10 + 15*(2*a^8*m*r^5 - a^8*r^6 - (a^10 + a^8*q^2)*r^4)*cos(th)^8 + 20*(2*a^6*m*r^7 - a^6*r^8 - (a^8 + a^6*q^2)*r^6)*cos(th)^6 + 15*(2*a^4*m*r^9 - a^4*r^10 - (a^6 + a^4*q^2)*r^8)*cos(th)^4 + 6*(2*a^2*m*r^11 - a^2*r^12 - (a^4 + a^2*q^2)*r^10)*cos(th)^2)" ] }, "execution_count": 59, "metadata": {}, "output_type": "execute_result" } ], "source": [ "Kr_scalar = uR['^ijkl']*dR['_ijkl']\n", "Kr_scalar.display()" ] }, { "cell_type": "markdown", "metadata": {}, "source": [ "

A variant of this expression can be obtained by invoking the factor() method on the coordinate function representing the scalar field in the manifold's default chart:

" ] }, { "cell_type": "code", "execution_count": 60, "metadata": { "collapsed": false }, "outputs": [ { "data": { "text/html": [ "" ], "text/plain": [ "-8*(6*a^6*m^2*cos(th)^6 - 7*a^4*q^4*cos(th)^4 + 60*a^4*m*q^2*r*cos(th)^4 - 90*a^4*m^2*r^2*cos(th)^4 + 34*a^2*q^4*r^2*cos(th)^2 - 120*a^2*m*q^2*r^3*cos(th)^2 + 90*a^2*m^2*r^4*cos(th)^2 - 7*q^4*r^4 + 12*m*q^2*r^5 - 6*m^2*r^6)/(a^2*cos(th)^2 + r^2)^6" ] }, "execution_count": 60, "metadata": {}, "output_type": "execute_result" } ], "source": [ "Kr = Kr_scalar.coord_function()\n", "Kr.factor()" ] }, { "cell_type": "markdown", "metadata": {}, "source": [ "

As a check, we can compare Kr to the formula given by R. Conn Henry, Astrophys. J. 535, 350 (2000):

" ] }, { "cell_type": "code", "execution_count": 61, "metadata": { "collapsed": false }, "outputs": [ { "data": { "text/html": [ "" ], "text/plain": [ "True" ] }, "execution_count": 61, "metadata": {}, "output_type": "execute_result" } ], "source": [ "Kr == 8/(r^2+(a*cos(th))^2)^6 *( \n", " 6*m^2*(r^6 - 15*r^4*(a*cos(th))^2 + 15*r^2*(a*cos(th))^4 - (a*cos(th))^6) \n", " - 12*m*q^2*r*(r^4 - 10*(a*r*cos(th))^2 + 5*(a*cos(th))^4) \n", " + q^4*(7*r^4 - 34*(a*r*cos(th))^2 + 7*(a*cos(th))^4) )" ] }, { "cell_type": "markdown", "metadata": {}, "source": [ "

The Schwarzschild value of the Kretschmann scalar is recovered by setting $a=0$ and $q=0$:

" ] }, { "cell_type": "code", "execution_count": 62, "metadata": { "collapsed": false }, "outputs": [ { "data": { "text/html": [ "" ], "text/plain": [ "48*m^2/r^6" ] }, "execution_count": 62, "metadata": {}, "output_type": "execute_result" } ], "source": [ "Kr.expr().subs(a=0, q=0)" ] }, { "cell_type": "markdown", "metadata": {}, "source": [ "

Let us plot the Kretschmann scalar for $m=1$, $a=0.9$ and $q=0.5$:

" ] }, { "cell_type": "code", "execution_count": 63, "metadata": { "collapsed": false }, "outputs": [ { "data": { "text/html": [ "\n", "\n" ], "text/plain": [ "Graphics3d Object" ] }, "execution_count": 63, "metadata": {}, "output_type": "execute_result" } ], "source": [ "K1 = Kr.expr().subs(m=1, a=0.9, q=0.5)\n", "plot3d(K1, (r,1,3), (th, 0, pi), viewer=viewer3D, axes_labels=['r', 'theta', 'Kr'])" ] } ], "metadata": { "kernelspec": { "display_name": "SageMath 7.5", "language": "", "name": "sagemath" }, "language": "python", "language_info": { "codemirror_mode": { "name": "ipython", "version": 2 }, "file_extension": ".py", "mimetype": "text/x-python", "name": "python", "nbconvert_exporter": "python", "pygments_lexer": "ipython2", "version": "2.7.13" } }, "nbformat": 4, "nbformat_minor": 0 }