meta user
network profile
| bio | website | jacobi.luc.edu |
|---|---|---|
| location | Chicago, IL | |
| age | ||
| visits | member for | 2 years, 3 months |
| seen | 19 hours ago | |
| stats | profile views | 108 |
I'm an assistant professor of physics at a university in Chicago.
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Apr 14 |
awarded | Quorum |
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Feb 2 |
awarded | Yearling |
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Jan 21 |
answered | What exactly are we doing when we set $c=1$? |
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Nov 22 |
answered | What does Friedrichs mean by “Myriotic fields”? |
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Nov 13 |
comment |
Cubic term in gauge theories I'm not sure why you'd do that. Do you know of some way of building a sensible F^3 theory? |
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Nov 12 |
awarded | Commentator |
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Nov 12 |
comment |
Cubic term in gauge theories Adding F^3 to the standard YM Lagrangian gives a non-renormalizable theory; you should only consider it as part of a low-dimensional effective theory. F^3 is the "least irrelevant" gauge-invariant operator for pure YM. So the low-energy expansion of some theory that holds at higher energies might have F^2 as the leading term and F^3 term as the first "correction". |
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Nov 9 |
answered | Cubic term in gauge theories |
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Nov 7 |
awarded | Yearling |
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Nov 7 |
answered | Einstein tensor in Friedmann equations : where is the missing $c^2$? |
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Sep 3 |
answered | How do I calculate the induced metric in the Gibbons–Hawking–York boundary term? |
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Aug 12 |
awarded | Citizen Patrol |
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May 28 |
awarded | Critic |
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Aug 12 |
comment |
Does the lack of modular nuclearity in string theory mean anything? You don't even need quantum gravity to see that extensivity breaks down when gravity is important. Solve the Tolman-Oppenheimer-Volkov equation for a self-gravitating perfect fluid with equation of state $p=\kappa\rho$. This gives an energy density $\rho \sim r^{-2}$. Cut off the solution at some radial size $R$ and join it on to a solution that goes to zero at a finite distance. Relate the entropy density to the energy density using the EOS, integrate, and you get entropy $\sim R^{\frac{1+3\kappa}{1+\kappa}}$. The entropy of the self-gravitating object never grows faster than the area. |
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Aug 2 |
comment |
Cheat sheet of elementary particles Here is a handy Eightfold Way reference chart from an undergrad class I taught on particle physics: cl.ly/8yhy . Of course, it will only be useful if you understand what it represents! There is a good review in "Introduction to Elementary Particles" by Griffiths. |
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Jun 7 |
answered | 2nd order variation of Hilbert-Einstein action + Gibbons-Hawking-York boundary term |
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Jun 3 |
comment |
Explicit Variation of Gibbons-Hawking-York Boundary Term You're right -- simply preserving $n^{\mu}n_{\mu} = 1$ would only determine $\delta n^{\mu}$ up to a vector orthogonal to $n^{\mu}$. Instead, you should consider the definition of $n^{\mu}$. Let $\partial M$ be an isosurface of some coordinate $r$. Then $\alpha_{\mu} = \nabla_{\mu} r$ is orthogonal to the surface. Now normalize that vector to obtain: $$ n_{\mu} = \frac{\alpha_{\mu}}{\sqrt{g^{\nu\lambda}\alpha_{\nu}\alpha_{\lambda}}}$$ Consider how this expression behaves under a small variation of the metric and you obtain the result for $\delta n_{\mu}$. |
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May 31 |
awarded | Editor |
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May 31 |
revised |
Explicit Variation of Gibbons-Hawking-York Boundary Term added 108 characters in body |
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May 31 |
answered | Explicit Variation of Gibbons-Hawking-York Boundary Term |
