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location Cambridge, MA
age 26
visits member for 2 years, 6 months
seen 9 hours ago

Physics Graduate student at Harvard University.


1d
answered Non-invariance of the Interaction term in QED lagrangian
Oct
16
reviewed Close Use a Delayed Choice Quantum Eraser to communicate Faster Than Light
Oct
16
reviewed Approve suggested edit on Difference between sound wave and lightwave scattering
Oct
14
comment What is the central charge about?
This is a very broad question. I'm sure you will find the answer on wikipedia or some other questions in this forum.
Oct
14
reviewed Close Local Galilean coordinate system?
Oct
6
reviewed Close How damaging is light?
Oct
6
reviewed Close How long does it take for $25~\text{mC}$ to pass a point if the current is $12.5~\text{mA}$?
Oct
6
reviewed Close Magnetic field of a living human
Oct
5
reviewed Leave Open What prevents photons from getting mass from higher order Feynman diagrams
Oct
4
reviewed Close What's the conserved stress energy tensor?
Oct
4
reviewed Close What is the final velocity of a stone dropped out of a rising balloon?
Oct
2
revised Dependence of the Capacitance on the Material and Geometry of the Plates
fixed link
Oct
2
reviewed Close Energy Stored In A Capacitor (Slowly Moving Parallel Plates Together)
Oct
2
comment Dirac group representation
Even for your second point - I think your confusion will be alleviated if you realize that physicists often talk about representations of the algebra, whereas mathematicians like to talk about representations of the group (which in general, are not equivalent things). The conjugacy classes and character tables are usually used to discuss representations of groups (as far as I know). The analogue of these things in an algebra are invariant subalgebras.
Oct
2
comment Dirac group representation
I think your confusion arises from thinking about representations of an algebra vs. representations of the group. The group rep. must always have the unit matrix. The group rep. $g$ is obtained from a representation of its algebra $X$ via exponentiation $g = e^X$. Existence of a unit matrix in the group rep. implies existence of a "zero" matrix in the algebra. That a zero matrix exists in the algebra is obvious since it is the additive identity (which must exist for any algebra.)
Oct
1
comment Group Theoretic definition of a particle
@UserAnonymous The construction of representations of Poincare group is done very well in Section 2.5 of Wieinberg. He discusses representations of ISO(2). Representations of SO(3) can be found in any standard textbook on quantum mechanics (for instance, Section 4.3 of Griffiths).
Oct
1
comment Group Theoretic definition of a particle
@UserAnonymous - No problem. You can ask questions if you have doubts in my answer.
Oct
1
revised Group Theoretic definition of a particle
added 12 characters in body
Oct
1
comment Group Theoretic definition of a particle
@joshphysics - of course. Done!
Sep
30
awarded  Explainer