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Nov
21
comment What are orbifolds and why are they useful and interesting for physics?
Is there any intuition for why wavefunctions tend to concentrate near the singular points?
Nov
17
comment Is it possible to derive the effective potential of a given theory by only using the RGE equations?
If you only have a (first-order) differential equation, then will you not need some "initial/boundary condition" to fix a solution? Also, I don't see how this relates to extended Higgs sectors.
Nov
14
comment Are Matsubara states pure states?
One more thing realized: We use Wick rotation all over the place, to calculate loop integrals in zero temperature QFT. At zero temperature, one better not have any decoherence -- that should be a coherent sum.
Nov
13
comment Are Matsubara states pure states?
If you think of the "in-out" S-matrix (density-matrix like object) then once you compactify and impose boundary conditions for going around that circle, you're saying that the "initial" and "final" states must be related in a particular way. It sort of removes the off-diagonal elements of the matrix. I interpret that as decohering.
Nov
13
comment Are Matsubara states pure states?
That confuses me too -- I thought it might still be some linear combination of pure states (though any semblance of normalization is now lost) -- which tempts me to believe that the decohering might depend on the compactification. I'm not sure if one can define unitary basis vectors after compactification (without Wick rotation). There's no unique way to get from one time to another (you could move into the past or the future) :-?
Nov
13
comment Are terms with spinors analogous to $ ( \partial_\mu \Phi )(\partial^\mu \Phi)$ forbidden in the Lagrangian?
To me, the crux of the question is why can we not take ${(\partial \psi)}^2$ as the kinetic term instead of the usual one, and have $[\psi] = 1$. With regards to that, it seems that due to the extra derivative, this term is always going to have a larger mass scaling dimension than the usual kinetic term, so might not survive in the IR. I wonder if such a term is common in EFTs closer to the cutoff.
Nov
12
comment Are terms with spinors analogous to $ ( \partial_\mu \Phi )(\partial^\mu \Phi)$ forbidden in the Lagrangian?
Doesn't one usually use $[\psi] = 3/2$? The kinetic energy is taken to be scale-invariant, not the density.
Nov
9
comment Landau level degeneracy in symmetry gauge, finite system
I found the following to be a very useful resource when trying to understand Landau levels: hitoshi.berkeley.edu/221a/landau.pdf
Nov
9
comment Death by entropy
BTW, definitely something is imperfect in the way a living "body" replenishes itself, leading to aging and eventually death. It's not obvious whether this is something characterisable as "entropy". Suppose it were -- could you think of any concrete estimation that one might be able to compare with observations? That might help us decide one way or another.
Nov
9
comment Death by entropy
@Joshua: Love the idea of a story based on entropy clocks, whether or not it's dystopic. On a slightly different note, there's a lot of biophysics we are yet to understand, the field is slowly picking up.
Nov
8
comment Definition of Fine-Tuning
In practice, everyone uses a definition of fine-tuning that puts their model in favourable light :P Then again, there since there is no precise definition, you must forgive all those attempts for one of them might turn out to be the right way to look at things.
Nov
8
comment Is there a relation between (non-) existence of magnetic monopoles and thermodynamics?
What current configuration will give a magnetic field with the same isotropic $\frac{1}{r^2}$ profile that a point electric charge has?
Nov
8
comment Is there a relation between (non-) existence of magnetic monopoles and thermodynamics?
If I believed in something like Electric-Magnetic duality, that seems to be a fairly fundamental support for the idea of magnetic monopoles (which might make one feel that technical trickery is missing something essential :-?) -- not to mention, that is the only reason we have till today, for why charge need be quantized.
Nov
4
comment Are there QFTs in which a field cannot produce a real particle?
Howard Georgi has written some articles over the last few years about "unparticle physics".
Nov
4
comment Statistics of many body systems in pure states
@lionelbrits: I'm not sure why one cannot pose a similar question in the quantum mechanics of one mode (single "particle", but multiple levels). Maybe I don't understand the essence of your question then.
Nov
3
comment Statistics of many body systems in pure states
If I made a caricature of the problem (Single mode, 2 levels (fermionic), high temperature limit so approximately equal probabilities and "maximum" thermal entropy), you're asking about the entropy of $|\psi\rangle = \frac{|0\rangle + |1\rangle}{\sqrt{2}}$ vs $|\psi\rangle \langle\psi| = \frac{1}{2}|0\rangle \langle0| + \frac{1}{2} |1\rangle \langle 1| $
Nov
3
comment Statistics of many body systems in pure states
What you're thinking about is the difference between states defined as a coherent sum -vs- a decoherent sum :-? I wonder if the coupling of the modes to the cavity will "decohere" the system into a mixed state rather than a pure state (by "dissipating" off-diagonal elements) -- I think this might happen if the the modes are eigenmodes of the free theory but not the interacting theory.
Nov
2
comment Spontaneous symmetry breaking to subspace not giving massless bosons
BTW (general comment), you would get 2 massive bosons and one massless if the Higgs were in the adjoint (triplet) representation of $SU(2)$. It's easy to see that from similarity to $SO(3)$ -- any direction is left invariant under a particular axis of rotation. Since experiments show 2+1 massive bosons and 1 massless, we need an extra U(1), but to give mass to 3 bosons, the Higgs should be in the fundamantal (doublet) representation of $SU(2)$.
Nov
2
comment What is the meaning of a state in QFT?
BTW, we needn't necessarily talk of relativistic theories. QFT is perfectly applicable in non-relativistic contexts as well, eg: cond-mat.
Oct
31
comment Is it THE Higgs?
To add to Anna's answer, it seems like it's the Higgs of the Standard Model, but it's quite plausible that there will be other "similar" particles in some viable extensions of the Standard Model.