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Feb
14
comment Yang-Mills instanton
@RubenVerresen: I think you might be right. Do you have a physical explanation for why the relevant objects are homotopies instead of homologies, when talking about instantons on various manifolds?
Feb
3
comment What physics does the Super Proton Proton Collider intend to explore in the $\lesssim 100\:\mathrm{TeV}$ range?
It must be noted that the scent of a 100TeV collider will induce theorists to come up with hundreds of new, testable models ;-) <cough> 750 GeV <cough>
Feb
3
comment What physics does the Super Proton Proton Collider intend to explore in the $\lesssim 100\:\mathrm{TeV}$ range?
The point of the above comment was to induce comments from you, on the matter :-)
Feb
3
comment What physics does the Super Proton Proton Collider intend to explore in the $\lesssim 100\:\mathrm{TeV}$ range?
I find a circular electron-positron collider surprising, especially given that a collaboration led by the Japanese is exploring a possible Higgs-factory at the International Linear Collider. Electrons lose energy due to bremsstrahlung quite quickly in a circular collider, but I guess it should be feasible if the energies considered are not far from the LEP, and with a significantly higher tunnel radius.
Jan
31
comment Is what statisticians call a “random variable” what physicists call an “observable” in QM?
I think your statement applies only for the energy operator since it is the generator of time evolution. Eg: Suppose you measure the X-directional spin of a system and "collapse" it into the spin-X-up eigenstate, then further time evolution could change the spin of the particle if, for example it was subjected to a magnetic field in the Z-direction. A second measurement could then give spin-X-up or spin-X-down with some respective probabilities. In essence, if a random variable evolves in time classically, then it does the same quantum mechanically.
Oct
27
comment Bose-Einstein condensation and phase transition
@Thomas: Do you have a particular system in mind? Naively, I would consider all kinds of transitions where a scalar order parameter picks up an expectation value (in the zero momentum mode) as an example of Bose-Einstein condensation. Therefore, I can think of it happening at first-order or second-order.
Oct
27
comment How is the efficiency of a heat engine related to the entropy produced during the process?
If you fallow march's answer, in a complete cycle there is no entropy created due to heat exchange. When the temperature of the cold reservoir is very low, the negative entropy change to cancel out the positive entropy change only needs a small amount of heat to be dumped into the cold reservoir.
Oct
27
comment Gauge theory for mathematicians?
Check out "Gauge fields, knots and gravity" by Baez and Munian. I think it strikes a nice balance between mathematical formalism and physical intuition.
Sep
10
comment Calculating $\mathrm{Tr}[\log \Delta_F]$
Suppose we're restricted to a circle, in one dimension. In what sense would translational invariance be broken? After translating by $2 \pi R$ we would be back to our starting point, but translations would still be a symmetry. (In fact, translations which are integer multiples of $2 \pi R$ might well be considered a gauge redundancy!)
Sep
10
comment Calculating $\mathrm{Tr}[\log \Delta_F]$
No, a UV cutoff would break translational invariance down to a discrete subgroup. An IR cutoff leads to quantized momenta, and does not lead to a broken translational symmetry.
Sep
8
comment Calculating $\mathrm{Tr}[\log \Delta_F]$
@TwoBs: I think the situation only breaks $SO(4)$. All 4 translations are still symmetries (eg: theory on a cylinder, a la finite temperature). It's not quite a Casimir force calculation; it does compute the free energy.
Jun
28
comment Doubts with basic renormalization
Try one of the more recent books (there's been a surge of QFT textbooks in the last few years) -- one of them might have a more modern viewpoint. Alternatively, here are some of the EFT reviews; pick one you like: inspirehep.net/search?ln=en&p=65027a%3AI-c-11
Jun
28
comment Doubts with basic renormalization
It's just something I came up with to phrase my understanding, once things finally clicked. I also love it, because it allows me to capture the sentiment :-)
Jun
26
comment What happens to theoretical physics if a photon has non-zero mass?
The photon can acquire an effective mass due to a few different mechanisms, which respectively cause the following effects: 1. en.wikipedia.org/wiki/Meissner_effect 2. en.wikipedia.org/wiki/Debye_length
Jun
25
comment Doubts with basic renormalization
Just out of curiosity: Which QFT texts are you talking about?
Jun
25
comment Ice bath is always 3C, why?
+1! I think this is very important to bear in mind because we seem to be in a rush to prefer "digital" devices which have an apparent precision to many decimal points, but the accuracy could be quite bad, like you point out. I have seen many (school/college) students fall for this precision fetish.
May
21
comment What is meant by the phrase “this operator does not renormalize this other operator”, and how can understand it using diagrammatic arguments?
BTW, this recent paper might be of interest: arxiv.org/abs/1505.01844
May
16
comment Can bosons have anti-particles?
Taylor's point seems to be centered on the following idea "Bosons operate under different laws and can be created singly. This is a crucial distinction and is in nature of being either matter particles or force carriers." (which I simply don't understand)
May
16
comment Can bosons have anti-particles?
By definition charge conjugation $C$ is that operator which swaps particles and anti-particles. And I have to agree with @innisfree.
May
16
comment Can bosons have anti-particles?
Would you call the Higgs (doublet; not just the radial mode) an elementary scalar that is electrically carged?