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I'm a physics grad student just trying to figure out all this stuff like everyone else.


Apr
7
comment What forbids the existence of a $\lambda (A^\mu A_\mu)^2$ term in the Stueckelberg action?
Note: the renormalizability is only restored in the abelian case with this trick. In the non-abelian case you have a nonlinear sigma model, which has a higher cut off, but its still non-renormalizable.
Apr
6
comment Minimal vs. Non-minimal coupling
I think its best to not get to caught up in this question in the specific context of GR. That is, look at the question in the more general context of gauge theories and effective field theory. For a discussion, see the reference: arxiv.org/abs/1305.0017
Apr
3
comment Anomalous Dimensions of Gauge Interactions
Where do they say this?
Mar
24
comment What does BICEP2's results tell us about gravitation waves and quantum gravity?
Thanks for the links.
Mar
19
comment What does BICEP2's results tell us about gravitation waves and quantum gravity?
@sunspots - thanks for the link. I read all the blogs already, but I am looking for a something more technical than Strassler's explanation.
Mar
11
comment Which types of particles are affected by the wave-particle duality?
The largest thing I have heard of is buckyballs: univie.ac.at/qfp/research/matterwave/c60
Mar
10
comment Why quantising gravity necessarily give us gravitons?
To make the graviton a fermion would be more than a 'tweak'.
Mar
8
comment Prerequsites for Zee's QFT
It sounds like you are looking for a more thorough treatment. I would suggest reading Srednicki: web.physics.ucsb.edu/~mark/ms-qft-DRAFT.pdf with Zee as a complement.
Feb
27
comment How to study physics as a first year student?
Lastly, you will simply not have time to do even half the problems in the back of each chapter. So again just put some faith in the the instructor as its his/her job to help you navigate through all this. Definitely do all the problems assigned and ask you professor if there are extra problems they might recommend. This way you can maximize the number of problems you are doing while keeping on pace with the class.
Feb
27
comment How to study physics as a first year student?
It is your professors job to help you navigate through the textbook, so don't get to caught up in trying to do this by yourself. Moreover, Halliday is a pretty big textbook that is typically not covered in its entirety in even 3 semesters at most US schools.
Feb
17
comment Can dimensional regularization solve the fine-tuning problem?
@innisfree - so did you mean that Martin's Primer answered your question from 2 lines above? If so where exactly does he say it? If he makes a clearer argument I would like to read it.
Feb
17
comment Can dimensional regularization solve the fine-tuning problem?
@innisfree - one thing that I forgot from my prior comment, there actually is a physical scale to fine tune against in $\phi^4$ theory. There is the Landau pole at $m \ e^{ 16 \pi^2 / (3 g )}$ where m is the mass of the particle and g is the quartic interaction at the measurable energy scale. So here is where my prior argument picks up - we expect new particles or some other new physics at this scale to tune against and so forth....
Feb
17
comment Can dimensional regularization solve the fine-tuning problem?
Honestly if you find a way to interpret $\frac{1}{\epsilon}$ divergences physically purely based on dim reg let me know. Any arguments I have seen are ultimately grounded in the intuition one gets from more 'physical' regulators like a hard cutoff or Pauli- Villars.
Feb
17
comment Can dimensional regularization solve the fine-tuning problem?
That is, assuming one could actually calculate such non-perturbative corrections.
Feb
17
comment Can dimensional regularization solve the fine-tuning problem?
For example: take the toy $\phi^4$ model you describe above - I would say this model is not fine tuned. However, this is only a toy model. A real particle of interest is the Higgs and this is only a $\phi^4$ model in the low energy limit. It is extremely likely there is new physics that talks to the Higgs that will result in a fine tuning of its mass. At the very least there is gravity and would expect new particles of the planck mass.
Feb
17
comment Can dimensional regularization solve the fine-tuning problem?
@innisfree I get what you are saying that $\Lambda$ does not have to correspond to a massive particle and I agree. I would go even further and say the following: Say you have a model with a light scalar field. And say there are no new massive particles that are being ignored and no new physics of scale M that creates perturbative OR non-perturbative corrections to your light scalar. Then I would say your model is absolutely not fine tuned.
Feb
15
comment Wald General Relativity, Chap 7.1
I think you might need to flesh this out for those of us without Wald sitting in front of us...
Feb
15
comment Can dimensional regularization solve the fine-tuning problem?
@JeffDror - what I mean is that even dim reg won't hide tuning against a physical scale like that of a massive particle, and that is the fine tuning that matters. That is, start with a model that has some heavy particles coupled to some light scalar fields and integrate out the heavy fermions - then you will see the fine tuning in any regularization procedure, dim reg or otherwise.
Feb
15
comment Can dimensional regularization solve the fine-tuning problem?
@innisfree : It is like JeffDror said above - $\Lambda$, the cutoff, is the energy scale at which our model fails and new physics comes in. The energy scale at which our model fails is that one at which there are new particles of mass $\Lambda$ that we were otherwise ignoring.
Feb
14
comment Can dimensional regularization solve the fine-tuning problem?
I really disagree with this answer but I am not going downvote because I find it a bit antagonistic in this situation. I posted my answer below, please feel free to comment and we can discuss.