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bio website motls.blogspot.com
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Hi, I am a string theorist and a publicist.


8h
awarded  Nice Answer
11h
answered How do you add temperatures?
11h
answered Do massive particles exchange Higgs bosons?
16h
comment Is the Standard Model consistent (UV complete)?
Dear CuriousOne, the neutrino masses were once considered not to be a part of the "Standard Model" but the theory with these extra terms added - and we need to add them, as experiments show - is consistent up to the very high (GUT etc.) scales, too. The experimentally demonstrated ninimal ones are the Majorana masses for the left-handed neutrinos. They may arise as effective terms from the see-saw mechanism from a completely consistent, gauge-invariant grand unified or similar theory at the GUT scale. There are arguments that this GUT-scale physics has to exist for the neutrino masses
16h
comment Is the Standard Model consistent (UV complete)?
No, Prof Wen, the Standard Model has no inconsistencies at scales 200 GeV or at least a few orders of magnitude above it. All the would-be inconsistencies are cured by having added the right massive gauge bosons with the right coupling to the Higgs boson, and so on. This theory with the electroweak scale as its characteristic scale also has nonperturbative effects like instantons but they are effects, not inconstencies.
1d
awarded  Enlightened
1d
awarded  Nice Answer
2d
comment Spontaneous symmetry breaking and time-reversal symmetry
Dear CMFT, it's unphysical to be looking for eigenstates of the symmetry generator that is spontaneously broken because they're superpositions of states from different superselection sectors. An example is a superposition of a bar magnet magnetized in one direction with the state of the bar magnet magnetized in a different direction. A typical Schrodinger's cat state. But yes, if you don't mind that this is a superposition across superselection sectors, you may find eigenstates of the generators. What's your problem with that?
2d
comment Is the Standard Model consistent (UV complete)?
And yes, at low enough energies below the instability scale, and perhaps even above it, the Standard Model is consistent even nonperturbatively. I am sure that I have already answered that question. You may put the Standard Model on a lattice, for example (ignoring technical issues with fermion doublings etc. which are basically solvable). And yes, the perturbative consistency with a perturbative analysis of the RG flows etc. is enough to prove the nonperturbative consistency, too. The perturbative expansions know about "almost everything".
2d
comment Is the Standard Model consistent (UV complete)?
Dear akrasia, the quartic Higgs coupling doesn't diverge assuming the (now) known value of the Higgs mass, below 200 GeV. So there are two inconsistencies, but they're the Landau pole and the Higgs instability. The latter is something else than a divergent quartic coupling - to some extent, it's the opposite problem because it occurs because the measured mass of the Higgs boson is too low for the Standard Model. ... I personally consider metastability of this kind to be an inconsistency.
2d
answered Is the Standard Model consistent (UV complete)?
2d
comment an example where changing the frame of reference of an observer changes the outcome of events!
This extra magnetic field $B$ will indeed contribute a positive attraction you may calculate - it will reduce the original repulsive force even further. If you combine all these things, you will see that the charges are accelerating as expected from a transformation of the trajectories.
2d
comment an example where changing the frame of reference of an observer changes the outcome of events!
There is first of all an electrostatic repulsive force between the two like-sign charges, $$ F = \frac{Q_1 Q_2}{4\pi \epsilon_0 r^2} $$ That's it in the frame where the charges are at rest. In a frame that is moving by speed $v$ perpendicular to the charges' separation, both charges look $\gamma$ times heavier because they're moving. The same electrostatic force will therefore cause a lower acceleration, which is OK - it may be interpreted as time dilation. There will also be a magnetic field $v\times E/c^2$ in that moving frame.
Aug
24
revised Spontaneous symmetry breaking and time-reversal symmetry
added 739 characters in body
Aug
24
answered Spontaneous symmetry breaking and time-reversal symmetry
Aug
24
comment Why don't atoms emit gravitational waves?
Thanks - only on Physics Stack Exchange, I guess. There are some higher scores at maths and elsewhere.
Aug
23
comment Possible Error in deriving conformal generator
There are several issues, I've mentioned some of them, and one must be careful about the conventions and strategy used by someone else. If you have a problem with someone's derivation, try to check the "big claims" only and derive it yourself - all the hard ideas of the derivation may clearly be seen even in the derivation following slightly different strategy, conventions, and active vs passive distinction. I feel that if you can't derive it yourself even while looking at the "template derivation", it's useless to follow someone else's derivation, anyway.
Aug
23
answered Why don't atoms emit gravitational waves?
Aug
21
comment Possible Error in deriving conformal generator
Also, the most general transformation always fixes some point, so it may be obtained from a transformation fixing the origin, by conjugating it with a translation by $Y$ which is the point that is fixed.
Aug
21
comment Possible Error in deriving conformal generator
Hi, thanks. I wasn't quite able to figure out what the first question is. The full transformation is composed of two things: finding the right $x'$ for a given $x$, and evaluating the components at the new point (that's the orbital part); and mixing the components with each other (that's the spin part). The full generator may be divided in this way. If we specialize to transformations that do not change $x$, the orbital part is trivial so it may be subtracted or added without spoiling the formula.