Nuclear and Particle Physics

I understand that in the early universe there was a time when particles did not have mass yet. I'm wonder in what cosmological era did particles get their mass. Was this in the electroweak era < 10-32 seconds or afterwards? And is it true that then afterwards the higgs field acquired a vacuum expectation value so that particle fields could couple to the higgs field and gain mass?

My suspicion is that there may have been a time that the higgs field was so energetic and fluctuating so wildly that particle fields could not couple to it. How can there be a coupling "constant" between fields that are fluctuating to rapidly? This perspective allows me to understand that it may have been the heavier particles that coupled to the higgs field first (because their frequencies were higher than the higgs fluctuations and so would appear more stable wrt these higher mass, higher frequency particles). And then after the higgs field cooled down and fluctuation were not so energetic, the lower mass particles could couple to the higgs field and gain mass too. This would seem to be consistent with the strong force freezing out of the unified field first because it has higher mass particles with higher frequency (compared to the higgs fluctuations). And then the electromagnetic and weak forces froze out latter because they have lower mass particles. Is this the right picture of things?

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Stam Nicolis: You can tell them apart by the fact that you have to impose that the state of many identical fermions is antisymmetric when you permute them, while that of many identical bosons is symmetric. This then has consequences for the quantum corrections their mass can receive. Fermions have a symmetry, known as chiral symmetry, that implies that corrections to their mass, due to interactions with other particles, are proportional to the logarithm of the energy scale one is looking at; the same holds for gauge bosons, due to a symmetry called gauge invariance-here, absent their interactions with the Higgs, they would be massless, as would the fermions, such as the charged leptons, that require the interaction with the Higgs to acquire their mass, in the first place. However the mass of the Higgs itself and its vev, also are subject to corrections, due to the interactions of the Higgs with the other particles-and there's no symmetry that protects the corrections from leading to a mass or vev that would be arbitrarily
large much faster, as the square of the energy scale one is looking at, and this would lead to observable consequences. One way to describe the fact that such a sensitivity isn't observed, is to imagine the existence of, hitherto, unknown particles, whose contributions to the corrections to the mass and vev of the Higgs, partially, cancel the corrections from the known particles. If one then tries to organize this calculation, one finds that the new particles are related to the known particles by the fact that they have spin that differs by 1/2, so the new particles behave as fermions, if the known particles were bosons and vice versa. This is called supersymmetry, that would imply that the ``partners'', though of different spin, would have the same mass-there would be a particle of spin 0, but of charge and mass equal to that of the electron, for instance, whose contribution to the corrections to the mass and vev of the Higgs would cancel that of the electron; and so on. Since such a particle doesn't exist with such properties, its mass must be different, supersymmetry must be broken. How isn't known and must be parametrized. And that's what's being done.

In addition, while we're on the subject, it's interesting to remark that all, hitherto known, particles that describe matter, the quarks and leptons, are fermions, while all particles that describe forces, the photon, the W and Z bosons and the gluons (and the graviton, too) are bosons. The Higgs, in fact, is the first particle that describes bosonic matter.So it's natural to imagine a situation, where matter is described by bosons and forces are described by fermions, which is another way one is led to introduce supersymmetry.

Stam Nicolis: +Malik Matwi Some of the statements are incorrect: the mass and spin of particles are Poincaré invariants, for instance. In quantum field theory the number of particles isn't fixed-it's known that it isn't possible to describe the dynamics of a fixed number of particles, in a relativistically invariant way, unless the particles, in fact, don't interact. So one should be careful. It is known how to describe quantum fields in general, and quarks in particular, at finite temperature. Look here: http://web.mit.edu/redingtn/www/netadv/XthermalFT.html

Stam Nicolis: +Malik Matwi But not for the reasons stated. This is standard material of a quantum field theory course, so it's useful to go beyond the background knowledge, as presented, for instance, in the links provided.

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Andrey Feldman

Nuclear and Particle Physics Quantum Field Theory

Aug 30, 2015

"Fields" by Warren Siegel

Siegel (http://inspirehep.net/author/profile/W.D.Siegel.1?ln=ru) published a preliminary version of 4th edition of his online book on Classical and Quantum Field Theory and basics in String Theory. New edition already contains more than 970 pages (3rd edition had 885 pp.). Siegel added sections on AdS/CFT correspondence, vertex operators in String Theory, coset models and many others.

Highly Recommended!

FIELDS

Where to get v3 (but see below for preliminary v4). arXiv.org: usual formats -- pdf, ps, tex + eps figures, etc. archive here: tex + eps figures + pdf figures, suitable for pdftex (or TeXShop); pdf here: produced by pdftex (may be slightly better than arXiv.org version) ...

insti.physics.sunysb.edu

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Andrey Feldman

Nuclear and Particle Physics Quantum Field Theory

Jun 18, 2015

An intriguing paper by ATLAS collaboration on unknown resonance of approximately 2 TeV mass. The results were obtained during the first LHC run. It seems that we have to wait till the second run is finished in order to get more accurate results.

arxiv.org/pdf/1506.00962v2.pdf

arxiv.org

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Dyslexic Artist Theory on the Physics of 'Time'

Nuclear and Particle Physics Quantum Field Theory

Jul 7, 2014

Is it possible to have an objective understanding to the subatomic world of Quarks, Protons and Neutrons that fits in with the reality of our everyday life? The subatomic world of Quarks, Protons and Neutrons is very different to our everyday life with the flow of time with a future and a past! The link between the two seems to be the light photon oscillation or vibration. Light Photons are responsible for all electron and proton interactions everything we do in our everyday life from moving a mouse to control our computer to dancing upon a dance floor relies on the exchange of photon energy! This energy is shifting and changing electric and magnetic fields! This also represents the flow of positive and negative charge that had it origin with the positive Protons and negative electrons. Therefore we can see a link between the subatomic world and the fundamental nature of reality of everyday life!
Quarks, Proton, Electron and Photon Interaction. Fundamental Nature of Reality

Stam Nicolis: The force that binds quarks into protons and neutrons is not the electromagnetic force, but the strong force. It isn't mediated by photons, but by gluons.

We do understand all these issues quantitatively and in detail. (The electric and magnetic fields, whose sources are electric charges and currents, are responsible for the energy exchanges in this context.)
This doesn't have anything to do with any ``physics of time'', which doesn't mean anything.
A much better presentation is given by Feynman in
Feynman: FUN TO IMAGINE 4: F*****' magnets, how do they work?

Cassandra .X: I know... it's so interesting... what I don't understand is, how gluons can be that strong to keep matter and anti-matter in a quark, away from each other. Can somebody explain this to me?

Stam Nicolis: It's not easy to explain. If one focuses only on the quarks that describe the particular properties of, say, a proton, then one sees that we're talking about three quarks: two ``up'' quarks and one ``down'' quark. So the issue of keeping matter from antimatter doesn't arise here, or for the neutron
(two ``down'' quarks and one ``up'' quark; there are some subtle issues that have been left out here, because the structure is much more complicated, but we can set them aside here.). The question does arise for mesons, that can be bound states of a quark and the same anti-quark. The answer then is that it is possible to make a bound state of them-even though the strong interaction, at that scale, is, in fact, quite weak- thanks to the fact that the two quarks carry angular momentum and, thus, can be kept apart by a centrifugal barrier-for some time. In fact the same issue arises in electrodynamics, where an electron and a positron can form a bound state, that decays into two, or three, photons.

Edmund Kwa

Nuclear and Particle Physics Quantum Field Theory

Feb 23, 2013

What does the spin of a particle tell us ? And what does it means ?

Lorong Seri Setali 69, Perkampungan Seri Setali, Kuantan, Pahang

Luke Burns: Check out: http://www.markusehrenfried.de/science/physics/hermes/whatisspin.html

Alexander Anderson-Natale: The spin of a particle tells us how it behaves under interchange.... Yes, that is true, but what does that mean for physical systems? Things with integer values of spin (0,1,2, etc.) can be in the same place at the same time in the same quantum state. These are called bosons, and a consequence of this is that at low temperatures bosons form condensates where they clump together around the ground state and create Bose-Einstein condensates. Things with half-integer spin (1/2,3/2,5/2,etc.) are called fermions and are a reason why you would still have electrical current even at zero temperature; electrons are fermions and even if they are at zero temperature they cannot be in the same quantum state and so they will always have some distribution of momentum in a metal (see: fermi surface).

There is a lot we could talk about spin, but it also can tell us how a particle decays. Spin is conserved, and so if a particle decays the spin of the products can give limits on the spin of the original object (with restrictions). For instance a spin 0 object can decay into two spin 1/2 objects, but so can a spin 1 object. How do we tell the difference? Well, the decay products will be distributed differently in the detector (eg they will have a different angular distribution) due to the different spins of the mother particles (the particle that decayed).

As a very theoretical side note, spin also has a deep connection to relativity.

Mithrahee Zor-El: +Alexander Anderson-Natale
right!, that sounds to be an well interpretative for more... "What does it means?", "for meaning?" to "tell" approach to some numbers(?) - hihi.

Edmund Kwa

Nuclear and Particle Physics Quantum Field Theory

Jan 11, 2013

Izit quark the smallest particle in universe ?

Lorong Seri Setali 69, Perkampungan Seri Setali, Kuantan, Pahang

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Cliff Harvey: +Edmund Kwa There are two different kinds of waves that you should be careful to distinguish. Electromagnetic waves are not like quantum waves.

Electromagnetism has to do with the electromagnetic field. Every elementary particle is associated with a field, and the particle is a single quantum-mechanical unit of its vibration. So it is a quantum effect that creates the particles, however, the electromagnetic field is mostly known as a classical system, including most electromagnetic waves. Waves in a field are just like any other waves you are familiar with, just dont confuse them with quantum wavefunctions.

A quantum wavefunction is a more difficult and radical concept. It would be unreasonable for me to try to explain it here. It is a wave in the "space of possible states" of a physical system.

To try to answer your question, a quantum particle doesn't have a "wave form" and a "particle form". Roughly speaking, a particle will be more wave-like when it is physically extended, and more particle like when it is more condensed. If its position is measured, all of the wavefunction will collapse to a single point. If its momentum is measured, it will collapse a long plane-wave.

Edmund Kwa: +Cliff Harvey is this related to Heisenberg uncertainty principle ?

Josh Cogan: Hey +Cliff Harvey and +Edmund Kwa ,

Not sure if this thread is dead, but I thought I'd contribute. First off, electromagnetic waves are absolutely quantum waves. The better question is why could we explain light so well with only classical wave theory. If photons interacted very strongly with each other (ie they bounced off of each other with some non-miniscule probability) then classical theory wouldn't have sufficed. Also since you can stick many photons in an identical state, you dont' notice the quantized nature of the photon. (Contrast this with electrons who can only have 1 per state).

The Heisenberg uncertainty principle isn't really as magical as the Internetz would have you believe. Once you believe all particles (even electrons) are mathematically described by a wave equation, then the "uncertainty principle" is a really anti-climactic mathematical consequence of Fourier theory. It has physical consequences but not is not caused by a deep physical axiom.

If you do wanna really get confused by quantum information being non-intuitive, read the Stern Gerlach experiment which has nothing to do with (classical) waves, and everything to do with quantum wierdeness. I think Townsend's QM book gives an excellent 10 pages devoted to it!

Good luck!

Josh

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