I am currently building a real time high performance parallel particle simulator with C++, OpenGL, and OpenMP. I was able to successfully parallelize the broad phase, narrow phase, and physics steps. Unfortunately I have a pretty significant bottleneck when building the pair list and adjacency list during the broad phase and narrow phase.

My algorithm is as follows.

1. Sort all particles by cell ID while maintaining Z order every 1/60 frames for spatial locality.
2. Partition the particles into their appropriate cell based on their aabb. A particle is inserted into every cell it's aabb intersects with.
3. Perform the broad phase step by processing each cell in the world in parallel. Each thread has a private spatial hash which is created and queried every timestep to compute the pairs which is stored in a private pair list. A pair consist of the 2 particle integer ids with minmax ordering (Lower particle id is first).
4. The private pair lists is merged in a critical section. A hash set is used to keep track to pairs to prevent duplicates from being added to the merged pair list. This is very expensive.
5. Perform the narrow phase step in parallel using the pairs generated from step 4. Each thread contains a private adjacency list to represent a undirected graph and a private inequality constraint list. Each new collision pair is inserted twice into the adjacency list and once into a inequality constraint list.
6. The private adjacency lists and constraint list is merged in a critical section. Just like step 4 this is expensive.
7. Perform graph coloring in parallel over the merged adjacency list and partition the particles based on color to prevent any dependencies between them.
8. Perform the physics step in parallel using the gauss seidel method and solve each inequality constraint for each particle in the partitions.

Is there anyway I can optimize step 4 and 6? I thought about removing the critical sections and instead using shared memory with atomics for pair list and hash set but I am worried about performance penalties from using atomics as well as false sharing. Maybe a parallel merge or hash join algorithm would be appropriate? Is there a faster way to generate the pair list without duplicate pairs?

Sort of like how Q = I +Y/2,do we have extended relations with colour from GUTs? Idk which GUT (I think SO(10)?) had a relation going something like Q=-1/6(r+b+w)......(Can't remember the rest of the terms lol.)

Anyone know how the current job market looks? Or have tips on getting a resume on someone's desk? I'm ABD on a HEP PhD with CMS and looking for a job. Got unexpectedly laid off in January from a ML Engineer position and the job search has been extremely slow.

Why can't BSM particles enter at tree level and why can they only exist in loops? Afterall, whether the W boson(say) enters at tree level decay or in loops, it is an off-shell W boson regardless!

For example Tree level : B --> J/psi Ks (Off shell W boson, two weak vertices ) Loop level: B --> Ks Ks (Gluconic penguin decay with an off-shell W boson, two weak vertices+ two strong vertices) ?

https://preview.redd.it/gci8l9vse9sc1.jpg?width=1080&format=pjpg&auto=webp&s=ddf1b0a174c5140dac6021a1ff917e11bd3af6c1

I have heard that if an electron collides with another atom in an accelerator, the electron jumps to another excitement level but soon it falls back and emits a photon. Please correct me if I'm wrong. I was just wondering, how do we know which excitement level did it hop on? I don't know much about it and I'm sorry if it's a stupid question for you.

Thanks in advance

I want to know if there is a formula for calculating the angle of deviation or deflection a charged particle experiences while exiting a magnetic field

Basically the question. I want to understand how exactly the GIM mechanism suppress FCNC at tree level but allows at loop level. I understand the Z to ffbar thing, were ∆S = 1 cancels out. But I am still a bit confused on this as why FCNC this happen?

Thank you!

And/or how can I get them?

In the book "The historical development of Quantum Theory", volume 3, chapter 5, page 202 of my edition, there's a quote from Bohr I really want to understand

For context, the idea of spin had been published just a few weeks ago by Samuel and George, Bohr read it but he was unconvinced, then he found Einstein at a party and they talked about it. Then as Bohr wrote in a letter to Ralph Kronig:

"...Einstein asked the very first moment I saw him what I believed about the spinning electron. Upon my question about the cause of the necessary mutual coupling between the spin axis and the orbital motion, he explained that this coupling was an immediate consequence of the theory of relativity. This remark acted as a complete relivation [sic, revelation] to me, and I have never since faltered in my conviction that we at last were at the end of our sorrows"

Bohr to Kronig, 26 March 1926

Here's the thing, I know that if you take Schrödinger's Equation, you apply relativity to it and then you "take the square root" you get Dirac equation and then you get spin for free. I've done that derivation many times, i saw it in class, I understand that part

The problem is that back then they didn't have Dirac's equation, they didn't even have Schrödinger's, so how did Einstein see this? What reasoning led him to conclude this? I am so supremely confused

Also, I'm not entirely sure what Bohr means by "mutual coupling between the spin axis and the orbital motion". Is he talking about about the relationship between the quantum numbers for the energy level and the angular momentum? Is he talking about the fact that each combination of angular momentum and energy level has to be unique, in other words, is he talking about the exclusion principle?

This conversation was important because Einstein convinced Bohr to take the idea of spin seriously, Bohr convinced Heisenberg, and Heisenberg convinced Pauli, who then finally found his famous matrices, so this conversation is like the first domino in the chain and that's why I want to understand it

I want to know how can I test the accuracy of the Lorentz force equation (F = qE + qVB sin(ø)) using a real life experiment with a charged particle

I was looking at the decay series for radium the other day, and it eventually decays to lead through three separate emissions of alpha particles. Helium nuclei are quite stable, but carbon is even more stable (given that helium can fuse into carbon and release energy by doing so). So what keeps radium from just expelling a carbon nucleus all in one shot?

My guess is the electrostatic repulsion and weak nuclear force in a radium nucleus is only strong enough to spit out helium, and the strong force prevents it from spitting out anything larger in a single shot, but I’m not sure. Can anyone either confirm or tell me what’s actually going on?

Sorry if this is a dumb question, I'm trying to be less dumb

Forces result from symmetries in the Lagrangian, right? Well, fermions have a kind of symmetry and this symmetry creates quantum pressure, which in many ways behaves like a force keeping fermions apart

Of course the strength of this force depends on temperature, so that near absolute zero we have things like Cooper Pairs and quantum pressure seemingly disappears, but this also sounds like a force

The fine structure constant has a value of ~1/137 only in our energy range, if you go up in temperature it gets larger and the electromagnetic force becomes stronger. This seems analogous to how quantum pressure also depends on temperature. The difference is that quantum pressure can reach an alpha of 0 while electromagnetism has a floor of ~1/137

Maybe what happens is that since this symmetry is extremely simple this force is also extremely simple and we can represent it in the lagrangian with a simple negative sign, but the way I see it, that doesn't mean it's not a force

Hi, would it be possible to control how carbon bonds to itself with electro-magnetic frequencies? So as to apply it to generating carbon nanotubes and then using that principle to fabricate components at a nano-scale?

Hi, i would like someone to help me with a plasma-gas interface and refraction of an electron due to it. ref article 1 and ref article 2, these are the articles which i am referring to, i also need help with some calculations and other stuff. if anyone wants to help us please drop a comment and ill dm you. thanks

Suppose that we put a non Newtonian fluid in a beam, Preferable proton ( since its a bit heavier than an electron ), what would we notice? I know that nothing would be visible but would the particles exhibit enough stress for the fluid to change its viscosity?

Im trying to build a cyclotron and i want to make it similer to the 4 inch cyclotron but it only has one dee. How is that suppose to work. I tried doing reaserch about it but there is no usefull answer . I think it will work in the same way as the two dee cyclotron just less velocity and efficiency is that correct ?

Question is a continuation of https://www.reddit.com/r/ParticlePhysics/s/AKWtWLBqB8

https://www.reddit.com/r/ParticlePhysics/s/VNDY20ZEbX

Also, if the Schrödinger equation doesn’t bother about electrical attraction, then why can’t there be an atom with a single neutron(not withstanding the stability of a single neutron) and electron?

Is there an atom with one neutron, on electron and no proton?

I was going through beta decay and I was looking in depth with it and suddenly a question poped up within me, that is, how did the electron get the charge? And later it evolved as, what is charge exactly!

In Schwartz it's stated, "We actually have three global continuous symmetries in the Standard Model: lepton number (leptons only), baryon number (quarks only) and charge. Thus, we can pick three phases, which conventionally are taken so that the proton, neutron and electron all have parity +1. Then, every other particle has parity +/-1."

Are the three global symmetries defined, such that we can recover the conserved current for the corresponding conserved quantities (lepton number, baryon number and electric charge) from Noether's theorem?

For the intrinsic parity, I'm not exactly sure how the fixing is done. If we consider an electron and a positron, and the parity operator with the global phases,

P' = P exp(iαB+iβL+iγQ)

Where B is the baryon number, L is the lepton number and Q is the electric charge sign. While the rest of the symbols are the gauge parameters.

For the electron we have B = 0, Q = -1 and L = 1, the phase factor would need γ = β for the phase factor to give +1. For the positron we have B = 0, Q = 1 and L = -1, the phase factor would need γ = β+π for the phase factor to give -1. Is that right?

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