[hep-th] A Simple Introduction to Particle Physics

 By: Unknown    10:24 AM  arxiv, gauge theory, group theory, hep-th, high energy physics, particle physics, physics, standard model   No comments

A Simple Introduction to Particle Physics

This is a wonderfully written paper introducing the topic of particle physics to undergraduates. It approaches the subject leisurely in Part 1 by reviewing some important classical physics concepts. These include Noether's theorem, gauge transformations, and the Classical Electrodynamics Lagrangian $$ \mathcal{L_{EM}} = -\frac{1}{4} F_{\mu \nu}F^{\mu \nu} - J^{\mu}A_{\mu} $$

Following this, Part 2 introduces the algebraic concepts needed to be successful and harness a true understanding of particle physics. Using these foundations, the generators and Lie algebras for any group may be discovered. This portion of the paper is somewhat mathematically rigorous due to the generality of the discussion.

The fun really begins in Part 3 of the paper where Quantum Field Theory is finally introduced. The author starts with the typical derivation of the Klein-Gordon equation for spin-0 fields through the relativistic Hamiltonian. Moving forward Robinson et al. discuss spinors and why the irreducible representation of the Lorentz group turns out to be $ SU(2) \otimes SU(2) $. After discussing the Dirac sea of antiparticles and the correct QFT interpretation of antiparticles, we move on to discuss the Dirac Lagrangian for a particle in an electromagnetic field and the coupling of the particle's field (e.g. electron) with the gauge field (photon).

Once you reach the section on quantization the paper starts to pick up and get pretty difficult for a reader encountering particle physics for the first time. I suggest only skimming this section or looking up other resources if you have not had experience with this before.

Finally, some investigation of the Standard Model is done. The authors look at spontaneous symmetry breaking, the Higgs sector, and the quark sector. You will need to understand what was going on in the quantization section to keep up with their tempo here.

This is a fantastic paper that will introduce advanced undergraduates to the beauty and rigor of particle physics without assuming too much early on. The paper becomes difficult in the later portions of Part 3 so is pretty approachable. I hope you all enjoy this paper!

P.S. for those of you who highly enjoyed the paper, there is a second paper that goes much deeper into the geometrical approach to gauge theories. 

Numerical Relativity: Black Holes and Gravity - Part 1

 By: Unknown    8:35 PM  gravitational physics, gravity, newton, physics   No comments

Before getting into the gr-qc publications, I would like to give you some information on this field of study. I recommend knowledge of special relativity, but it is not required. These posts will begin at a low level and become a bit more difficult as we go on. If you are already well acquainted with the concepts and the jargon, you are welcomed to skip them and start at the first gr-qc post.

What is Gravity and How Do We Think about It?

Gravity is one of the four fundamental forces. In fact, it is the weakest one! However, an advantage of gravity is that it is a long-range force, which is useful to us when trying to measure interactions. Gravity is the force behind the big bang, black holes, and stars. Gravitational physics is of extreme importance is both large and small scales - from cosmology to quantum physics.

A look into Newtonian gravity will give you the following equation:

$$  F_{grav} =  \frac{Gm_1m_2}{r_{1,2}^2} $$

which says that the force between two bodies is related to their mass and distance. However, the problem with Newton's view is that the force is instantaneous. This is not allowed, as shown in special relativity where nothing can travel faster than the speed of light. Therefore, we say that Newtonian gravity is an approximation only. 

We first think of gravity as an accelerating force. For example, in classical physics we are introduced to objects falling from a certain height of being thrown upward at a certain angle. However, when we are exposed to more advanced topics, we begin thinking of gravity as a field with stored energy. However, we can all agree that gravity is geometry. We first study gravity using Euclidean geometry and then go on to learn about non-Euclidean geometry, such as that of the surface of a two dimensional sphere of a radius R. We could go on to talk about different coordinates and invariance, but what we have talked about suffices for now. 

[q-bio.BM] An Introduction to Biomolecular Simulations and Docking -- Mura and McAnany

 By: Unknown    10:15 AM  arxiv, biophysics, computational, molecular dynamics, physics, simulation   No comments

http://arxiv.org/abs/1407.3752
http://arxiv.org/ftp/arxiv/papers/1407/1407.3752.pdf

Any arguments with opinions in this post are welcome. I write this as (hopefully) a guide for those interested in the topic but do not want to go head first into the paper. This paper is a wonderful explanation of molecular dynamics as a tool in computational biophysics, and I highly recommend reading it if you are interested in the field. This is the best paper I've read so far that covers the computational biophysicist's toolset as a whole.