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18 Oct 2021: 5 Phase Transitions. 5 Phase Transitions. A phase transition is an abrupt, discontinuous change in the properties of a system. We’ve already seen one example of a phase transition in our discussion of Bose-Einstein condensation. In that case, we

18 Oct 2021: Figure 24:. Expressing the work as. -. d. W. =. -. p. d. V. also allows us to underline the meaning of the new symbol. -.

18 Oct 2021: 3 Quantum Gases. 3 Quantum Gases. In this section we will discuss situations where quantum effects are important. We’ll still restrict attention to gases — meaning a bunch of particles moving around and barely interacting — but one of the

18 Oct 2021: 2 Classical Gases. 2 Classical Gases. Our goal in this section is to use the techniques of statistical mechanics to describe the dynamics of the simplest system: a gas. This means a bunch of particles, flying around in a box. Although much of the

18 Oct 2021: ρ. =. e. -. β. H. Z. (1.24). If we make a measurement described by an operator. ... In the quantum context, it is sometimes written in terms of the density matrix (1.24) as.

16 Oct 2021: ζ. Δ. ϕ. ϕ. (. 𝐱. ). Figure 24: RG flows when.

16 Oct 2021: 1.24). Here, the notation. {. s. i. }. |. m. (. 𝐱. ). means that we sum over all configurations of spins such that the coarse graining yields. ... We will invoke one last notational flourish. We’re left in (1.24) with a sum over all possible

18 Oct 2021: and. -. 𝑑. x. x. e. -. a. x. 2. =. 0. (2.24). where the second equality follows because the integrand is odd (and suitably well behaved at infinity). ... σ. ). exp. (. -. x. 2. σ. |. α. |. 2. ). =. k. 0. where, to get the final equality, we did the

18 Oct 2021: v. r. (. p. ). Figure 23: An incoming anti-fermion. Figure 24: An outgoing anti-fermion. •.

18 Oct 2021: 24. d. 𝒪. (. a. 2. ). where, in the last line, we’ve used the fact that. ... π. 24. (. 1. d. 1. L. -. d. ). 𝒪. (. a. 2. ). (2.113). This is still infinite in the limit.