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## Hot answers tagged hamiltonian-formalism

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I) In this answer we will consider the standard Nambu-Goto string and show that the Hessian has co-rank 2. The target space metric has $(-,+,\ldots,+)$ sign convention, and $c=1=\hbar$. The Nambu-Goto Lagrangian density is $${\cal L}_{NG}~:=~-T_0\sqrt{{\cal L}_{(1)}},$$ $${\cal L}_{(1)}~:=~-\det\left(\partial_{\alpha} X\cdot \partial_{\beta} ... 3 The answer is Yes. Define function g(q):= \frac{1}{f(q)} for later convenience. Then the classical Hamiltonian reads$$2h~=~g(q)p^2.$$One may show that the Weyl-ordered Hamiltonian reads$$2H_W~=~ (g(q)p^2)_W ~=~ \frac{1}{4}P^2 g(Q)+\frac{1}{2} Pg(Q)P+\frac{1}{4} g(Q)P^2~=~ Pg(Q)P - \frac{1}{4}\hbar^2g^{\prime\prime}(Q),see e.g. Ref. 1 and this ... 3 I) In this alternative answer we resolve the singular Hessian H_{\mu\nu} of the Nambu-Goto string action by introducing two auxiliary variables from the onset, thereby indirectly showing that the Hessian H_{\mu\nu} must have co-rank 2. The target space metric has (-,+,\ldots,+) sign convention, and c=1=\hbar. Consider the extended Nambu-Goto ... 2 1) The spacelike hypersurface has three spacelike directions tangent to it. Any vector that is normal to all three spacelike directions in the eneveloping space is necessarily timelike. Equivalently, the spacelike surfaces can be thought to be labeled by a function \tau which gives the "time coordinate"'s value on those surfaces. the normal to the ... 1 This depends on whether the corresponding quadratures have physical meaning in your specific example. This is because if a=x+ip, then changing a\mapsto a'=e^{i\theta}a corresponds to the canonical transformation \begin{align} x\mapsto x'= \cos(\theta)\, x -\sin(\theta) \,p, \\ p\mapsto p'=\sin(\theta)\, x +\cos(\theta) \,p. \end{align} This could be ... 1 I'm not so sure, if this is really, what you're looking for, but you can of course solve this easy problem analytically. To do this, it is clever to first analyze the easier Hamiltonian H_0 = 2g (\vec L \cdot \vec S), where the L_i and S_j fulfill independent SU(2)-algebrae [L_i, L_j] = i \epsilon_{ijk} L_k\\ [S_i, S_j] = i \epsilon_{ijk} S_k. ...

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You are at a point where you'll need $v_1$ and $v_2$. Observe from the original transformation that: $$v_2 = v_1 - v$$ $$\implies V = \frac{(m_1+m_2)v_1 -m_2v}{m_1+m_2}$$ $$v_1 = V + \frac{m_2v}{m_1+m_2}$$ We also get, by a similar procedure, $$v_2 = V - \frac{m_1v}{m_1+m_2}$$ We have expressed $v_1$ and $v_2$ in terms of the new variables, $V$ and $v$. ...

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The first thing we can do is to split up $\Gamma$ according to the number of particles in the given states. Let $\gamma_N$ be a state with $N$ particles. The grand canonical partition function is then \begin{align} \mathcal{Z} = & \sum_\Gamma \exp\left(-\beta(\mathcal{H} - \mu N)\right)\\ =& \sum_{N=0}^\infty\exp\left(\beta \mu N ...

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Normally we do NOT calculate the phase space density of a system. In the phase space formulation of classical statistical mechanics, the phase space density $\rho(p,q;t)$ has its specified form for different ensembles. Normally for systems at equilibrium the density $\rho$ has no explicit time dependence and thus we work with $\rho(p,q)$. (1) For ...

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Some of the mathematical aspects of the Liouville operator can be found in the second book by Reed and Simon, in section X.14 (it is not a comprehensive account, but it gives the basic ideas and proofs). In the notes at the end of chapter X, in the part dedicated to section X.14, there is also a quite extensive bibliography that may be useful.

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Here is an outline of the reduction from the Nambu-Goto (NG) action to the light-cone (LC) formulation from a Hamiltonian perspective: The starting point is the Hamiltonian formulation of the Nambu-Goto string, cf. e.g. this Phys.SE post. The Hamiltonian density is of the form "Lagrange multipliers times constraints" $${\cal H}~=~\lambda^{\alpha} ... 1 You should think of the definite integral operation as a function of two arguments: a region over which to integrate (here, [x_0,x_1]), and another function f called the integrand (here, f:\xi \mapsto (E-V(\xi))^{-\frac{1}{2}}). So first of all, in my definition of f above, we could have used (almost) any other symbol instead of \xi and the ... 1 You're actually dealing with the Potts model, which is a slight generalization of Ising. Not that it really matters, as you won't need any results from Potts. The point of mean field theory is typically to make each site independent of their neighbors, which allows you to evaluate the partition function by only iterating through the possible states of one ... 1 For simplicity consider the 1-d case, with \psi =\sqrt{n} e^{2i\phi}, then$$i \psi_t =\frac{i}{2} \frac{\dot{n}}{\sqrt{n}} e^{2i\phi} -\sqrt{n} e^{2i\phi} 2\dot{\phi}.$$Similarly$$ \frac{\partial H}{\partial \psi^*} = \frac{\partial H}{\partial n}\frac{\partial n}{\partial \psi^*} + \frac{\partial H}{\partial \phi}\frac{\partial \phi}{\partial ...

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