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7 votes
Accepted

Time-evolution operator in QFT

Maggiore is assuming there that the field interacts with itself or with other fields in a stationary way. In other words, there is no direct appearance of time in the total Hamiltonian. This is a ...
Valter Moretti's user avatar
6 votes
Accepted

How to get a lower bound of the ground state energy?

It depends a lot on the specifics of the Hamiltonian and system being examined. One approach that works sometimes is to cast the computation as a semidefinite program and use the duality theory there ...
ors's user avatar
  • 549
1 vote

Relationship between unitaries generated by a Hamiltonian and its negative sign

Short answer: Your guess is correct, for general time-dependent Hamiltonians $U_1^\dagger(t)\neq U_2(t)$ and there is usually no relation between these two (we will give two simple counterexamples ...
Frederik vom Ende's user avatar

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