Bilal Hawashin

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Spontaneous symmetry breaking can persist at all temperatures in certain biconical O(N) x Z_2 vector models when the underlying field theories are ultraviolet complete. So far, the existence of such theories has been established in fractional dimensions for local but non-unitary models or in 2+1 dimensions but for non-local models. Here, we study local models at zero and finite temperature directly in 2+1 dimensions employing functional methods. At zero temperature, we establish that our approach describes the quantum critical behavior with good accuracy for all N ≥ 2. We then exhibit the mechanism of discrete symmetry breaking from O(N) x Z_2 -> O(N) for increasing temperature near the biconical critical point when N is finite but large. We calculate the corresponding finite-temperature phase diagram and further show that the Coleman-Hohenberg-Mermin-Wagner theorem is fully respected within this approach, i.e., symmetry breaking only occurs in the Z_2 sector. Finally, we determine the critical N above which this phenomenon can be observed to be N_c ≈ 15, and give an outlook for candidate theories showing similar behavior.

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Ruhr-University Bochum
0.03
Contact: Simon Trebst