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This paper studies the critical behavior of the 3d classicalO (N) ( N ) model with a boundary. Recently, one of us established that upontreating N N as a continuous variable, there exists a critical value N_c > 2 N c > 2 such that for 2 \leq N < N_c 2 ≤ N < N c the model exhibits a new extraordinary-log boundary universality class,if the symmetry preserving interactions on the boundary are enhanced. N_c N c is determined by a ratio of universal amplitudes in the normaluniversality class, where instead a symmetry breaking field is appliedon the boundary. We study the normal universality class using thenumerical conformal bootstrap. We find truncated solutions to thecrossing equation that indicate N_c \approx 5 N c ≈ 5 .Additionally, we use semi-definite programming to place rigorous boundson the boundary CFT data of interest to conclude that N_c > 3 N c > 3 ,under a certain positivity assumption which we check in variousperturbative limits.
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Boundary criticality of the O(N) model in d = 3 critically revisited
It is known that the classical O(N) O ( N ) model in dimension d > 3 d gt; 3 at its bulk critical point admits three boundary universality classes:the ordinary, the extra-ordinary and the special. For the ordinarytransition the bulk and the boundary order simultaneously; theextra-ordinary fixed point corresponds to the bulk transition occurringin the presence of an ordered boundary, while the special fixed pointcorresponds to a boundary phase transition between the ordinary and theextra-ordinary classes. While the ordinary fixed point survives in d = 3 d = 3 ,it is less clear what happens to the extra-ordinary and special fixedpoints when d = 3 d = 3 and N \ge 2 N ≥ 2 .Here we show that formally treating N N as a continuous parameter, there exists a critical value N_c > 2 N c gt; 2 separating two distinct regimes. For 2 \leq N < N_c 2 ≤ N < N c the extra-ordinary fixed point survives in d = 3 d = 3 ,albeit in a modified form: the long-range boundary order is lost,instead, the order parameter correlation function decays as a power of \log r log r .For N > N_c N gt; N c there is no fixed point with order parameter correlations decayingslower than power law. We discuss several scenarios for the evolution ofthe phase diagram past N = N_c N = N c .Our findings appear to be consistent with recent Monte Carlo studies ofclassical models with N = 2 N = 2 and N = 3 N = 3 .We also compare our results to numerical studies of boundary criticalityin 2+1D quantum spin models.
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- Award ID(s):
- 1847861
- PAR ID:
- 10394238
- Date Published:
- Journal Name:
- SciPost Physics
- Volume:
- 12
- Issue:
- 4
- ISSN:
- 2542-4653
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.21468/SciPostPhys.12.4.131
