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NonWilsonFisher kinks of $O(N)$ numerical bootstrap: from the deconfined phase transition to a putative new family of CFTs
by YinChen He, Junchen Rong, Ning Su
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Submission summary
Authors (as registered SciPost users):  Junchen Rong 
Submission information  

Preprint Link:  https://arxiv.org/abs/2005.04250v3 (pdf) 
Date accepted:  20210517 
Date submitted:  20210415 12:31 
Submitted by:  Rong, Junchen 
Submitted to:  SciPost Physics 
Ontological classification  

Academic field:  Physics 
Specialties: 

Approach:  Theoretical 
Abstract
It is well established that the $O(N)$ WilsonFisher (WF) CFT sits at a kink of the numerical bounds from bootstrapping four point function of $O(N)$ vector. Moving away from the WF kinks, there indeed exists another family of kinks (dubbed nonWF kinks) on the curve of $O(N)$ numerical bounds. Different from the $O(N)$ WF kinks that exist for arbitary $N$ in $2<d<4$ dimensions, the nonWF kinks exist in arbitrary dimensions but only for a large enough $N>N_c(d)$ in a given dimension $d$. In this paper we have achieved a thorough understanding for few special cases of these nonWF kinks. The first case is the $O(4)$ bootstrap in 2d, where the nonWF kink turns out to be the $SU(2)_1$ WessZuminoWitten (WZW) model, and all the $SU(2)_{k>2}$ WZW models saturate the numerical bound on the left side of the kink. We further carry out dimensional continuation of the 2d $SU(2)_1$ kink towards the 3d $SO(5)$ deconfined phase transition. We find the kink disappears at around $d=2.7$ dimensions indicating the $SO(5)$ deconfined phase transition is weakly first order. The second interesting observation is, the $O(2)$ bootstrap bound does not show any kink in 2d ($N_c=2$), but is surprisingly saturated by the 2d free boson CFT (also called Luttinger liquid) all the way on the numerical curve. The last case is the $N=\infty$ limit, where the nonWF kink sits at $(\Delta_\phi, \Delta_T)=(d1, 2d)$ in $d$ dimensions. We manage to write down its analytical four point function in arbitrary dimensions, which equals to the subtraction of correlation functions of a free fermion theory and generalized free theory. An important feature of this solution is the existence of a full tower of conserved higher spin current. We speculate that a new family of CFTs will emerge at nonWF kinks for finite $N$, in a similar fashion as $O(N)$ WF CFTs originating from free boson at $N=\infty$.
Author comments upon resubmission
List of changes
We have corrected the grammar mistakes and typos pointed out by both referees.
 In response to Requested Change 14 in Report 2, we added footnote 8 on page 10.
 In response to Requested Change 15 in Report 2, we added footnote 10 on page 12.
 In response to Requested Change 16 in Report 2: It is hard to say which of the two kinks does the nonWF kink corresponds to. In fact, it would be important to study the two kinks more carefully, especially to find a distinguishing operator content feature to confirm that they indeed correspond to two separate solutions of the crossing equation. We mentioned this in footnote 11.
 In response to Requested Change 1 in Report 1, we added footnote 5 on page 7.
 In response to Requested Change 3 in Report 1, we modified Figure 3.
 In response to Requested Change 4 in Report 1: In the second to the last paragraph of section 1, we added a sentence to refer the definition of Lambda to an earlier paper. Since we did not present any explicit OPE coefficients in this paper, we figure that the convention of the block is not important therefore we will not mention it here.
Published as SciPost Phys. 10, 115 (2021)
Reports on this Submission
Report #1 by Connor Behan (Referee 2) on 202158 (Invited Report)
Report
The paper has undergone nice improvements and meets all the criteria to be published.