Disturbing news about the $d=2+ε$ expansion II. Assessing the recombination scenario
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2026
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| author | De Cesare, Fabiana Rychkov, Slava |
| author_facet | De Cesare, Fabiana Rychkov, Slava |
| contents | In [De Cesare, Rychkov (2025)], we revisited the $d=2+ε$ expansion in the $O(N)$ Non-Linear Sigma Model (NLSM), emphasizing the existence of a protected operator which is a closed form with $N-1$ indices. The scaling dimension of this operator stays exactly equal to $N-1$, independently of $ε$. Its existence is problematic for the identification of the NLSM fixed point in $d=2+ε$ with the Wilson-Fisher fixed point family obtained by analytically continuing from near $d=4$, which does not possess such a protected operator. Multiplet recombination is one scenario discussed in [De Cesare, Rychkov (2025)], which could allow to connect the two families continuously (although not analytically). In this scenario, the protected dimension is lifted at some critical value of $ε$, thanks to the short conformal multiplet of scaling dimension $N-1$ eating a long conformal multiplet of higher scaling dimension. In this followup work, we assess this scenario for the cases $N=3$ and $N=4$. We identify the lowest candidates for the long multiplet which could be eaten, and compute their one-loop anomalous dimensions. We find that at one loop, scaling dimensions of these candidates grow with $ε$, while it should decrease down to $N$ for the recombination to occur. We conclude that multiplet recombination is unlikely. |
| format | Preprint |
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arxiv_https___arxiv_org_abs_2602_10194 |
| institution | arXiv |
| publishDate | 2026 |
| record_format | arxiv |
| spellingShingle | Disturbing news about the $d=2+ε$ expansion II. Assessing the recombination scenario De Cesare, Fabiana Rychkov, Slava High Energy Physics - Theory Statistical Mechanics Strongly Correlated Electrons In [De Cesare, Rychkov (2025)], we revisited the $d=2+ε$ expansion in the $O(N)$ Non-Linear Sigma Model (NLSM), emphasizing the existence of a protected operator which is a closed form with $N-1$ indices. The scaling dimension of this operator stays exactly equal to $N-1$, independently of $ε$. Its existence is problematic for the identification of the NLSM fixed point in $d=2+ε$ with the Wilson-Fisher fixed point family obtained by analytically continuing from near $d=4$, which does not possess such a protected operator. Multiplet recombination is one scenario discussed in [De Cesare, Rychkov (2025)], which could allow to connect the two families continuously (although not analytically). In this scenario, the protected dimension is lifted at some critical value of $ε$, thanks to the short conformal multiplet of scaling dimension $N-1$ eating a long conformal multiplet of higher scaling dimension. In this followup work, we assess this scenario for the cases $N=3$ and $N=4$. We identify the lowest candidates for the long multiplet which could be eaten, and compute their one-loop anomalous dimensions. We find that at one loop, scaling dimensions of these candidates grow with $ε$, while it should decrease down to $N$ for the recombination to occur. We conclude that multiplet recombination is unlikely. |
| title | Disturbing news about the $d=2+ε$ expansion II. Assessing the recombination scenario |
| topic | High Energy Physics - Theory Statistical Mechanics Strongly Correlated Electrons |
| url | https://arxiv.org/abs/2602.10194 |