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Dimensional Reduction and Crossover to Mean-Field Behavior for Branched Polymers

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 نشر من قبل John Z. Imbrie
 تاريخ النشر 2003
  مجال البحث فيزياء
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 تأليف John Z. Imbrie




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This article will review recent results on dimensional reduction for branched polymers, and discuss implications for critical phenomena. Parisi and Sourlas argued in 1981 that branched polymers fall into the universality class of the Yang-Lee edge in two fewer dimensions. Brydges and I have proven in [math-ph/0107005] that the generating function for self-avoiding branched polymers in D+2 continuum dimensions is proportional to the pressure of the hard-core continuum gas at negative activity in D dimensions (which is in the Yang-Lee or $i phi^3$ class). I will describe how this equivalence arises from an underlying supersymmetry of the branched polymer model. - I will also use dimensional reduction to analyze the crossover of two-dimensional branched polymers to their mean-field limit, and to show that the scaling is given by an Airy function (the same as in [cond-mat/0107223]).



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We establish an exact relation between self-avoiding branched polymers in D+2 continuum dimensions and the hard-core continuum gas at negative activity in D dimensions. We review conjectures and results on critical exponents for D+2 = 2,3,4 and show that they are corollaries of our result. We explain the connection (first proposed by Parisi and Sourlas) between branched polymers in D+2 dimensions and the Yang-Lee edge singularity in D dimensions.
105 - John Z. Imbrie 2004
Dimensional reduction occurs when the critical behavior of one system can be related to that of another system in a lower dimension. We show that this occurs for directed branched polymers (DBP) by giving an exact relationship between DBP models in D +1 dimensions and repulsive gases at negative activity in D dimensions. This implies relations between exponents of the two models: $gamma(D+1)=alpha(D)$ (the exponent describing the singularity of the pressure), and $ u_{perp}(D+1)= u(D)$ (the correlation length exponent of the repulsive gas). It also leads to the relation $theta(D+1)=1+sigma(D)$, where $sigma(D)$ is the Yang-Lee edge exponent. We derive exact expressions for the number of DBP of size N in two dimensions.
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