Current operators in integrable spin chains: lessons from long range deformations

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We point out that two classes of deformations of integrable models, developed completely independently, have deep connections and share the same algebraic origin. One class includes the TT -deformation of 1+1 dimensional integrable quantum field theory and related solvable irrelevant deformations proposed recently. The other class is a specific type of long range integrable deformation of quantum spin chains introduced a decade ago, in the context of N = 4 super-Yang-Mills theory. We show that the detailed structures of the two deformations are formally identical and therefore share many features. Both deformations preserve integrability and lead to non-local deformed theories, resulting in a change of the corresponding factorized S-matrices. We also prove a factorisation formula for the expectation value of the operators which trigger the deformation on the lattice; similar results in quantum field theory play an essential role in the solvability of such deformations. We point out that the long range deformation is a natural counterpart of the TT -deformation for integrable spin chains, and argue that this observation leads to interesting new avenues to explore.

“…for some α also generates quasi-local charges. This deformation was treated in detail in [24], where it was shown that the κ-derivative of the charges is…”

Section: The Charges Continue To Form a Commuting Familymentioning

confidence: 99%

Section: Action On Bethe Statesmentioning

confidence: 99%

“…The specific form of the one-particle eigenvalues is not relevant for us; explicit formulas can be found in [27,24]. The total quasi-momentum of the state can be expressed as…”

Section: Action On Bethe Statesmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 95%

Section: Introductionmentioning

confidence: 99%

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$$ T\overline{T} $$-deformation and long range spin chains

Pozsgay

Jiang

Takács

2020

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Non-linear supersymmetry and $$ T\overline{T} $$-like flows

Ferko

Jiang

Sethi

et al. 2020

The TT deformation of a supersymmetric two-dimensional theory preserves the original supersymmetry. Moreover, in several interesting cases the deformed theory possesses additional non-linearly realized supersymmetries. We show this for certain N = (2, 2) models in two dimensions, where we observe an intriguing similarity with known N = 1 models in four dimensions. This suggests that higher-dimensional models with non-linearly realized supersymmetries might also be obtained from TT -like flow equations.We show that in four dimensions this is indeed the case for N = 1 Born-Infeld theory, as well as for the Goldstino action for spontaneously broken N = 1 supersymmetry. arXiv:1910.01599v1 [hep-th] 3 Oct 2019Contents 1 Introduction 1 2 D = 2 N = (2, 2) Flows and Non-Linear N = (2, 2) Supersymmetry 4 2.1 TT deformations with N = (2, 2) supersymmetry 4 2.2 The TT -deformed twisted-chiral model and partial-breaking 7 2.3 The TT -deformed chiral model and partial-breaking 13 3 D = 4 T 2 Deformations and Their Supersymmetric Extensions 16 3.1 Comments on the T 2 operator in D = 4 16 3.2 D = 4 N = 1 supercurrent-squared operator 18 4 Bosonic Born-Infeld As a T 2 Flow 20 5 Supersymmetric Born-Infeld From Supercurrent-Squared Deformation 22 7 Conclusions and Outlook 33 A Deriving a Useful On-shell Identity 36 construct two models describing the partial supersymmetry breaking pattern N = (4, 4) → N = (2, 2) in D = 2. These models have manifest N = (2, 2) supersymmetry from the superspace structure used in their construction, but they also admit another hidden nonlinear N = (2, 2) supersymmetry. It turns out the resulting actions are exactly the same as the N = (2, 2) chiral and twisted chiral TT -deformed actions of [18]. The intriguing relation between non-linear supersymmetry and TT therefore persists for models with manifest N = (2, 2) supersymmetry. Interestingly, even the D = 2 Volkov-Akulov action, describing the dynamics of the Goldstinos which arise from the spontaneous breaking of N = (2, 2) supersymmetry, satisfies a TT flow equation [21]. This collection of examples motivates us to see whether any higher-dimensional theories with non-linear supersymmetries might also satisfy TT -like flow equations. It has been known for more than two decades that the Bagger-Galperin action for the D = 4 N = 1 Born-Infeld theory describes N = 2 → N = 1 partial supersymmetry breaking [22]. Does the Bagger-Galperin action arise from a TT -like deformation of N = 1 Maxwell theory? That the linear order deformation is given by a supercurrent-squared operator was noted long ago in [23]. Much more recently, bosonic Born-Infeld theory was shown to satisfy a T 2 flow equation, where T 2 is an operator quadratic in the stress-energy tensor [24]. In this work, we explicitly show that the Bagger-Galperin action indeed satisfies a supercurrentsquared flow equation, generalizing the observation of [23] to all orders in the deformation parameter. The supercurrent-squared deformation operator is constructed from supercurrent multiplets, but its to...

On the hydrodynamics of unstable excitations

Castro-Alvaredo

Fazio

Doyon

et al. 2020

The generalized hydrodynamic (GHD) approach has been extremely successful in describing the out-of-equilibrium properties of a great variety of integrable many-body quantum systems. It naturally extracts the large-scale dynamical degrees of freedom of the system, and is thus a particularly good probe for emergent phenomena. One such phenomenon is the presence of unstable particles, traditionally seen via special analytic structures of the scattering matrix. Because of their finite lifetime and energy threshold, these are especially hard to study. In this paper we apply the GHD approach to a model possessing both unstable excitations and quantum integrability. The largest family of relativistic integrable quantum field theories known to have these features are the homogeneous sine-Gordon models. We consider the simplest non-trivial example of such theories and investigate the effect of an unstable excitation on various physical quantities, both at equilibrium and in the non-equilibrium state arising from the partitioning protocol. The hydrodynamic approach sheds new light onto the physics of the unstable particle, going much beyond its definition via the analytic structure of the scattering matrix, and clarifies its effects both on the equilibrium and out-of-equilibrium properties of the theory. Crucially, within this dynamical perspective, we identify unstable particles as finitely-lived bound states of co-propagating stable particles of different types, and observe how stable populations of unstable particles emerge in large-temperature thermal baths.