I. Jack, R. Purdy
We discuss the structure of the non-anticommutative N=2 non-linear sigma-model in two dimensions, constructing differential operators which implement the deformed supersymmetry generators and using them to reproduce the classical action. We then compute the one-loop quantum corrections and express them in a more compact form using the differential operators.
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Certain supersymmetric sigma models in 2+1 dimensions feature multi-soliton solutions, with and without scattering. We subject these systems to a non-anticommutative deformation by replacing the Grassmann algebra of the odd superspace coordinates with a Clifford algebra. Static CP^1 and scattering U(2) solitons are constructed and carry an additional spin-1/2 degree of freedom due to the deformation. Abelian BPS solutions exist as well but have infinite action, in contrast to the Moyal case.
We study the UV properties of the three-dimensional ${\cal N}=4$ SUSY nonlinear sigma model whose target space is $T^*(CP^{N-1})$ (the cotangent bundle of $CP^{N-1}$) to higher orders in the 1/N expansion. We calculate the $β$-function to next-to-leading order and verify that it has no quantum corrections at leading and next-to-leading orders.
We study the quantum structure of four-dimensional ${\cal N}=2$ superfield sigma-model formulated in harmonic superspace in terms of the omega-hypermultiplet superfield $ω$. The model is described by harmonic superfield sigma-model metric $g_{ab}(ω)$ and two potential-like superfields $L^{++}_{a}(ω)$ and $L^{(+4)}(ω)$. In bosonic component sector this model describes some hyper-Kähler manifold. The manifestly ${\cal N}=2$ supersymmetric covariant background-quantum splitting is constructed and the superfield proper-time technique is developed to calculate the one-loop effective action. The one…
We present a simple, new method for the 1-loop renormalization of integrable $σ$-models. By treating equations of motion and Bianchi identities on an equal footing, we derive 'universal' formulae for the 1-loop on-shell divergences, generalizing case-by-case computations in the literature. Given a choice of poles for the classical Lax connection, the divergences take a theory-independent form in terms of the Lax currents (the residues of the poles), assuming a 'completeness' condition on the zero-curvature equations. We compute these divergences for a large class of theories with simple poles …
Six-loop divergences in the supersymmetric Kahler sigma model
Kähler流形上的二维超对称$\s$ -模型在四个环上有一个非零的$\b$ -函数，但在五个环上的$\b$ -函数可以通过特定的重整化方案的选择而消失。我们调查这种现象是否持续在六个循环，并得出结论，它不存在，有一个非零的六个循环$\b$ -功能，不论重正化方案的模糊性。
Topological Renormalisation of the O(3) Sigma Model
我们证明了O（3）西格玛模型的单瞬子扇形模空间发散导致了格林函数对任意方式的不可接受的依赖性，即场被分裂成关于经典背景的量子涨落。由于发散是与退化的领域配置的零瞬子部门这种任意性可能会被取消的“拓扑反长期”，我们的建设。
One-Loop Quadratic Divergences of the Dual Non-Linear Sigma Model in Four-Dimensional Spacetime
在回顾了非线性西格玛模型的对偶描述之后，我们研究了单圈二次发散。对于一般情况，我们采用协变背景场方法，并将所得结果应用于$SU(2)$的重要例子。
Quantization of Complementary ADHM Sigma Model
本研究参照Lambert对Witten原始ADHM sigma模型的量子化工作，开展互补ADHM sigma模型的量子化研究，发现二者的发散抵消机制存在差异。
Equivalence of 1-loop RG flows in 4d Chern-Simons and integrable 2d sigma-models
本文利用 4d 路径积分与有效作用量的替代表述，证明带 Disorder 缺陷的 4d Chern-Simons 理论的 1 圈发散局域于 2d 缺陷，并与非超局域可积 2d sigma 模型的普适 RG 流公式一致。
We formulate a gauged linear sigma model on a supermanifold. The structure of classical vacua is investigated and one-loop corrections are calculated for an auxiliary D-field. We find out a constraint for the one-loop divergence to vanish, which is consistent with a Ricci flatness condition for the supermanifold. Two types of D-branes are obtained by analysing supersymmetric boundary conditions. We also provide extensions to a non-abelian gauged linear sigma model and a (0,2) supersymmetric model.
We review Buchler and Colangelo's result that leading divergences at any loop order can be calculated using only one-loop calculations and we provide an alternative proof. We then use this method to calculate the leading divergences of and thus the leading logarithmic corrections to the meson mass in the massive O(N) nonlinear sigma model to five-loop order. We also calculate the all-loop result to leading order in the large $N$ expansion by showing that only cactus diagrams contribute and by summing these via a generalized gap equation.
We study line operators in the two-dimensional sigma-model on PSl(n|n) using the current-current OPEs. We regularize and renormalize these line operators, and compute their fusion up to second order in perturbation theory. In particular we show that the transfer matrix associated to a one-parameter family of flat connections is free of divergences. Moreover this transfer matrix satisfies the Hirota equation (which can be rewritten as a Y-system, or Thermodynamic Bethe Ansatz equations) for all values of the two parameters defining the sigma-model. This provides a first-principles derivation of…
Following our previous paper (hep-th/9909027), we generalize a supersymmetric boundary state so that arbitrary configuration of the gauge field coupled to the boundary of the worldsheet is incorpolated. This generalized boundary state is BRST invariant and satisfy the non-linear boundary conditions with non-constant gauge field strength. This boundary state contains divergence which is identical with the loop divergence in a superstring sigma model. Hence vanishing of the beta function in the superstring sigma model corresponds to a well-defined boundary state with no divergence. The coupling …
We study non-local non-linear sigma models in arbitrary dimension, focusing on the scale invariant limit in which the scalar fields naturally have scaling dimension zero, so that the free propagator is logarithmic. The classical action is a bi-local integral of the square of the arc length between points on the target manifold. One-loop divergences can be canceled by introducing an additional bi-local term in the action, proportional to the target space laplacian of the square of the arc length. The metric renormalization that one encounters in the two-derivative non-linear sigma model is abse…
Nonlinear sigma models (NLSM) in d=3 have many interesting and non-trivial features, which were explored poorly in contrast with NLSM in d=2 and d=4. We present a few results from our study of the perturbative and non-perturbative properties of three-dimensional (3D) NLSM. i) We have shown that cancellation of ultra-violet (UV) divergences takes place in 3D extended (N=2,4) supersymmetric NLSM in low orders of the 1/n expansion. ii) We consider noncommutative extension of the 3D CP(n) model, and study low-energy dynamics of BPS solitons in this model. We also discuss briefly dynamics of non-BP…
We show that the noncommutativity of space-time destroys the renormalizability of the 1/N expansion of the O(N) Gross-Neveu model. A similar statement holds for the noncommutative nonlinear sigma model. However, we show that, up to the subleading order in 1/N expansion, the noncommutative supersymmetric O(N) nonlinear sigma model becomes renormalizable in D=3. We also show that dynamical mass generation is restored and there is no catastrophic UV/IR mixing. Unlike the commutative case, we find that the Lagrange multiplier fields, which enforce the supersymmetric constraints, are also renormali…
We adress ourselves the question of the quantum equivalence of non abelian dualised $\si$-models on the simple example of the T-dualised $SU(2) \si$-model. This theory is classically canonically equivalent to the standard chiral $SU(2) \si$-model. It is known that the equivalence also holds at the first order in perturbations with the same $\be$ functions. However, this model has been claimed to be non-renormalisable at the two-loop order. The aim of the present work is the proof that it is - at least up to this order - still possible to define a correct quantum theory. Its target space metric…
Recently a perturbative theory has been constructed, starting from the Feynman rules of the nonlinear sigma model at the tree level in the presence of an external vector source coupled to the flat connection and of a scalar source coupled to the nonlinear sigma model constraint (flat connection formalism). The construction is based on a local functional equation, which overcomes the problems due to the presence (already at one loop) of non chiral symmetric divergences. The subtraction procedure of the divergences in the loop expansion is performed by means of minimal subtraction of properly no…
In the present paper we extend to the massive case the procedure of divergences subtraction, previously introduced for the massless nonlinear sigma model (D=4). Perturbative expansion in the number of loops is successfully constructed. The resulting theory depends on the Spontaneous Symmetry Breaking parameter v, on the mass m and on the radiative correction parameter Λ. Fermions are not considered in the present work. SU(2) X SU(2) is the group used.
1-loop renormalisability of integrable sigma-models from 4d Chern-Simons theory
本文证明了由4d Chern-Simons理论表面缺陷构造的一大类经典可积二维sigma模型在1-loop阶可重整化，推导了twist 1-form的流，适用于有理、三角和椭圆型模型。
Rederiving the one-loop divergences for the most general coupling of the open string sigma model by the heat kernel technique, we distinguish the classical background field from the mean field of the effective action. The latter is arbitrary, i.e. does not fulfil the boundary conditions. As a consequence a new divergent counter term strongly suggests the introduction of another external one-form field (beside the usual gauge field), coupled to the normal derivative at the boundary. Actually such a field has been proposed in the literature for different reasons, but its full impact never seems …
We study IR-renormalon divergences in N=1 supersymmetric Yang Mills gauge theories and in two dimensional non linear sigma models with mass gap. We derive, in both types of theories, a direct connection between IR- renormalons and fractional instanton effects. From the point of view of large $N$ dualities we work out a connection between IR-renormalons and $c=1$ matrix models.
Kosterlitz-Thouless Phase Transition In The Two Dimensional Linear Sigma Model
利用精确的非微扰发展方程研究了二维O（N）对称线性$σ$ -模型。微扰红外发散在这个公式中是不存在的。我们使用一个简单的近似解的流量方程对应于一个衍生的有效行动的扩展。对于N=2，这给出了一个很好的图片的Kosterlitz无相变。
We summarize recent progress on the symmetric subtraction of the Non-Linear Sigma Model in $D$ dimensions, based on the validity of a certain Local Functional Equation (LFE) encoding the invariance of the SU(2) Haar measure under local left transformations. The deformation of the classical non-linearly realized symmetry at the quantum level is analyzed by cohomological tools. It is shown that all the divergences of the one-particle irreducible (1-PI) amplitudes (both on-shell and off-shell) can be classified according to the solutions of the LFE. Applications to the non-linearly realized Yang-…
Quantum non-local charges are central to the quantum integrability of a sigma-model. In this paper we study the quantum consistency and UV finiteness of non-local charges of string theory in AdS(5)xS(5). We use the pure spinor formalism. We develop the near-flat space expansion of the transfer matrix and calculate the one-loop divergences. We find that the logarithmic divergences cancel at the level of one loop. This gives strong support to the quantum integrability of the full string theory. We develop a calculational setup for the renormalization group analysis of Wilson line type of operato…
One-loop mass shifts to the classical masses of stable kinks arising in a massive non-linear ${\mathbb S}^2$-sigma model are computed. Ultraviolet divergences are controlled using the heat kernel/zeta function regularization method. A comparison between the results achieved from exact and high-temperature asymptotic heat traces is analyzed in depth.
We write general one-loop anomalies of string field theory as path integrals on a torus for the corresponding nonlinear sigma model. This extends the work of Alvarez-Gaumé and Witten from quantum mechanics to two dimensions. Higher world-volume loops contribute in general to nontopological anomalies and a formalism to compute these is developed. We claim that (i) for general anomalies one should not use the propagator widely used in string theory but rather the one obtained by generalization from quantum mechanics, but (ii) for chiral anomalies both propagators give the same result. As a check…
We analyze one loop scattering amplitudes of the massless states on a stack of D3-branes. We use the vertex operators that have been obtained in the direct open string analysis developed in arXiv:0708.3452. The method does not have the obstacle of the D9 computation which is associated with the appearance of an $\e$-tensor. The divergence structure is not the same as the D9 brane case. What makes the analysis deviate from the D9 brane case is that the momenta of the states have non-zero components only along the brane directions. We ponder on the possibility that the one-loop divergence may be…
In this thesis we investigate quantum aspects of the Green-Schwarz superstring in various AdS backgrounds relevant for the AdS/CFT correspondence, providing several examples of perturbative computations in the corresponding integrable sigma-models. We start by reviewing in details the supercoset construction of the superstring action in $AdS_5 \times S^5$, pointing out the limits of this procedure for $AdS_4$ and $AdS_3$ backgrounds. For the $AdS_4 \times CP^3$ case we give a thorough derivation of an alternative action, based on the double-dimensional reduction of eleven-dimensional super-mem…
Trace Anomalies from Quantum Mechanics
d维量子场论的1-圈反常可以通过计算调节的路径积分雅可比矩阵的迹来计算，如Fujikawa所示。在1983年，阿尔瓦雷斯-高梅和威滕观察到，人们可以通过用具有相同（反）对易关系的量子力学算符替换出现在调节器和雅可比矩阵中的算符来简化这种计算。通过将这一量子力学迹线重写为一维超对称非线性西格玛模型的周期边界条件下的路径积分，他们获得了d维自旋1/2和3/2场的手征反常和自对偶反对称张量。在这篇文章中，我们处理的情况下，跟踪异常自旋0，1/2和1场的重力和杨米尔斯背景。我们没有引入超对称的西格玛模型，而是在路径积分中保留了原有的Dirac矩阵$\g^\m$和内部对称生成元$T^a$。结果，我们得到一个矩阵值作用。然后，路径积分的规范协方差需要通过时间排序定义作用的指数。为了更清楚地展示西格玛模型发散的消除，我们利用矢量鬼对路径积分测度中的因子$\sqrt g$取幂。我们计算d=2和d=4时的迹异常。
Pauli-Villars Regularization of Globally Supersymmetric Theories
结果表明，只要规范群的生成元在物质表象中是无迹的，重Pauli-Villars手征超多重态的引入可以调节可重整化超对称理论中的单圈紫外发散.该程序扩展到包括超对称规范非线性西格玛模型。
In this paper, we generalize a boundary state to the one incorporating non-constant gauge field strength as an external background coupled to the boundary of a string worldsheet in bosonic string theory. This newly defined boundary state satisfies generalized nonlinear boundary conditions with non-constant gauge field strength, and is BRST invariant. The divergence immanent in this boundary state coincide with the one calculated in a string sigma model. We extract the relevant massless part of this generalized boundary state, and give a part of the D-brane action with the non-constant gauge fi…
Trans-series from condensates in the non-linear sigma model
本文提出一个无质量的微扰框架，用于二维非线性σ模型，用于计算算子乘积展开中算子凝聚态的微扰级数。该框架基于四次线性σ模型的极限，且显式保持O(N)对称性，并在1/N展开的次主导项中重现了两点函数的微扰贡献及其因拉格朗日算子凝聚态产生的指数小修正。
k-Anomalies and Space-Time Supersymmetry in the Green-Schwarz Heterotic Superstring
Green-Schwarz杂化超弦σ模型中$κ$ -反常的计算和相应的Wess-Zumino相容性条件构成了一个强有力的替代方法，用于推导明显超对称的弦有效作用量.相对于β函数方法，该技术具有的优点是，通过计算\hbox{$n-1$}循环处的$κ$异常可以获得在$n$循环处计算β函数所获得的结果。本文用直接的单圈微扰计算导出了与Yang-Mills Chern-Simons三型相关联的$κ$ -反常，并首次导出了与Lorentz Chern-Simons三型相关联的$κ$ -反常.与文献中经常提到的相反，我们证明了洛伦兹$κ$ -反常从弦的费米子{ \it}和玻色子自由度的积分中得到贡献。对所有这些异常的绝对系数进行仔细分析后发现，可以通过设置$dH={α'\over4}(\trace F^2-\trace R^2)$来吸收这些异常，其中$α'$是弦张力，这是预期的结果。我们表明，这种关系也确保规范和洛伦兹异常的情况下，在西格玛模型的有效行动。我们证明了红外发散的存在。
Complete one-loop self-energies of the linear sigma model coupled to quarks at finite temperature and in a magnetic field
本文研究了线性西格玛模型在有限温度和磁场下的完整一阶自能，通过马苏巴拉方法和施温格正时表示法，统一处理中性与带电自由度，分离真空与物质贡献，为QCD有效模型中的热磁一阶修正提供系统框架。
The scalar theory is ultraviolet (UV) quadratically divergent on ordinary spacetime. On noncommutative (NC) spacetime, this divergence will generally induce pole-like infrared (IR) singularities in external momenta through the UV/IR mixing. In spontaneous symmetry breaking theory this would invalidate the Goldstone theorem which is the basis for mass generation when symmetry is gauged. We examine this issue at two loop level in the U(N) linear sigma model which is known to be free of such IR singularities in the Goldstone self-energies at one loop. We analyze the structures in the NC parameter…
More than four decades ago, Lee and Symanzik proved that, in the Gell Mann-Levy (GML) model with partially conserved axial-vector currents (PCAC), tadpole renormalization (a Higgs Vacuum Stability Condition) forces all S-matrix ultra-violet quadratic divergences (UVQD) to be absorbed into the physical renormalized pseudo-scalar pion (pole) mass squared. We show that this includes "new" UVQD (widely unfamiliar to modern audiences). We also show that tadpole renormalization is an automatic consequence of Ward-Takahashi identities. We prove that all UVQD therefore vanish identically in the Goldst…
In this work, a possible description for quantum dynamics of the cuscuton within the sigma-model approach is presented. Lower order perturbative corrections and the structure of divergences are found. Motivated by the results generated by the perturbative approach, we investigate the existence of topological structures in the cuscuton-like model. The structures we study are, first, kink-like configurations in two dimensional spacetime, second, vortex solutions in three dimensional one with gauge field ruled by the Maxwell term. In fact, to show the existence of kink solutions it is needed to i…
We study one-loop photon (Pi) and neutrino (Sigma) self-energies in a U(1) covariant gauge-theory on d-dimensional noncommutative spaces determined by a antisymmetric-constant tensor theta^{mu nu}. For the general fermion-photon (S_f) and photon self-interaction (S_g) the closed form results reveal self-energies besetting with all kind of pathological terms: the UV divergence, the quadratic UV/IR mixing terms as well as a logarithmic IR divergent term of the type ln(mu^2(theta p)^2). In addition, the photon-loop produces new tensor structures satisfying transversality condition by themselves. …
We investigate the noncommutative analogue of the spontaneously broken linear sigma model at the one-loop quantum level. In the commutative case, renormalization of a theory with a spontaneously broken continuous global symmetry depends on cancellations that enable the limited set of counterterms consistent with that symmetry to remove the divergences even after its spontaneous breaking, while preserving the masslessness of the associated Goldstone modes. In the noncommutative case, we find that these cancellations are violated, and the renormalized one-loop correction to the inverse pion prop…
In this work, we mainly study the one-loop effective action for real scalar theories in non-homogeneous backgrounds in odd dimensions. It is shown that through the method studied in Ref. [1], it is possible to obtain a unified result for the one-loop correction to the Euclidean effective action in 2+1 dimensions. Our result simplifies into the ones given in the literature calculated via different techniques based on some assumptions of field and its derivative. The one-loop correction is obtained in (2n+1)-dimensional Euclidean space-times, as well. Moreover, its generic behavior is discussed …
Even-point Multi-loop Unitarity and its Applications: Exponentiation, Anomalies and Evanescence
本文利用偶数点有效场论的特殊性质进行基于幺正性的多圈振幅构造，发现NLSM振幅红外发散指数化，系统计算了Born-Infeld两圈反常行为，并验证了DBIVA振幅在两圈阶的双拷贝构造。
Kontsevich's formality theorem states that the differential graded Lie algebra of multidifferential operators on a manifold M is L-infinity-quasi-isomorphic to its cohomology. The construction of the L-infinity map is given in terms of integrals of differential forms on configuration spaces of points in the upper half-plane. Here we consider configuration spaces of points in the disk and work equivariantly with respect to the rotation group. This leads to considering the differential graded Lie algebra of multivector fields endowed with a divergence operator. In the case of R^d with standard v…
Self-dual monopole loops, instantons and confinement
本文指出四维杨-米尔斯瞬子分析存在红外发散问题，通过类比$U(1)$格点规范理论中的磁单极环，证明考虑$1/r^4$相互作用后可消除发散，并猜想瞬子内部结构导致四维禁闭。
In order to investigate the systematics of the loop expansion in high temperature gauge theories beyond the leading order hard thermal loop (HTL) approximation, we calculate the two-loop electron proper self-energy in high temperature QED. The two-loop bubble diagram contains a linear infrared divergence. Even if regulated with a non-zero photon mass M of order of the Debye mass, this infrared sensitivity implies that the two-loop self-energy contributes terms to the fermion dispersion relation that are comparable to or even larger than the next-to-leading-order (NLO) contributions at one-loop…
This work is a step towards a non-perturbative continuum definition of quantum field theory (QFT), beginning with asymptotically free two dimensional non-linear sigma-models, using recent ideas from mathematics and QFT. The ideas from mathematics are resurgence theory, the trans-series framework, and Borel-Ecalle resummation. The ideas from QFT use continuity on R^1 x S^1_L, i.e, the absence of any phase transition as N \to infinity, or rapid-crossovers for finite-N, and the small-L weak coupling limit to render the semi-classical sector well-defined and calculable. We classify semi-classical …
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