arXiv subjects

Matteo Beccaria

Publications and source records attributed to Matteo Beccaria.

At least 109 records · Page 6Linked to original sources

arXiv2008

On the large spin limit of twist operators in N=4 SYM

The long range Bethe Ansatz solution of the mixing problem in N=4 SYM allows to compute in a very efficient way multiloop anomalous dimensions of various composite operators. In the case of sl(2) twist operators it is important to obtain closed expressions for the anomalous dimensions in terms of the Lorentz spin. Conjectures are available altough analytical proofs are missing beyond one-loop. In this paper, we will present a method to expand at large spin the solution of the long range Baxter equation in twist 2 and 3. We will also propose sum rules for special singlet states at higher twist.

hep-th↗

arXiv2008

QCD-like properties for anomalous dimensions in N=4 SYM

In this contribution it is shown how closed formulas for anomalous dimensions of two classes of operators in N=4 SYM can be derived, either by investigating the numerics or on the basis of QCD-inspired assumptions. We discuss the case of twist three "gauge" operators in which a complete proof of reciprocity can be carried out.

hep-th↗

arXiv2008

The generalized scaling function of AdS/CFT and semiclassical string theory

Recently, Freyhult, Rej and Staudacher (FRS) proposed an integral equation determining the leading logarithmic term of the anomalous dimension of sl(2) twist-operators in N=4 SYM for large Lorentz spin M and twist L at fixed j = L/log(M). We discuss the large j limit of the FRS equation. This limit can be matched with the {\em fast long string} limit of AdS_5 X S^5 superstring perturbation theory at all couplings. In particular, a certain part of the classical and one-loop string result is known to be protected and can be computed in the weakly coupled large-j limit of the FRS equation. We present various analytical and numerical results supporting agreement at one and two loops in the gauge theory.

hep-th↗

arXiv2008

On the strong coupling expansion in the su(1|1) sector of N=4 SYM

We consider the anomalous dimension of the fermionic highest states Tr(psi^L) in the su(1|1) sector of N=4 SYM at strong coupling. In the thermodynamical L->OO limit it is described by a BES-like integral equation recently proposed by Rej, Staudacher and Zieme. The strong coupling regime of this equation is analyzed numerically and analytically by Neumann expansion methods which have been developed for the sl(2) sector. We compute analytically the first two terms of the strong coupling expansion and present numerical results for the next correction. We illustrate various specific features valid for the su(1|1) sector. In particular, at next-to-leading order, we find and solve a singular integral equation describing the scaling continuum limit of the Neumann coefficients.

hep-th↗

arXiv2008

Sum rules for higher twist sl(2)operators in N=4 SYM

The spectrum of anomalous dimensions of twist sl(2) operators in N=4 SYM has an intriguing feature in low twist 2 or 3. The anomalous dimension of the lowest state, dual a folded string on AdS_5 X S^5, can be computed by Bethe Ansatz at 3, 4 loops respectively as a simple closed function of the Lorentz spin. This feature is apparently lost at higher twist. We propose sum rules for the excited anomalous dimensions where closed expressions can still be provided, even at higher twist. We present several explicit three loop examples. Many structural regularities can be observed leading to closed expressions which depend parametrically both on the spin and the twist. They allow to compute the subleading term in the logarithmic large spin expansion of the sum rules as a compact simple function of the twist, in analogy with the recent results by Freyhult, Rej and Staudacher in arXiv:0712.2743 [hep-th].

hep-th↗

arXiv2008

Reciprocity of gauge operators in N=4 SYM

A recently discovered generalized Gribov-Lipatov reciprocity holds for the anomalous dimensions of various twist operators in N=4 SYM. Here, we consider a class of scaling psu(2,2|4) operators that reduce at one-loop to twist-3 maximal helicity gluonic operators. We extract from the asymptotic long-range Bethe Ansatz a closed expression for the spin dependent anomalous dimension at four loop order and provide a complete proof of reciprocity. We comment about the interplay with possible, yet unknown, wrapping corrections.

hep-th↗

arXiv2008

Large spin expansion of the long-range Baxter equation in the sl(2) sector of N=4 SYM

Recently, several multi-loop conjectures have been proposed for the spin dependence of anomalous dimensions of twist-2 and 3 operators in the sl(2) sector of N=4 SYM. Currently, these conjectures are not proven, although several consistency checks have been performed on their large spin expansion. In this paper, we show how these expansions can be efficiently computed without resorting to any conjecture. To this aim we present in full details a method to expand at large spin the solution of the long-range Baxter equation. We treat the twist-2 and 3 cases at two loops and the twist-3 case at three loops. Several subtleties arise whose resolution leads to a simple algorithm computing the expansion.

hep-th↗

arXiv2007

Anomalous dimensions of finite size field strength operators in N=4 SYM

In the N=4 super Yang-Mills theory, we consider the higher order anomalous dimensions gamma_L(g) of purely gluonic operators Tr(F^L) where F is a component of the self-dual field strength. We propose compact closed expressions depending parametrically on L that reproduce the prediction of Bethe Ansatz equations up to five loop order, including transcendental dressing corrections. The size dependence follows a simple pattern as the perturbative order is increased and suggests hidden relations for these special operators.

hep-th↗

arXiv2007

Evidence for a floating phase of the transverse ANNNI model at high frustration

We study the transverse quantum ANNNI model in the region of high frustration (k>0.5) using the DMRG algorithm. We obtain a precise determination of the phase diagram, showing clear evidence for the existence of a floating phase, separated from the paramagnetic modulated phase by a high-order critical line ending at the multicritical point. We obtain simple and accurate formulae for the two critical lines.

cond-mat.stat-mech↗

arXiv2007

Three loop anomalous dimensions of twist-3 gauge operators in N=4 SYM

We propose a closed expression for the three loop anomalous dimension of a class of twist-3 operators built with gauge fields and covariant derivatives. To this aim, we solve the long-range Bethe Ansatz equations at finite spin and provide a consistent analytical formula obtained assuming maximal transcendentality violation as suggested by the known one-loop anomalous dimension. The final result reproduces the universal cusp anomalous dimension and obeys recursion relations inspired by the principle of reciprocity invariance.

hep-th↗

arXiv2007

Universality of three gaugino anomalous dimensions in N=4 SYM

We study maximal helicity three gaugino operators in N=4 Super Yang-Mills theory. We show that the lowest anomalous dimension of scaling operators with generic finite spin can be expressed in terms of the universal anomalous dimension appearing at twist-2. This statement is rigourously proved at three loops. The reason for this universality between sectors with different twist is the hidden psu(1|1) invariance of the su(2|1) subsector of the theory.

hep-th↗

arXiv2007

Anomalous dimensions at twist-3 in the sl(2) sector of N=4 SYM

We consider twist-3 operators in the sl(2) sector of N=4 SYM built out of three scalar fields with derivatives. We extract from the Bethe Ansatz equations of this sector the exact lowest anomalous dimension gamma(s) of scaling fields for several values of the operator spin s. We propose compact closed expressions for the spin dependence of gamma(s) up to the four loop level and show that they obey a simple new twist-3 transcendentality principle. As a check, we reproduce the four loop universal cusp anomalous dimension governing the logarithmic large spin limit of gamma(s).

hep-th↗

arXiv2007

The scaling function at strong coupling from the quantum string Bethe equations

We study at strong coupling the scaling function describing the large spin anomalous dimension of twist two operators in ${\cal N}=4$ super Yang-Mills theory. In the spirit of AdS/CFT duality, it is possible to extract it from the string Bethe Ansatz equations in the $\mathfrak{sl}(2)$ sector of the $\ads$ superstring. To this aim, we present a detailed analysis of the Bethe equations by numerical and analytical methods. We recover several short string semiclassical results as a check. In the more difficult case of the long string limit providing the scaling function, we analyze the strong coupling version of the Eden-Staudacher equation, including the Arutyunov-Frolov-Staudacher phase. We prove that it admits a unique solution, at least in perturbation theory, leading to the correct prediction consistent with semiclassical string calculations.

hep-th↗

arXiv2007

On the supersymmetric vacua of the Veneziano-Wosiek model

We study the supersymmetric vacua of the Veneziano-Wosiek model in sectors with fermion number F=2, 4 at finite 't Hooft coupling lambda. We prove that for F=2 there are two zero energy vacua for lambda > lambda_c = 1 and none otherwise. We give the analytical expressions of both vacua. One of them was previously known, the second one is obtained by solving the cohomology of the supersymmetric charges. At F=4 we compute the would-be supersymmetric vacua at high order in the the strong coupling expansion and provide strong support to the conclusion that lambda = 1 is a critical point in this sector too. It separates a strong coupling phase with two symmetric vacua from a weak coupling phase with positive spectrum.

hep-th↗

arXiv2007

Highest states in light-cone $AdS_5\times S^5$ superstring

We study the highest states in the compact rank-1 sectors of the AdS5 X S5 superstring in the framework of the recently proposed light cone Bethe Ansatz equations. In the su(1|1) sector we present strong coupling expansions in the two limits L,lambda -> OO (expanding in power of lambda^{-1/4} with fixed large L) and lambda, L -> OO (expanding in power of 1/L with fixed large lambda) where lambda is the 't Hooft coupling and L is the number of Bethe momenta. The two limits do not commute apart from the leading term which reproduces the result obtained with the Arutyunov-Frolov-Staudacher phase in the lambda, L -> OO limit. In the su(2) sector we perform the strong coupling expansions in the L->OO limit up to O(lambda^{-1/4}), and our result is in agreement with previuos String Bethe Ansatz analysis.

hep-th↗

arXiv2006

AdS/CFT duality at strong coupling

We study the strong coupling limit of AdS/CFT correspondence in the framework of a recently proposed fermionic formulation of the Bethe Ansatz equations governing the gauge theory anomalous dimensions. We provide examples of states that do not follow the Gubser-Klebanov-Polyakov law at large 't Hooft coupling $λ$, in contrast with recent results on the quantum string Bethe equations valid in that regime. This result indicates that the fermionic construction cannot be trusted at large $λ$, although it remains an efficient tool to compute the weak coupling expansion of anomalous dimensions.

hep-th↗

arXiv2006

Bethe Ansatz solutions for highest states in ${\cal N}=4$ SYM and AdS/CFT duality

We consider the operators with highest anomalous dimension $Δ$ in the compact rank-one sectors $\mathfrak{su}(1|1)$ and $\mathfrak{su}(2)$ of ${\cal N}=4$ super Yang-Mills. We study the flow of $Δ$ from weak to strong 't Hooft coupling $λ$ by solving (i) the all-loop gauge Bethe Ansatz, (ii) the quantum string Bethe Ansatz. The two calculations are carefully compared in the strong coupling limit and exhibit different exponents $ν$ in the leading order expansion $Δ\sim λ^ν$. We find $ν= 1/2$ and $ν= 1/4$ for the gauge or string solution. This strong coupling discrepancy is not unexpected, and it provides an explicit example where the gauge Bethe Ansatz solution cannot be trusted at large $λ$. Instead, the string solution perfectly reproduces the Gubser-Klebanov-Polyakov law $Δ= 2\sqrt{n} λ^{1/4}$. In particular, we provide an analytic expression for the integer level $n$ as a function of the U(1) charge in both sectors.

hep-th↗

arXiv2006

Strong coupling anomalous dimensions of ${\cal N} = 4$ super Yang-Mills

We study the strong coupling behaviour of fixed length single trace operators in the scalar SU(2) sector of ${\cal N} = 4$ SYM. We assume the recently proposed connection with a twisted half-filled Hubbard model. By explicit direct diagonalization of operators with length $L=4, 6, 8$ we study the full {\em perturbative multiplet} of those lattice states which have a clear correspondence with gauge theory composite operators. For this multiplet, we follow the weak-strong coupling flow to free fermion states and identify in particular the precise asymptotic fermion configuration. Next, we analyze the Lieb-Wu equations of the twisted Hubbard model. For the antiferromagnetic state we derive its strong coupling expansion working at $L$ up to 32. We also study the lightest state in the perturbative multiplet. This state is non trivial since involves complex solutions of the Lieb-Wu equations. It is particularly interesting for $AdS_5\times S^5$ duality since it is dual to the folded string semiclassical solution in the thermodynamical limit. We are able to perform the full analysis and compute the next-to-next-to leading terms in the strong coupling expansion for the non trivial lengths L=12 and L=20. A general formula is proposed for the NLO expansion for any $L=4(2k+1)$, $k\in\mathbb{N}$.

hep-th↗