34 research outputs found

### The composite operator T\bar{T} in sinh-Gordon and a series of massive minimal models

The composite operator T\bar{T}, obtained from the components of the
energy-momentum tensor, enjoys a quite general characterization in
two-dimensional quantum field theory also away from criticality. We use the
form factor bootstrap supplemented by asymptotic conditions to determine its
matrix elements in the sinh-Gordon model. The results extend to the breather
sector of the sine-Gordon model and to the minimal models M_{2/(2N+3)}
perturbed by the operator phi_{1,3}.Comment: 29 page

### Matrix elements of the operator T\bar{T} in integrable quantum field theory

Recently A. Zamolodchikov obtained a series of identities for the expectation
values of the composite operator T\bar{T} constructed from the components of
the energy-momentum tensor in two-dimensional quantum field theory. We show
that if the theory is integrable the addition of a requirement of factorization
at high energies can lead to the exact determination of the generic matrix
element of this operator on the asymptotic states. The construction is
performed explicitly in the Lee-Yang model.Comment: 22 pages, one reference adde

### Jain states on a torus: an unifying description

We analyze the modular properties of the effective CFT description for Jain
plateaux corresponding to the fillings nu=m/(2pm+1). We construct its
characters for the twisted and the untwisted sector and the diagonal partition
function. We show that the degrees of freedom entering the partition function
go to complete a Z_{m}-orbifold construction of the RCFT U(1)xSU(m)$ proposed
for the Jain states. The resulting extended algebra of the chiral primary
fields can be also viewed as a RCFT extension of the U(1)xW(m) minimal models.
For m=2 we prove that our model, the TM, gives the RCFT closure of the extended
minimal models U(1)xW(2).Comment: 27 pages, Latex, JHEP style, no figure

### Transport properties in bilayer Quantum Hall systems in the presence of a topological defect

Following a suggestion given in Phys. Lett. B 571(2003) 621, we show how a
bilayer Quantum Hall system at fillings nu =1/p+1 can exhibit a point-like
topological defect in its edge state structure. Indeed our CFT theory for such
a system, the Twisted Model (TM), gives rise in a natural way to such a feature
in the twisted sector. Our results are in agreement with recent experimental
findings (Phys. Rev. B 72 (2005) 041305) which evidence the presence of a
topological defect in the transport properties of the bilayer system.Comment: 10 pages, 4 figures; talk given by A. Naddeo at "X Training Course in
the Physics of Correlated Electron Systems and High-Tc Superconductors,
Vietri sul Mare (SA),Italy, 3-14 October 200

### A new Rational Conformal Field Theory extension of the fully degenerate W_{1+\infty}^{(m)}

We found new identities among the Dedekind eta-function, the characters of
the W_{m} algebra and those of the level 1 affine Lie algebra su(m)_{1}. They
allow to characterize the Z_{m}-orbifold of the m-component free bosons
u(1)_{K_{m,p}} (our theory TM) as an extension of the fully degenerate
representations of W_{1+infty}^{(m)}. In particular, TM is proven to be a Gamma
_{theta}-RCFT extension of the chiral fully degenerate W_{1+infty}^{(m)}.Comment: 37 pages, minor revisions, one definition added, no formula or result
has been modifie

### Form factors of descendant operators in the massive Lee-Yang model

The form factors of the descendant operators in the massive Lee-Yang model
are determined up to level 7. This is first done by exploiting the conserved
quantities of the integrable theory to generate the solutions for the
descendants starting from the lowest non-trivial solutions in each operator
family. We then show that the operator space generated in this way, which is
isomorphic to the conformal one, coincides, level by level, with that implied
by the $S$-matrix through the form factor bootstrap. The solutions we determine
satisfy asymptotic conditions carrying the information about the level that we
conjecture to hold for all the operators of the model.Comment: 23 page

### Point-like topological defects in bilayer quantum Hall systems

Following a suggestion given in Phys. Lett. B 571 (2003) 250, we show how a
bilayer Quantum Hall system at fillings nu =m/pm+2 can exhibit a point-like
topological defect in its edge state structure. Indeed our CFT theory for such
a system, the Twisted Model (TM), gives rise in a natural way to such a feature
in the twisted sector. Our results are in agreement with recent experimental
findings (cond-mat/0503478) which evidence the presence of a topological defect
in the bilayer system.Comment: 9 pages, 3 figure

### CFT description of the Fully Frustrated XY model and phase diagram analysis

Following a suggestion given in Nucl. Phys. B 300 (1988)611,we show how the
U(1)*Z_{2} symmetry of the fully frustrated XY (FFXY) model on a square lattice
can be accounted for in the framework of the m-reduction procedure developed
for a Quantum Hall system at "paired states" fillings nu =1 (cfr. Cristofano et
al.,Mod. Phys. Lett. A 15 (2000)1679;Nucl. Phys. B 641 (2002)547). The
resulting twisted conformal field theory (CFT) with central charge c=2 is shown
to well describe the physical properties of the FFXY model. In particular the
whole phase diagram is recovered by analyzing the flow from the Z_{2}
degenerate vacuum of the c=2 CFT to the infrared fixed point unique vacuum of
the c=3/2 CFT. The last theory is known to successfully describe the critical
behavior of the system at the overlap temperature for the Ising and
vortex-unbinding transitions.Comment: 18 pages, 1 figure, to appear in JSTA

### Fully frustrated Josephson junction ladders with Mobius boundary conditions as topologically protected qubits

We show how to realize a ``protected'' qubit by using a fully frustrated
Josephson Junction ladder (JJL) with Mobius boundary conditions. Such a system
has been recently studied within a twisted conformal field theory (CFT)
approach (Mod. Phys. Lett. A 15 (2000) 1679; Nucl. Phys. B 641 (2002) 547) and
shown to develop the phenomenon of flux fractionalization (Eur. Phys. J. B 49
(2006) 83). The relevance of a ``closed'' geometry has been fully exploited in
relating the topological properties of the ground state of the system to the
presence of half flux quanta and the emergence of a topological order has been
predicted (JSTAT (2005) P03006). In this letter the stability and
transformation properties of the ground states under adiabatic magnetic flux
change are analyzed and the deep consequences on the realization of a solid
state qubit, protected from decoherence, are presented.Comment: 21 pages, 2 figures, in print in Phys. Lett.