45 research outputs found
Lorentz completion of effective string action
In the presence of a confining flux tube between a pair of sources the vacuum
is no longer Poincare' invariant. This symmetry is nonlinearly realized in the
effective string action. A general method for finding a large class of Lorentz
invariant contributions to the action is described. The relationship between
this symmetry and diffeomorphism invariance is further investigated.Comment: 8 pages, 3 figures, Contribution to the Proceedings of the conference
'Xth Quark Confinement and the Hadron Spectrum', October 8-12, 2012, TUM
Campus Garching, Munich, Germany; references adde
Effective string description of confining flux tubes
We review the current knowledge about the theoretical foundations of the
effective string theory for confining flux tubes and the comparison of the
predictions to pure gauge lattice data. A concise presentation of the effective
string theory is provided, incorporating recent developments. We summarize the
predictions for the spectrum and the profile/width of the flux tube and their
comparison to lattice data. The review closes with a short summary of open
questions for future research.Comment: 21 pages, 8 figures, Contribution to IJMPA special issue "Lattice
gauge theory beyond QCD
Colliders and conformal interfaces
We set up a scattering experiment of matter against an impurity which
separates two generic one-dimensional critical quantum systems. We compute the
flux of reflected and transmitted energy, thus defining a precise measure of
the transparency of the interface between the related two-dimensional conformal
field theories. If the largest symmetry algebra is Virasoro, we find that the
reflection and transmission coefficients are independent of the details of the
initial state, and are fixed in terms of the central charges and of the
two-point function of the displacement operator. The situation is more
elaborate when extended symmetries are present. Positivity of the total energy
flux at infinity imposes bounds on the coefficient of the two-point function of
the displacement operator, which controls the free-energy cost of a small
deformation of the interface. Finally, we study out-of-equilibrium steady
states of a critical system connecting two reservoirs at different
temperatures. In the absence of extended symmetries, our result implies that
the energy flux across an impurity is proportional to the difference of the
squared temperatures and controlled by the reflection coefficient.Comment: 32+10 pages, 14 figures, a discussion on non-equilibrium steady
states adde
Radial coordinates for defect CFTs
We study the two-point function of local operators in the presence of a
defect in a generic conformal field theory. We define two pairs of cross
ratios, which are convenient in the analysis of the OPE in the bulk and defect
channel respectively. The new coordinates have a simple geometric
interpretation, which can be exploited to efficiently compute conformal blocks
in a power expansion. We illustrate this fact in the case of scalar external
operators. We also elucidate the convergence properties of the bulk and defect
OPE decompositions of the two-point function. In particular, we remark that the
expansion of the two-point function in powers of the new cross ratios converges
everywhere, a property not shared by the cross ratios customarily used in
defect CFT. We comment on the crucial relevance of this fact for the numerical
bootstrap.Comment: Matches journal version; the attached mathematica file (Bulk CB.nb +
rec.txt) computes the conformal blocks in the bulk channe
Sailing past the End of the World and discovering the Island
Large black holes in anti-de Sitter space have positive specific heat and do
not evaporate. In order to mimic the behavior of evaporating black holes, one
may couple the system to an external bath. In this paper we explore a rich
family of such models, namely ones obtained by coupling two holographic CFTs
along a shared interface (ICFTs). We focus on the limit where the bulk solution
is characterized by a thin brane separating the two individual duals. These
systems may be interpreted in a double holographic way, where one integrates
out the bath and ends up with a lower-dimensional gravitational braneworld dual
to the interface degrees of freedom. Our setup has the advantage that all
observables can be defined and calculated by only relying on standard rules of
AdS/CFT. We exploit this to establish a number of general results, relying on a
detailed analysis of the geodesics in the bulk. Firstly, we prove that the
entropy of Hawking radiation in the braneworld is obtained by extremizing the
generalized entropy, and moreover that at late times a so-called `island
saddle' gives the dominant contribution. We also derive Takayanagi's
prescription for calculating entanglement entropies in BCFTs as a limit of our
ICFT results.Comment: 46 pages, 13 figures. v2: minor corrections, references added. v3:
minor corrections. v4: references adde
Recent progress in the effective string theory description of LGTs.
In presence of a static pair of sources, the spectrum of low-lying states of
any confining gauge theory in D space-time dimensions is described, at large
source separations, by an effective string theory. Recently two important
advances improved our understanding of this effective theory. First, it was
realized that the form of the effective action is strongly constrained by the
requirement of the Lorentz invariance of the gauge theory, which is
spontaneously broken by the formation of a long confining flux tube in the
vacuum. This constraint is strong enough to fix uniquely the first few
subleading terms of the action. Second, it has been realized that the first of
these allowed terms - a quartic polynomial in the field derivatives - is
exactly the composite field , built with the chiral components,
and , of the energy-momentum tensor of the 2d QFT describing the
infrared limit of the effective string. This irrelevant perturbation is quantum
integrable and yields, through the thermodynamic Bethe Ansatz (TBA), the energy
levels of the string which exactly coincide with the Nambu-Goto spectrum. In
this talk we first review the general implications of these two results and
then, as a test of the power of these methods, use them to construct the first
few boundary corrections to the effective string action.Comment: Presented at the 31st International Symposium on Lattice Field Theory
(Lattice 2013), 29 July - 3 August 2013, Mainz, German