13,230 research outputs found
RG-flows and Open/Closed String Duality
We discuss the interpaly between IR and UV divergences in theories with open
and unoriented strings in view of the AdS/CFT correspondence. We start by
deriving general formulas for the computation of threshold corrections to gauge
couplings in generic configurations with open and unoriented strings. These
allow us to discuss the IR/UV correspondence between beta-function coefficients
and ``dilaton'' tadpoles for several brane configurations probed by D3-branes.
Finally we comment on the AdS supergravity descriptions of gauge theories that
are (super)conformal in the large N limit.Comment: Minor corrections. References added. Version to be published in
JHEP08(2000)035. 22 pages, Late
Anomalies & Tadpoles
We show that massless RR tadpoles in vacuum configurations with open and
unoriented strings are always related to anomalies. RR tadpoles arising from
sectors of the internal SCFT with non-vanishing Witten index are in one-to-one
correspondence with conventional irreducible anomalies. The anomalous content
of the remaining RR tadpoles can be disclosed by considering anomalous
amplitudes with higher numbers of external legs. We then provide an explicit
parametrization of the anomaly polynomial in terms of the boundary reflection
coefficients, i.e. one-point functions of massless RR fields on the disk. After
factorization of the reducible anomaly, we extract the relevant WZ couplings in
the effective lagrangians.Comment: 20 pages, Late
Phase diagram of an Ising model with competitive interactions on a Husimi tree and its disordered counterpart
We consider an Ising competitive model defined over a triangular Husimi tree
where loops, responsible for an explicit frustration, are even allowed. After a
critical analysis of the phase diagram, in which a ``gas of non interacting
dimers (or spin liquid) - ferro or antiferromagnetic ordered state'' transition
is recognized in the frustrated regions, we introduce the disorder for studying
the spin glass version of the model: the triangular +/- J model. We find out
that, for any finite value of the averaged couplings, the model exhibits always
a phase transition, even in the frustrated regions, where the transition turns
out to be a glassy transition. The analysis of the random model is done by
applying a recently proposed method which allows to derive the upper phase
boundary of a random model through a mapping with a corresponding non random
one.Comment: 19 pages, 11 figures; content change
On stringy AdS_5 x S^5 and higher spin holography
We derive the spectrum of Kaluza-Klein descendants of string excitations on
AdS_5 x S^5. String states are organized in long multiplets of the AdS
supergroup SU(2,2|4,R) with a rich pattern of shortenings at the higher spin
enhancement point \lambda=0. The string states holographically dual to the
higher spin currents of SYM theory in the strict zero coupling limit are
identified together with the corresponding Goldstone particles responsible for
the Higgsing of the higher spin symmetry at \lambda\neq 0. Exploiting higher
spin symmetry we propose a very simple yet effective mass formula and establish
a one-to-one correspondence between the complete spectrum of \Delta_0 <= 4
string states and relevant/marginal single-trace deformations in N=4 SYM theory
at large N. To this end, we describe how to efficiently enumerate scaling
operators in `free' YM theory, with the inclusion of fermionic `letters', by
resorting to Polya theory. Comparison between the spectra of 1/4-BPS states is
also presented. Finally, we discuss how to organize the spectrum of N=4 SYM
theory in SU(2,2|4,R) supermultiplets by means of some kind of `Eratostenes's
sieve'.Comment: 38 pages, LateX2e, references adde
Supersolid phase of hardcore bosons on triangular lattice
We establish the nature of the supersolid phase observed for hardcore bosons
on the triangular lattice near half-integer filling factor, and study the phase
diagram of the system at finite temperature. We find that the solid order is
always of the (2m,-m',-m') with m changing discontinuously from positive to
negative values at half-filling, contrary to predictions of other phases, based
on an analogy with the properties of Ising spins in transverse magnetic field.
At finite temperature we find two intersecting second-order transition lines,
one in the 3-state Potts universality class and the other of the
Kosterlitz-Thouless type
A Canonical Decomposition in Collective and Relative Variables of a Klein-Gordon Field in the Rest-Frame Wigner-Covariant Instant Form
The canonical decomposition of a real Klein-Gordon field in collective and
relative variables proposed by Longhi and Materassi is reformulated on
spacelike hypersurfaces. This allows to obtain the complete canonical reduction
of the system on Wigner hyperplanes, namely in the rest-frame Wigner-covariant
instant form of dynamics. From the study of Dixon's multipoles for the
energy-momentum tensor on the Wigner hyperplanes we derive the definition of
the canonical center-of-mass variable for a Klein-Gordon field configuration:
it turns out that the Longhi-Materassi global variable should be interpreted as
a center of phase of the field configuration. A detailed study of the
kinematical "external" and "internal" properties of the field configuration on
the Wigner hyperplanes is done. The construction is then extended to charged
Klein-Gordon fields: the centers of phase of the two real components can be
combined to define a global center of phase and a collective relative variable
describing the action-reaction between the two Feshbach-Villars components of
the field with definite sign of energy and charge. The Dixon multipoles for
both the energy-momentum and the electromagnetic current are given. Also the
coupling of the Klein-Gordon field to scalar relativistic particles is studied
and it is shown that in the reduced phase space, besides the particle and field
relative variables, there is also a collective relative variable describing the
relative motion of the particle subsytem with respect to the field one.Comment: 86 pages, no figure
Determinants of international migrations to Italian provinces
International migration flows constitute one of the most policy-relevant elements of modern economies. The Italian experience is a case of particular interest given the rapid growth of immigration flows, the large number of countries of origin involved, and regional economic heterogeneity. This paper analyses the bilateral stocks of migrants coming from 142 countries and living in 103 Italian provinces to ascertain what characteristics of home countries and destination provinces are associated with international migrations. The results of the estimation of a gravity model on the stock of migrants show that economic, demographic and institutional variables are correlated with migration patterns. In light of the recent Arab Spring, it is interesting to note that migrants come to Italy predominantly from geographically close, democratic and middle-income countries.International migrations, Italy, Gravity model
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