1,890 research outputs found
On the Lagrangian formulation of the double copy to cubic order
We investigate the Lagrangian formulation of the double-copy correspondence
between gauge theories and gravity, up to the cubic order. Building on the
definition of the double-copy field as a convolution of two vectors, we obtain
free gravitational Lagrangians as products of two Yang-Mills Lagrangians, in a
form amenable to be easily extended to the massive case. We discuss the origin
of these results from tensionless strings and show the existence of gauge
fixings that mix the two spin-one sectors and lead to an alternative,
especially simple, version of the free Lagrangian. We then construct cubic
vertices for the full double-copy multiplet, comprising a graviton, a two-form
and a scalar particle, by means of the Noether procedure. Both at the free and
at the cubic level the result gets uniquely fixed only upon imposing, on top of
gauge invariance, a left-right Lorentz symmetry ruling contraction of indices
among double-copy fields. Whereas the outcome nicely matches the cubic
interactions of supergravity, including the gauge-invariant
coupling between the scalar particle and the two-form, such a twofold Lorentz
symmetry seems to conflict with the perturbative reconstruction of space-time
geometry.Comment: 28 pages. minor editing, matches published versio
More on holographic correlators: Twisted and dimensionally reduced structures
Recently four-point holographic correlators with arbitrary external BPS
operators were constructively derived in [1,2] at tree-level for maximally
superconformal theories. In this paper, we capitalize on these theoretical
data, and perform a detailed study of their analytic properties. We point out
that these maximally supersymmetric holographic correlators exhibit a hidden
dimensional reduction structure \`a la Parisi and Sourlas. This emergent
structure allows the correlators to be compactly expressed in terms of only
scalar exchange diagrams in a dimensionally reduced spacetime, where formally
both the AdS and the sphere factors have four dimensions less. We also
demonstrate the superconformal properties of holographic correlators under the
chiral algebra and topological twistings. For and
, we obtain closed form expressions for the meromorphic
twisted correlators from the maximally R-symmetry violating limit of the
holographic correlators. The results are compared with independent field theory
computations in 4d SYM and the 6d theory, finding
perfect agreement. For , we focus on an infinite family of
near-extremal four-point correlators, and extract various protected OPE
coefficients from supergravity. These OPE coefficients provide new holographic
predictions to be matched by future supersymmetric localization calculations.
In deriving these results, we also develop many technical tools which should
have broader applicability beyond studying holographic correlators.Comment: Minor changes, matches published versio
Gluon scattering in AdS at finite string coupling from localization
We consider gluons scattering in Type IIB string theory on AdS5 × S5/ℤ2 in the presence of D7 branes, which is dual to the flavor multiplet correlator in a certain 4d N = 2 USp(2N) gauge theory with SO(8) flavor symmetry and complexified coupling τ. We compute this holographic correlator in the large N and finite τ expansion using constraints from derivatives of the mass deformed sphere free energy, which we compute to all orders in 1/N and finite τ using supersymmetric localization. In particular, we fix the F4 higher derivative correction to gluon scattering on AdS at finite string coupling τs = τ in terms of Jacobi theta functions, which feature the expected relations between the SL(2, ℤ) duality and the SO(8) triality of the CFT, and match it to the known flat space term. We also use the flat space limit to compute D2F4 corrections of the correlator at finite τ in terms of a non-holomorphic Eisenstein series. At weak string coupling, we find that the AdS correlator takes a form which is remarkably similar to that of the flat space Veneziano amplitude
Gluon scattering in AdS at finite string coupling from localization
We consider gluons scattering in Type IIB string theory on AdS in the presence of D7 branes, which is dual to the flavor
multiplet correlator in a certain 4d gauge theory
with flavor symmetry and complexified coupling . We compute this
holographic correlator in the large and finite expansion using
constraints from derivatives of the mass deformed sphere free energy, which we
compute to all orders in and finite using supersymmetric
localization. In particular, we fix the higher derivative correction to
gluon scattering on AdS at finite string coupling in terms of
Jacobi theta functions, which feature the expected relations between the
duality and the triality of the CFT, and match it to
the known flat space term. We also use the flat space limit to compute
corrections of the correlator at finite in terms of a non-holomorphic
Eisenstein series. At weak string coupling, we find that the AdS correlator
takes a form which is remarkably similar to that of the flat space Veneziano
amplitude.Comment: 24 pages plus appendice
Crossing symmetry, transcendentality and the Regge behaviour of 1d CFTs
We develop the technology for Polyakov-Mellin (PM) bootstrap in
one-dimensional conformal field theories (CFT). By adding appropriate
contact terms, we bootstrap various effective field theories in AdS and
analytically compute the CFT data to one loop. The computation can be extended
to higher orders in perturbation theory, if we ignore mixing, for any external
dimension. We develop PM bootstrap for theories and derive the necessary
contact terms for such theories (which also involves a new higher gradient
contact term absent for ). We perform cross-checks which include
considering the diagonal limit of the Ising model in terms of the PM
blocks. As an independent check of the validity of the results obtained with PM
bootstrap, we propose a suitable basis of transcendental functions, which
allows to fix the four-point correlators of identical scalar primaries
completely, up to a finite number of ambiguities related to the number of
contact terms in the PM basis. We perform this analysis both at tree level
(with and without exchanges) and at one loop. We also derive expressions for
the corresponding CFT data in terms of harmonic sums. Finally, we consider the
Regge limit of one-dimensional correlators and derive a precise connection
between the latter and the large-twist limit of CFT data. Exploiting this
result, we study the crossing equation in the three OPE limits and derive some
universal constraints for the large-twist limit of CFT data in Regge-bounded
theories with a finite number of exchanges.Comment: 90 pages, 6 figure
Gluon Scattering in AdS from CFT
We present a systematic study of holographic correlators in a vast array of
SCFTs with non-maximal superconformal symmetry. These theories include 4d
SCFTs from D3-branes near F-theory singularities, 5d Seiberg
exceptional theories and 6d E-string theory, as well as 3d and 4d
phenomenological models with probe flavor branes. We consider current
multiplets and their generalizations with higher weights, dual to massless and
massive super gluons in the bulk. At leading order in the inverse central
charge expansion, connected four-point functions of these operators correspond
to tree-level gluon scattering amplitudes in AdS. We show that all such
tree-level four-point amplitudes in all these theories are fully fixed by
symmetries and consistency conditions and explicitly construct them. Our
results encode a wealth of SCFT data and exhibit various interesting emergent
structures. These include Parisi-Sourlas-like dimensional reductions, hidden
conformal symmetry and an AdS version of the color-kinematic duality.Comment: typos corrected, published on JHE
Micro-structured rough surfaces by laser etching for heat transfer enhancement on flush mounted heat sinks
Abstract. The aim of this work is to improve heat transfer performances of
ush mounted heat
sinks used in electronic cooling. To do this we patterned 1.23 cm2 heat sinks surfaces by micro-
structured roughnesses built by laser etching manufacturing technique, and experimentally
measured the convective heat transfer enhancements due to dierent patterns. Each roughness
diers from the others with regards to the number and the size of the micro-ns (e.g. the micro-
n length ranges from 200 to 1100 m). Experimental tests were carried out in forced air cooling
regime. In particular fully turbulent
ows (heating edge based Reynolds number ranging from
3000 to 17000) were explored. Convective heat transfer coecient of the best micro-structured
heat sink is found to be roughly two times compared to the smooth heat sinks one. In addition,
surface area roughly doubles with regard to smooth heat sinks, due to the presence of micro-ns.
Consequently, patterned heat sinks thermal transmittance [W/K] is found to be roughly four
times the smooth heat sinks one. We hope this work may open the way for huge boost in the
technology of electronic cooling by innovative manufacturing techniques
In Situ Block Size Distribution Aimed at the Choice of the Design Block for Rockfall Barriers Design: A Case Study along Gardesana Road
When studying rockfall phenomena, a single value of the block volume is not sucient to
take into account the natural variability of the geometrical features (orientation, spacing, persistence)
of the discontinuity sets. Dierent approaches for obtaining cumulative distributions of potentially
detachable block volumes are compared. A highly fractured rock mass outcropping along the western
Lake Garda (Italy), consisting of prevailing limestone and interbedded marls, is studied in detail
from geological and geostructural points of view. Then, a representative rock face has been selected
and analyzed with traditional and non-contact survey methods to identify the main discontinuity
sets and to collect spacing samples. Based on these data, in situ block size distributions for dierent
combinations of sets are built following statistically-based approaches, without the use of a Discrete
Fracture Network (DFN) generator. The validation of the obtained distributions is attempted based
on the detached block surveyed at the foot of the slope. However, in this particular case study, the
detached blocks cover only a minimal volume range compared to both theoretical values and visible
rockfall scars. The fallen rock blocks have a marginal role in design block determination, since their
volume depends on geological discontinuities (bedding and fractures) and could be aected by
other processes after the detachment (e.g., fragmentation). The procedure here described should be
standard practice in the study of rockfall events, and it should be uniform in European standards
such as Eurocodes. Future developments should involve the scientific community for setting the
percentiles of the probability distribution to be considered for block design definition
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