22,755 research outputs found
Operator analysis of -widths of TMDs
Transverse momentum dependent (TMD) parton distribution functions (PDFs),
TMDs for short, are defined as the Fourier transform of matrix elements of
nonlocal combinations of quark and gluon fields. The nonlocality is bridged by
gauge links, which for TMDs have characteristic paths (future or past
pointing), giving rise to a process dependence that breaks universality. It is
possible, however, to construct sets of universal TMDs of which in a given
process particular combinations are needed with calculable, process-dependent,
coefficients. This occurs for both T-odd and T-even TMDs, including also the
{\it unpolarized} quark and gluon TMDs. This extends the by now well-known
example of T-odd TMDs that appear with opposite sign in single-spin azimuthal
asymmetries in semi-inclusive deep inelastic scattering or in the Drell-Yan
process. In this paper we analyze the cases where TMDs enter multiplied by
products of two transverse momenta, which includes besides the -broadening
observable, also instances with rank two structures. To experimentally
demonstrate the process dependence of the latter cases requires measurements of
second harmonic azimuthal asymmetries, while the -broadening will require
measurements of processes beyond semi-inclusive deep inelastic scattering or
the Drell-Yan process. Furthermore, we propose specific quantities that will
allow for theoretical studies of the process dependence of TMDs using lattice
QCD calculations.Comment: 10 pages, no figures; expanded discussions, matches version accepted
by JHE
Thermodynamics of Higher Spin Black Holes in AdS
We discuss the thermodynamics of recently constructed three-dimensional
higher spin black holes in SL(N,R)\times SL(N,R) Chern-Simons theory with
generalized asymptotically-anti-de Sitter boundary conditions. From a
holographic perspective, these bulk theories are dual to two-dimensional CFTs
with W_N symmetry algebras, and the black hole solutions are dual to thermal
states with higher spin chemical potentials and charges turned on. Because the
notion of horizon area is not gauge-invariant in the higher spin theory, the
traditional approaches to the computation of black hole entropy must be
reconsidered. One possibility, explored in the recent literature, involves
demanding the existence of a partition function in the CFT, and consistency
with the first law of thermodynamics. This approach is not free from
ambiguities, however, and in particular different definitions of energy result
in different expressions for the entropy. In the present work we show that
there are natural definitions of the thermodynamically conjugate variables that
follow from careful examination of the variational principle, and moreover
agree with those obtained via canonical methods. Building on this intuition, we
derive general expressions for the higher spin black hole entropy and free
energy which are written entirely in terms of the Chern-Simons connections, and
are valid for both static and rotating solutions. We compare our results to
other proposals in the literature, and provide a new and efficient way to
determine the generalization of the Cardy formula to a situation with higher
spin charges.Comment: 30 pages, PDFLaTeX; v2: typos corrected, explicit expressions for the
free energy adde
Twisted Open Strings from Closed Strings: The WZW Orientation Orbifolds
Including {\it world-sheet orientation-reversing automorphisms}
in the orbifold program, we construct the operator
algebras and twisted KZ systems of the general WZW {\it orientation orbifold}
. We find that the orientation-orbifold sectors corresponding
to each are {\it twisted open} WZW strings, whose
properties are quite distinct from conventional open-string orientifold
sectors. As simple illustrations, we also discuss the classical (high-level)
limit of our construction and free-boson examples on abelian .Comment: 65 pages, typos correcte
Inversion symmetry in the spin-Peierls compound NaV2O5
At room-temperature NaV2O5 was found to have the centrosymmetric space group
Pmmn. This space group implies the presence of only one kind of V site in
contrast with previous reports of the non-centrosymmetric counterpart P21mn.
This indicates a non-integer valence state of vanadium.
Furthermore, this symmetry has consequences for the interpretation of the
transition at 34 K, which was ascribed to a spin-Peierls transition of one
dimensional chains of V4+.Comment: Revtex, 3 pages, 2 postscript pictures embedded in the text.
Corrected a mistake in one pictur
Direct Mediation of Meta-Stable Supersymmetry Breaking
The supersymmetric SU(Nc) Yang-Mills theory coupled to Nf matter fields in
the fundamental representation has meta-stable vacua with broken supersymmetry
when Nc < Nf < 3/2 Nc. By gauging the flavor symmetry, this model can be
coupled directly to the standard model. We show that it is possible to make a
slight deformation to the model so that gaugino masses are generated and the
Landau pole problem can be avoided. The deformed model has simple realizations
on intersecting branes in string theory, where various features of the
meta-stable vacua are encoded geometrically as brane configurations.Comment: 22 pages, 4 figures, a reference added, version to appear in PR
In-flight measurements of energetic radiation from lightning and thunderclouds
In the certification procedure aircraft builders carry out so-called icing
tests flights, where the zero degree Celsius altitude is deliberately sought
and crossed in or under thunderstorms. Airbus also used these flights to test
ILDAS, a system aimed to determine lightning severity and attachment points
during flight from high speed data on the electric and magnetic field at the
aircraft surface. We used this unique opportunity to enhance the ILDAS systems
with two x-ray detectors coupled to high speed data recorders in an attempt to
determine the x-rays produced by lightning in-situ, with synchronous
determination of the lightning current distribution and electric field at the
aircraft. Such data are of interest in a study of lightning physics. In
addition, the data may provide clues to the x-ray dose for personnel and
equipment during flights. The icing campaign ran in April 2014; in six flights
we collected data of 61 lightning strikes on an Airbus test aircraft. In this
communication we briefly describe ILDAS and present selected results on three
strikes, two aircraft initiated and one intercepted. Most of the x-rays have
been observed synchronous with initiating negative leader steps, and as bursts
immediately preceding the current of the recoil process. Those processes
include the return stroke. The bursts last one to four micro-second and attain
x-ray energies up to 10 MeV. Intensity and spectral distribution of the x-rays
and the association with the current distribution are discussed. ILDAS also
continuously records x-rays at low resolution in time and amplitude.Comment: 28 pages, 9 figure
Single transverse-spin asymmetry in Drell-Yan lepton angular distribution
We calculate a single transverse-spin asymmetry for the Drell-Yan
lepton-pair's angular distribution in perturbative QCD. At leading order in the
strong coupling constant, the asymmetry is expressed in terms of a twist-3
quark-gluon correlation function T_F^{(V)}(x_1,x_2). In our calculation, the
same result was obtained in both light-cone and covariant gauge in QCD, while
keeping explicit electromagnetic current conservation for the virtual photon
that decays into the lepton pair. We also present a numerical estimate of the
asymmetry and compare the result to an existing other prediction.Comment: 15 pages, Revtex, 5 Postscript figures, uses aps.sty, epsfig.st
Time-resolved photometry of the young dipper RX~J1604.3-2130A:Unveiling the structure and mass transport through the innermost disk
Context. RX J1604.3-2130A is a young, dipper-type, variable star in the Upper Scorpius association, suspected to have an inclined inner disk, with respect to its face-on outer disk. Aims. We aim to study the eclipses to constrain the inner disk properties. Methods. We used time-resolved photometry from the Rapid Eye Mount telescope and Kepler 2 data to study the multi-wavelength variability, and archival optical and infrared data to track accretion, rotation, and changes in disk structure. Results. The observations reveal details of the structure and matter transport through the inner disk. The eclipses show 5 d quasi-periodicity, with the phase drifting in time and some periods showing increased/decreased eclipse depth and frequency. Dips are consistent with extinction by slightly processed dust grains in an inclined, irregularly-shaped inner disk locked to the star through two relatively stable accretion structures. The grains are located near the dust sublimation radius (similar to 0.06 au) at the corotation radius, and can explain the shadows observed in the outer disk. The total mass (gas and dust) required to produce the eclipses and shadows is a few % of a Ceres mass. Such an amount of mass is accreted/replenished by accretion in days to weeks, which explains the variability from period to period. Spitzer and WISE infrared variability reveal variations in the dust content in the innermost disk on a timescale of a few years, which is consistent with small imbalances (compared to the stellar accretion rate) in the matter transport from the outer to the inner disk. A decrease in the accretion rate is observed at the times of less eclipsing variability and low mid-IR fluxes, confirming this picture. The v sin i = 16 km s(-1) confirms that the star cannot be aligned with the outer disk, but is likely close to equator-on and to be aligned with the inner disk. This anomalous orientation is a challenge for standard theories of protoplanetary disk formation.Science & Technology Facilities Council (STFC): ST/S000399/1.
ESO fellowship.
European Union (EU): 823 823.
German Research Foundation (DFG): FOR 2634/1 TE 1024/1-1.
French National Research Agency (ANR): ANR-16-CE31-0013.
Alexander von Humboldt Foundation.
European Research Council (ERC): 678 194.
European Research Council (ERC): 742 095.
National Aeronautics & Space Administration (NASA).
National Science Foundation (NSF).
National Aeronautics & Space Administration (NASA): NNG05GF22G.
National Science Foundation (NSF): AST-0909182, AST-1 313 422
Black Hole Meiosis
The enumeration of BPS bound states in string theory needs refinement.
Studying partition functions of particles made from D-branes wrapped on
algebraic Calabi-Yau 3-folds, and classifying states using split attractor flow
trees, we extend the method for computing a refined BPS index, arXiv:0810.4301.
For certain D-particles, a finite number of microstates, namely polar states,
exclusively realized as bound states, determine an entire partition function
(elliptic genus). This underlines their crucial importance: one might call them
the `chromosomes' of a D-particle or a black hole. As polar states also can be
affected by our refinement, previous predictions on elliptic genera are
modified. This can be metaphorically interpreted as `crossing-over in the
meiosis of a D-particle'. Our results improve on hep-th/0702012, provide
non-trivial evidence for a strong split attractor flow tree conjecture, and
thus suggest that we indeed exhaust the BPS spectrum. In the D-brane
description of a bound state, the necessity for refinement results from the
fact that tachyonic strings split up constituent states into `generic' and
`special' states. These are enumerated separately by topological invariants,
which turn out to be partitions of Donaldson-Thomas invariants. As modular
predictions provide a check on many of our results, we have compelling evidence
that our computations are correct.Comment: 46 pages, 8 figures. v2: minor changes. v3: minor changes and
reference adde
Near Horizon Limits of Massless BTZ and Their CFT Duals
We consider the massless BTZ black hole and show that it is possible to take
its "near horizon" limit in two distinct ways. The first one leads to a null
self-dual orbifold of AdS3 and the second to a spacelike singular AdS3/Z_K
orbifold in the large K limit, the "pinching orbifold". We show that from the
dual 2d CFT viewpoint, the null orbifold corresponds to the p^+=0 sector of the
Discrete Light-Cone Quantisation (DLCQ) of the 2d CFT where a chiral sector of
the CFT is decoupled, while the pinching orbifold corresponds to taking an
infinite mass gap limit in both the right and left sectors of the 2d CFT,
essentially leaving us with the states L_0=\bar L_0=c/24 only. In the latter
case, one can combine the near horizon limit with sending the 3d Planck length
l_P to zero, or equivalently the dual CFT central charge c to infinity. We
provide preliminary evidence that in that case some nontrivial dynamics may
survive the limit.Comment: 22 pages, no figures, v2: minor improvements, references adde
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