2,290 research outputs found
Baryonic Generating Functions
We show how it is possible to use the plethystic program in order to compute
baryonic generating functions that count BPS operators in the chiral ring of
quiver gauge theories living on the world volume of D branes probing a non
compact CY manifold. Special attention is given to the conifold theory and the
orbifold C^2/Z_2 times C, where exact expressions for generating functions are
given in detail. This paper solves a long standing problem for the
combinatorics of quiver gauge theories with baryonic moduli spaces. It opens
the way to a statistical analysis of quiver theories on baryonic branches.
Surprisingly, the baryonic charge turns out to be the quantized Kahler modulus
of the geometry.Comment: 44 pages, 7 figures; fonts change
Theoretical approaches in adsorption: alkali adatom investigations
We discuss how different properties at surfaces could require for different theoretical treatments within the first-principles density functional theory. Energies and structures are accurately determined by adopting the supercell geometry. Surface states are more conveniently described by the Green function embedding approach, which is able to take into account a truly semi-infinite solid and hence real continuous spectra. In this way a detailed analysis of discrete and resonant states is provided. We mainly describe the embedding method and provide examples to compare the two approaches. We focus next on the structural and electronic properties of alkali adatoms. The adsorption structure of Na/Cu(001) at low coverages is calculated within the supercell geometry motivated by the results of the Cambridge group on surface diffusion by 3He spin echo scattering. The dispersion, energy, effective mass, and width of surface (quantum well and image) states of alkali atoms on Cu(111) are worked out by the embedding approach and compared with experiments
Electronic structure and lifetime broadening of a quantum-well state on p(2x2) K/Cu(111)
We studied a quantum-well state (QWS) generated by the adsorption of one monolayer of K on Cu(111) surface by means of a first principles approach. We calculated the electronic properties of the system within the Inglesfield's embedding method, which enables us to investigate the elastic linewidth of surface states. Our findings are in good agreement with recent experimental results obtained from photoemission spectroscopy measurements for binding energy and k(vertical bar vertical bar) dispersion. We also studied the contributions to the QWS linewidth due to electron-electron many-body effects and electron-phonon scattering in Hedin's GW approach and within the Debye model, respectively. The main contribution to the linewidth is due to intraband transitions within the QWS itself, accounting for similar to 16 meV to the total width. The elastic, electron-phonon, and interband transition contributions are smaller than 3 meV each
Comments on Anomalies and Charges of Toric-Quiver Duals
We obtain a simple expression for the triangle `t Hooft anomalies in quiver
gauge theories that are dual to toric Sasaki-Einstein manifolds. We utilize the
result and simplify considerably the proof concerning the equivalence of
a-maximization and Z-minimization. We also resolve the ambiguity in defining
the flavor charges in quiver gauge theories. We then compare coefficients of
the triangle anomalies with coefficients of the current-current correlators and
find perfect agreement.Comment: 22 pages, 3 figure
Time-dependent embedding: surface electron emission
An embedding method for solving the time-dependent Schr\"odinger equation is
developed using the Dirac-Frenkel variational principle. Embedding allows the
time-evolution of the wavefunction to be calculated explicitly in a limited
region of space, the region of physical interest, the embedding potential
ensuring that the wavefunction satisfies the correct boundary conditions for
matching on to the rest of the system. This is applied to a study of the
excitation of electrons at a metal surface, represented by a one-dimensional
model potential for Cu(111). Time-dependent embedding potentials are derived
for replacing the bulk substrate, and the image potential and vacuum region
outside the surface, so that the calculation of electron excitation by a
surface perturbation can be restricted to the surface itself. The excitation of
the Shockley surface state and a continuum bulk state is studied, and the
time-structure of the resulting currents analysed. Non-linear effects and the
time taken for the current to arrive outside the surface are discussed. The
method shows a clear distinction between emission from the localized surface
state, where the charge is steadily depleted, and the extended continuum state
where the current emitted into the vacuum is compensated by current approaching
the surface from the bulk.Comment: 15 figure
A-D-E Quivers and Baryonic Operators
We study baryonic operators of the gauge theory on multiple D3-branes at the
tip of the conifold orbifolded by a discrete subgroup Gamma of SU(2). The
string theory analysis predicts that the number and the order of the fixed
points of Gamma acting on S^2 are directly reflected in the spectrum of
baryonic operators on the corresponding quiver gauge theory constructed from
two Dynkin diagrams of the corresponding type. We confirm the prediction by
developing techniques to enumerate baryonic operators of the quiver gauge
theory which includes the gauge groups with different ranks. We also find that
the Seiberg dualities act on the baryonic operators in a non-Abelian fashion.Comment: 46 pages, 17 figures; v2: minor corrections, note added in section 1,
references adde
Counting Chiral Operators in Quiver Gauge Theories
We discuss in detail the problem of counting BPS gauge invariant operators in
the chiral ring of quiver gauge theories living on D-branes probing generic
toric CY singularities. The computation of generating functions that include
counting of baryonic operators is based on a relation between the baryonic
charges in field theory and the Kaehler moduli of the CY singularities. A study
of the interplay between gauge theory and geometry shows that given geometrical
sectors appear more than once in the field theory, leading to a notion of
"multiplicities". We explain in detail how to decompose the generating function
for one D-brane into different sectors and how to compute their relevant
multiplicities by introducing geometric and anomalous baryonic charges. The
Plethystic Exponential remains a major tool for passing from one D-brane to
arbitrary number of D-branes. Explicit formulae are given for few examples,
including C^3/Z_3, F_0, and dP_1.Comment: 75 pages, 22 figure
Is Social Training Delivered with a Head-Mounted Display Suitable for Patients with Hereditary Ataxia?
Social cognition is fundamental in everyday life to understand “others’ behavior”, which is a key feature of social abilities. Previous studies demonstrated the efficacy of a rehabilitative intervention in semi-immersive virtual reality (VR) controlled by whole-body motion to improve the ability of patients with cerebellar disorders to predict others’ intentions (VR-SPIRIT). Patients with severe ataxia that have difficulties at multiple levels of social processing could benefit from this intervention in terms of improving their social prediction skills, but they may have difficulties in controlling VR with whole-body movements. Therefore, we implemented VR-SPIRIT on a wearable, affordable, and easy-to-use technology, such as the Oculus Quest, a head-mounted display. The aim of this work was to evaluate the usability and tolerability of this VR application. We recruited 10 patients (37.7 ± 14.8 years old, seven males) with different types of hereditary ataxia who performed a single VR-SPIRIT session using the Oculus Quest viewer. After the session, patients answered a series of questionnaires to investigate the overall usability of the system and its potential effects in terms of cyber sickness. The preliminary results demonstrated system usability and tolerability. Indeed, only three patients did not complete the session due to different problems (dizziness, nausea, and boredom). In future studies, more patients will be enrolled to assess the effectiveness of the application, paving the way for the implementation of social training that can also be delivered at home
Toric AdS4/CFT3 duals and M-theory Crystals
We study the recently proposed crystal model for three dimensional
superconformal field theories arising from M2-branes probing toric Calabi-Yau
four-fold singularities. We explain the algorithms mapping a toric Calabi-Yau
to a crystal and vice versa, and show how the spectrum of BPS meson states fits
into the crystal model.Comment: 24 pages, 24 figure
Type IIB Flows with N=1 Supersymmetry
We write general and explicit equations which solve the supersymmetry
transformations with two arbitrary complex-proportional Weyl spinors on
supersymmetric type IIB strings backgrounds with all R-R ,
, and NS-NS fluxes turned on using SU(3) structures. The
equations are generalizations of the ones found for specific relations between
the two spinors by Grana, Minasian, Petrini and Tomasiello in [1] and by Butti,
Grana, Minasian, Petrini and Zaffaroni in [2]. The general equations allow to
study systematically generic type IIB backgrounds with
supersymmetry. We then explore some specific classes of flows with constant
axion, flows with constant dilaton, flows on conformally Calabi-Yau
backgrounds, flows with imaginary self-dual 3-form flux, flows with constant
ratio of the two spinors, the corresponding equations are written down and some
of their features and relations are discussed.Comment: 28 page
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