1,929 research outputs found
Anomaly mediated neutrino-photon interactions at finite baryon density
We propose new physical processes based on the axial vector anomaly and
described by the Wess-Zumino-Witten term that couples the photon, Z-boson, and
the omega-meson. The interaction takes the form of a pseudo-Chern-Simons term,
. This term
induces neutrino-photon interactions at finite baryon density via the coupling
of the Z-boson to neutrinos. These interactions may be detectable in various
laboratory and astrophysical arenas. The new interactions may account for the
MiniBooNE excess. They also produce a competitive contribution to neutron star
cooling at temperatures >10^9 K. These processes and related axion--photon
interactions at finite baryon density appear to be relevant in many
astrophysical regimes.Comment: 4 pages, 2 figures; references adde
Pion distribution amplitude from holographic QCD and the electromagnetic form factor F_pi(Q2)
The holographic QCD prediction for the pion distribution amplitude (DA)
is used to compute the pion spacelike electromagnetic form
factor within the QCD light-cone sum rule method. In
calculations the pion's renormalon-based model twist-4 DA, as well as the
asymptotic twist-4 DA are employed. Obtained theoretical predictions are
compared with experimental data and with results of the holographic QCD
Pion Form Factor in Chiral Limit of Hard-Wall AdS/QCD Model
We develop a formalism to calculate form factor and charge density
distribution of pion in the chiral limit using the holographic dual model of
QCD with hard-wall cutoff. We introduce two conjugate pion wave functions and
present analytic expressions for these functions and for the pion form factor.
They allow to relate such observables as the pion decay constant and the pion
charge electric radius to the values of chiral condensate and hard-wall cutoff
scale. The evolution of the pion form factor to large values of the momentum
transfer is discussed, and results are compared to existing experimental data.Comment: 21 page, 7 figures. Short comparison with NJL predictions for pion
radius and new references added. To be published in Phys.Rev.
Couplings of the Rho Meson in a Holographic dual of QCD with Regge Trajectories
The couplings of the meson with any hadron H are
calculated in a holographic dual of QCD where the Regge trajectories for mesons
are manifest. The resulting couplings grow linearly with the exciting number of
H, thus are far from universal. A simple argument has been given for this
behavior based on quasi-classical picture of excited hadrons. It seems that in
holographic duals with exact Regge trajectories the universality
should be violated. The -dominance for the electromagnetic form factors
of H are also strongly violated, except for the lowest state, the pion. Quite
unexpected, the form factor of the pion is completely saturated by the
contribution of the . The asymptotic behavior of the form factors are
also calculated, and are found to be perfectly accordant with the prediction of
conformal symmetry and pertubative QCD.Comment: 9 page
Self-bound dense objects in holographic QCD
We study a self-bound dense object in the hard wall model. We consider a
spherically symmetric dense object which is characterized by its radial density
distribution and non-uniform but spherically symmetric chiral condensate. For
this we analytically solve the partial differential equations in the hard wall
model and read off the radial coordinate dependence of the density and chiral
condensate according to the AdS/CFT correspondence. We then attempt to describe
nucleon density profiles of a few nuclei within our framework and observe that
the confinement scale changes from a free nucleon to a nucleus. We briefly
discuss how to include the effect of higher dimensional operator into our
study. We finally comment on possible extensions of our work.Comment: 17 pages, 5 figures, figures replaced, minor revision, to appear in
JHE
Pion Form Factors in Holographic QCD
Using a holographic dual model of QCD, we compute the pion electromagnetic
form factor F_pi(Q^2) in the spacelike momentum transfer region, as well as
pion couplings to vector mesons g_rho^(n) pi pi. Spontaneous and explicit
chiral symmetry breaking are intrinsic features of this particular holographic
model. We consider variants with both ``hard-wall'' and ``soft-wall'' infrared
cutoffs, and find that the F_pi(Q^2) data tend to lie closer to the hard-wall
model predictions, although both are too shallow for large Q^2. By allowing the
parameters of the soft-wall model (originally fixed by observables such as
m_rho) to vary, one finds fits that tend to agree better with F_pi(Q^2). We
also compute the pion charge radius for a variety of parameter
choices, and use the values of f^(n)_rho, g_{rho^(n) pi pi} and m^(n)_rho to
observe the saturation of F_pi(0) by rho poles.Comment: 17 pages, 2 figures, revised fits using consistent normalization of
f_pi. References update
Symmetry energy of dense matter in holographic QCD
We study the nuclear symmetry energy of dense matter using holographic QCD.
To this end, we consider two flavor branes with equal quark masses in a
D4/D6/D6 model. We find that at all densities the symmetry energy monotonically
increases. At small densities, it exhibits a power law behavior with the
density, .Comment: 9 pages, 3 figure
Four-point functions and kaon decays in a minimal AdS/QCD model
We study the predictions of holographic QCD for various observable four-point
quark flavour current-current correlators. The dual 5-dimensional bulk theory
we consider is a Yang Mills theory in a slice of
spacetime with boundaries. Particular UV and IR boundary conditions
encode the spontaneous breaking of the dual 4D global chiral symmetry down to
the subgroup. We explain in detail how to calculate the 4D four-point
quark flavour current-current correlators using the 5D holographic theory,
including interactions. We use these results to investigate predictions of
holographic QCD for the rule for kaon decays and the
parameter. The results agree well in comparison with experimental data, with an
accuracy of 25% or better. The holographic theory automatically includes the
contributions of the meson resonances to the four-point correlators. The
correlators agree well in the low-momentum and high-momentum limit, in
comparison with chiral perturbation theory and perturbative QCD results,
respectively.Comment: Published version, title changed to conform with Journal format,
references and clarifying remarks added, 40 pages, 5 figure
On the Evaluation of Gluon Condensate Effects in the Holographic Approach to QCD
In holographic QCD the effects of gluonic condensate can be encoded in a
suitable deformation of the 5D metric. We develop two different methods for the
evaluation of first order perturbative corrections to masses and decay
constants of vector resonances in 5D Hard-Wall models of QCD due to small
deformations of the metric. They are extracted either from a novel compact form
for the first order correction to the vector two-point function, or from
perturbation theory for vector bound-state eigenfunctions: the equivalence of
the two methods is shown. Our procedures are then applied to flat and to AdS 5D
Hard-Wall models; we complement results of existing literature evaluating the
corrections to vector decay constant and to two-pion-one-vector couplings: this
is particularly relevant to satisfy the sum rules. We concentrate our attention
on the effects for the Gasser-Leutwyler coefficients; we show that, as in the
Chiral Quark model, the addition of the gluonic condensate improves the
consistency, the understanding and the agreement with phenomenology of the
holographic model.Comment: 23 pages, three figures, sign error in pion wave function fixed,
numerical analysis extended, general conclusions unchange
Influence of Charge Transport Layers on Open Circuit Voltage and Hysteresis in Perovskite Solar Cells
Perovskite materials have experienced an impressive improvement in photovoltaic performance due to their unique combination of optoelectronic properties. Their remarkable progression, facilitated by the use of different device architectures, compositional engineering, and processing methodologies, contrasts with the lack of understanding of the materials properties and interface phenomena. Here we directly target the interplay between the charge-transporting layers (CTLs) and open-circuit potential (VOC) in the operation mechanism of the state-of-the-art CH3NH3PbI3 solar cells. Our results suggest that the VOC is controlled by the splitting of quasi-Fermi levels and recombination inside the perovskite, rather than being governed by any internal electric field established by the difference in the CTL work functions. In addition, we provide novel insights into the hysteretic origin in perovskite solar cells, identifying the nature of the contacts as a critical factor in defining the charge accumulation at its interface, leading to either ionic, electronic, or mixed ionic-electronic accumulation
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