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Holographic Schwinger effect in the confining background with D-instanton
Using the gauge-gravity duality, we study the holographic Schwinger effect by
performing the potential analysis on the confining D3- and D4-brane background
with D-instantons then evaluate the pair production/decay rate by taking
account into a fundamental string and a single flavor brane respectively. The
two confining backgrounds with D-instantons are obtained from the black
D(-1)-D3 and D0-D4 solution with a double Wick rotation. The total potential
and pair production/decay rate in the Schwinger effect are calculated
numerically by examining the NG action of a fundamental string and the DBI
action of a single flavor brane all in the presence of an electric field. In
both backgrounds our numerical calculation agrees with the critical electric
field evaluated from the DBI action and shows the potential barrier is
increased by the presence of the D-instantons, thus the production/decay rate
is suppressed by the D-instantons. Our interpretation is that particles in the
dual field theory could acquire an effective mass through the Chern-Simons
interaction or the theta term due to the presence of D-instantons so that the
pair production/decay rate in Schwinger effect is suppressed since it behaves
as . Our conclusion is in agreement with the previous results
obtained in the deconfined D(-1)-D3 background at zero temperature limit and
from the approach of the flavor brane in the D0-D4 background. In this sense,
this work may be also remarkable to study the phase transition in
Maxwell-Chern-Simons theory and observable effects by the theta angle in QCD.Comment: 2 tables,9 figures,23 page
The interaction of glueball and heavy-light flavoured meson in holographic QCD
We construct the D4/D8 brane configuration in the Witten-Sakai-Sugimoto model
by introducing a pair of heavy flavour brane with a heavy-light open string.
The multiplets created by the heavy-light string acquire mass due to the finite
separation of the heavy and light flavour branes thus they could be identified
as the heavy-light meson fields in this model. On the other hand the glueball
field is identified as the gravitational fluctuations carried by the close
string in the bulk, so this model is able to describe the interaction of
glueball and heavy-light meson through the open-close string interaction in
gauge-gravity duality. We explicitly derive the effective action for the
various glueballs and heavy-light mesons then numerically evaluate the
associated coupling constants. Afterwards the decay widths of various glueballs
to the lowest heavy-light meson, which is identified as meson, are
calculated by using our effective action. This work extends the previous
investigations of glueball in holographic QCD and it is also a further
prediction of glueball-meson interaction.Comment: 33 pages, 2 figures, 2 table
Glueball-baryon interactions in holographic QCD
Studying the Witten-Sakai-Sugimoto model with type IIA string theory, we find
the glueball-baryon interaction is predicted in this model. The glueball is
identified as the 11D gravitational waves or graviton described by the M5-brane
supergravity solution. Employing the relation of M-theory and type IIA string
theory, glueball is also 10D gravitational perturbations which are the excited
modes by close strings in the bulk of this model. On the other hand, baryon is
identified as a D4-brane wrapped on which is named as baryon vertex, so
the glueball-baryon interaction is nothing but the close string/baryon vertex
interaction in this model. Since the baryon vertex could be equivalently
treated as the instanton configurations on the flavor brane, we identify the
glueball-baryon interaction as "graviton-instanton" interaction in order to
describe it quantitatively by the quantum mechanical system for the collective
modes of baryons. So the effective Hamiltonian can be obtained by considering
the gravitational perturbations in the flavor brane action. With this
Hamiltonian, the amplitudes and the selection rules of the glueball-baryon
interaction can be analytically calculated in the strong coupling limit. We
show our calculations explicitly in two characteristic situations which are
"scalar and tensor glueball interacting with baryons". Although there is a long
way to go, our work provides a holographic way to understand the interactions
of baryons in hadronic physics and nuclear physics by the underlying string
theory.Comment: 16 pages, adding the Appendix C and transition amplitude in this
versio
Holographic three flavor baryon in the Witten-Sakai-Sugimoto model with the D0-D4 background
With the construction of the Witten-Sakai-Sugimoto model in the D0-D4
background, we systematically investigate the holographic baryon spectrum in
the case of three flavors. The background geometry in this model is
holographically dual to Yang-Mills theory in large
limit involving an excited state with a nonzero angle or glue
condensate , which is proportional to the charge density of
the smeared D0-branes through a parameter or . The
classical solution of baryon in this model can be modified by embedding the
Belavin-Polyakov-Schwarz-Tyupkin (BPST) instanton and we carry out the
quantization of the collective modes with this solution. Then we extend the
analysis to include the heavy flavor and find that the heavy meson is always
bound in the form of the zero mode of the flavor instanton in strong coupling
limit. The mass spectrum of heavy-light baryons in the situation with single-
and double-heavy baryon is derived by solving the eigen equation of the
quantized collective Hamiltonian. Afterwards we obtain that the constraint of
stable baryon states has to be and the difference in the baryon
spectrum becomes smaller as the D0 charge increases. It indicates that quarks
or mesons can not form stable baryons if the angle or glue condensate
is sufficiently large. Our work is an extension of the previous study of this
model and also agrees with those conclusions.Comment: 35 pages, 2 figures, 1 table, this version includes the
acknowledgement and some revision
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