Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userSound waves in the compactified D0-D4 brane system
53
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
As an extension to our previous work, we study the transport properties of the Witten-Sakai-Sugimoto model in the black D4-brane background with smeared D0-branes (D0-D4/D8 system). Because of the presence of the D0-branes, in the bubble configuration this model is holographically dual to 4d QCD or Yang-Mills theory with a Chern-Simons term. And the number density of the D0-branes corresponds to the coupling constant ($theta$ angle) of the Chern-Simons term in the dual field theory. In this paper, we accordingly focus on small number density of the D0-branes to study the sound mode in the black D0-D4 brane system since the coupling of the Chern-Simons term should be quite weak in QCD. Then we derive its 5d effective theory and analytically compute the speed of sound and the sound wave attenuation in the approach of Gauge/Gravity duality. Our result shows the speed of sound and the sound wave attenuation is modified by the presence of the D0-branes. Thus they depend on the $theta$ angle or chiral potential in this holographic description.
rate research
Read More
Using the Witten-Sakai-Sugimoto model in the D0-D4 background, we holographically compute the vacuum decay rate of the Schwinger effect in this model. Our calculation contains the influence of the D0-brane density which could be identified as the $theta$ angle or chiral potential in QCD. Under the strong electromagnetic fields, the instability appears due to the creation of quark-antiquark pairs and the associated decay rate can be obtained by evaluating the imaginary part of the effective Euler-Heisenberg action which is identified as the action of the probe brane with a constant electromagnetic field. In the bubble D0-D4 configuration, we find the decay rate decreases when the $theta$ angle increases since the vacuum becomes heavier in the present of the glue condensate in this system. And the decay rate matches to the result in the black D0-D4 configuration at zero temperature limit according to our calculations. In this sense, the Hawking-Page transition of this model could be consistently interpreted as the confined/deconfined phase transition. Additionally there is another instability from the D0-brane itself in this system and we suggest that this instability reflects to the vacuum decay triggered by the $theta$ angle as it is known in the $theta$-dependent QCD.
We extend the holographic analysis of light-baryon spectrum in cite{key-50} to the case involving the heavy flavors. With the construction of the Witten-Sakai-Sugimoto model in the D0-D4 background, we use the mechanism proposed in cite{key-59,key-60,key-61} by including two light and one heavy flavor branes, to describe the heavy-light baryons as heavy mesons bound to a flavor instanton. The background geometry of this model corresponds to an excited state in the dual field theory with nonzero glue condensate $leftlangle mathrm{Tr}mathcal{F}wedgemathcal{F}rightrangle =8pi^{2}N_{c}tilde{kappa}$, or equivalently a $theta$ angle, which is proportional to the number density of the D0-brane charge. At strongly coupled limit, this model shows that the heavy meson is always bound in the form of the zero mode of the flavor instanton in the fundamental representation. We systematically study the quantization for the effective Lagrangian of heavy-light baryons by employing the soliton picture, and derive the mass spectrum of heavy-light baryons in the situation with single- and double-heavy baryon. We find the difference in the mass spectrum becomes smaller if the density of D0-brane charge increases and the constraint of stable states of the heavy-light baryons is $1<b<3$. It indicates that baryon can not stably exist for sufficiently large density of D0 charge which is in agreement with the conclusions in the previous study of this model.
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 $Uleft(N_{c}right)$ Yang-Mills theory in large $N_{c}$ limit involving an excited state with a nonzero $theta$ angle or glue condensate $leftlangle mathrm{Tr}mathcal{F}wedgemathcal{F}rightrangle =8pi^{2}N_{c}tilde{kappa}$, which is proportional to the charge density of the smeared D0-branes through a parameter $b$ or $tilde{kappa}$. 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 $1<b<3$ 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 $theta$ 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.
We point out that the location of renormalon singularities in theory on a circle-compactified spacetime $mathbb{R}^{d-1} times S^1$ (with a small radius $R Lambda ll 1$) can differ from that on the non-compactified spacetime $mathbb{R}^d$. We argue this under the following assumptions, which are often realized in large $N$ theories with twisted boundary conditions: (i) a loop integrand of a renormalon diagram is volume independent, i.e. it is not modified by the compactification, and (ii) the loop momentum variable along the $S^1$ direction is not associated with the twisted boundary conditions and takes the values $n/R$ with integer $n$. We find that the Borel singularity is generally shifted by $-1/2$ in the Borel $u$-plane, where the renormalon ambiguity of $mathcal{O}(Lambda^k)$ is changed to $mathcal{O}(Lambda^{k-1}/R)$ due to the circle compactification $mathbb{R}^d to mathbb{R}^{d-1} times S^1$. The result is general for any dimension $d$ and is independent of details of the quantities under consideration. As an example, we study the $mathbb{C} P^{N-1}$ model on $mathbb{R} times S^1$ with $mathbb{Z}_N$ twisted boundary conditions in the large $N$ limit.
Equations of motion for the D0-brane on AdS_4 x CP^3 superbackground are shown to be classically integrable by extending the argument previously elaborated for the massless superparticle model.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
