arXiv subjects

Jacob Sonnenschein

Publications and source records attributed to Jacob Sonnenschein.

At least 73 records · Page 4Linked to original sources

arXiv2012

Towards brane-antibrane inflation in type $II_A$: The holographic MQCD model

We describe type $II_A$ cosmological brane inflation scenarios based on the holographic MQCD model of Aharony et al \cite{Aharony:2010mi}. The scenarios can be related via T-duality to the type $II_B$ KKLMMT model \cite{Kachru:2003sx}. They describe a probe brane configuration of $p$ D4 branes stretching between an $NS5$ and $NS5'$ branes in the holographic background of large $N$ D4 branes. The resulting cosmological models have a Wick-rotated D4-brane metric, with transverse dimensions compactified, and a spiralling brane with flux $p$. In one model, the background has a small nonextremality, and the inflaton is provided by the position of a "sliding" D4-brane, and in the other, the background is supersymmetric, but with a sliding anti-D4-brane. We obtain good and generic inflationary models, though several unknowns remain, in particular about subleading corrections. The usual caveat of volume stabilization generically spoiling slow-roll still applies.

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arXiv2011

Searching for an Attractive Force in Holographic Nuclear Physics

We are looking for a holographic explanation of nuclear forces, especially the attractive forces. Recently, the repulsive hard core of a nucleon-nucleon potential was obtained in the Sakai-Sugimoto model, and we show that a generalized version of that model -- with an asymmetric configuration of the flavor D8 branes -- also has an attractive potential. While the repulsive potential stems from the Chern-Simons interactions of the U(2) flavor gauge fields in 5D, the attractive potential is due to a coupling of the gauge fields to a scalar field describing fluctuations of the flavor branes' geometry. At intermediate distances r between baryons -- smaller than R_KK=O(1)/M_{omega meson} but larger than the radius rho=R_KK/sqrt('t Hooft coupling) of the instanton at the core of a baryon -- both the attractive and the repulsive potentials behave as 1/r^2, but the attractive potential is weaker: Depending on the geometry of the flavor D8 branes, the ratio C=-V_attr/V_rep ranges from 0 to 1/9. The 5D scalar fields also affect the isovector tensor and spin-spin forces, and the overall effect is similar to the isoscalar central forces: V(r)->(1-C)*V(r). At longer ranges $r\gtrsim R_{\rm KK}$, we find that the attractive potential decays faster than the repulsive potential, so the net potential is always repulsive. This unrealistic behavior may be peculiar to the Sakai-Sugimoto-like models, or it could be a general problem of the large N_c limit inherent in holography.

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arXiv2011

Can holography reproduce the QCD Wilson line?

Recently a remarkable agreement was found between lattice simulations of long Wilson lines and behavior of the Nambu Goto string in flat space-time. However, the latter fails to fit the short distance behavior since it admits a tachyonic mode for a string shorter than a critical length. In this paper we examine the question of whether a classical holographic Wilson line can reproduce the lattice results for Wilson lines of any length. We determine the condition on the the gravitational background to admit a Coulombic potential at short distances. We analyze the system using three different renormalization schemes. We perform an explicit best fit comparison of the lattice results with the holographic models based on near extremal D3 and D4 branes, non-critical near extremal AdS6 model and the Klebanov Strassler model. We find that all the holographic models examined admit after renormalization a constant term in the potential. We argue that the curves of the lattice simulation also have such a constant term and we discuss its physical interpretation.

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arXiv2010

Attractive Holographic Baryons

We propose a holographic model of baryon interactions based on non-supersymmetric D7-anti-D7 flavor branes embedded in the Klebanov-Strassler background. The baryons are D3-branes wrapping the 3-sphere of the conifold with M strings connecting the D3 and the flavor branes. Depending on the location of the latter there are two possibilities: the D3 either remains separate from the flavor branes or dissolves in them and becomes a flavor instanton. The leading order interaction between the baryons is a competition between the attraction and the repulsion due to the sigma and omega mesons. The lightest 0++ particle sigma is a pseudo-Goldstone boson associated with the spontaneous breaking of scale invariance. In a certain range of parameters it is parametrically lighter than any other massive state. As a result at large distances baryons attract each other. At short distances the potential admits a repulsive core due to an exchange of the omega vector meson. We discuss baryon coupling to glueballs, massive mesons and pions and point out the condition for the model to have a small binding energy.

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arXiv2010

Holographic MQCD

We study a brane configuration of D4-branes and NS5-branes in weakly coupled type IIA string theory, which describes in a particular limit d=4 N=1 SU(N+p) supersymmetric QCD with 2N flavors and a quartic superpotential. We describe the geometric realization of the supersymmetric vacuum structure of this gauge theory. We focus on the confining vacua of the gauge theory, whose holographic description is given by the MQCD brane configuration in the near-horizon geometry of N D4-branes. This description, which gives an embedding of MQCD into a field theory decoupled from gravity, is valid for 1 << p << N, in the limit of large five dimensional `t Hooft couplings for the color and flavor groups. We analyze various properties of the theory in this limit, such as the spectrum of mesons, the finite temperature behavior, and the quark-anti-quark potential. We also discuss the same brane configuration on a circle, where it gives a geometric description of the moduli space of the Klebanov-Strassler cascading theory, and some non-supersymmetric generalizations.

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arXiv2010

Non-Perturbative Field Theory - From two dimensional conformal field theory to QCD in four dimensions

This note is based on the summary of our book entitled "Non-perturbative field theoryfrom two dimensional conformal field theory to QCD in four dimensions", published recently by Cambridge University Press. It includes 436 pages. The book provides a detailed description of the tool box of non-perturbative techniques, presents applications of them to simplified systems, mainly of gauge dynamics in two dimensions, and examines the lessons one can learn from those systems about four dimensional QCD and hadron physics. In particular the book deals with conformal invariance, integrability, bosonization, large N, solitons in two dimensions and monopoles and instantons in four dimensions, confinement versus screening and finally the hadronic spectrum and scattering. We also attach the table of contents and the list of references of the book. We would be grateful for any comments or suggestions related to the material in the book. These may be incorporated in a possible future edition. They may be sent via the e-mails below.

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arXiv2009

Holographic Dual of QCD from Black D5 Branes

We study the dynamics of probe D7 $\overline{\rm D7}$ flavor probe branes in the background of near extremal D5 branes. This model is a holographic dual to a gauge theory with spontaneous breaking of a $U(N_f)_L\times U(N_f)_R$ chiral symmetry. The spectrum of two such D7 $\overline{\rm D7}$ embeddings, contains a single massive 4D meson coming from the world volume U(1) gauge field, the pion, and a single massive 4D scalar meson coming from fluctuations of the embedding of the brane. In addition, there are continuum five dimensional states due to the finite height of the effective potential in the radial direction. We investigate baryons in this model, and find that the size is stabilized due to the Chern-Simons term in the D7 world volume action. The model admits a Hagedorn temperature of $\frac{1}{2πR}$ where $R$ is the radius parameter in the D5 branes metric. We investigate the pattern of chiral symmetry breaking in the deconfined phase as a function of the asymptotic separation of the branes $L$. We find that for $\fracπ{3}R<L\lessapprox 1.068 R$ that chiral symmetry is restored, and that chiral symmetry is broken for $L$ outside this window. We further argue that the solutions with $L<\fracπ{3}$ are only classically stable, and in fact no D7 embedding exists with these boundary conditions.

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arXiv2009

Holographic technicolor models and their S-parameter

We study the Peskin-Takeuchi S-parameter of holographic technicolor models. We present the recipe for computing the parameter in a generalized holographic setup. We then apply it to several holographic models that include: (a) the Sakai-Sugimoto model and (b) its non-compactified cousin, (c) a non-critical analog of (a) based on near extremal AdS_6 background, (d) the KMMW model which is similar to model (a) but with D6 and anti-D6 flavor branes replacing the D8 and anti-D8 branes, (e) a model based on D5 branes compactified on two S^1s with D7 and anti-7 probe branes and (f) the conifold model with the same probe branes as in (e). The models are gravity duals of gauge theories with U(N_{TC}) gauge theory and with a breakdown of a flavor symmetry U(N_{TF})xU(N_{TF}) to U_V(N_{TF}). The models (a), (c),(d) and (e) are duals of a confining gauge theories whereas (b) and (f) associate with non confining models. The S-parameter was found to be S=sN_{TC} where s is given by 0.017λ_{TC}, 0.016λ_{TC}, 0.095, 0.50 and 0.043 for the (a),(b),(c),(d), (f) models respectively and for model (e) s is divergent. These results are valid in the large N_{TC} and large λ_{TC} limit. We further derive the dependence of the S-parameter on the "string endpoint" mass of the techniquarks for the various models. We compute the masses of the low lying vector technimesons.

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arXiv2009

Chiral Symmetry Breaking with non-SUSY D7-branes in ISD backgrounds

Supersymmetric probe branes satisfy the kappa-symmetry condition which ensures that the action is minimized with respect to both variations of the embedding and of the world-volume gauge field. We observe that the kappa-symmetry condition for a D7-brane in an imaginary self-dual (ISD) background can be generalized yielding minimization of the action with respect to variations of the gauge field only but not of the embedding. This provides a new way to construct non-BPS solutions for D7-branes once the embedding extremizes the geometrical volume of the brane. We then apply this method to the Klebanov-Strassler background and find a new D7-anti D7-brane configuration that realizes the spontaneous breaking of flavor chiral symmetry as evidenced by the Goldstone boson identified in the spectrum. This result generalizes our previous construction for the Klebanov-Witten model. We compare our setup with the Sakai-Sugimoto model and discuss possible applications to QCD-like physics.

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arXiv2009

Rho meson condensation at finite isospin chemical potential in a holographic model for QCD

We analyze the effect of an isospin chemical potential μ_I in the Sakai-Sugimoto model, which is the string dual of a confining gauge theory related to large N_c QCD, at temperatures below the chiral symmetry restoration temperature. For small chemical potentials we show that the results agree with expectations from the low-energy chiral Lagrangian, and the charged pion condenses. When the chemical potential reaches a critical value μ_I = μ_{crit} ~ 1.7 m_ρ, the lowest vector meson (the "rho meson") becomes massless, and it condenses (in addition to the pion condensate) for μ_I > μ_{crit}. This spontaneously breaks the rotational symmetry, as well as a residual U(1) flavor symmetry. We numerically construct the resulting new ground state for μ_I > μ_{crit}.

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arXiv2009

Comments on Baryons in Holographic QCD

We generalize the description of baryons as instantons of Sakai-Sugimoto model to the case where the flavor branes are non-anti-podal. The later corresponds to quarks with a "string endpoint mass". We show that the baryon vertex is located on the flavor branes and hence the generalized baryons also associate with instantons. We calculate the baryon mass spectra, the isoscalar and axial mean square radii, the isoscalar and isovector magnetic moments and the axial coupling as a function of the mass scale M_{KK} and the location ζof the tip of U-shaped flavor D8-branes. We determine the values of M_{KK} and ζfrom a best fit comparison with the experimental data. The later comes out to be in a forbidden region, which may indicate that the incorporation of baryons in Sakai-Sugimoto model has to be modified. We discuss the analogous baryons in a non-critical gravity model. A brief comment on the single flavor case (N_f=1) is also made.

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arXiv2009

A New Holographic Model of Chiral Symmetry Breaking

A new family of models of flavour chiral symmetry breaking is proposed. The models are based on the embedding of a stack of D7-branes and a stack of anti D7-branes in the conifold background. This family of gravity models is dual to a field theory with spontaneous breaking of conformal invariance and chiral flavour symmetry. We identify the corresponding Goldstone bosons and compute the spectra of massive scalar and vector mesons. The dual quiver gauge theory is also discussed. We further analyse a model where chiral symmetry is not broken.

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arXiv2008

On the spectra of scalar mesons from HQCD models

We determine the holographic spectra of scalar mesons from the fluctuations of the embedding of flavor D-brane probes in HQCD models. The models we consider include a generalization of the Sakai Sugimoto model at zero temperature and at the "high-temperature intermediate phase", where the system is in a deconfining phase while admitting chiral symmetry breaking and a non-critical 6d model at zero temperature. All these models are based on backgrounds associated with near extremal N_c D4 branes and a set of N_f<<N_c flavor probe branes that admit geometrical chiral symmetry breaking. We point out that the spectra of these models include a 0^{--} branch which does not show up in nature. At zero temperature we found that the masses of the mesons M_n depend on the "constituent quark mass" parameter m^c_q and on the excitation number n as M_n^2 m^c_q and M^2_n n^{1.7} for the ten dimensional case and as M_n m^c_q and M_n n^{0.75} in the non-critical case. At the high temperature intermediate phase we detect a decrease of the masses of low spin mesons as a function of the temperature similar to holographic vector mesons and to lattice calculations.

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arXiv2008

Holographic melting and related properties of mesons in a quark gluon plasma

We analyse mesons at finite temperature in a chiral, confining string dual. The temperature dependence of low-spin as well as high-spin meson masses is shown to exhibit a pattern familiar from the lattice. Furthermore, we find the dissociation temperature of mesons as a function of their spin, showing that at a fixed quark mass, mesons with larger spins dissociate at lower temperatures. The Goldstone bosons associated with chiral symmetry breaking are shown to disappear above the chiral symmetry restoration temperature. Finally, we show that holographic consideration imply that large-spin mesons do not experience drag effects when moving through the quark gluon plasma. They do, however, have a maximum velocity for fixed spin, beyond which they dissociate.

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arXiv2008

Localized Backreacted Flavor Branes in Holographic QCD

We investigate the perturbative (in $g_s N_{D8}$) backreaction of localized D8 branes in D4-D8 systems including in particular the Sakai Sugimoto model. We write down the explicit expressions of the backreacted metric, dilaton and RR form. We find that the backreaction remains small up to a radial value of $u \ll \ell_s/(g_s N_{D8})$, and that the background functions are smooth except at the D8 sources. In this perturbative window, the original embedding remains a solution to the equations of motion. Furthermore, the fluctuations around the original embedding, describing scalar mesons, do not become tachyonic due to the backreaction in the perturbative regime. This is is due to a cancelation between the DBI and CS parts of the D8 brane action in the perturbed background.

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arXiv2008

Non critical holographic models of the thermal phases of QCD

We analyze the thermal phases of a non critical holographic model of QCD. The model is based on a six dimensional background of $N_c$ non extremal D4 branes wrapping a spacial circle of radius $R$ and the compactified Euclidean time direction of radius $β=1/T$. We place in this background stacks of $N_f$ D4 and anti-D4 flavor probe branes with a separation distance $L$ at large radial direction. %The dual theory is a 4+1 dimensional $SU(N_c)$ gauge theory %compactified on a radius $R$ with anti-periodic boundary conditions for the fermions. The analysis of the DBI effective action yields the following phase diagram: At low temperature the system is in a confining phase with broken chiral symmetry. In the high temperature deconfining phase chiral symmetry can be either restored for $L>L_c=1.06 R$ or broken for $L<L_c$. All of these phase transitions are of first order. We analyze the spectrum of the low-spin and high-spin mesons. High spin mesons above certain critical angular momentum ``melt''. We detect (no) drag for (mesons) quarks moving in hot quark-gluon fluid. The results resemble the structure and properties of the thermal Sakai-Sugimoto model derived in hep-th/0604161.

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arXiv2007

Quark mass and condensate in HQCD

We extend the Sakai-Sugimoto holographic model of QCD (HQCD) by including the scalar bi-fundamental "tachyon" field in the 8-brane-anti-8-brane probe theory. We show that this field is responsible both for the spontaneous breaking of the chiral symmetry, and for the generation of (current algebra) quark masses, from the point of view of the bulk theory. As a by-product we show how this leads to the Gell-Mann- Oakes-Renner relation for the pion mass.

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arXiv2006

On the pp-wave limit and the BMN structure of new Sasaki-Einstein spaces

We construct the pp-wave string associated with the Penrose limit of $Y^{p,q}$ and $L^{p,q,r}$ families of Sasaki-Einstein geometries. We identify in the dual quiver gauge theories the chiral and the non-chiral operators that correspond to the ground state and the first excited states. We present an explicit identification in a prototype model of $L^{1,7,3}$.

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