arXiv subjects

Christiana Pantelidou

Publications and source records attributed to Christiana Pantelidou.

32 records · Page 2Linked to original sources

arXiv2019

Spectrum of a Supersymmetric Color Superconductor

We have recently shown that the ground state of ${\cal N} = 4$, SU($N_{\rm{\tiny c}}$) super Yang--Mills coupled to $N_{\rm{\tiny f}} \ll N_{\rm{\tiny c}}$ flavors, in the presence of non-zero isospin and R-symmetry charges, is a supersymmetric, superfluid, color superconductor. The holographic description consists of $N_{\rm{\tiny f}}$ D7-brane probes in AdS$_5\times$S$^5$ with electric and instantonic fields on their worldvolume. These correspond to fundamental strings and D3-branes dissolved on the D7-branes, respectively. Here we use this description to determine the spectrum of mesonic excitations. As expected for a charged superfluid we find non-relativistic, massless Goldstone modes. We also find extra ungapped modes that are not associated to the breaking of any global symmetries but to the supersymmetric nature of the ground state. If the quark mass is much smaller than the scale of spontaneous symmetry breaking a pseudo-Goldstone boson is also present. We highlight some new features that appear only for $N_{\rm{\tiny f}}> 2$. We show that, in the generic case of unequal R-symmetry charges, the dissolved strings and D3-branes blow up into a D5-brane supertube stretched between the D7-branes.

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arXiv2019

Towards a Holographic Quark Matter Crystal

We construct the gravity dual of $d=4$, $\mathcal{N}=4$, SU($N_\rm{c}$) super Yang-Mills theory, coupled to $N_\rm{f}$ flavors of dynamical quarks, at non-zero temperature $T$ and non-zero quark density $N_\rm{q}$. The supergravity solutions possess a regular horizon if $T>0$ and include the backreaction of $N_\rm{c}$ color D3-branes and $N_\rm{f}$ flavor D7-branes with $N_\rm{q}$ units of electric flux on their worldvolume. At zero temperature the solutions interpolate between a Landau pole singularity in the ultraviolet and a Lifshitz geometry in the infrared. At high temperature the thermodynamics is directly sensitive to the Landau pole, whereas at low temperature it is not, as expected from effective field theory. At low temperature and sufficiently high charge density we find thermodynamic and dynamic instabilities towards the spontaneous breaking of translation invariance.

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arXiv2019

A Supersymmetric Color Superconductor from Holography

We use holography to study $d=4$, $\mathcal{N}=4$, SU($N_{\rm \tiny{c}}$) super Yang-Mills coupled to $N_{\rm \tiny{F}} \ll N_{\rm \tiny{c}}$ quark flavors. We place the theory at finite isospin density $n_{\rm \tiny{I}}$ by turning on an isospin chemical potential $μ_{\rm \tiny{I}}=M_{\rm \tiny{q}}$, with $M_{\rm \tiny{q}}$ the quark mass. We also turn on two R-symmetry charge densities $n_1=n_2$. We show that the ground state is a supersymmetric, superfluid, color superconductor, namely a finite-density state that preserves a fraction of supersymmetry in which part of the global symmetries and part of the gauge symmetries are spontaneously broken. The holographic description consists of $N_{\rm \tiny{F}}$ D7-brane probes in $\mbox{AdS}_5 \times \mbox{S}^5$. The symmetry breaking is due to the dissolution of some D3-branes inside the D7-branes triggered by the electric field associated to the isospin charge. The massless spectrum contains Goldstone bosons and their fermionic superpartners. The massive spectrum contains long-lived, mesonic quasi-particles if $n_{\rm \tiny{I}} \ll μ_{\rm \tiny{I}}^3$, and no quasi-particles otherwise. We discuss the possibility that, despite the presence of mass scales and charge densities in the theory, conformal and relativistic invariance arise as emergent symmetries in the infrared.

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arXiv2019

Holographic transport and density waves

We consider transport of heat and charge in holographic lattices which are phases of strongly coupled matter in which translations are broken explicitly. In these systems, we study a spontaneous density wave that breaks translations incommensurately to the lattice. The emergent gapless mode due to symmetry breaking couples to the heat current impacting transport at low frequencies. We study the effects of this coupling when the mode is freely sliding as well as after the introduction of a small deformation parameter which pins down the density wave. We prove that the DC transport coefficients are discontinuous in the limit of the pinning parameter going to zero. From the perspective of finite frequency thermoelectric conductivity, this limiting process is accompanied by the transfer of spectral weight to frequencies set by the pinning parameter. As expected, for weak momentum relaxation, this spectral weight transfer appears as a shift of the Drude peak.

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arXiv2018

Large D holography with metric deformations

We consider Einstein gravity in AdS in the presence of a deformed conformal boundary metric, in the limit of large spacetime dimension. At leading order we find a new set of effective near-horizon equations. These can be understood as covariant generalisations of the undeformed equations with new source terms due to the curvature. We show that these equations are given by the conservation of the exact second-order Landau-frame hydrodynamic stress tensor. No derivative expansions are invoked in this identification. We use the new equations to study CFTs with 2d lattice deformations, computing their quasi-normal mode spectra and thermal conductivities, both numerically and analytically to quartic order in small lattice amplitude. Many of our results also apply to asymptotically flat spacetimes.

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arXiv2017

Holography with a Landau pole

Holography for UV-incomplete gauge theories is important but poorly understood. A paradigmatic example is $d=4$, $\mathcal{N}=4$ super Yang-Mills coupled to $N_f$ quark flavors, which possesses a Landau pole at a UV scale $Λ_{LP}$. The dual gravity solution exhibits a UV singularity at a finite proper distance along the holographic direction. Despite this, holographic renormalization can be fully implemented via analytic continuation to an AdS solution. The presence of a UV cut-off manifests itself in several interesting ways. At energies $E \ll Λ_{LP}$ no pathologies appear, as expected from effective field theory. In contrast, at scales $E \lesssim Λ_{LP}$ the gravitational potential becomes repulsive, and at temperatures $T \lesssim Λ_{LP}$ the specific heat becomes negative. Although we focus on $\mathcal{N}=4$ super Yang-Mills with flavor, our qualitative results apply to a much more general class of theories, since they only depend on the fact that the metric near the UV singularity is a hyper-scaling violating metric with exponent $θ> d-1$.

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arXiv2016

Unquenched flavor on the Higgs branch

We construct the gravity duals of the Higgs branches of three-dimensional (four-dimensional) super Yang-Mills theories coupled to $N_\textrm{f}$ quark flavors. The effect of the quarks on the color degrees of freedom is included, and corresponds on the gravity side to the backreaction of $N_\textrm{f}$ flavor D6-branes (D7-branes) on the background of $N_\textrm{c}$ color D2-branes (D3-branes). The Higgsing of the gauge group arises from the dissolution of some color branes inside the flavor branes. The dissolved color branes are represented by non-Abelian instantons whose backreaction is also included. The result is a cascading-like solution in which the effective number of color branes varies along the holographic direction. In the three-dimensional case the solution may include an arbitrary number of quasi-conformal (walking) regions.

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arXiv2016

Holographic Magnetisation Density Waves

We numerically construct asymptotically $AdS$ black brane solutions of $D=4$ Einstein theory coupled to a scalar and two $U(1)$ gauge fields. The solutions are holographically dual to $d=3$ CFTs in a constant external magnetic field along one of the $U(1)$'s. Below a critical temperature the system's magnetisation density becomes inhomogeneous, leading to spontaneous formation of current density waves. We find that the transition can be of second order and that the solutions which minimise the free energy locally in the parameter space of solutions have averaged stressed tensor of a perfect fluid.

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arXiv2015

Three-dimensional super Yang-Mills with compressible quark matter

We construct the gravity dual of three-dimensional, $SU(N_{\textrm{c}})$ super Yang-Mills theory with $N_{\textrm{f}}$ flavors of dynamical quarks in the presence of a non-zero quark density $N_{\textrm{q}}$. The supergravity solutions include the backreaction of $N_{\textrm{c}}$ color D2-branes and $N_{\textrm{f}}$ flavor D6-branes with $N_{\textrm{q}}$ units of electric flux on their worldvolume. For massless quarks, the solutions depend non-trivially only on the dimensionless combination $ρ=N_{\textrm{c}}^2 N_{\textrm{q}} / λ^2 N_{\textrm{f}}^4$, with $λ=g_{\textrm{YM}}^2 N_{\textrm{c}}$ the 't Hooft coupling, and describe renormalization group flows between the super Yang-Mills theory in the ultraviolet and a non-relativistic theory in the infrared. The latter is dual to a hyperscaling-violating, Lifshitz-like geometry with dynamical and hyperscaling-violating exponents $z=5$ and $θ=1$, respectively. If $ρ\ll 1$ then at intermediate energies there is also an approximate AdS$_4$ region, dual to a conformal Chern-Simons-Matter theory, in which the flow exhibits quasi-conformal dynamics. At zero temperature we compute the chemical potential and the equation of state and extract the speed of sound. At low temperature we compute the entropy density and extract the number of low-energy degrees of freedom. For quarks of non-zero mass $M_{\textrm{q}}$ the physics depends non-trivially on $ρ$ and $M_{\textrm{q}} N_{\textrm{c}}/λN_{\textrm{f}}$.

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arXiv2015

Conformal field theories in $d=4$ with a helical twist

Within the context of holography we study the general class of $d=4$ conformal field theories after applying a universal helical deformation. At finite temperature we construct the associated black hole solutions of Einstein gravity, numerically, by exploiting a Bianchi $VII_0$ ansatz for the bulk $D=5$ metric. At $T=0$ we show that they flow in the IR to exactly the same CFT. The deformation gives rise to a finite, non-zero DC thermal conductivity along the axis of the helix, which we determine analytically in terms of black hole horizon data. We also calculate the AC thermal conductivity along this axis and show that it exhibits Drude-like peaks.

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arXiv2013

Competing p-wave orders

We construct electrically charged, asymptotically $AdS_5$ black hole solutions that are dual to $d=4$ CFTs in a superfluid phase with either p-wave or $(p+ip)$-wave order. The two types of black holes have non-vanishing charged two-form in the bulk and appear at the same critical temperature in the unbroken phase. Both the p-wave and the $(p+ip)$-wave phase can be thermodynamically preferred, depending on the mass and charge of the two-form, and there can also be first order transitions between them. The p-wave black holes have a helical structure and some of them exhibit the phenomenon of pitch inversion as the temperature is decreased. Both the p-wave and the $(p+ip)$-wave black holes have zero entropy density ground states at zero temperature and we identify some new ground states which exhibit scaling symmetry, including a novel scenario for the emergence of conformal symmetry in the IR.

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arXiv2013

Semi-local quantum criticality in string/M-theory

Semi-local quantum critical behaviour in $D-1$ spacetime dimensions can be holographically described by metrics that are conformal to $AdS_2\times\mathbb{R}^{D-2}$, with the conformal factor characterised by a parameter $η$. We analyse such "$η$-geometries" in a top-down setting by focussing on the $U(1)^4$ truncation of D=4 N=8 gauged supergravity. The model has extremal black hole solutions carrying three non-zero electric or magnetic charges which approach $AdS_4$ in the UV and an $η=1$ geometry in the IR. Adding a fourth charge provides a mechanism to resolve the singularity of the $η$-geometry, replacing it with an $AdS_2\times\mathbb{R}^2$ factor in the IR, while maintaining a large region where the $η$-geometry scaling is approximately valid. Some of the magnetically charged black hole solutions preserve supersymmetry while others just preserve it in the IR. Finally, we show that $η$-geometries, with various values of $η$, can be obtained from the dimensional reduction of geometries consisting of $AdS$ or Lifshitz geometries with flat directions.

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arXiv2012

Magnetic and electric AdS solutions in string- and M-theory

The stability properties of a family of magnetic $AdS_{3}\times \mathbb{R}^{2}$ solutions of D=5, SO(6) gauged SUGRA are investigated in more detail. We construct an analogous family of magnetic $AdS_{2}\times \mathbb{R}^{2}$ solutions of D=4, SO(8) gauged SUGRA, including a family of supersymmetric solutions, and also investigate their stability. We construct supersymmetric domain walls that interpolate between AdS_5 and an $AdS_3\times\mathbb{R}^2$ solution and also between AdS_4 and an $AdS_2\times\mathbb{R}^2$ solution which provide stable zero temperature ground states for the corresponding dual CFTs. We also construct new families of electric $AdS_{2}\times \mathbb{R}^{3}$ and $AdS_{2}\times \mathbb{R}^{2}$ solutions.

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arXiv2012

Spatially modulated instabilities of magnetic black branes

We investigate spatially modulated instabilities of magnetically charged $AdS_{2}\times\mathbb{R}^2$, $AdS_{3}\times\mathbb{R}^2$ and $AdS_{2}\times\mathbb{R}^3$ backgrounds in a broad class of theories, including those arising from KK reductions of ten and eleven dimensional supergravity. We show that magnetically charged black brane solutions in D=4,5 spacetime dimensions, whose zero temperature near horizon limit approach these backgrounds, can have instabilities that are dual to phases with current density waves that spontaneously break translation symmetry. Our examples include spatially modulated instabilities for a new class of magnetic black brane solutions of D=5 SO(6) gauged supergravity, that we construct in closed form, which are dual to new phases of N=4 SYM theory.

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