arXiv subjects

Dibakar Roychowdhury

Publications and source records attributed to Dibakar Roychowdhury.

At least 19 recordsLinked to original sources

arXiv2026

Holographic Krylov Complexity for Charged, Composite and Extended Probes

We study the holographic spread/Krylov complexity of operators with non-trivial internal structure and of genuinely extended operators. We first consider a massive particle in AdS$_5\times S^5$ carrying conserved $R$-charge, and show how motion in the internal space modifies the complexity growth, yielding a natural holographic realisation of symmetry-resolved Krylov complexity. We then move to probes that are effectively pointlike from the field-theory viewpoint but possess an intrinsic structure in the bulk: baryon-vertex configurations and giant gravitons. Our results indicate that, for this broad class of structured but pointlike probes, the leading large-time behaviour retains the characteristic form expected for local operators in conformal theories, while the internal structure and induced charges produce informative subleading effects. We also study a genuinely extended probe, a fundamental string falling in AdS while stretched along a spatial direction, as a model for the spread complexity of a non-local operator. In this case, although the leading behaviour still exhibits the expected growth pattern, the subleading terms and intermediate regimes differ qualitatively from those of pointlike probes. This provides concrete evidence that extended operators carry a finer notion of spread complexity, sensitive to their spatial structure. Our results broaden the class of probes for which holographic Krylov complexity can be analysed explicitly, clarify which features are universal and which depend on the nature of the operator, and open a promising route toward a sharper field-theory understanding of complexity for charged, composite and extended excitations.

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arXiv2026

BMN Spread Complexity Across Phase Transitions

We investigate the dynamical behavior and spread complexity of quantum states within the mass-deformed BMN matrix model equipped with an emergent $U(1)$ global charge at finite temperature $β^{-1}$ and chemical potential $ν$. Focusing on the strong-coupling regime ($μ\gg 1$), we model the dynamics via a charged Thermofield Double (cTFD) state and trace the evolution of spread complexity across three distinct thermodynamic regimes. In the low-temperature gapped phase ($βμ\gg 1$), discrete mass-gap bound states dominate, trapping wavepacket dispersion and producing non-chaotic, oscillatory early-time growth. Conversely, in the high-temperature continuum phase ($βμ\ll 1$), thermal excitations overwhelm the mass gap, driving a transition to a continuous advection field that exhibits maximal chaotic scrambling with a Krylov Lyapunov exponent $λ_K = π/ β$ that saturates the universal bound. In the intermediate temperature regime ($βμ\sim 1, βν\sim 1$), the interplay between mass-gap bound states and the continuous thermal background induces a sub-leading correction to the Lanczos coefficients $b_n \sim \fracπβ n + γ\sqrt{n}$, governing a continuous sub-exponential crossover before full chaotic thermalization. Technical derivations regarding KMS boundary conditions, grand canonical spectral moments, residue analysis, and time-reversal symmetry breaking in Krylov space are detailed in four dedicated appendices.

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arXiv2026

Krylov complexity for $η$ deformed superstring backgrounds

We compute the holographic Krylov complexity for a class of strongly coupled Quantum Field Theory (QFT) (with broken scale invariance) in a top down approach, where the dual gravitational counterpart corresponds to $η$ deformed superstring solutions in a type IIB set up. The full 10d solution contains the anti-de Sitter ($AdS$) as the subspace, along with the dilaton and the background Ramond-Ramond (RR) and Neveu-Schwarz (NS) fluxes. The Krylov complexity in the dual operator picture is obtained by computing the proper momentum of the massive particle along its geodesic in the bulk spacetime. We explore the effects of $η$ deformation on the bulk momentum of the particle, which in turn affects the rate of growth of complexity in the dual QFTs. Our results boil down into the undeformed case in the appropriate limit of the Yang-Baxter (YB) parameter. We also comment on the complexity of the dual quantum mechanical model with broken scale invariance.

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arXiv2026

Probing sine dilaton gravity with flow central charge

We construct a holographic c-function for sine dilaton gravity (sDG) in the domain wall gauge. We show the equivalence between sDG and the two copies of Liouville conformal field theory (LCFT) and compute the associated central charge. We reproduce the central charge of LCFT from the holographic c-function of sDG corresponding to the UV limit. In contrast, in the deep IR limit, the c-function flows to the pure JT gravity, where the central charge becomes identically zero.

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arXiv2026

Holographic Krylov complexity in confining gauge theories

We study holographic Krylov complexity in the Anabalon-Ross solitonic background, a top-down Type IIB solution describing a twisted-circle compactification of ${\cal N}=4$ SYM that flows to a confining, gapped three-dimensional theory. Following the proposal that the time derivative of Krylov complexity is dual to the proper radial momentum of a falling bulk particle, we analyze probe geodesics in this geometry. We obtain exact analytic solutions for the radial trajectory in terms of elliptic functions, confirming and extending UV and IR asymptotic expansions. The proper momentum and resulting complexity exhibit oscillatory behaviour, which we interpret as a holographic signature of the finite Hilbert-space truncation induced by the UV cutoff together with the IR end-of-space. Our results provide a controlled top-down test of the spread-momentum correspondence and highlight qualitative differences between conformal and confining holographic dynamics.

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arXiv2026

Krylov Complexity and $c$-function along RG Flows

We investigate Krylov spread complexity along holographic renormalisation-group flows using the proposal that its growth rate is captured by the proper radial momentum of an in-falling massive probe. We focus on the second time derivative of the complexity ${U}$, which is determined locally by the redshift and radial metric functions of the dual geometry. For Lorentz-invariant domain-wall flows preserving the spacetime dimension, we derive a new relation between ${U}$ and the covariant central charge $c_{\text{cov}}$. The decrease of the covariant central function towards the infrared is accompanied by a monotonic increase of the complexity acceleration. For the top-down Dp-brane family, we obtain a universal relation. We then examine flows across dimensions, including a twisted compactification from four to two dimensions and from six to four dimensions. In these examples $c_{\rm cov}$ and ${U }$ are co-monotonic, in sharp contrast with the inverse correlation characteristic of fixed-dimensional flows. We argue that this reversal reflects the reorganisation, rather than simple depletion, of degrees of freedom into lower-dimensional sectors under compactification. Our results identify complexity acceleration as a sensitive geometric diagnostic connecting information spreading, holographic central functions and RG evolution.

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arXiv2026

Krylov complexity and spectral density of BMN matrix model

We use Krylov complexity as a typical diagnostic of quantum many body dynamics in the context of BMN matrix model at large mass gap. We calculate several physical entities, for example, the moments and return amplitudes at large mass deformation. We calculate them for both spread complexity of states as well as Krylov growth of operators in the matrix model. We propose a general expression for the moments at any given order $n$. We also discuss orthogonal polynomials for spread as well as operator Krylov complexity. In the context of the Krylov operator growth we further compute the spectral function and the density of states. A careful analysis of the spectral function near the resonance reveals various IR divergences in addition to the physical collective modes. These collective modes appear to be exceptionally stable due to large mass gap. On the other hand, the UV of the theory appears to be extremely damped due to higher scattering rates. We carefully diagnose these IR divergences near resonance which reveals that these collective modes are in fact non-propagating and should be thought of as diffusion modes or relaxation modes with infinite relaxation time. We also calculate the Krylov variance and Krylov entropy for the matrix model and in particular at early time. The linear early time growth of the Krylov entropy confirms the onset of quantum chaos in the matrix model at large mass gap.

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arXiv2026

Krylov Complexity for Plane Wave Matrix Model

We study Krylov complexity in BMN Plane Wave Matrix Model at large mass deformation. We consider various consistent reductions of the matrix model that allow us to perform a Hamiltonian analysis which leads to different notions of the Krylov complexity. In the first part of the paper, we study the Krylov state complexity considering systematic reduction of $N=3$ and $N=4$ representations of the matrix model, which reveals a universal characteristic scaling for the Lanczos coefficients and fix them completely in terms of the mass deformation parameter. In the second part of the paper, we study the Krylov operator growth in the matrix model and compute the corresponding Lanczos coefficients. In both cases, we observe a \emph{linear} scaling of Lanczos coefficients with the mass parameter. The early time growth in Krylov complexity receives quadratic correction due to the presence of the massive deformation in the matrix model. Our analysis reveals that such massive corrections appear at same order in time for both the notion of the Krylov complexity.

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arXiv2026

Krylov state complexity for BMN matrix model

We explore Krylov complexity in the BMN matrix model following a systematic reduction of it, known as the pulsating fuzzy sphere model. We present an analytical setup that allows us to calculate Lanczos coefficients in both large and small deformation limits of the matrix model.

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arXiv2026

Krylov complexity for Lin-Maldacena geometries and their holographic duals

We compute the rate of growth of operator size in matrix models by probing the Lin-Maldacena class of geometries with classical probes. We consider massive point particle probes whose proper momentum equals the size of the gauge invariant operator in the matrix model. We work out the example of the BMN Plane Wave Matrix Model using the electrostatic approach and the method of background fluxes. We also work out complexities in the D2 brane as well as NS5 brane limits of the BMN matrix model along with an example of the irrelevant deformation namely the non-Abelian T-dual of $AdS_5 \times S^5$. Finally, we carry out a possible calculation of the Krylov complexity on the matrix model counterpart by using a simple reduction ansatz known as the pulsating fuzzy sphere model. We outline an algorithm to define Krylov basis elements for the matrix model and compute a few Lanczos coefficients. Our analysis reveals that both the Krylov basis states as well as Lanczos coefficients are uniquely fixed in terms of the mass parameter of the matrix model.

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arXiv2026

Hall transports from Taub-NUT AdS black holes

We compute Hall transport coefficients associated with Taub-NUT AdS black holes in four space-time dimensions using the probe D-brane approach. In particular, we examine the effects due to the NUT parameter ($n$), or equivalently, the novel frame-dragging on the holographic charge transport properties. In our analysis, we treat the external electric field as a constant background, while varying the magnetic field ($B$) from small to finite. Within this framework, we analyze conductivities in both low and high temperature regions, focusing on locations that are both near and far from the Misner string. Our calculations show that frame-dragging effects are significant primarily at lower temperatures and near the Misner string, while a small magnetic field is maintained. However, these effects become negligibly small at a ``finite" magnetic field and even at lower temperatures. Our analysis reveals the existence of finite Hall transport, that has its origin in the novel frame-dragging.

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arXiv2025

Holographic Krylov complexity in ${\cal N}=4$ SYM

We propose and calculate a holographic Krylov complexity in ${\cal N}=4$ SYM via the proper momentum for motion in $AdS_5$ sliced by $AdS_3$. The motion in an $AdS_3$ subgroup corresponds to the Krylov complexity of the $Sl(2)$ subsector. The general motion corresponds to the Krylov complexity of the ${\cal N}=4$ SYM.

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arXiv2025

Holographic Krylov Complexity for Conformal Quiver Gauge Theories

We investigate holographic Krylov complexity in fully top-down AdS$_3$ and AdS$_2$ supergravity backgrounds dual to two-dimensional linear-quiver SCFTs and one-dimensional conformal quantum mechanics. In these geometries, the warp factors, dilaton and other fields depend non-trivially on the 'quiver coordinate' (denoted by $η$ in this paper). This $η$-coordinate encodes the color and flavor data of the dual theories. As a consequence, a massive probe following a holographic geodesic necessarily moves simultaneously in the radial AdS direction and along the 'quiver direction'. This produces new contributions to the proper momentum and hence to the rate of Krylov complexity growth, which is absent in bottom-up AdS models. We show that the $η$-motion is generically damped, with a time-scale governed by the UV cutoff of the geodesic problem, and modifies the early-time evolution of complexity in a quiver-dependent way. At late times, the $η$-dynamics freezes and the growth becomes universal, matching pure Poincare AdS predictions. Studying Abelian and non-Abelian T-dual backgrounds of AdS$_3\times S^3\times T^4$, quivers with localized flavor groups, and quivers with smeared flavor groups, we quantify how quiver parameters shape the operator-spreading dynamics. Our results provide a systematic characterization of Krylov complexity in top-down AdS$_3$/AdS$_2$ duals and reveal a holographic mechanism through which complexity probes both ultraviolet quiver structure and emergent infrared universality.

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arXiv2025

Holographic Timelike Entanglement Across Dimensions

We develop a holographic framework for computing timelike entanglement entropy (tEE) in quantum field theories, extending the Ryu-Takayanagi prescription into Lorentzian settings. Using three broad classes of supergravity backgrounds, we derive both exact and approximate tEE expressions for slab, spherical, and hyperbolic regions, and relate them to the central charges of the dual conformal field theories. The method is applied to infinite families of supersymmetric linear quivers in dimensions from d=2 to d=6, showing that Liu-Mezei and slab central charges scale universally like the holographic central charge. We then analyse gapped and confining models, including twisted compactifications and wrapped brane constructions, identifying how a mass gap modifies tEE and when approximate formulas remain accurate. In all cases, we uncover robust scaling with invariant separations and signature dependent phase behaviour, distinguishing spacelike from timelike embeddings. Our results unify the treatment of tEE in both conformal and nonconformal theories, clarifying its role as a probe of causal structure, universal data, and nonperturbative dynamics in holography.

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arXiv2025

Metallic transports from Taub-NUT AdS black holes

We compute holographic DC conductivity associated with the Taub-NUT-$AdS_4$ black holes following the probe D-brane approach. In particular, we examine the effects of frame dragging on charge transport in both low and high temperature regimes. Our analysis reveals that in the low temperature regime, the conductivity is sensitive to the presence of the Misner string that causes frame dragging. Notably, the increase in the conductivity near the Misner string is sharper as compared to points farther away from it. On the other hand, in the high temperature regime, the effects due to frame dragging are significantly suppressed, and the thermal contribution to the charge transport takes over that due to the U(1) charge carriers.

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arXiv2025

Interpolating between Space-like and Time-like Entanglement via Holography

We study entanglement entropy for slab like regions in quantum field theories, using their holographic duals. We focus on the transition between space like and time like separations. By considering boosted subsystems in conformal and confining holographic backgrounds, we identify two classes of extremal surfaces: real ones (Type I) and complex surfaces (Type II). These interpolate between the usual Ryu Takayanagi prescription and its time like generalisations. We derive explicit expressions for the entanglement entropy in both conformal and confining cases. We discuss their behaviour across phase transitions and null limits. The interpolation between Type I and Type II surfaces reveals an analytic continuation of the extremal surface across the light cone. Our analysis also finds the existence of a Ryu Takayanagi surface (Type I) even for time like separations in the confining field theory case.

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arXiv2025

Timelike entanglement and central charge for quantum BTZ black holes

We compute holographic timelike entanglement entropy for quantum BTZ black holes in a Karch-Randall braneworld scenario. These black holes are exact solutions of massive 3d gravity on the brane and are conjectured to be dual to thermal states in 2d defect CFTs, living at the interface of the brane and the boundary of the bulk $AdS_4$. Our analysis reveals an interesting relation between the tEE and the central charge pertaining to the dual CFT, which receives nontrivial corrections due to quantum backreaction effects on the Karch-Randall brane, which is explored non-perturbatively.

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arXiv2025

Holographic central charge for sine dilaton gravity

In this paper, we calculate the holographic central charge ($c_{sDG}$) associated with sine dilaton gravity (sDG) in the semiclassical limit. In the low energy limit, the sDG flows into the ordinary JT gravity which is a conjectured dual of ordinary Schwarzian quantum mechanics at strong coupling. We compute the associated central charge ($c_{JT}$), which reveals $c_{sDG}>c_{JT}$. We identify this as an artifact of the UV completion of JT gravity in terms of sine dilaton gravity.

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