arXiv subjects

Horatiu Nastase

Publications and source records attributed to Horatiu Nastase.

At least 37 records · Page 2Linked to original sources

arXiv2024

Novel knotted non-abelian gauge fields

In analogy to null electromagnetic fields we define null YM fields. We show that the null non-abelian $SU(N)$ gauge fields admit a set of $2 N^2$ conserved "helicities". We derive null YM solutions that carry finite helicities by uplifting the abelian Hopfion solution and their generalizations. Another method that we implement is to deform YM solutions which do not carry helicities into ones that have nontrivial helicities. A nontrivial non-Abelian solution with helicities is found as a wave of infinite energy. We also discuss non-abelian generalizations of the Bateman parameterization for null abelian gauge fields.

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arXiv2024

Rotational holographic transport from KN-AdS black hole

We consider rotational holographic transport in strongly coupled 2+1 dimensional systems, from the point of view of 3+1 dimensional gravity. We consider the moment of inertia $I$ as a kind of transport coefficient, identified with the moment of inertia of a charged rotating black hole in $AdS_4$ background. In the low-temperature region, we find the behaviour of the density $I/A$ with temperature $T$ and angular velocity $Ω$, and find a quadratic behaviour for $\partial(I/A)/\partialΩ$ with $T$, in the presence of some charge $Q$.

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arXiv2024

Penrose limits of I-branes, twist-compactified D5-branes and spin chains

In this paper we consider the Penrose limit in the case of two gravity duals. One of them, consists of compactified I-branes (intersecting sets of D5-branes over $(1+1)$ dimensions). The second consists of D5-branes compactified on a circle. Both compactifications preserve SUSY. We find a match of the oscillators and masses of string modes on the resulting pp wave against a spin chain in a $(2+1)-$dimensional field theory in the first case, and a spin chain in a $(1+1)-$dimensional field theory in the second.

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arXiv2024

Supersymmetric AdS Solitons and the interconnection of different vacua of ${\cal N}=4$ Super Yang-Mills

We find AdS soliton solutions in 5-dimensional gauged supergravity, obtained from the $S^5$ compactification of type IIB, with a dilaton saturating the Breitenlohner-Freedman bound. The solutions depend on the value of the periodicity of an $S^1$ cycle and the boundary values for two $U(1)$ gauge fields, and give a scalar VEV in the dual field theory. At certain values of the gauge sources we have supersymmetric solutions, corresponding to supersymmetric flows, which are a deformation of the Coulomb Branch flow in ${\cal N}=4$ SYM. The solutions parameterize quantum phase transitions between a discrete spectrum phase, a continuous above a mass gap phase, and a continuous without a mass gap phase, in 2+1 dimensions. We analyze the phase diagram in terms of the QFT sources and we find that for every value for them, there are always two branches of supergravity solutions. We find that these two branches of solitons correspond to two possible vacua existing in the dual QFT when fermions are anti-periodic on an $S^1$. We describe the interconnection of these states in the QFT at strong 't Hooft coupling in the large $N$ limit. In 10 dimensions, our solutions are related to deformations of D3-brane distributions.

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arXiv2024

3-point function of currents for holographic cosmology and monopole non-Gaussianities

In this paper we present the calculation of the three-point function in momentum space of currents for a $SO(3)$ global symmetry, in a three-dimensional toy model within phenomenological holographic cosmology. Since the two-point function gives, via electric-magnetic duality, the resolution of the cosmological monopole problem, the three-point function is related to the monopole non-Gaussianities. We check that the final result is UV and IR finite and satisfies the transverse Ward identities and consider the $k_1\ll k_2,k_3$ case, relevant for cosmology. We also show that the two-loop result for the 3-point function is completely independent of the explicit form of the potential, meaning that, like the solution to the monopole problem, also the non-Gaussianities are universal within the phenomenological holographic cosmology.

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arXiv2024

Universal IR Holography, Scalar Fluctuations and Glueball spectra

We show that the d'Alembertian operator with a possible mass term in the AdS soliton and more general confining gravity dual backrounds admits infinitely many different spectra. These can be interpreted as different theories in the infrared and correspond to multitrace deformations of either the Dirichlet or the Neumann theory. We prove that all these fluctuations are normalizable and provide examples of their spectra. Therefore, the AdS soliton can be interpreted as giving a holographic RG flow between an universal UV theory at the AdS boundary and these infinitely many possibilities in the IR, obtained by deformations. The massive spectrum of the double trace deformation in $AdS_5$ allows the matching of the large-$N$ glueball masses of lattice $QCD_3$; the ratio of the ground states of the $2^{++}$ and $0^{++}$ channels are in full agreement with the lattice prediction. When considering $AdS_7$ and the 4-dimensional pure glue theory, a remarkably general picture emerges, where we can write formulas for the fluctuations that are in agreement with ones from holographic high-energy scattering and from AdS/CFT with IR and UV cut-off. We point out that this log branch in the IR in $D$-dimensions can be seen as the usual logarithmic branch of scalar fields saturating the Breitenlohner-Freedman bound in a conformally rescaled metric, with $AdS_{D-1}\times S^1$ asymptotics.

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arXiv2024

Euler fluid in 2+1 dimensions as a gauge theory, and an action for the Euler fluid in any dimension

In this paper we parallel the construction of Tong of a gauge theory for shallow water, by writing a gauge theory for the Euler fluid in 2+1 dimensions. We then extend it to an Euler fluid coupled to electromagnetic background. We argue that the gauge theory formulation provides a topological argument for the quantization of 2+1 dimensional Euler Hopfion solution. In the process, we find a (non-gauge) action for the Euler fluid that can be extended to any dimension, including the physical 3+1 dimensions. We discuss several aspects of the ABC flow.

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arXiv2023

Holographic Cosmology $n$-point function map from the Wavefunction of the Universe

In this note we show explicitly that, applying an extension of Maldacena's map for the wavefunction of the Universe $Z[ϕ]=Ψ[ϕ]$ from de Sitter inflation to holographic cosmology, we find the relations previously derived for 2-point functions, $\langle h_{ij}(p) h_{kl}(-p)\rangle \sim 1/[{\rm Im}\langle T_{ij}(-ip)T_{kl}(+ip)\rangle]$ and a similar one for currents, which were used to show that holographic cosmology matches CMBR data and solves Big Bang problems as well as inflation. Higher point functions are done similarly, and as an application, we check the result for the 3-point functions of scalar and tensor fluctuations and find the result for the monopole non-Gaussianity arising from the 3-point functions of currents. The method is simple and potentially could be applied to calculate any observable in holographic cosmology.

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arXiv2023

Penrose limit of T-dual of MNa solution and dual orbifold field theory

In this paper we study the Penrose limit of the T-dual of the MNa solution and its field theory dual, in order to better understand the effect of T-duality in this case. We find a matching of string pp wave oscillators and their masses to the field theory modes, that are rearranged after T-duality. The effect of T-duality on the long "annulon-type" operators is found, as a symmetry of the 2+1 dimensional confining theory with spontaneous susy breaking.

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arXiv2023

CSBIon -- a charged soliton of the 3-dimensional CS + BI Abelian gauge theory

In this paper, we construct a charged soliton with a finite energy and no delta function source in a pure Abelian gauge theory. Specifically, we first consider the 3-dimensional Abelian gauge theory, with a Maxwell term and a l evel $N$ CS term. We find a static solution that carries charge $N$, angular momentum $\frac{N}{2}$ and whose radius is $N$ independent. However, this solution has a divergent energy. In analogy to the replacement of the 4 dimensional Maxwell action with the BI action, which renders the classical energy of a point charge finite, for the 3 dimensional theory which includes a CS term such a replacement leads to a finite energy for the solution of above. We refer to this soliton as a CSBIon solution, representing a finite energy version of the fundamental (sourced) charged electron of Maxwell theory in 4 dimensions. In 3 dimensions the BI+CS action has a static charged solution with finite energy and no source, hence a soliton solution. The CSBIon, similar to its Maxwellian predecessor, has a charge $N$, angular momentum proportional to $N$ and an $N$-independent radius. We also present other nonlinear modifications of Maxwell theory that admit similar solitons. The CSBIon may be relevant in various holographic scenarios. In particular, it may describe a D6-brane wrapping an $S^4$ in a compactified D4-brane background. We believe that the CSBIon may play a role in condensed matter systems in 2+1 dimensions like graphene sheets.

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arXiv2023

$T\bar T$ deformations and the pp wave correspondence

In this paper we consider $T\bar T$ deformations in the context of pp waves obtained from gravity duals. We propose a deformation of $AdS_5\times S^5$ similar to the deformation of the single trace $T\bar T$ deformation of $AdS_3\times S^3\times T^4$ with NS-NS flux, and study it through the Penrose limit, concluding that it must correspond to some dipole theory, probably noncommutative. We $T\bar T$ deform the worldsheet string for the $AdS_5\times S^5$ pp wave, and find a corresponding spin chain Hamiltonian. Finally, directly $T\bar T$ deforming the spin chain Hamiltonian obtained from the pp wave, we find that it corresponds to an equivalent BMN sector of the ${\cal N}=4$ SYM.

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arXiv2023

Holographic transport with topological term and entropy function

In this paper we consider the effect of a topological Maxwell term $W(Φ)F_{μν}\tilde F^{μν}$ on holographic transport and thermodynamics in 2+1 dimensions, in the case with a dyonic black hole in the gravity dual. We find that for a constant $W$ the modifications to the thermodynamics are easily quantified, and transport is affected only for $σ_{xy}$. If one consider also the attractor mechanism, and writing the horizon transport in terms of charges, the transport coefficients are affected explicitly. We also introduce the case of case of radially dependent $W(z)$, in which case, however, analytical calculations become very involved. We also consider the implications of the two models for the S-duality of holographic transport coefficients.

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arXiv2022

Susceptibilities from holographic transport with topological term

In this note we calculate susceptibilities, as derivatives of a thermodynamical potential, for the general perturbative holographic set-up for transport with magnetic field, charge density and topological term, and compare with the quantities obtained in the standard $AdS_4$ dyonic black hole analysis of Hartnoll and Kovtun. We find that the results do not match, despite previous expectations.

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arXiv2022

Fluid-electromagnetic helicities and knotted solutions of the fluid-electromagnetic equations

In this paper we consider an Euler fluid coupled to external electromagnetism. We prove that the Hopfion fluid-electromagnetic knot, carrying fluid and electromagnetic (EM) helicities, solves the fluid dynamical equations as well as the Abanov Wiegmann (AW) equations for helicities, which are inspired by the axial-current anomaly of a Dirac fermion. We also find a nontrivial knot solution with truly interacting fluid and electromagnetic fields. The key ingredients of these phenomena are the EM and fluid helicities. An EM dual system, with a magnetically charged fluid, is proposed and the analogs of the AW equations are written down. We consider a fluid coupled to a nonlinear generalizations for electromagnetism. The Hopfions are shown to be solutions of the generalized equations. We write down the formalism of fluids in 2+1 dimensions, and we dimensionally reduce the 3+1 dimensional solutions. We determine the EM knotted solutions, from which we derive the fluid knots, by applying special conformal transformations with imaginary parameters on un-knotted null constant EM fields.

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arXiv2022

Coupling ModMax theory precursor with scalars, and BIon-type solutions

Recently, the most general theory of electromagnetism invariant under duality and conformal invariance was written, and dubbed ModMax. It arises from a generalization of Born-Infeld (BI) theory by taking the infinite tension limit, $T\rightarrow\infty$. In this note we show that this generalization can be obtained from a brane-like construction, just like BI, and can thus be coupled to scalars in the same way to obtain a DBI-like action. All the BIon and catenoid solutions, and their interpolations, are still solutions of the generalized DBI-like action, suggesting that an interpretation within string theory could be possible. We also show that Rañada's knotted solutions (with nonzero helicities) are still valid, both in the ModMax theory, and in its precursor.

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arXiv2022

Penrose limit of MNa solution and spin chains in three-dimensional field theories

In three dimensions, a theory with spontaneous breaking of supersymmetry was described holographically by the Maldacena-Nastase (MNa) solution. We revisit the issue of its Penrose limit, and compare the resulting pp wave and its string eigenstates to a sector of the theory on 5-branes reduced on $S^3$, and a spin chain-like system. We obtain many of the features of the pp wave analysis, but a complete matching still eludes us. We suggest possible explanations for the resulting partial mismatch, and compare against other spin chains for 3-dimensional field theories with gravity duals.

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arXiv2021

Celestial IR divergences in general most-subleading-color gluon and gravity amplitudes

Gluon amplitudes at most-subleading order in the $1/N$ expansion share a remarkable simplicity with graviton amplitudes: collinear divergences are completely absent in both and, as a consequence, their full IR behavior arises from soft gluon/graviton exchange among the external states. In this paper we study the effect of all-loop IR divergences of celestial most-subleading color gluon amplitudes and their similarities with the celestial gravity case. In particular, a simple celestial exponentiation formula for the dipole part can be written. We also analize how this exponentiation is modified by non-dipole contributions. Finally we also show that, in the Regge limit, the soft factor satisfies the Knizhnik-Zamolodchikov equation hinting at the possibility that, in this limit, an effective Wess-Zumino-Witten model would describe the dynamics of the infrared sector.

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arXiv2021

Reheating in holographic cosmology and connecting to $Λ$-MSSM constructions for particle physics

In this paper we model the transition from the non-geometric holographic cosmology regime, to the usual radiation dominated (RD) cosmology, known as reheating in the case of (perturbative) inflation. We find that we can easily transition into any MSSM construction of intersecting D6-branes, via $α'$ corrections in the 3 dimensional field theory as well as in cosmology, followed by cosmological reheating via S-NS5-branes. Moreover, we can naturally obtain the (true) cosmological constant $Λ$ of the observed order of magnitude. The resulting supersymmetry breaking is just outside the currently observed energies. The model is consistent with large (TeV scale) extra dimensions, but it prefers smaller ones, and the string scale is generically low.

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