arXiv subjects

Horatiu Nastase

Publications and source records attributed to Horatiu Nastase.

At least 91 records · Page 5Linked to original sources

arXiv2015

More on Heisenberg's model for high energy nucleon-nucleon scattering

We revisit Heisenberg's model for nucleon-nucleon scattering which admits a saturation of the Froissart bound. We examine its uniqueness, and find that up to certain natural generalizations, it is the only action that saturates the bound. We find that we can extract also sub-leading behaviour for $σ_{\rm tot}(s)$ from it, though that requires a knowledge of the wavefunction solution that is hard to obtain, and a black-disk model allows the calculation of $σ_{elastic}(s)$ as well. The wavefunction solution is analyzed perturbatively, and its source is interpreted. Generalizations to several mesons, addition of vector mesons, and curved space regimes are also found. We discuss the relations between Heisenberg's model and holographic models that are dual to QCD-like theories.

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arXiv2015

Abelian reductions of deformed ${\cal N}=4$ SYM

Following the work in \cite{Mohammed:2012gi}, where the massive ABJM model in 2+1 dimensions was shown to have an abelian reduction to the relativistic Landau-Ginzburg, and motivated by the implications for condensed matter through AdS/CFT, we show that a FI deformation of ${\cal N}=4$ SYM in 3+1 dimensions with a mass term can also be reduced to a relativistic Landau-Ginzburg model, with the possibility of coupling it to a real scalar, whereas the simply mass deformed ${\cal N}=4$ SYM reduces only to a massive $ϕ^4$ model (scalar QED) coupled to a real scalar. We study the classical solutions of the model, in particular vortex solutions.

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arXiv2015

Open strings on D-branes from ABJM

We study open strings on giant gravitons (D-branes on cycles) in the ABJM/$AdS_4\times \mathbb{CP}^3$ correspondence. We find that their energy spectrum has the same form as the one for closed strings, with a nontrivial function of the coupling, avoiding BMN scaling. A similar, Cuntz oscillator, Hamiltonian description for the string (operators at strong coupling) to the $AdS_5$ case is valid also in this case.

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arXiv2014

Comments on the T-dual of the gravity dual of D5-branes on $S^3$

We consider an abelian T-duality on a deformation of the gravitational solution of \cite{Maldacena2001}, which is the gravity dual of $N_c$ D5-branes wrapping a three-cycle inside a manifold that admits a $G_2$ structure. Performing the T-duality we find $N_c$ D$4$-branes wrapping a two-cycle with non-trivial antisymmetric fields in the NS-NS and RR sector. We study some aspects of its dual field theory and we compare with the original solution.

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arXiv2014

Conformal inflation from the Higgs

We modify the conformal inflation set-up of \cite{Kallosh:2013hoa}, with a local Weyl invariance, a dynamical Planck scale and an $SO(1,1)$ invariance at high energies, in order to be able to identify the physical scalar with the physical Higgs at low energies, similar to the cyclic Higgs models of \cite{Bars:2013vba}. We obtain a general class of exponentially-corrected potentials that gives a generalized Starobinsky model with an infinite series of $R^p$ corrections, tracing a line in the $(r,n_s)$ plane for CMB fluctuations, with an $r$ that can be made to agree with the recent BICEP2 measurement. Introducing a coupling different from the conformal value, thus breaking the local Weyl symmetry, leads nevertheless to a very strong attractor motion towards the generalized Starobinsky line.

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arXiv2014

Particle-vortex and Maxwell duality in the $AdS_4\times \mathbb{CP}^3$/ABJM correspondence

We revisit the notion of particle-vortex duality in abelian theories of complex scalar fields coupled to gauge fields, formulating the duality as a transformation at the level of the path integral. This transformation is then made symmetric and cast as a self-duality that maps the original theory into itself with the role of particles and vortices interchanged. After defining the transformation for a pure Chern-Simons gauge theory, we show how to embed it into (a sector of) the $(2+1)-$dimensional ABJM model, and argue that this duality can be understood as being related to 4-dimensional Maxwell duality in the $AdS_{4}\times\mathbb{CP}^{3}$ bulk.

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arXiv2013

Conductivity in the gravity dual to massive ABJM and the membrane paradigm

In this paper we analyze the effect of the massive deformation of the ABJM model on the calculation of conductivity of the dual theory. We show that some of the difficulties presented by the dual geometry, in particular the construction of black holes therein, can be at least partially circumvented by adopting a membrane paradigm-like computation of the conductivity, which requires us to know just the effect of the deformation on the {\it horizon} of a black hole in AdS${}_{4}$. The deformation at the horizon itself is found by first deforming the flat space near the horizon, and then using the corresponding solution near the horizon as initial conditions for the Einstein's equations. We find the same result, showing an increase in conductivity, using two types of membrane paradigm computations.

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arXiv2013

On abelianizations of the ABJM model and applications to condensed matter

In applications of AdS/CFT to condensed matter systems in 2+1 dimensions, the ABJM model is often used, however the condensed matter models are usually abelian and contain charged fields. We show that a naive reduction of the ABJM model to N=1 does not have the desired features, but we can find an abelian reduction that has most features, and we can also add fundamental fields to the ABJM model to obtain other models with similar properties.

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arXiv2013

Chameleons on the Racetrack

We modify the ansatz for embedding chameleon scalars in string theory proposed in [1] by considering a racetrack superpotential with two KKLT-type exponentials $e^{ia\varrho}$ instead of one. This satisfies all experimental constraints, while also allowing for the chameleon to be light enough on cosmological scales to be phenomenologically interesting.

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arXiv2013

Chameleonic inflation

We attempt to incorporate inflation into a string theory realization of the chameleon mechanism. Previously, it was found that the volume modulus, stabilized by the supersymmetric potential used by Kachru, Kallosh, Linde and Trivedi (KKLT) and with the right choice of parameters, can generically work as a chameleon. In this paper, we ask whether inflation can be realized in the same model. We find that we need a large extra dimensions set-up, as well as a semi-phenomenological deformation of the Kahler potential in the quantum region. We also find that an additional KKLT term is required so that there are now two pieces to the potential, one which drives inflation in the early universe, and one which is responsible for chameleon screening at late times. These two pieces of the potential are separated by a large flat desert in field space. The scalar field must dynamically traverse this desert between the end of inflation and today, and we find that this can indeed occur under the right conditions.

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arXiv2013

All-loop infrared-divergent behavior of most-subleading-color gauge-theory amplitudes

The infrared singularities of gravitational amplitudes are one-loop exact, in that higher-loop divergences are characterized by the exponential of the one-loop divergence. We show that the contributions to SU(N) gauge-theory amplitudes that are most-subleading in the 1/N expansion are also one-loop exact, provided that the dipole conjecture holds. Possible corrections to the dipole conjecture, beginning at three loops, could violate one-loop-exactness, though would still maintain the absence of collinear divergences. We also demonstrate a relation between L-loop four-point N=8 supergravity and most-subleading-color N=4 SYM amplitudes that holds for the two leading IR divergences, O(1/ε^L) and O(1/ε^{L-1}), but breaks down at O(1/ε^{L-2}).

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arXiv2012

Abelian-Higgs and Vortices from ABJM: towards a string realization of AdS/CMT

We present ansätze that reduce the mass-deformed ABJM model to gauged Abelian scalar theories, using the fuzzy sphere matrices $G^α$. One such reduction gives a Toda system, for which we find a new type of nonabelian vortex. Another gives the standard Abelian-Higgs model, thereby allowing us to embed all the usual (multi-)vortex solutions of the latter into the ABJM model. By turning off the mass deformation at the level of the reduced model, we can also continuously deform to the massive $ϕ^4$ theory in the massless ABJM case. In this way we can embed the Landau-Ginzburg model into the AdS/CFT correspondence as a consistent truncation of ABJM. In this context, the mass deformation parameter $μ$ and a field VEV $<ϕ>$ act as $g$ and $g_c$ respectively, leading to a well-motivated AdS/CMT construction from string theory. To further this particular point, we propose a simple model for the condensed matter field theory that leads to an approximate description for the ABJM abelianization. Finally, we also find some BPS solutions to the mass-deformed ABJM model with a spacetime interpretation as an M2-brane ending on a spherical M5-brane.

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arXiv2012

Towards a Realization of the Condensed-Matter/Gravity Correspondence in String Theory via Consistent Abelian Truncation

We present an embedding of the 3-dimensional relativistic Landau-Ginzburg model for condensed matter systems in an $\mathcal{N}=6$, $U(N)\times U(N)$ Chern-Simons-matter theory (the ABJM model) by consistently truncating the latter to an abelian effective field theory encoding the collective dynamics of ${\cal O}(N)$ of the ${\cal O}(N^2)$ modes. In fact, depending on the VEV on one of the ABJM scalars, a mass deformation parameter $μ$ and the Chern-Simons level number $k$, our abelianization prescription allows us to interpolate between the abelian Higgs model with its usual multi-vortex solutions and a $ϕ^4$ theory. We sketch a simple condensed matter model that reproduces all the salient features of the abelianization. In this context, the abelianization can be interpreted as giving a dimensional reduction from four dimensions.

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arXiv2012

Eliminating ambiguities for quantum corrections to strings moving in $AdS_4\times \mathbb{CP}^3$

We apply a physical principle, previously used to eliminate ambiguities in quantum corrections to the 2 dimensional kink, to the case of spinning strings moving in $AdS_4\times \mathbb{CP}^3$, thought of as another kind of two dimensional soliton. We find that this eliminates the ambiguities and selects the result compatible with AdS/CFT, providing a solid foundation for one of the previous calculations, which found agreement. The method can be applied to other classical string "solitons".

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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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arXiv2012

Introduction to supergravity

These lectures present an introduction to supergravity, and are intended for graduate students with a working knowledge of quantum field theory, including the elementary group theory needed for it, but no prior knowledge of general relativity, supersymmetry or string theory is assumed. I will start by introducing the needed elements of general relativity and supersymmetry. I will then describe the simplest cases of supergravity, ${\cal N}=1$ on-shell in 4 dimensions and ${\cal N}=1$ off-shell in 3 dimensions. I will introduce superspace formalisms in their simplest cases, and apply them to ${\cal N}=1$ in 4 dimensions, after which I will show how to couple to matter using superspace. I will introduce the procedure of KK dimensional reduction and describe general supergravity theories, in particular the unique 11 dimensional supergravity. I will then exemplify the issues of KK dimensional reduction on the only complete example of full nonlinear compactification, on the gravitational space $AdS_7\times S^4$. Finally, I will show how we can use supergravity compactifications together with some string theory information, for realistic embeddings of the Standard Model, via ${\cal N}=1$ supergravity in 4 dimensions.

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arXiv2011

Applications of Subleading-color Amplitudes in N=4 SYM Theory

A number of features and applications of subleading color amplitudes of N=4 SYM theory are reviewed. Particular attention is given to the IR divergences of the subleading-color amplitudes, the relationships of N=4 SYM theory to N=8 supergravity, and to geometric interpretations of one-loop subleading color and N^k MHV amplitudes of N=4 SYM theory.

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arXiv2011

Linear relations between N >= 4 supergravity and subleading-color SYM amplitudes

The IR divergences of supergravity amplitudes are less severe than those of planar SYM amplitudes, and are comparable to those subleading-color SYM amplitudes that are most subleading in the 1/N expansion, namely O(1/epsilon^L) for L-loop amplitudes. We derive linear relations between one- and two-loop four-point amplitudes and one-loop five-point amplitudes of N = 4, 5, and 6 supergravity and the most-subleading-color contributions of the analogous amplitudes of N = 0, 1, and 2 SYM theory, extending earlier results for N = 8 supergravity amplitudes. Our work relies on linear relations between N >= 4 supergravity and planar SYM amplitudes that were recently derived using the double-copy property of gravity, and color-kinematic duality of gauge theories.

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