Tachyon ≈ Tachyon
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New class of ghost- and tachyon-free metric affine gravities Open
We construct the spin-projection operators for a theory containing a symmetric two-index tensor and a general three-index tensor. We then use them to analyse, at linearized level, the most general action for a metric-affine theory of gravi…
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Positivity of Curvature-Squared Corrections in Gravity Open
We study the Gauss-Bonnet (GB) term as the leading higher-curvature correction to pure Einstein gravity. Assuming a tree-level ultraviolet completion free of ghosts or tachyons, we prove that the GB term has a nonnegative coefficient in di…
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Towards the determination of the dimension of the critical surface in asymptotically safe gravity Open
We compute the beta functions of Higher Derivative Gravity within the\nFunctional Renormalization Group approach, going beyond previously studied\napproximations. We find that the presence of a nontrivial Newtonian coupling\ninduces, in ad…
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Low energy ghosts and the Jeans’ instability Open
We show that a massless canonical scalar field minimally coupled to general relativity can become a tachyonic ghost at low energies around a background in which the scalar’s gradient is spacelike. By performing a canonical transformation w…
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Ghost and tachyon free Poincaré gauge theories: A systematic approach Open
A systematic method is presented for determining the conditions on the\nparameters in the action of a parity-preserving gauge theory of gravity for it\nto contain no ghost or tachyon particles. The technique naturally accommodates\ncritica…
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Cosmology in modified f(R, T)-gravity Open
In present paper we propose further modification of $f(R,T)$-gravity (where\n$T$ is trace of energy-momentum tensor) by introducing higher derivatives\nmatter fields. We discuss stability conditions in proposed theory and find\nrestriction…
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Constant-roll tachyon inflation and observational constraints Open
For the constant-roll tachyon inflation, we derive the analytical expressions for the scalar and tensor power spectra, the scalar and tensor spectral tilts and the tensor to scalar ratio up to the first order by using the method of Bessel …
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Tachyons in classical de Sitter vacua Open
We revisit the possibility of de Sitter vacua and slow-roll inflation in type II string theory at the level of the classical two-derivative supergravity approximation. Previous attempts at explicit constructions were plagued by ubiquitous …
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Chaotic scattering of highly excited strings Open
A bstract Motivated by the desire to understand chaos in the S -matrix of string theory, we study tree level scattering amplitudes involving highly excited strings. While the amplitudes for scattering of light strings have been a hallmark …
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Non-tachyonic semi-realistic non-supersymmetric heterotic-string vacua Open
\n The heterotic-string models in the free fermionic formulation gave rise to some of the most realistic-string models to date, which possess $$N=1$$ spacetime supersymmetry. Lack of evidence for supersymmetry at the LHC instigated recent …
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Composite Higgs and Dark Matter model in SU(6)/SO(6) Open
A bstract We consider a realisation of composite Higgs models in the context of SU(6) / SO(6) symmetry, which features a custodial bi-triplet, two Higgs doublets and dark matter candidates. This model can arise from an underlying gauge-fer…
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Bayesian evidences for dark energy models in light of current observational data Open
We do a comprehensive study of the Bayesian evidences for a large number of dark energy models using a combination of latest cosmological data from SNIa, CMB, BAO, Strong lensing time delay, Growth measurements, measurements of Hubble para…
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Soft gravitational radiation from ultra-relativistic collisions at sub- and sub-sub-leading order Open
A bstract Using soft-graviton theorems a well-known zero-frequency limit (ZFL) for the gravitational radiation flux dE GW /dω is re-derived and extended to order $$ \mathcal{O}\left(\omega \right) $$ and $$ \mathcal{O}\left({\omega}^2\righ…
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NANOGrav signal from axion inflation Open
Several pulsar timing arrays including NANOGrav, EPTA, PPTA, and CPTA have recently reported the observation of a stochastic background of gravitational wave spectrum in the nanohertz frequencies. An inflationary interpretation of this obs…
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Low redshift observational constraints on tachyon models of dark energy Open
The background evolution of an accelerated, dark energy dominated universe is aptly described by non-canonical tachyon scalar field models. The accelerated expansion of the universe is determined by the choice of a suitable scalar field po…
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Tachyon constant-roll inflation Open
The constant-roll inflation is studied where the inflaton is taken as a tachyon field. Since in this approach the second slow-roll parameter is assumed to be of order one instead of being small, then the perturbation parameters will be con…
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A parallel content-based image retrieval system using spark and tachyon frameworks Open
With the huge increase of large-scale multimedia over Internet, especially images, building Content-Based Image Retrieval (CBIR) systems for large-scale images has become a big challenge. One of the drawbacks associated with CBIR is the ve…
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Spontaneous growth of spinor fields in gravity Open
We show that spinor fields nonminimally coupled to gravity can grow\nspontaneously in the presence of matter. We name this phenomenon spontaneous\nspinorization after the spontaneous scalarization scenario in scalar-tensor\ntheories. Under…
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Kubo Formula for Non-Hermitian Systems and Tachyon Optical Conductivity Open
Linear response theory plays a prominent role in various fields of physics and provides us with extensive information about the thermodynamics and dynamics of quantum and classical systems. Here we develop a general theory for the linear r…
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Dynamical tachyonic AdS/QCD and information entropy Open
The configurational entropy setup is employed to study dynamical tachyonic\nholographic AdS/QCD models. The phenomenology of light-flavour mesonic states\nis then corroborated by the Shannon's information. Tachyonic bulk corrections\nto th…
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Supersymmetry breaking, brane dynamics and Swampland conjectures Open
We investigate interactions between branes of various dimensions, both charged and uncharged, in three non-supersymmetric string models. These include the USp(32) and U(32) orientifold projections of the type IIB and type 0B strings, as we…
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Radiatively stable ghost and tachyon freedom in metric affine gravity Open
We report the existence of a ghost- and tachyon-free sector in metric-affine\ntheories of gravity, that is invariant under diffeomorphism and a particular\nabelian symmetry. In contrast with many studied cases in the literature, the\nconst…
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String Theory and Non-Riemannian Geometry Open
The O(D,D) covariant generalized metric, postulated as a truly fundamental variable, can describe novel geometries where the notion of Riemannian metric ceases to exist. Here we quantize a closed string upon such backgrounds and identify f…
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Non-invertible symmetries, brane dynamics, and tachyon condensation Open
A bstract We study the Symmetry Topological Field Theory in holography associated with 4d 𝒩 = 1 Super Yang-Mills theory with gauge algebra 𝔰𝔲( M ). From this, all the bulk symmetry operators are computed and matched to various D-brane conf…
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Helicity methods for high multiplicity subleading soft and collinear limits Open
The factorization of multi-leg gauge theory amplitudes in the soft and collinear limits provides strong constraints on the structure of amplitudes, and enables efficient calculations of multi-jet observables at the LHC. There is significan…
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Classical and quantum cosmology of Born-Infeld type models Open
We discuss Born-Infeld type fields (tachyon fields) in classical and quantum cosmology. We first partly review and partly extend the discussion of the classical solutions and focus in particular on the occurrence of singularities. For quan…
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Anisotropic instability in a higher order gravity theory Open
We study a metric cubic gravity theory considering odd-parity modes of linear\ninhomogeneous perturbations on a spatially homogeneous Bianchi type I manifold\nclose to the isotropic de Sitter spacetime. We show that in the regime of small\…
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Recovering <i>P</i>(<i>X</i>) from a canonical complex field Open
We study the correspondence between models of a self-interacting canonical\ncomplex scalar field and P(X)-theories/shift-symmetric k-essence. Both describe\nthe same background cosmological dynamics, provided that the amplitude of the\ncom…
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Power-counting renormalizable, ghost-and-tachyon-free Poincaré gauge theories Open
We present 48 further examples, in addition to the 10 identified in [1], of\nghost-and-tachyon-free critical cases of parity-conserving Poincar\\'e gauge\ntheories of gravity (PGT$^+$) that are also power-counting renormalizable\n(PCR). Th…
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Nonlinear realization of chiral symmetry breaking in holographic soft wall models Open
We investigate nonlinear extensions of the holographic soft wall model\nproposed by Karch, Katz, Son and Stephanov \\cite{Karch:2006pv} with a positive\nquadratic dilaton. We consider a Higgs potential for the tachyonic field that\nbrings …