Search results for "SCALAR"
showing 10 items of 1002 documents
Quantum corrections to inflation: the importance of RG-running and choosing the optimal RG-scale
2017
We demonstrate the importance of correctly implementing RG running and choosing the RG scale when calculating quantum corrections to inflaton dynamics. We show that such corrections are negligible for single-field inflation, in the sense of not altering the viable region in the ${n}_{s}\ensuremath{-}r$ plane, when imposing Planck constraints on ${A}_{s}$. Surprisingly, this also applies, in a nontrivial way, for an inflaton coupled to additional spectator degrees of freedom. The result relies on choosing the renormalization scale (pseudo-)optimally, thereby avoiding unphysical large logarithmic corrections to the Friedmann equations and large running of the couplings. We find that the viabl…
A one-electron variant of direct perturbation theory for the treatment of scalar-relativistic effects
2018
The different importance of scalar-relativistic two-electron contributions in second-order direct perturbation theory (DPT2) and the spin-free one-electron variant of exact two-component theory (SF...
Cost-Effective Treatment of Scalar Relativistic Effects for Multireference Systems: A CASSCF Implementation Based on the Spin-free Dirac-Coulomb Hami…
2016
We present an implementation of the complete active space-self-consistent field (CASSCF) method specifically designed to be used in four-component scalar relativistic calculations based on the spin-free Dirac-Coulomb (SFDC) Hamiltonian. Our implementation takes full advantage of the properties of the SFDC Hamiltonian that allow us to use real algebra and to exploit point-group and spin symmetry to their full extent while including in a rigorous way scalar relativistic effects in the treatment. The SFDC-CASSCF treatment is more expensive than its non-relativistic counterpart only in the orbital optimization step, while exhibiting the same computational cost for the rate-determining full conf…
Metric-affine f(R,T) theories of gravity and their applications
2018
We study $f(R,T)$ theories of gravity, where $T$ is the trace of the energy-momentum tensor ${T}_{\ensuremath{\mu}\ensuremath{\nu}}$, with independent metric and affine connection (metric-affine theories). We find that the resulting field equations share a close resemblance with their metric-affine $f(R)$ relatives once an effective energy-momentum tensor is introduced. As a result, the metric field equations are second-order and no new propagating degrees of freedom arise as compared to GR, which contrasts with the metric formulation of these theories, where a dynamical scalar degree of freedom is present. Analogously to its metric counterpart, the field equations impose the nonconservatio…
Quantum-corrected rotating black holes and naked singularities in ( 2+1 ) dimensions
2019
We analytically investigate the perturbative effects of a quantum conformally coupled scalar field on rotating (2+1)-dimensional black holes and naked singularities. In both cases we obtain the quantum-backreacted metric analytically. In the black hole case, we explore the quantum corrections on different regions of relevance for a rotating black hole geometry. We find that the quantum effects lead to a growth of both the event horizon and the ergosphere, as well as to a reduction of the angular velocity compared to their corresponding unperturbed values. Quantum corrections also give rise to the formation of a curvature singularity at the Cauchy horizon and show no evidence of the appearan…
Numerical evolutions of spherical Proca stars
2017
Vector boson stars, or $\textit{Proca stars}$, have been recently obtained as fully non-linear numerical solutions of the Einstein-(complex)-Proca system. These are self-gravitating, everywhere non-singular, horizonless Bose-Einstein condensates of a massive vector field, which resemble in many ways, but not all, their scalar cousins, the well-known (scalar) $\textit{boson stars}$. In this paper we report fully-non linear numerical evolutions of Proca stars, focusing on the spherically symmetric case, with the goal of assessing their stability and the end-point of the evolution of the unstable stars. Previous results from linear perturbation theory indicate the separation between stable and…
Dynamical symmetry breaking and fermion mass hierarchy in the scale-invariant 3-3-1 model
2020
We propose an extension of the Standard Model (SM) based on the $SU(3)_C\otimes SU(3)_L\otimes U(1)_X$ (3-3-1) gauge symmetry and scale invariance. Maintaining the main features of the so-called 3-3-1 models, such as the cancellation of gauge anomalies related to the number of chiral fermion generations, this model exhibits a very compact scalar sector. Only two scalar triplets and one singlet are necessary and sufficient to break the symmetries dynamically via the Coleman-Weinberg mechanism. With the introduction of an Abelian discrete symmetry and assuming a natural hierarchy among the vacuum expectation values of the neutral scalar fields, we show that all particles in the model can get …
Big bounce and future time singularity resolution in Bianchi i cosmologies: The projective invariant Nieh-Yan case
2021
We extend the notion of the Nieh-Yan invariant to generic metric-affine geometries, where both torsion and nonmetricity are taken into account. Notably, we show that the properties of projective invariance and topologicity can be independently accommodated by a suitable choice of the parameters featuring this new Nieh-Yan term. We then consider a special class of modified theories of gravity able to promote the Immirzi parameter to a dynamical scalar field coupled to the Nieh-Yan form, and we discuss in more detail the dynamics of the effective scalar tensor theory stemming from such a revised theoretical framework. We focus, in particular, on cosmological Bianchi I models and we derive cla…
Dynamical formation of a Reissner-Nordström black hole with scalar hair in a cavity
2016
In a recent Letter [Sanchis-Gual et al., Phys. Rev. Lett. 116, 141101 (2016)], we presented numerical relativity simulations, solving the full Einstein--Maxwell--Klein-Gordon equations, of superradiantly unstable Reissner-Nordstr\"om black holes (BHs), enclosed in a cavity. Low frequency, spherical perturbations of a charged scalar field trigger this instability. The system's evolution was followed into the nonlinear regime, until it relaxed into an equilibrium configuration, found to be a hairy BH: a charged horizon in equilibrium with a scalar field condensate, whose phase is oscillating at the (final) critical frequency. Here, we investigate the impact of adding self-interactions to the …
Imaging magnetic scalar potentials by laser-induced fluorescence from bright and dark atoms
2014
We present a spectroscopic method for mapping two-dimensional distributions of magnetic field strengths (magnetic scalar potential lines) using charge-coupled device (CCD) recordings of the fluorescence patterns emitted by spin-polarized Cs vapour in a buffer gas exposed to inhomogeneous magnetic fields. The method relies on the position-selective destruction of spin polarization by magnetic resonances induced by multi-component oscillating magnetic fields, such that magnetic potential lines can be directly detected by the CCD camera. We also present a generic algebraic model allowing for the calculation of the fluorescence patterns and find excellent agreement with the experimental observa…