arXiv subjects

Joan Sola

Publications and source records attributed to Joan Sola.

At least 19 recordsLinked to original sources

arXiv2023

Borinot: an agile torque-controlled robot for hybrid flying and contact loco-manipulation (workshop version)

This paper introduces Borinot, an open-source flying robotic platform designed to perform hybrid agile locomotion and manipulation. This platform features a compact and powerful hexarotor that can be outfitted with torque-actuated extremities of diverse architecture, allowing for whole-body dynamic control. As a result, Borinot can perform agile tasks such as aggressive or acrobatic maneuvers with the participation of the whole-body dynamics. The extremities attached to Borinot can be utilized in various ways; during contact, they can be used as legs to create contact-based locomotion, or as arms to manipulate objects. In free flight, they can be used as tails to contribute to dynamics, mimicking the movements of many animals. This allows for any hybridization of these dynamic modes, like the jump-flight of chicken and locusts, making Borinot an ideal open-source platform for research on hybrid aerial-contact agile motion. To demonstrate the key capabilities of Borinot, we have fitted a planar 2DoF arm and implemented whole-body torque-level model-predictive-control. The result is a capable and adaptable platform that, we believe, opens up new avenues of research in the field of agile robotics.

cs.RO↗

arXiv2022

A Feasibility-Driven Approach to Control-Limited DDP

Differential dynamic programming (DDP) is a direct single shooting method for trajectory optimization. Its efficiency derives from the exploitation of temporal structure (inherent to optimal control problems) and explicit roll-out/integration of the system dynamics. However, it suffers from numerical instability and, when compared to direct multiple shooting methods, it has limited initialization options (allows initialization of controls, but not of states) and lacks proper handling of control constraints. In this work, we tackle these issues with a feasibility-driven approach that regulates the dynamic feasibility during the numerical optimization and ensures control limits. Our feasibility search emulates the numerical resolution of a direct multiple shooting problem with only dynamics constraints. We show that our approach (named BOX-FDDP) has better numerical convergence than BOX-DDP+ (a single shooting method), and that its convergence rate and runtime performance are competitive with state-of-the-art direct transcription formulations solved using the interior point and active set algorithms available in KNITRO. We further show that BOX-FDDP decreases the dynamic feasibility error monotonically--as in state-of-the-art nonlinear programming algorithms. We demonstrate the benefits of our approach by generating complex and athletic motions for quadruped and humanoid robots. Finally, we highlight that BOX-FDDP is suitable for model predictive control in legged robots.

cs.RO↗

arXiv2022

WOLF: A modular estimation framework for robotics based on factor graphs

This paper introduces WOLF, a C++ estimation framework based on factor graphs and targeted at mobile robotics. WOLF can be used beyond SLAM to handle self-calibration, model identification, or the observation of dynamic quantities other than localization. The architecture of WOLF allows for a modular yet tightly-coupled estimator. Modularity is enhanced via reusable plugins that are loaded at runtime depending on application setup. This setup is achieved conveniently through YAML files, allowing users to configure a wide range of applications without the need of writing or compiling code. Most procedures are coded as abstract algorithms in base classes with varying levels of specialization. Overall, all these assets allow for coherent processing and favor code re-usability and scalability. WOLF can be used with ROS, and is made publicly available and open to collaboration.

cs.RO↗

arXiv2021

Inflationary physics and transplanckian conjecture in the Stringy Running-Vacuum-Model: from the phantom vacuum to the true vacuum

In previous works we have embedded the Running Vacuum Model (RVM) of Cosmology in the framework of string theory. Specifically, we considered a string-inspired Cosmology with primordial gravitational waves (GW) and gravitational anomalies, which were argued to lead, via appropriate condensation during the very-early-universe era, to dynamical inflation, of RVM type, without the need for extra inflaton fields. A crucial role for the associated slow-roll nature of the inflationary era was played by the fundamental axion field that exists in the gravitational multiplet of strings, viz. the Kalb-Ramond (KR) axion. In this paper, we study further this model and demonstrate several novel facts, completing our previous studies. We clarify the different roles played by the background KR axions, which constitute a form of stiff matter that dominates a pre-RVM-inflationary epoch of the Universe. We show that the KR axion when combined with the gravitational Chern-Simons contribution obey together a peculiar equation of state $p=-ρ$, with negative energy density $ρ< 0$, which we call `phantom vacuum'. Eventually, this state transmutes into the standard vacuum state thanks to the contribution from the gravitational Chern-Simons condensate, which makes the total $ρ_{\rm total} =-p_{\rm total} >0$. At this point the RVM vacuum picture emerges naturally, with an overall equation of state of true vacuum type. We find that our scenario is consistent with the trans-Planckian censorship hypothesis, given that the rate of change of the KR axion takes only sub-Planckian values. We also discuss some explicit scenarios on the creation of GWs within the context of supergravity models that could be embedded in our string theory framework. {Finally, we argue how the RVM in our context can help to alleviate the current tensions of the $Λ$CDM.}

hep-th↗

arXiv2021

Cosmographic approach to Running Vacuum dark energy models: new constraints using BAOs and Hubble diagrams at higher redshifts

In this work we study different types of dark energy (DE) models in the framework of the cosmographic approach, with emphasis on the Running Vacuum models (RVMs). We assess their viability using different information criteria and compare them with the so-called Ghost DE models (GDEs) as well as with the concordance $Λ$CDM model. We use the Hubble diagrams for Pantheon SnIa, quasars (QSOs), gamma-ray bursts (GRBs) as well as the data on baryonic acoustic oscillations (BAOs) in four different combinations. Upon minimizing the $χ^2$ function of the distance modulus in the context of the Markov Chain Monte Carlo method (MCMC), we put constraints on the current values of the standard cosmographic parameters in a model-independent way. It turns out that, in the absence of BAOs data, the various DE models generally exhibit cosmographic tensions with the observations at the highest redshifts (namely with the QSOs and GRBs data). However, if we include the robust observations from BAOs to our cosmographic sample, the $Λ$CDM and RVMs are clearly favored against the GDEs. Finally, judging from the perspective of the deviance information criterion (DIC), which enables us to compare models making use of the Markov chains of the MCMC method, we conclude that the RVMs are the preferred kind of DE models. We find it remarkable that these models, which had been previously shown to be capable of alleviating the $σ_8$ and $H_0$ tensions, appear now also as the most successful ones at the level of the cosmographic analysis.

astro-ph.CO↗

arXiv2021

Running vacuum against the $H_0$ and $σ_8$ tensions

The cosmological term, $Λ$, was introduced $104$ years ago by Einstein in his gravitational field equations. Whether $Λ$ is a rigid quantity or a dynamical variable in cosmology has been a matter of debate for many years, especially after the introduction of the general notion of dark energy (DE). $Λ$ is associated to the vacuum energy density, $ρ_{\rm vac}$, and one may expect that it evolves slowly with the cosmological expansion. Herein we present a devoted study testing this possibility using the promising class of running vacuum models (RVM's). We use a large string $SNIa+BAO+H(z)+LSS+CMB$ of modern cosmological data, in which for the first time the CMB part involves the full Planck 2018 likelihood for these models. We test the dependence of the results on the threshold redshift $z_*$ at which the vacuum dynamics is activated in the recent past and find positive signals up to $\sim4.0σ$ for $z_*\simeq 1$. The RVM's prove very competitive against the standard $Λ$CDM model and give a handle for solving the $σ_8$ tension and alleviating the $H_0$ one.

astro-ph.CO↗

arXiv2020

Stringy-Running-Vacuum-Model Inflation: from primordial Gravitational Waves and stiff Axion Matter to Dynamical Dark Energy

In previous works we have derived a Running Vacuum Model (RVM) for a string Universe, which provides an effective description of the evolution of 4-dimensional string-inspired cosmologies from inflation till the present epoch. In the context of this "stringy RVM" version, it is assumed that the early Universe is characterised by purely gravitational degrees of freedom, from the massless gravitational string multiplet, including the antisymmetric tensor field. The latter plays an important role, since its dual gives rise to a `stiff' gravitational-axion "matter", which in turn couples to the gravitational anomaly terms, assumed to be non-trivial at early epochs. In the presence of primordial gravitational wave (GW) perturbations, such anomalous couplings lead to an RVM-like dynamical inflation, without external inflatons. We review here this framework and discuss potential scenarios for the generation of such primordial GW, among which the formation of unstable domain walls, which eventually collapse in a non-spherical-symmetric manner, giving rise to GW. We also remark that the same type of "stiff" axionic matter could provide, upon the generation of appropriate potentials during the post-inflationary eras, (part of) the Dark Matter (DM) in the Universe, which could well be ultralight, depending on the parameters of the string-inspired model. All in all, the new (stringy) mechanism for RVM-inflation preserves the basic structure of the original (and more phenomenological) RVM, as well as its main advantages: namely, a mechanism for graceful exit and for generating a huge amount of entropy capable of explaining the horizon problem. It also predicts axionic DM and the existence of mild dynamical Dark Energy (DE) of quintessence type in the present universe, both being "living fossils" of the inflationary stages of the cosmic evolution.

hep-ph↗

arXiv2020

Brans-Dicke cosmology with a $Λ$- term: a possible solution to $Λ$CDM tensions

We present a full-fledged analysis of Brans-Dicke cosmology with a cosmological constant and cold dark matter (BD-$Λ$CDM for short). We extend the scenarios where the current cosmological value of the BD-field is restricted by the local astrophysical domain to scenarios where that value is fixed only by the cosmological observations, which should be more natural in view of the possible existence of local screening mechanims. Our analysis includes both the background and perturbations equations in different gauges. We find that the BD-$Λ$CDM is favored by the overall cosmological data as compared to the concordance GR-$Λ$CDM model, namely data on distant supernovae, cosmic chronometers, local measurements of the Hubble parameter, baryonic acoustic oscillations, Large-Scale Structure formation and the cosmic microwave background under full Planck 2018 CMB likelihood. We also test the impact of Strong and Weak-Lensing data on our results, which can be significant. We find that the BD-$Λ$CDM can mimic effective quintessence with a significance of about $3-3.5σ$ c.l. (depending on the lensing datasets). The fact that the BD-$Λ$CDM behaves effectively as a Running Vacuum Model (RVM) when viewed from the GR perspective helps to alleviate some of the existing tensions with the data, such as the $σ_8$ excess predicted by GR-$Λ$CDM. On the other hand, the BD-$Λ$CDM model has a crucial bearing on the acute $H_0$-tension with the local measurements, which is rendered virtually harmless owing to the small increase of the effective value of the gravitational constant with the expansion. The simultaneous alleviation of the two tensions is a most remarkable feature of BD-gravity with a cosmological constant in the light of the current observations, and hence goes in support of BD-$Λ$CDM against GR-$Λ$CDM

astro-ph.CO↗

arXiv2020

Running vacuum in quantum field theory in curved spacetime: renormalizing $ρ_{vac}$ without $\sim m^4$ terms

The $Λ$-term in Einstein's equations is a fundamental building block of the `concordance' $Λ$CDM model of cosmology. Even though the model is not free of fundamental problems, they have not been circumvented by any alternative dark energy proposal either. Here we stick to the $Λ$-term, but we contend that it can be a `running quantity' in quantum field theory (QFT) in curved spacetime. A plethora of phenomenological works have shown that this option can be highly competitive with the $Λ$CDM with a rigid cosmological term. The, so-called, `running vacuum models' (RVM's) are characterized by the vacuum energy density, $ρ_{vac}$, being a series of (even) powers of the Hubble parameter and its time derivatives. Such theoretical form has been motivated by general renormalization group arguments, which look plausible. Here we dwell further upon the origin of the RVM structure within QFT in FLRW spacetime. We compute the renormalized energy-momentum tensor with the help of the adiabatic regularization procedure and find that it leads essentially to the RVM form. This means that $ρ_{vac}(H)$ evolves as a constant term plus dynamical components ${\cal O}(H^2)$ and ${\cal O}(H^4)$, the latter being relevant for the early universe only. However, the renormalized $ρ_{vac}(H)$ does not carry dangerous terms proportional to the quartic power of the masses ($\sim m^4$) of the fields, these terms being a well-known source of exceedingly large contributions. At present, $ρ_{vac}(H)$ is dominated by the additive constant term accompanied by a mild dynamical component $\sim νH^2$ ($|ν|\ll1$), which mimics quintessence.

gr-qc↗

arXiv2020

Quantum Anomalies in String-Inspired Running Vacuum Universe: Inflation and Axion Dark Matter

In this letter, we elaborate further on a Cosmological "Running-Vacuum" type model for the Universe, suggested previously by the authors within the context of a string-inspired effective theory in the presence of a Kalb-Ramond (KR) gravitational axion field which descends from the antisymmetric tensor of the massless gravitational string multiplet. In the presence of this field, which has anomalous CP violating interactions with the gravitons, primordial gravitational waves induce gravitational anomalies, which in turn are responsible for the appearance of $H^2$ and $H^4$ contributions to the vacuum energy density, these terms being characteristic of generic "running-vacuum-model (RVM) type", where $H$ is the Hubble parameter. In this work we prove in detail the appearance of the $H^4$ terms due to gravitational-anomaly-induced condensates in the energy density of the primordial Universe, which can self-consistently induce inflation, and subsequent exit from it, according to the generic features of RVM. We also argue in favour of the robustness of our results, which were derived within an effective low-energy field theory approach, against Ultra Violet completion of the theory. During the radiation and matter-dominated eras, gravitational anomalies cancel, as required for the consistency of the quantum matter/radiation field theory. However, chiral and QCD-axion-type anomalies survive and have important consequences for both cosmic magnetogenesis and axionic dark matter in the Universe. Finally, the stringy RVM scenario presented here predicts quintessence-like dynamical dark energy for the current Universe, which is compatible with the existing fitting analyses of such model against observations

gr-qc↗

arXiv2020

Particle and entropy production in the Running Vacuum Universe

We study particle production and the corresponding entropy increase in the context of cosmology with dynamical vacuum. We focus on the particular form that has been called "running vacuum model" (RVM), which is known to furnish a successful description of the overall current observations at a competitive level with the concordance $Λ$CDM model. It also provides an elegant global explanation of the cosmic history from a non-singular initial state in the very early universe up to our days and further into the final de Sitter era. The model has no horizon problem and provides an alternative explanation for the early inflation and its graceful exit, as well as a powerful mechanism for generating the large entropy of the current universe. The energy-momentum tensor of matter is generally non-conserved in such context owing to particle creation or annihilation. We analyze general thermodynamical aspects of particle and entropy production in the RVM. We first study the entropy of particles in the comoving volume during the early universe and late universe. Then, in order to obtain a more physical interpretation, we pay attention to the entropy contribution from the cosmological apparent horizon, its interior and its surface. On combining the inner volume entropy with the entropy on the horizon, we elucidate with detailed calculations whether the evolution of the entropy of the RVM universe satisfies the Generalized Second Law of Thermodynamics. We find it is so and we prove that the essential reason for it is the existence of a positive cosmological constant.

gr-qc↗

arXiv2020

Gravitational and Chiral Anomalies in the Running Vacuum Universe and Matter-Antimatter Asymmetry

We present a model for the Universe in which quantum anomalies are argued to play an important dual role: they are responsible for generating matter-antimatter asymmetry, but also provide time-dependent contributions to the vacuum energy density of "running-vacuum" type, which drive the Universe evolution. During the inflationary phase of a string-inspired Universe, and its subsequent exit, the existence of primordial gravitational waves induce gravitational anomalies, which couple to the Kalb-Ramond (KR)axion field of the massless gravitational string multiplet. Such anomalous CP violating interactions have two important effects: first, they lead to contributions to the vacuum energy density of the form appearing in the "running vacuum model" (RVM) framework, proportional to both the square and the fourth power of the effective Hubble parameter $H$, the $H^4$ terms being associated with anomaly-induced inflation within the RVM framework. Second, there is an undiluted KR axion at the end of inflation, which plays an important role in generating matter-antimatter asymmetry through baryogenesis via leptogenesis in models with heavy right handed neutrinos. As the Universe exits inflation and enters a radiation dominated era, the generation of chiral fermionic matter is responsible for the cancellation of gravitational anomalies, thus restoring diffeomorphism invariance for the matter/radiation (quantum) theory, as required for consistency. Chiral U(1) anomalies may remain uncompensated, though, during matter/radiation dominance, providing RVM-like $H^2$ and $H^4$ contributions to the Universe energy density. Finally, in the current era, gravitational anomalies resurface, leading to much weaker RVM-like $H_0^2$ contributions to the vacuum energy density.Our model favours axionic Dark Matter,the source of which can be the KR axion.

hep-ph↗

arXiv2019

Scalar Field Theory Description of the Running Vacuum Model: the Vacuumon

We investigate the running vacuum model (RVM) in the framework of scalar field theory.This dynamical vacuum model provides an elegant global explanation of the cosmic history, namely the universe starts from a non-singular initial de Sitter vacuum stage, it passes smoothly from an early inflationary era to a radiation epoch ("graceful exit") and finally it enters the dark matter and dark energy (DE) dominated epochs, where it can explain the large entropy problem and predicts a mild dynamical evolution of the DE. Within this phenomenologically appealing context, we formulate an effective {\it classical} scalar field description of the RVM through a field $ϕ$, called the {\it vacuumon}, which turns out to be very helpful for an understanding and practical implementation of the physical mechanisms of the running vacuum during both the early universe and the late time cosmic acceleration. In the early universe the potential for the vacuumon may be mapped to a potential that behaves similarly to that of the scalaron field of Starobinsky-type inflation at the {\it classical} level, whilst in the late universe it provides an effective scalar field description of DE. The two representations, however, are not physically equivalent since the mechanisms of inflation are entirely different. Moreover, unlike the scalaron, vacuumon is treated as a classical background field, and not a fully fledged quantum field, hence cosmological perturbations will be different between the two pictures of inflation.

gr-qc↗

arXiv2019

Brans-Dicke gravity with a cosmological constant smoothes out $Λ$CDM tensions

We analyze Brans-Dicke gravity with a cosmological constant, $Λ$, and cold dark matter (BD-$Λ$CDM for short) in the light of the latest cosmological observations on distant supernovae, Hubble rate measurements at different redshifts, baryonic acoustic oscillations, large scale structure formation data, gravitational weak-lensing and the cosmic microwave background under full Planck 2015 CMB likelihood. Our analysis includes both the background and perturbations equations. We find that BD-$Λ$CDM is observationally favored as compared to the concordance $Λ$CDM model, which is traditionally defined within General Relativity (GR). In particular, some well-known persisting tensions of the $Λ$CDM with the data, such as the excess in the mass fluctuation amplitude $σ_8$ and specially the acute $H_0$-tension with the local measurements, essentially disappear in this context. Furthermore, viewed from the GR standpoint, BD-$Λ$CDM cosmology mimics quintessence at $\gtrsim3σ$ c.l. near our time.

astro-ph.CO↗

arXiv2019

Can dark energy be expressed as a power series of the Hubble parameter?

In this work we examine the possibility that the dark energy (DE) density, $ρ_{de}$ can be dynamical and appear as a power series expansion of the Hubble rate (and its derivatives), i.e.$ρ_{de}(H,\dot{H},...)$. For the present universe, however, only the terms $H$, $\dot{H}$ and $H^2$ can be relevant, together with an additive constant term. We fit these models to the current cosmological data on the main observables SNIa+$H(z)$+BAO+LSS+CMB+BBN. Our analysis involves both the background as well as the cosmic perturbation equations. The latter include, apart from the matter density perturbations, also the DE density perturbations. We assume that matter and dynamical DE are separately self-conserved. As a result the equation of state of the DE becomes a nontrivial function of the cosmological redshift, $w_D=w_D(z)$. The particular subset of DE models of this type having no additive constant term in $ρ_{de}$ include the so-called entropic-force and QCD-ghost DE models, as well as the pure linear model $ρ_{de} \sim H$ all of which are strongly disfavored in our fitting analysis. In contrast, the models that include the additive term plus one or both of the dynamical components $\dot{H}$ and $H^2$ appear more favored than the $Λ$CDM. In particular, the dynamical DE models provide a value of $σ_8\simeq 0.74-0.77$ which is substantially lower than that of the $Λ$CDM and hence more in accordance with the observations. This helps to significantly reduce the $σ_8$-tension in the structure formation data. At the same time the predicted value for $H_0$ is in between the local and Planck measurements, thus helping to alleviate this tension as well.

gr-qc↗

arXiv2019

Do we Come from a Quantum Anomaly?

We present a string-based picture of the cosmological evolution in which (CP-violating) gravitational anomalies acting during the inflationary phase of the universe cause the vacuum energy density to "run" with the effective Hubble parameter squared, $H^2$, thanks to the axion field of the bosonic string multiplet. This leads to baryogenesis through leptogenesis with massive right-handed neutrinos. The generation of chiral matter after inflation helps in cancelling the anomalies in the observable radiation- and matter- dominated eras. The present era inherits the same "running vacuum" structure triggered during the inflationary time by the axion field. The current dark energy is thus predicted to be mildly dynamical, and dark matter should be made of axions. Paraphrasing Carl Sagan: "we are all anomalously made from starstuff " .

hep-th↗

arXiv2019

Quantum Anomalies, Running Vacuum and Leptogenesis: an Interplay

We discuss a connection between gravitational-wave physics, quantum theory anomalies, right-handed (sterile) neutrinos, (spontaneous) CPT Violation and Leptogenesis, within the framework of string-inspired cosmological models. In particular, we present a scenario, according to which (primordial) gravitational waves induce gravitational anomalies during inflation. This, in turn, results in the existence of an undiluted (at the exit of inflation/beginning of radiation era) bakcground of the Kalb-Ramond (KR) axion of the massless bosonic string gravitational multiplet. The latter may violate spontaneously CP and CPT symmetries, and induce leptogenesis during the radiation-dominated era in models involving right-handed neutrinos. The so-generated lepton asymmetry may then be communicated to the baryon sector by appropriate baryon-minus-lepton-number (B - L)-conserving, but (B + L)-violating, (sphaleron) processes in the Standard Model sector, thus leading to matter dominance over antimatter in the Universe.In the current (approximately de Sitter) era, the KR axion background may provide a source for an axionic dark matter in the Universe, through its mixing with other axions that are abundant in string models. As an interesting byproduct of our analysis, we demonstrate that the anomalies contribute to the vacuum energy density of the Universe terms of 'running-vacuum' type, proportional to the square of the Hubble parameter, $H^2$.

hep-ph↗

arXiv2019

Signs of Interacting Vacuum and Dark Matter in the Universe

We consider the impact of dynamical dark energy (DDE) in the possible solution of the existing tensions in the $Λ$CDM. We test both interacting and non-interacting DE models with dark matter (DM). Among the former, the running vacuum model (RVM) interacting with DM appears as a favored option. The non-interacting scalar field model based on the potential $V\sim ϕ^{-α}$, and the generic XCDM parametrization, also provide consistent signs of DDE. The important novelty of our analysis with respect to the existing ones in the literature is that we use the matter bispectrum, together with the power spectrum. Using a complete and updated set of cosmological observations on $SNIa+BAO+H(z)+LSS+CMB$, we find that the crucial triad $BAO+LSS+CMB$ (i.e. baryonic acoustic oscillations, large scale structure formation data and the cosmic microwave background) provide the bulk of the signal. The bispectrum data is instrumental to get hold of the DDE signal, as our analysis shows. If the bispectrum is not included, the DDE signal could not be currently perceived at a significant confidence level.

astro-ph.CO↗