Parametric Resonance in the Early Universe - A Fitting Analysis

Particle production via parametric resonance in the early Universe, is a nonperturbative, non-linear and out-of-equilibrium phenomenon. Although it is a well studied topic, whenever a new scenario exhibits parametric resonance, a full re-analysis is normally required. To avoid this tedious task, many works present often only a simplified linear treatment of the problem. In order to surpass this circumstance in the future, we provide a fitting analysis of parametric resonance through all its relevant stages: initial linear growth, non-linear evolution, and relaxation towards equilibrium. Using lattice simulations in an expanding grid in 3 + 1 dimensions, we parametrize the dynamics outcome scanning over the relevant ingredients: role of the oscillatory field, particle coupling strength, initial conditions, and background expansion rate. We emphasize the inaccuracy of the linear calculation of the decay time of the oscillatory field, and propose a more appropriate definition of this scale based on the subsequent non-linear dynamics. We provide simple fits to the relevant time scales and particle energy fractions at each stage. Our fits can be applied to post-inflationary preheating scenarios, where the oscillatory field is the inflaton, or to spectator-field scenarios, where the oscillatory field can be e.g. a curvaton, or the Standard Model Higgs.Comment: Extended discussion about the late-time dynamics of the system in quadratic models. Minor changes in numerical fits with respect first version. It matches version published in JCAP (30 pages + Appendices + Bibliography, 13 figures

Higgs-curvature coupling and post-inflationary vacuum instability

We study the post-inflationary dynamics of the Standard Model (SM) Higgs field in the presence of a non-minimal coupling $\xi|\Phi|^2R$ to gravity, both with and without the electroweak gauge fields coupled to the Higgs. We assume a minimal scenario in which inflation and reheating are caused by chaotic inflation with a quadratic potential, and no additional new physics is relevant below the Planck scale. By using classical real-time lattice simulations with a renormalisation group improved effective Higgs potential and by demanding the stability of the Higgs vacuum after inflation, we obtain upper bounds for $\xi$, taking into account the experimental uncertainty of the top-Yukawa coupling. We compare the bounds in the absence and presence of the electroweak gauge bosons, and conclude that the addition of gauge interactions has a rather minimal impact. In the unstable cases, we parametrize the time when such instability develops. For a top-quark mass $m_t \approx173.3 {\rm GeV}$, the Higgs vacuum instability is triggered for $\xi \gtrsim 4 -5$, although a slightly lower mass of $m_t \approx 172.1 {\rm GeV}$ pushes up this limit to $\xi \gtrsim 11 - 12$. This, together with the estimation $\xi \gtrsim 0.06$ for stability during inflation, provides tight constraints to the Higgs-curvature coupling within the SM.Comment: 15 pages, 13 figures. Minor changes to match version published in PR

Estudio de los aspectos legales, retos y limitaciones en la implementación de tecnologías DLT y smart contracts en la sindicación de préstamos corporativos

La irrupción de la tecnología blockchain /DLT y el advenimiento de los denominados smart contracts , o contratos inteligentes, promete revolucionar múltiples aspectos de nuestra vida cotidiana. Esta tecnología tiene el potencial de alterar de manera fundamental y definitiva la forma en la que empresas, personas, gobiernos y administraciones públicas interactúan entre sí. El impacto de las nuevas infraestructuras, servicios y plataformas basados en la tecnología blockchain es latentemente disruptivo. En este trabajo estudiamos la irrupción de la tecnología blockchain /DLT y los s mart contracts en la industria de servicios financieros, y en particular en el sector bancario, con especial atención a las aplicaciones dirigidas a la gestión de la sindicación de préstamos corporativos, la distribución de dichos préstamos en los mercados secundarios, y los servicios de agencia asociados. En la actualidad, se plantean diferentes alternativas técnicas y múltiples interrogantes sobre los aspectos legales asociados a la implementación de dicha tecnología, y se cuestiona la capacidad e idoneidad del marco legal europeo e internacional actual para adaptarse a los cambios que la industria reclama. El siguiente trabajo intenta ofrecer luz al respecto, y presenta de manera crítica la situación actual del desarrollo de la tecnología en el ámbito propuesto, estudiando las limitaciones que en el marco regulatorio y legal actual podrían afectar al desarrollo de esta, con especial énfasis en el ámbito europeo.The irruption of the blockchain, and DLT technologies in general, and the advent of smart contracts promises to revolutionise multiple aspects of our daily lives. This technology has the potential to fundamentally and definitively alter the way in which companies, individuals, governments and public administrations interact with each other. The impact of new infrastructures, services and platforms based on blockchain technology is latently disruptive. In this paper, we study the emergence of blockchain / DLT technologies and smart contracts in the financial services industry, and the banking sector in particular, with special attention to applications in the syndication of corporate loans, secondary market distribution, and loan agency services. Currently, different technical alternatives are considered, and multiple questions raised about the legal aspects associated with the implementation of such technology, as well as the capacity and suitability of the current European and international legal framework to adapt to the changes demanded by the industry. The following work tries to shed some light in this respect, and presents in a critical way the development of the technology in the proposed field, studying the limitations that in the current regulatory and legal framework could affect its development, with special emphasis on a European scope and framework.La irrupció de la tecnologia blockchain /DLT i l'adveniment dels denominats smart contracts , o contractes intel·ligents, promet revolucionar múltiples aspectes de la nostra vida quotidiana. Aquesta tecnologia té el potencial d'alterar de manera fonamental i definitiva la forma en la qual empreses, persones, governs i administracions públiques interactuen entre si. L'impacte de les noves infraestructures, serveis i plataformes basats en la tecnologia blockchain és latentment disruptivo. En aquest treball estudiem la irrupció de la tecnologia blockchain /DLT i els s mart contracts en la indústria de serveis financers, i en particular en el sector bancari, amb especial atenció a les aplicacions dirigides a la gestió de la sindicació de préstecs corporatius, la distribució d'aquests préstecs en els mercats secundaris, i els serveis d'agència associats. En l'actualitat, es plantegen diferents alternatives tècniques i múltiples interrogants sobre els aspectes legals associats a la implementació d'aquesta tecnologia, i es qüestiona la capacitat i idoneïtat del marc legal europeu i internacional actual per a adaptar-se als canvis que la indústria reclama. El següent treball intenta oferir llum sobre aquest tema, i presenta de manera crítica la situació actual del desenvolupament de la tecnologia en l'àmbit proposat, estudiant les limitacions que en el marc regulador i legal actual podrien afectar el desenvolupament d'aquesta, amb especial èmfasi en l'àmbit europeu

The Decay of the Standard Model Higgs after Inflation

We study the nonperturbative dynamics of the Standard Model (SM) after inflation, in the regime where the SM is decoupled from (or weakly coupled to) the inflationary sector. We use classical lattice simulations in an expanding box in (3+1) dimensions, modeling the SM gauge interactions with both global and Abelian-Higgs analogue scenarios. We consider different post-inflationary expansion rates. During inflation, the Higgs forms a condensate, which starts oscillating soon after inflation ends. Via nonperturbative effects, the oscillations lead to a fast decay of the Higgs into the SM species, transferring most of the energy into $Z$ and $W^{\pm}$ bosons. All species are initially excited far away from equilibrium, but their interactions lead them into a stationary stage, with exact equipartition among the different energy components. From there on the system eventually reaches equilibrium. We have characterized in detail, in the different expansion histories considered, the evolution of the Higgs and of its dominant decay products, until equipartition is established. We provide a useful mapping between simulations with different parameters, from where we derive a master formula for the Higgs decay time, as a function of the coupling constants, Higgs initial amplitude and postinflationary expansion rate.Comment: Minor changes to match the PRD published version. Modulation of the Higgs amplitude removed for $q > 200$ in Sec. V, due to improving the time resolution in the Higgs equation of motion. Results unaffecte

Energy distribution and equation of state of the early Universe: matching the end of inflation and the onset of radiation domination

We study the energy distribution and equation of state of the universe between the end of inflation and the onset of radiation domination (RD), considering observationally consistent single-field inflationary scenarios, with a potential 'flattening' at large field values, and a monomial shape $V(\phi) \propto |\phi|^p$ around the origin. As a proxy for (p)reheating, we include a quadratic interaction $g^2\phi^2X^2$ between the inflaton $\phi$ and a light scalar 'daughter' field $X$, with $g^2>0$. We capture the non-perturbative and non-linear nature of the system dynamics with lattice simulations, obtaining that: $i)$ the final energy transferred to $X$ depends only on $p$, not on $g^2$, ; $ii)$ the final transfer of energy is always negligible for $2 \leq p < 4$, and of order $\sim 50\%$ for $p \geq 4$; $iii)$ the system goes at late times to matter-domination for $p = 2$, and always to RD for $p > 2$. In the latter case we calculate the number of e-folds until RD, significantly reducing the uncertainty in the inflationary observables $n_s$ and $r$.Comment: 7 pages + references, 5 figures. It matches published versio

Interpretation of very long-term basic creep tests of concrete

The prediction of very long-term delayed deformation of concrete is particularly important for prestressed structures. This deformation has a number of components, one of which is basic creep, which is the deformation of the concrete under loading, in the absence of any exchange of water with the environment. Analysis of experimental results shows that this component can be expressed as a logarithmic function of time. However, some very long-term tests seem to show a deviation from this trend. The aim of this article is to demonstrate that these deviations can be explained by experimental artefacts (either parasitic drying or leaching of the concrete)

Ultraviolet-regularized power spectrum without infrared distortions in cosmological spacetimes

We reexamine the regularization of the two-point function of a scalar field in a Friedmann-Lemaitre-Robertson-Walker (FLRW) spacetime. Adiabatic regularization provides a set of subtraction terms in momentum space that successfully remove its ultraviolet divergences at coincident points, but can significantly distort the power spectrum at infrared scales, especially for light fields. In this work we propose, by using the intrinsic ambiguities of the renormalization program, a new set of subtraction terms that minimize the distortions for scales $k \lesssim M$, with $M$ an arbitrary mass scale. Our method is consistent with local covariance and equivalent to general regularization methods in curved spacetime. We apply our results to the regularization of the power spectrum in de Sitter space: while the adiabatic scheme yields exactly $\Delta_{\phi}^{\rm (reg)} = 0$ for a massless field, our proposed prescription recovers the standard scale-invariant result $\Delta_{\phi}^{\rm (reg)} \simeq H^2 /(4\pi^2)$ at super-horizon scales.Comment: Title changed with respect to first version. New section added on renormalization conditions and coupling constants (Sect. 3). It matches the published version in PLB. 6 pages + references, 1 figur

On the relation between the mean compressive strength and the characteristic one

Since the beginning of the construction of structures with reinforced concrete, it has been known that concrete presents a variability that should be taken into account. In modern codes, this variability implies the use of a characteristic strength corresponding to a 5% fractile of the distribution of strength. The actual relation in Eurocode 2 between the characteristic and the mean strength fck = fcm ? 8 MPa was introducedseveral years ago by Rüsch and is integrated in CEB or fib model codes since 1978. In this article, it is presented how the relation was obtained and it is discussed if this relation is still valid considering the fact that the range of concrete strengths is now larger. Considering the scatter of the SD, the relation proposed by Rüsch could still be used but engineers should keep in mind that the SD on site could be very different from the one predicted by means of the relation between fck and fcm

Influence of limestone filler and of the size of the aggregates on DEF

This experimental study aims to determine the effect of limestone filler on concrete expansion due to delayed ettringite formation (DEF). Different mortars made with different sizes and percentages of limestone filler and Portland cement CEM I 52.5N are conserved in water. The expansion of the specimens is measured. Results show that DEF is not inhibited by limestone filler. The kinetics and the amplitude of the swelling depend on the size of the limestone filler. The volume fraction of aggregates changes only the kinetics: the relation between swelling and water uptake depends only on the size of the aggregates.Comment: 16 pages, 9 figures, 4 table