Javier de Perez

Javier de Perez
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Javier de Perez

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General Relativity and Quantum Cosmology (7)
High Energy Physics - Theory (6)
High Energy Physics - Phenomenology (6)
Cosmology and Nongalactic Astrophysics (6)
Mathematics - Numerical Analysis (3)

Publications Authored By Javier de Perez

Despite the outstanding achievements of modern cosmology, the classical dispute on the precise value of $H_0$, which is the first ever parameter of modern cosmology and one of the prime parameters in the field, still goes on and on after over half a century of measurements. Recently the dispute came to the spotlight with renewed strength owing to the significant tension (at $>3\sigma$ c.l. Read More

In this paper we assess the possibility that a rigid cosmological constant, $\Lambda$, and hence the traditional concordance $\Lambda$CDM model, might not be the best phenomenological description of the current cosmological data. We show that a large class of dynamical vacuum models (DVMs), whose vacuum energy density $\rho_{\Lambda}(H)$ consists of a nonvanishing constant term and a series of powers of the Hubble rate, provides a substantially better phenomenological account of the overall $SNIa+BAO+H(z)+LSS+CMB$ cosmological observations. We find that some models within the class of DVMs, particularly the running vacuum model (RVM), appear significantly much more favored than the $\Lambda$CDM, at an unprecedented confidence level of $\sim 4\sigma$. Read More

We introduce a new class of structured matrix polynomials, namely, the class of M_A-structured matrix polynomials, to provide a common framework for many classes of structured matrix polynomials that are important in applications: the classes of (skew-)symmetric, (anti-)palindromic, and alternating matrix polynomials. Then, we introduce the families of M_A-structured strong block minimal bases pencils and of M_A-structured block Kronecker pencils,, and show that any M_A-structured odd-degree matrix polynomial can be strongly linearized via an M_A-structured block Kronecker pencil. Finally, for the classes of (skew-)symmetric, (anti-)palindromic, and alternating odd-degree matrix polynomials, the M_A-structured framework allows us to perform a global and structured backward stability analysis of complete structured polynomial eigenproblems, regular or singular, solved by applying to an M_A-structured block Kronecker pencil a structurally backward stable algorithm that computes its complete eigenstructure, like the palindromic-QR algorithm or the structured versions of the staircase algorithm. Read More

The standard way of solving the polynomial eigenvalue problem associated with a matrix polynomial is to embed the matrix polynomial into a matrix pencil, transforming the problem into an equivalent generalized eigenvalue problem. Such pencils are known as linearizations. Many of the families of linearizations for matrix polynomials available in the literature are extensions of the so-called family of Fiedler pencils. Read More

Recent analyses in the literature suggest that the concordance $\Lambda$CDM model with rigid cosmological term, $\Lambda=$const., may not be the best description of the cosmic acceleration. The class of "running vacuum models", in which $\Lambda=\Lambda(H)$ evolves with the Hubble rate, has been shown to fit the string of $SNIa+BAO+H(z)+LSS+CMB$ data significantly better than the $\Lambda$CDM. Read More

Many applications give rise to structured matrix polynomials. The problem of constructing structure-preserving strong linearizations of structured matrix polynomials is revisited in this work and in the forthcoming ones \cite{PartII,PartIII}. With the purpose of providing a much simpler framework for structure-preserving linearizations for symmetric and skew-symmetric matrix polynomial than the one based on Fiedler pencils with repetition, we introduce in this work the families of (modified) symmetric and skew-symmetric block Kronecker pencils. Read More

In the centenary of the introduction of the cosmological constant, $\Lambda$, by Einstein in his gravitational field equations, and after about two decades of the first observational papers confirming the accelerated expansion of the universe, we are still facing the question whether the cause of it is a rigid $\Lambda$-term or a mildly evolving dynamical dark energy (DE). In this work we perform an overall fit to the $SNIa+BAO+H(z)+LSS+CMB$ data through the XCDM parametrization along with a triad of dynamical vacuum models (DVMs) in interaction with dark matter. We find clear signs (at $> 3. Read More

It is well-known that a constant $\Lambda$-term is a traditional building block of the concordance $\Lambda$CDM model. We show that this assumption is not necessarily the optimal one from the phenomenological point of view. The class of running vacuum models, with a possible running of the gravitational coupling G, are capable to fit the overall cosmological data SNIa+BAO+H(z)+LSS+BBN+CMB better than the $\Lambda$CDM, namely at a level of $\sim 3\sigma$ and with Akaike and Bayesian information criteria supporting a strong level of statistical evidence on this fact. Read More

Despite the fact that a rigid $\Lambda$-term is a fundamental building block of the concordance $\Lambda$CDM model, we show that a large class of cosmological scenarios with dynamical vacuum energy density $\rho_{\Lambda}$ and/or gravitational coupling $G$, together with a possible non-conservation of matter, are capable of seriously challenging the traditional phenomenological success of the $\Lambda$CDM. In this paper, we discuss these "running vacuum models" (RVM's), in which $\rho_{\Lambda}=\rho_{\Lambda}(H)$ consists of a nonvanishing constant term and a series of powers of the Hubble rate. Such generic structure is potentially linked to the quantum field theoretical description of the expanding Universe. Read More

Recently there have been claims on model-independent evidence of dynamical dark energy. Herein we consider a fairly general class of cosmological models with a time-evolving cosmological term of the form $\Lambda(H)=C_0+C_H H^2+C_{\dot{H}} \dot{H}$, where $H$ is the Hubble rate. These models are well motivated from the theoretical point of view since they can be related to the general form of the effective action of quantum field theory in curved spacetime. Read More