Search

We revisit the formation of a thermal population of hadronic axions in nonstandard cosmologies, in light of the recent developments in obtaining continuous and smooth interaction rates for both the gluon and photon couplings. For certain cosmological histories, such as low-temperature reheating (LTR) and kination-like scenarios, the thermalization of the axion can be severely delayed to higher masses. In the case that thermal equilibrium is achieved, we improve the constraints on LTR for axion masses around the eV scale with respect to previous works and we constrain for the first time early matter-dominated (EMD) cosmologies. We also point out the possibility of having the co-existence of cold and warm dark matter populations of axions in kination-like scenarios in the eV mass range., Comment: 44 pages, 12 figures; updated to match published version

We consider the production of axion dark matter through the misalignment mechanism in the context of a nonstandard cosmological history involving early matter domination by a scalar field with a time-dependent decay rate. In cases where the temperature of the Universe experiences a temporary period of increase, Hubble friction can be restored in the evolution of the axion field, resulting in the possibility of up to three "crossings" of the axion mass and the Hubble expansion rate. This has the effect of dynamically resetting the misalignment mechanism to a new initial state for a second distinct phase of oscillation. The resultant axion mass required for the present dark matter relic density is never bigger than the standard-history window and can be smaller by more than three orders of magnitude, which can be probed by upcoming experiments such as ABRACADABRA, KLASH, ADMX, MADMAX, and ORGAN, targeting the axion-photon coupling. This highlights the possibility of exploring the cosmological history prior to Big Bang Nucleosynthesis through searches for axion dark matter beyond the standard window., Comment: 28 pages, 8 figures; updated to match published version

The existence of hidden sectors weakly coupled to the visible one has been extensively studied as a way to extend the Standard Model (SM) and to provide a good dark matter candidate. In this work we analyze two models in which gauge and scalar hidden fields interact with the visible sector which, for simplicity we take as an Abelian Higgs model. In one of them, the hidden sector consists of an uncharged scalar. The connection with the visible Abelian Higgs sector is in this case provided by the interaction between the scalars in the two sectors and also by the coupling between the hidden scalar and the visible squared field strength. This model can be seen as an extension of previously studied ones both in high energy and in condensed matter physics and the solutions that we find indicate that it could be relevant in connection to establishing the dark matter relic density. In the second model, both sectors correspond to spontaneously broken gauge theories and hence they feature classical vortex solutions. Introducing three different portals between the two sectors, we analyze the dependence of the model dynamics on the portal parameters and discuss the physical implications in connection with dark matter and gravitational radiation issues., Comment: Matches the final version published in Int.J.Mod.Phys.A 37 (2022)

We study axion dark matter production from a misalignment mechanism in scenarios featuring a general nonstandard cosmology. Before the onset of Big Bang nucleosynthesis, the energy density of the universe is dominated by a particle field $\phi$ described by a general equation of state $\omega$. The ensuing enhancement of the Hubble expansion rate decreases the temperature at which axions start to oscillate, opening this way the possibility for axions heavier than in the standard window. This is the case for kination, or in general for scenarios with $\omega > 1/3$. However, if $\omega < 1/3$, as in the case of an early matter domination, the decay of $\phi$ injects additional entropy relative to the case of the standard model, diluting this way the preexisting axion abundance, and rendering lighter axions viable. For a misalignment angle $0.5 < \theta_i < \pi/\sqrt{3}$, the usual axion window becomes expanded to $4 \times 10^{-9}$ eV $\lesssim m_a \lesssim 2 \times 10^{-5}$ eV for the case of an early matter domination, or to $2 \times 10^{-6}$ eV $\lesssim m_a \lesssim 10^{-2}$ eV for the case of kination. Interestingly, the coupling axion-photon in such a wider range can be probed with next generation experiments such as ABRACADABRA, KLASH, ADMX, MADMAX, and ORGAN. Axion dark matter searches may therefore provide a unique tool to probe the history of the universe before Big Bang nucleosynthesis.

One of the grand challenges discussed during the Dagstuhl Seminar "Knowledge Graphs: New Directions for Knowledge Representation on the Semantic Web" and described in its report is that of a: "Public FAIR Knowledge Graph of Everything: We increasingly see the creation of knowledge graphs that capture information about the entirety of a class of entities. [...] This grand challenge extends this further by asking if we can create a knowledge graph of "everything" ranging from common sense concepts to location based entities. This knowledge graph should be "open to the public" in a FAIR manner democratizing this mass amount of knowledge." Although linked open data (LOD) is one knowledge graph, it is the closest realisation (and probably the only one) to a public FAIR Knowledge Graph (KG) of everything. Surely, LOD provides a unique testbed for experimenting and evaluating research hypotheses on open and FAIR KG. One of the most neglected FAIR issues about KGs is their ongoing evolution and long term preservation. We want to investigate this problem, that is to understand what preserving and supporting the evolution of KGs means and how these problems can be addressed. Clearly, the problem can be approached from different perspectives and may require the development of different approaches, including new theories, ontologies, metrics, strategies, procedures, etc. This document reports a collaborative effort performed by 9 teams of students, each guided by a senior researcher as their mentor, attending the International Semantic Web Research School (ISWS 2019). Each team provides a different perspective to the problem of knowledge graph evolution substantiated by a set of research questions as the main subject of their investigation. In addition, they provide their working definition for KG preservation and evolution.

We perform a detailed study of dark matter production via freeze-in under the assumption that some fluid dominates the early Universe before depositing its energy to the plasma causing entropy injection. As a dark matter candidate we consider a fermionic singlet that is produced through its interactions with a scalar particle in the thermal plasma. The fluid alters the expansion rate of the Universe, as well as the scaling of the temperature, which significantly affects the evolution of both the number density and the mean momentum of the dark matter particle. We identify and discuss in detail the effects of the evolution of these quantities by considering several examples representing dark matter production at different stages of expansion and entropy injection. We find that, since the dark matter density is reduced when the entropy injection to the plasma continues after freeze-in, in order to reproduce its observational value an enhanced rate of dark matter production is required relative to standard cosmology. Furthermore, the impact of the assumed non-standard cosmological history on the dark matter mean momentum can result in either a relaxed or a tightened bound on the dark matter mass from large structure formation data., Comment: 40 pages, 17 figures; v2: References updated, typos corrected, matches version published in JCAP

In the absence of sufficient medication for COVID patients due to the increased demand, disused drugs have been employed or the doses of those available were modified by hospital pharmacists. Some evidences for the use of alternative drugs can be found in the existing scientific literature that could assist in such decisions. However, exploiting large corpus of documents in an efficient manner is not easy, since drugs may not appear explicitly related in the texts and could be mentioned under different brand names. Drugs4Covid combines word embedding techniques and semantic web technologies to enable a drug-oriented exploration of large medical literature. Drugs and diseases are identified according to the ATC classification and MeSH categories respectively. More than 60K articles and 2M paragraphs have been processed from the CORD-19 corpus with information of COVID-19, SARS, and other related coronaviruses. An open catalogue of drugs has been created and results are publicly available through a drug browser, a keyword-guided text explorer, and a knowledge graph., Comment: Ontology-based technologies, NLP, Bio-annotations, Drugs-catalogue, Knowledge Graph, COVID-19

We investigate a scenario where the dark matter of the Universe is made from very light hidden photons transforming under a $Z_{2}$-symmetry. In contrast to the usual situation, kinetic mixing is forbidden by the symmetry and the dark photon interacts with the Standard Model photon only via an axion-like particle acting as a "messenger". Focusing on signatures involving the ordinary photon, our survey of the phenomenology includes limits from cosmological stability, CMB distortions, astrophysical energy loss, light-shining-through-walls experiments, helioscopes and solar X-ray observations., Comment: 45 pages, 8 figures

Once dark matter has been discovered and its particle physics properties have been determined, a crucial question rises concerning how it was produced in the early Universe. If its thermally averaged annihilation cross section is in the ballpark of few$\times 10^{-26}$ cm$^3$/s, the WIMP mechanism in the standard cosmological scenario (i.e. radiation dominated Universe) will be highly favored. If this is not the case one can either consider an alternative production mechanism, or a non-standard cosmology. Here we study the dark matter production in scenarios with a non-standard expansion history. Additionally, we reconstruct the possible non-standard cosmologies that could make the WIMP mechanism viable., Comment: 20 pages, 8 figures. V2: Accepted for publication in JCAP. arXiv admin note: text overlap with arXiv:1710.11006, arXiv:1804.06783 by other authors

We propose a model where the anapole appears as a hidden photon that is coupled to visible matter through a kinetic mixing. For low momentum $|{\bf p}| \ll M$ where $M$ is the cutoff the model (soft hidden photons limit) is reduced to the Ho-Scherrer description. We show that the hidden gauge boson is stable and therefore the hidden photons, indeed, are candidates for dark matter. Our approach shows that anapole and kinetic mixing terms are equivalent descriptions seen from different scales of energy., Comment: typos and references added, accepted in PLB

The Landau problem for inhomogeneous magnetic fields is examined in a very general context and several interesting analogies with the Nielsen-Olesen vortices are established. Firstly we show that the Landau problem with non-homogeneous magnetic fields exhibits Meissner effect that is unstable unless two-body interactions are added and vortices emerge. Using the scaling freedom we can write the Schr\"odinger equation in terms of the scales ratio $\kappa ={ E}/{ m }\propto 1- T/T_c $ where the last identification is realised simply by using the Gizburg-Landau theory. We find our equations are valid in the superconducting regime, and it is not possible for the Cooper pairs amplitude to reach to a constant, non-zero value, and therefore the theory is unstable. The supersymmetric quantum mechanics version, by completeness, is also considered., Comment: 5 pages, two columns, 1 figure. Comments welcomed

We explore the phenomenological consequences of a model with axion-like particles and hidden photons mixing with photons. In this model, the hidden photon is directly coupled to the photon, while the axion coupling is induced by an external electromagnetic field. We consider vacuum effects on a polarised photon beam, like changes in the ellipticity and rotation angles., Comment: 2 figures. Contributed to the 13th Patras Workshop on Axions, WIMPs and WISPs, Thessaloniki, May 15 to 19, 2017

We present a detailed study of the oscillations and optical properties for vacuum, in a model for the dark sector that contains axion-like particles and hidden photons. In this model, both can couple to photons. We provide bounds for the couplings versus the mass, using current results from ALPS-I and PVLAS. We also discuss the challenges for the detection of models with more than one hidden particle in light shining trough wall-like experiments., Comment: 23 pages, 7 figures. Figures are coloured

The effects of an external time-dependent magnetic field in the conversion probability of photon-to-axion-like particles are studied. Our findings show that for a certain time regime, the amplitude of the produced axion-like field can be enlarged with respect to the static case, thus, enhancing the probability of conversion., Comment: some clarifications. To appear in EPJC

We discuss the Aharonov-Bohm effect in the presence of hidden photons kinetically mixed with the ordinary electromagnetic photons. The hidden photon field causes a slight phase shift in the observable interference pattern. It is then shown how the limited sensitivity of this experiment can be largely improved. The key observation is that the hidden photon field causes a leakage of the ordinary magnetic field into the supposedly field-free region. The direct measurement of this magnetic field can provide a sensitive experiment with a good discovery potential, particularly below the $\sim$ meV mass range for hidden photons., Comment: 10 pages, 8 figures

We study the local effects of an external time-dependent magnetic field on axion-like particles assuming they are all the dark matter of the universe. We find that under suitable conditions the amplitude of the dark matter field can resonate parametrically. The resonance depends on the velocity of the axion-like particles and scales quadratically with the strength} of the external magnetic field, $\frac{\rho}{\rho_{DM}} \sim {B_0}^3$. By considering typical experimental benchmark values, we find the resonance could amplify around two orders of magnitude the local energy density stored in the dark matter condensate., Comment: This paper has been withdrawn due to errors in the solving of the equations of motion

We study vortex solutions in Abelian Chern-Simons-Higgs theories with visible and hidden sectors. We first consider the case in which the two sectors are connected through a BF-like gauge mixing term with no explicit interaction between the the two scalars. Since first order Bogomolny equations do not exist in this case, we derive the second order field equations. We then proceed to an ${\cal N}=2$ supersymmetric extension including a Higgs portal mixing among the visible and hidden charged scalars. As expected, Bogomolnyi equations do exist in this case and we study their string-like solutions numerically., Comment: 10 pages, 12 figures. Several typos fixed and the Gauss law is explicitly written, figures correctly shown. Accepted in PLB