arXiv subjects

Angels Ramos

Publications and source records attributed to Angels Ramos.

At least 37 records · Page 2Linked to original sources

arXiv2019

Interplay between $Δ$ Particles and Hyperons in Neutron Stars

We analyze the effects of including $Δ(1232)$ isobars in an equation of state (EoS) for cold, $β$-stable neutron star matter, employing relativistic nuclear mean field theory. The selected EoS reproduces the properties of nuclear matter and finite nuclei and, in the astrophysical context, allows for the presence of hyperons in neutron stars having masses larger than 2$M_{\odot}$. We find that the composition and structure of neutron stars is critically influenced by the addition of the $Δ$ isobars, which allows us to constrain their interaction with the meson fields taking into account astrophysical information. Imposing that the EoS is stable and ensures the existence of 2$M_{\odot}$ neutron stars, as well as requiring agreement with data of $Δ$ excitation in nuclei, we find that, in the absence of other mechanisms stiffening the EoS at high densities, the interaction of the $Δ$ isobars with the sigma and omega meson fields must be at least 10\% stronger than that of the nucleons. Moreover, the neutron star moment of inertia turns out to be sensitive to the presence of $Δ$ isobars, whereas the inclusion of $Δ$ isobars in the EoS allows for smaller stellar radii and for a lower value of the tidal deformability consistent with the analysis of the GW170817 merger event.

astro-ph.HE↗

arXiv2019

X(3872) in a hot pion bath

Right since its discovery in 2003 by the Belle collaboration, establishing the nature of the $X(3872)$ meson has been one of the main priorities in the field of quarkonium physics. Not qualifying as a conventional $c\bar{c}$ state, the multiquark structure of this exotic meson has received very different interpretations, ranging from a compact tetraquark configuration to an extended $D\bar D^*+c.c.$ molecule. In this work we explore the effect that a hot pion bath may have in the properties of the $X(3872)$, assuming this state to be a $D\bar D^*+c.c.$ molecule. We derive the finite temperature effects on the $X(3872)$ from a coupled channels unitarized amplitude, obtained including the properties of the charmed mesons under such conditions. We find that the $X(3872)$ develops a subtantial width, of the order of a few tens of MeV, in hot pionic environments at temperatures $100-150$ MeV, and its nominal mass moves above the $D D^*$ threshold. The fact that the $X(3872)$ in a hot pion gas may no longer be a narrow resonance needs to be considered in the estimation of production yields in relativistic heavy-ion collisions.

hep-ph↗

arXiv2019

Further Theoretical Analysis on the $K^{-} {}^{3} \text{He} \to Λp n$ Reaction for the $\bar{K} N N$ Bound-State Search in the J-PARC E15 Experiment

Based on the scenario that a $\bar{K} N N$ bound state is generated and it eventually decays into $Λp$, we calculate the cross section of the $K^{-} {}^{3} \text{He} \to Λp n$ reaction, which was recently measured in the J-PARC E15 experiment. We find that the behavior of the calculated differential cross section $d ^{2} σ/ d M_{Λp} d q_{Λp}$, where $M_{Λp}$ and $q_{Λp}$ are the $Λp$ invariant mass and momentum transfer in the $(K^{-} , \, n)$ reaction in the laboratory frame, respectively, is consistent with the experiment. Furthermore, we can reproduce almost quantitatively the experimental data of the $Λp$ invariant mass spectrum in the momentum transfer window $350 \text{ MeV} /c < q_{Λp} < 650 \text{ MeV} /c$. These facts strongly suggest that the $\bar{K} N N$ bound state was indeed generated in the J-PARC E15 experiment.

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arXiv2019

$S=-1$ meson-baryon interaction and the role of isospin filtering processes

A study of the meson-baryon interaction in the $S=-1$ sector is performed, employing a chiral SU(3) lagrangian up to next-to-leading order (NLO) and implementing unitarization in coupled channels. The model is constrained by a large set of experimental data, paying a especial attention to processes that are sensitive to the NLO contributions, such as the $K^- p\to K^+Ξ^-, K^0Ξ^0$ reactions. The consideration of additional cross sections in single isospin channels, $K^-p\to ηΛ, ηΣ$, has been found to provide more homogeneous and reliable values of the low-energy constants, the stability of which has also been tested by the inclusion of explicit resonant terms. Predictions for new isospin filtering processes, like the $I=1$ $K^0_L p \to K^+ Ξ^0$ reaction that could be measured at the proposed secondary $K^0_L$ beam at Jlab, or the weak decay of the $Λ_b$ into a $J/Ψ$ and different meson-baryon pairs in $I=0$, available at LHCb, are presented. The measurement of such reactions would put valuable constraints on the chiral models describing the $S=-1$ meson-baryon interaction.

hep-ph↗

arXiv2019

The Equation of State and Cooling of Hyperonic Neutron Stars

We present two recent parametrizations of the equation of state (FSU2R and FSU2H models) that reproduce the properties of nuclear matter and finite nuclei, fulfill constraints on high-density matter stemming from heavy-ion collisions, produce 2$M_{\odot}$ neutron stars, and generate neutron star radii below 13 km. Making use of these equations of state, cooling simulations for isolated neutron stars are performed. We find that two of the models studied, FSU2R (with nucleons) and, in particular, FSU2H (with nucleons and hyperons), show very good agreement with cooling observations, even without including nucleon pairing. This indicates that cooling observations are compatible with an equation of state that produces a soft nuclear symmetry energy and, thus, generates small neutron star radii. Nevertheless, both schemes produce cold isolated neutron stars with masses above $1.8 M_{\odot}$.

astro-ph.HE↗

arXiv2018

The molecular nature of some $Ω_c^0$ states

A vector meson exchange model based on effective Lagrangians is used to build the meson--baryon interaction in the charm $+1$, strangeness $-2$ and isospin $0$ sector. The s-wave scattering amplitudes resulting from the unitarization in coupled-channels show two resonances with masses and widths that are in very good agreement with those of the experimental $Ω_c(3050)^0$ and $Ω_c(3090)^0$ states observed by the LHCb collaboration. The interpretation of these resonances as pseudoscalar meson--baryon molecules would mean the assignment $J^P=1/2^-$ to their spin--parity.

hep-ph↗

arXiv2018

Exotic $Ω_c^0$ baryons from meson-baryon scattering

A meson-baryon interaction in the charm $+1$, strangeness $-2$ and isospin $0$ sector is built from a t-channel vector meson exchange model employing effective Lagrangians. The implementation of coupled-channel unitarization in the s-wave scattering amplitudes gives rise to two structures that have similar masses and widths to those of the $Ω_c(3050)^0$ and $Ω_c(3090)^0$ states recently observed by the LHCb collaboration. A meson-baryon molecular interpretation of these resonances would assign their spin-parity to be $J^P=1/2^-$.

hep-ph↗

arXiv2018

Cooling of Small and Massive Hyperonic Stars

We perform cooling simulations for isolated neutron stars using recently developed equations of state for their core. The equations of state are obtained from new parametrizations of the FSU2 relativistic mean-field functional that reproduce the properties of nuclear matter and finite nuclei, while fulfilling the restrictions on high-density matter deduced from heavy-ion collisions, measurements of massive 2$M_{\odot}$ neutron stars, and neutron star radii below 13 km. We find that two of the models studied, FSU2R (with nucleons) and in particular FSU2H (with nucleons and hyperons), show very good agreement with cooling observations, even without including extensive nucleon pairing. This suggests that the cooling observations are more compatible with an equation of state that produces a soft nuclear symmetry energy and, hence, generates small neutron star radii. However, both models favor large stellar masses, above $1.8 M_{\odot}$, to explain the colder isolated neutron stars that have been observed, even if nucleon pairing is present.

astro-ph.HE↗

arXiv2018

Theoretical analysis on the $K^{-} {}^{3} \text{He} \to Λp n$ reaction for the $\bar{K} N N$ bound-state search in the J-PARC E15 experiment

We theoretically analyze the $K^{-} {}^{3} \text{He} \to Λp n$ reaction for the $\bar{K} N N$ bound-state search in the J-PARC E15 experiment. We find that, by detecting a fast and forward neutron in the final state, an almost on-shell $\bar{K}$ is guaranteed, which is essential to make a bound state with two nucleons from ${}^{3} \text{He}$. Then, this almost on-shell $\bar{K}$ can bring a signal of the $\bar{K} N N$ bound state in the $Λp$ invariant-mass spectrum, although it inevitably brings a kinematic peak above the $\bar{K} N N$ threshold as well. As a consequence, we predict two peaks across the $\bar{K} N N$ threshold in the spectrum: the lower peak coming from the $\bar{K} N N$ bound state, and the higher one originating from the kinematics.

nucl-th↗

arXiv2017

The Equation of State for the Nucleonic and Hyperonic Core of Neutron Stars

We reexamine the equation of state for the nucleonic and hyperonic inner core of neutron stars that satisfies the 2$M_{\odot}$ observations as well as the recent determinations of stellar radii below 13 km, while fulfilling the saturation properties of nuclear matter and finite nuclei together with the constraints on the high-density nuclear pressure coming from heavy-ion collisions. The recent nucleonic FSU2R and hyperonic FSU2H models are fine tuned improving the density dependence of pure neutron matter at subsaturation densities. The corresponding nuclear matter properties at saturation, the symmetry energy and its slope turn out to be compatible with recent experimental and theoretical determinations. We obtain the mass, radius and composition of neutron stars for the two updated models and study the impact on these properties of the uncertainties in the hyperon-nucleon couplings estimated from hypernuclear data. We find that the onset of appearance of each hyperon strongly depends on the hyperon-nuclear uncertainties, whereas the maximum masses for neutron stars differ by at most 0.1 $M_{\odot}$, although a larger deviation should be expected tied to the lack of knowledge of the hyperon potentials at the high densities present in the center of $2 M_\odot$ stars. For easier use, we provide tables with the results from the FSU2R and FSU2H models for the equation of state and the neutron star mass-radius relation.

astro-ph.HE↗

arXiv2017

Properties of open and hidden charm mesons in light quark matter

In this work we study the implications of light-quark pionic matter at finite temperatures on the properties of open and hidden charm mesons. The meson-meson interactions are described by means of a chiral unitary approach accounting for coupled channels effects. The in-medium Lippmann-Schwinger Equations, which consider the change in self-energy that the mesons acquire from interacting with the surrounding pionic matter, are solved self-consistently, and the spectral functions of the mesons in the hot pion bath are obtained. It is observed that the charmed mesons develop a quite substantial pion-induced width, being of several tens at a temperature of 150 MeV. The $J/Ψ$ meson stays narrow, but its pionic width at 150 MeV, found to be around 0.1 MeV, is already larger that its vacuum width.

hep-ph↗

arXiv2017

What makes the peak structure of the $Λp$ invariant-mass spectrum in the $K^{-} {}^{3} {\rm He} \to Λp n$ reaction?

Recently a peak structure was observed near the $K^{-} p p$ threshold in the in-flight ${}^{3} {\rm He} (K^{-} , \, Λp) n$ reaction of the E15 experiment at J-PARC, which could be a signal of a $\bar{K} N N$ bound state. In order to investigate what is the origin of this peak, we calculate the cross section of this reaction, in particular based on the scenario that the $\bar{K} N N$ bound state is indeed generated and decays into $Λp$. We find that the numerical result of the $Λp$ invariant-mass spectrum in the $\bar{K} N N$ bound scenario is consistent with the J-PARC E15 data.

nucl-th↗

arXiv2016

Equation of State for Nucleonic and Hyperonic Neutron Stars with Mass and Radius Constraints

We obtain a new equation of state for the nucleonic and hyperonic inner core of neutron stars that fulfills the 2$M_{\odot}$ observations as well as the recent determinations of stellar radii below 13 km. The nucleonic equation of state is obtained from a new parametrization of the FSU2 relativistic mean-field functional that satisfies these latest astrophysical constraints and, at the same time, reproduces the properties of nuclear matter and finite nuclei while fulfilling the restrictions on high-density matter deduced from heavy-ion collisions. On the one hand, the equation of state of neutron star matter is softened around saturation density, which increases the compactness of canonical neutron stars leading to stellar radii below 13 km. On the other hand, the equation of state is stiff enough at higher densities to fulfill the 2$M_{\odot}$ limit. By a slight modification of the parametrization, we also find that the constraints of 2$M_{\odot}$ neutron stars with radii around 13 km are satisfied when hyperons are considered. The inclusion of the high magnetic fields present in magnetars further stiffens the equation of state. Hyperonic magnetars with magnetic fields in the surface of $ \sim 10^{15}$ G and with values of $\sim 10^{18}$ G in the interior can reach maximum masses of 2$M_{\odot}$ with radii in the 12-13 km range.

astro-ph.HE↗

arXiv2016

Properties of $J/ψ$ in light quark matter

With various experiments studying heavy-ion collisions a demand exists in the hadron physics community for theoretical predictions of hadronic properties at temperatures and densities far from equilibrium. In this work we will study the $J/ψ$ vector meson at finite temperatures surrounded by light quark matter. We will apply a chiral unitary approach to account for coupled channels, most importantly channels with open charm. The in-medium solution accounts for the change in self-energy that the $J/ψ$ acquires from interacting with the surrounding light quark matter, most notably pions and rho mesons. The results are preliminary and clearly show the importance of using dressed charmed mesons. Ultimately, the solutions to the corresponding Lippmann-Schwinger Equations are used to calculate observables such as the spectral function of the $J/ψ$.

hep-ph↗

arXiv2016

The Peak Structure in the In-Flight ${}^{3}\text{He} ( K^{-} , \, Λp ) n$ Reaction Around the $\bar{K} N N$ Threshold

We theoretically investigate the origin of the peak structure around the $K^{-} p p$ threshold observed in the in-flight ${}^{3}\text{He} ( K^{-} , \, Λp ) n$ reaction in the recent E15 experiment at J-PARC. For this purpose, we consider two scenarios to produce the peak. One is that the $Λ(1405)$ is generated but it does not correlate with $p$, and the uncorrelated $Λ(1405) p$ system subsequently decays into $Λp$. The other one is that the $\bar{K} N N$ bound state is indeed generated and decays into $Λp$. As a result, the experimental signal is qualitatively well reproduced in the $\bar{K} N N$ bound scenario, definitely discarding the uncorrelated $Λ(1405) p$ one.

nucl-th↗

arXiv2016

On the structure observed in the in-flight ${}^{3}\text{He} ( K^{-} , \, Λp ) n$ reaction at J-PARC

A theoretical investigation is done to clarify the origin of the peak structure observed near the $K^{-} p p$ threshold in the in-flight ${}^{3}\text{He} ( K^{-}, \, Λp ) n$ reaction of the J-PARC E15 experiment, which could be a signal of the lightest kaonic nuclei, that is, the $\bar{K} N N (I=1/2)$ state. For the investigation, we evaluate the $Λp$ invariant mass spectrum assuming two possible scenarios to interpret the experimental peak. One assumes that the $Λ(1405)$ resonance is generated after the emission of an energetic neutron from the absorption of the initial $K^-$, not forming a bound state with the remaining proton. This uncorrelated $Λ(1405) p$ system subsequently decays into the final $Λp$. The other scenario implies that, after the emission of the energetic neutron, a $\bar{K} N N$ bound state is formed, decaying eventually into a $Λp$ pair. Our results show that the experimental signal observed in the in-flight ${}^{3}\text{He} ( K^{-} , \, Λp ) n$ reaction at J-PARC is qualitatively well reproduced by the assumption that a $\bar{K} N N$ bound state is generated in the reaction, definitely discarding the interpretation in terms of an uncorrelated $Λ(1405) p$ state.

hep-ph↗

arXiv2016

Weak decays of heavy hadrons into dynamically generated resonances

In this review we give a perspective of the theoretical work done recently on the interpretation of results from $B$, $D$, $Λ_b$, $Λ_c$ weak decays into final states that contain interacting hadrons, and how it is possible to obtain additional valuable information that is increasing our understanding of hadron interactions and the nature of many hadronic resonances. The novelty of these processes is that one begins with a clean picture at the quark level which allows one to select the basic mechanisms by means of which the process proceeds. Finally, one has a final state described in terms of quarks. To make contact with the experiments, where mesons and baryons are observed, one must hadronize, creating pairs of $q \bar q$ and writing the new states in terms of mesons and baryons. This concludes the primary hadron production in these processes. After that, the interaction of these hadrons takes place, offering a rich spectrum of resonances and special features from where it is possible to learn much about the interaction of these hadrons and the nature of many resonances in terms of the components of their wave functions.

hep-ph↗

arXiv2014

Heavy Mesons in Nuclear Matter and Nuclei

Heavy mesons in nuclear matter and nuclei are analyzed within different frameworks, paying a special attention to unitarized coupled-channel approaches. Possible experimental signatures of the properties of these mesons in matter are addressed, in particular in connection with the future FAIR facility at GSI.

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