arXiv subjects

Irene Tamborra

Publications and source records attributed to Irene Tamborra.

At least 55 records · Page 3Linked to original sources

arXiv2023

Neutrino Decoupling Is Altered by Flavor Conversion

The large neutrino density in the deep interior of core-collapse supernovae and compact binary merger remnants makes neutrino flavor evolution non-linear because of the coherent forward scattering of neutrinos among themselves. Under the assumption of spherical symmetry, we model neutrino decoupling from matter in an idealized setup and present the first non-linear simulation of flavor evolution in the presence of charged current and neutral current collisions, as well as neutrino advection. Within our framework, we find that flavor transformation occurs before neutrinos fully decouple from matter, dynamically affecting the flavor distributions of all neutrino species and shifting the location of the neutrino decoupling surfaces. Our results call for further work as they may have implications on the explosion mechanism of supernovae, the nucleosynthesis of the heavy elements, as well as the observable neutrino signal, all of which is yet to be assessed.

astro-ph.HE↗

arXiv2023

Optically Informed Searches of High-Energy Neutrinos from Interaction-Powered Supernovae

The interaction between the ejecta of supernovae (SNe) of Type IIn and a dense circumstellar medium (CSM) can efficiently generate thermal UV/optical radiation and lead to the emission of neutrinos in the $1$-$10^{3}$~TeV range. We investigate the connection between the neutrino signal detectable at the IceCube Neutrino Observatory and the electromagnetic signal observable by optical wide-field, high-cadence surveys to outline the best strategy for upcoming follow-up searches. We outline a semi-analytical model that connects the optical lightcurve properties to the SN parameters and find that a large peak luminosity (${L_{\rm{peak}}\gtrsim 10^{43}-10^{44}\,\mathrm{erg \,s^{-1}}}$) and an average rise time ($t_{\rm{rise}}\gtrsim 10-40$~days) are necessary for copious neutrino emission. Nevertheless, the most promising $ L_{\rm{peak}}$ and $t_{\rm{rise}}$ can be obtained for SN configurations that are not optimal for neutrino emission. Such ambiguous correspondence between the optical lightcurve properties and the number of IceCube neutrino events implies that relying on optical observations only, a range of expected neutrino events should be considered (e.g.~the expected number of neutrino events can vary up to two orders of magnitude for some among the brightest SNe IIn observed by the Zwicky Transient Facility up to now, SN 2020usa and SN 2020in). In addition, the peak in the high-energy neutrino curve should be expected a few $t_{\rm{rise}}$ after the peak in the optical lightcurve. Our findings highlight that it is crucial to infer the SN properties from multi-wavelength observations rather than focusing on the optical band only to enhance upcoming neutrino searches.

astro-ph.HE↗

arXiv2023

Do we have enough evidence to invalidate the mean-field approximation adopted to model collective neutrino oscillations?

Recent body of work points out that the mean-field approximation, widely employed to mimic the neutrino field within a neutrino-dense source, might give different results in terms of flavor evolution with respect to the correspondent many-body treatment. In this paper, we investigate whether such conclusions derived within a constrained framework should hold in an astrophysical context. We show that the plane waves, commonly adopted in the many-body literature to model the neutrino field, provide results that are crucially different with respect to the ones obtained using wavepackets of finite size streaming with a non-zero velocity. The many-body approach intrinsically includes coherent and incoherent scatterings. The mean-field approximation, on the other hand, only takes into account the coherent scattering in the absence of the collision term. Even if incoherent scatterings are included in the mean-field approach, the nature of the collision term is different from that in the many-body approach. Because of this, if only a finite number of neutrinos is considered, as often assumed, the two approaches naturally lead to different flavor outcomes. These differences are further exacerbated by vacuum mixing. We conclude that existing many-body literature, based on closed neutrino systems with a finite number of particles, is neither able to rule out nor assess the validity of the mean-field approach adopted to simulate the evolution of the neutrino field in dense astrophysical sources, which are open systems.

astro-ph.HE↗

arXiv2023

Probing gamma-ray bursts observed at very high energies through their afterglow

A growing number of gamma-ray burst (GRB) afterglows is observed at very-high energies (VHE, $\gtrsim 100$ GeV). Yet, our understanding of the mechanism powering the VHE emission remains baffling. We make use of multi-wavelength observations of the afterglow of GRB 180720B, GRB 190114C, and GRB 221009A to investigate whether the bursts exhibiting VHE emission share common features. We assume the standard afterglow model and microphysical parameters consistent with a synchrotron self-Compton (SSC) scenario for the VHE radiation. By requiring that the blastwave should be transparent to $γ$-$γ$ pair production at the time of observation of the VHE photons and relying on typical prompt emission efficiencies and data in the radio, optical and X-ray bands, we infer for those bursts that the initial energy of the blastwave is $\tilde{E}_{k, \rm{iso}} \gtrsim \mathcal{O}(10^{54})$ erg and the circumburst density is $n_0 \lesssim \mathcal{O}(10^{-1})$ cm$^{-3}$ for a constant circumburst profile [or $A_\star \lesssim \mathcal{O}(10^{-1})$ cm$^{-1}$ for a wind scenario]. Our findings thus suggest that these VHE bursts might be hosted in low-density environments, if the SSC radiation is responsible for the VHE emission. While these trends are based on a small number of bursts, the Cherenkov Telescope Array has the potential to provide crucial insight in this context by detecting a larger sample of VHE GRBs. In addition, due to the very poor statistics, the non-observation of high-energy neutrinos cannot constrain the properties of these bursts efficiently, unless additional VHE GRBs should be detected at distances closer than $15$ Mpc when IceCube-Gen2 radio will be operational.

astro-ph.HE↗

arXiv2023

Fast Neutrino Flavor Conversion in Core-Collapse Supernovae: A Parametric Study in 1D Models

We explore the impact of small-scale flavor conversions of neutrinos, the so-called fast flavor conversions (FFCs), on the dynamical evolution and neutrino emission of core-collapse supernovae (CCSNe). In order to do that, we implement FFCs in the spherically symmetric (1D) CCSN simulations of a 20 solar-mass progenitor model parametrically, assuming that FFCs happen at densities lower than a systematically varied threshold value and lead to an immediate flavor equilibrium consistent with lepton number conservation. We find that besides hardening the electron neutrino and antineutrino spectra, which helps the expansion of the shock by enhanced postshock heating, FFCs can cause significant, nontrivial modifications of the energy transport in the SN environment via increasing the heavy-lepton neutrino luminosities. In our non-exploding models this results in extra cooling of the layers around the neutrinospheres, which triggers a faster contraction of the proto-neutron star and hence, in our 1D models, hampers the CCSN explosion. Although our study is limited by the 1D nature of our simulations, it provides valuable insights into how neutrino flavor conversions in the deepest CCSN regions can impact the neutrino release and the corresponding response of the stellar medium.

astro-ph.HE↗

arXiv2023

Neutrino Flavor Conversion, Advection, and Collisions: Towards the Full Solution

At high densities in compact astrophysical sources, the coherent forward scattering of neutrinos onto each other is responsible for making the flavor evolution non-linear. Under the assumption of spherical symmetry, we present the first simulations tracking flavor transformation in the presence of neutrino-neutrino forward scattering, neutral and charged current collisions with the matter background, as well as neutrino advection. We find that, although flavor equipartition could be one of the solutions, it is not a generic outcome, as often postulated in the literature. Intriguingly, the strong interplay between flavor conversion, collisions, and advection leads to a spread of flavor conversion across the neutrino angular distributions and neighboring spatial regions. Our simulations show that slow and fast flavor transformation can occur simultaneously. In the light of this, looking for crossings in the electron neutrino lepton number as a diagnostic tool of the occurrence of flavor transformation in the high-density regime is a limiting method.

astro-ph.HE↗

arXiv2023

Standing Accretion Shock Instability in the Collapse of a Rotating Stellar Core

Hydrodynamical instabilities, such as the standing accretion-shock instability (SASI), play an essential role in the dynamics of core-collapse supernovae, with observable imprints in the neutrino and gravitational wave signals. Yet, the impact of stellar rotation on the development of SASI is poorly explored. We investigate the conditions favoring the growth of SASI in the presence of rotation through a perturbative analysis. The properties of SASI are compared in two stationary configurations, cylindrical and spherical equatorial, which mainly differ by their advection timescales from the shock to the proto-neutron star surface. Without rotation, the mode $m=1$, corresponding to a one-armed spiral SASI deformation, can be significantly more unstable in the spherical equatorial configuration. In fact, the shorter advection time in the spherical equatorial geometry allows for a larger contribution of the entropic-acoustic coupling from the region of adiabatic compression near the surface of the proto-neutron star. The angular momentum of the collapsing core favors the growth of prograde spiral modes $m=1$ and $m = 2$ in both geometries. Although the growth rate of the spiral instability is systematically faster in spherical geometry, its oscillation frequency is remarkably insensitive to the geometry. Such a contrast with non-rotating flows calls for a deeper understanding of the role of advection in the mechanism of spiral SASI. Our findings suggest that the resonant coupling of acoustic waves with their corotation radius may play a major role in the instability mechanism of collapsing cores with rotation. Elucidating this physical mechanism is essential to interpret the signal from future multi-messenger supernova observations.

astro-ph.HE↗

arXiv2023

State-of-the-Art Collapsar Jet Simulations Imply Undetectable Subphotospheric Neutrinos

Mounting evidence suggests that the launching of collapsar jets is magnetically driven. Recent general relativistic magneto-hydrodynamic simulations of collapsars reveal that the jet is continuously loaded with baryons, owing to strong mixing with the cocoon. This results in a high photosphere at $\gtrsim 10^{12}$ cm. Consequently, collisionless internal shocks below the photosphere are disfavored, and the neutrino production in the deepest jet regions is prevented, in contrast to what has been assumed in the literature. We find that subphotospheric neutrino production could only take place in the presence of collisionless sub-shocks or magnetic reconnection. Efficient particle acceleration is not possible in the cocoon, at the cocoon-counter cocoon shock interface, or at the shock driven by the cocoon in the event of a jet halted in an extended envelope. These subphotospheric neutrinos have energy $E_ν\lesssim 10^5$ GeV for initial jet magnetizations $σ_0=15$-$2000$. More than one neutrino and antineutrino event is expected to be observed in Hyper-Kamiokande and IceCube DeepCore for sources located at $z \lesssim \mathcal{O}(0.1)$. Because of their energy, these neutrinos do not contribute to the diffuse flux detected by the IceCube Neutrino Observatory. Our findings have implications on neutrino searches ranging from gamma-ray bursts to luminous fast blue optical transients.

astro-ph.HE↗

arXiv2022

Resonant Production of Light Sterile Neutrinos in Compact Binary Merger Remnants

The existence of eV-mass sterile neutrinos is not ruled out because of persistent experimental anomalies. Upcoming multi-messenger detections of neutron-star merger remnants could provide indirect constraints on the existence of these particles. We explore the active-sterile flavor conversion phenomenology in a two-flavor scenario (1 active + 1 sterile species) as a function of the sterile neutrino mixing parameters, neutrino emission angle from the accretion torus, and temporal evolution of the merger remnant. The torus geometry and the neutron richness of the remnant are responsible for the occurrence of multiple resonant active-sterile conversions. The number of resonances strongly depends on the neutrino emission direction above or inside the remnant torus and leads to large production of sterile neutrinos (and no antineutrinos) in the proximity of the polar axis as well as more sterile antineutrinos than neutrinos in the equatorial region. As the black hole torus evolves in time, the shallower baryon density is responsible for more adiabatic flavor conversion, leading to larger regions of the mass-mixing parameter space being affected by flavor mixing. Our findings imply that the production of sterile states could have indirect implications on the disk cooling rate, its outflows, and related electromagnetic observables which remain to be assessed.

astro-ph.HE↗

arXiv2022

Snowmass Neutrino Frontier Report

This report summarizes the current status of neutrino physics and the broad and exciting future prospects identified for the Neutrino Frontier as part of the 2021 Snowmass Process.

hep-ex↗

arXiv2022

Neutrino Fast Flavor Pendulum. Part 2: Collisional Damping

In compact astrophysical objects, the neutrino density can be so high that neutrino-neutrino refraction can lead to fast flavor conversion of the kind $ν_e \barν_e \leftrightarrow ν_x \barν_x$ with $x=μ,τ$, depending on the neutrino angle distribution. Previously, we have shown that in a homogeneous, axisymmetric two-flavor system, these collective solutions evolve in analogy to a gyroscopic pendulum. In flavor space, its deviation from the weak-interaction direction is quantified by a variable $\cos\vartheta$ that moves between $+1$ and $\cos\vartheta_{\rm min}$, the latter following from a linear mode analysis. As a next step, we include collisional damping of flavor coherence, assuming a common damping rate $Γ$ for all modes. Empirically we find that the damped pendular motion reaches an asymptotic level of pair conversion $f=A+(1-A)\cos\vartheta_{\rm min}$ (numerically $A\simeq 0.370$) that does not depend on details of the angular distribution (except for fixing $\cos\vartheta_{\rm min}$), the initial seed, nor $Γ$. On the other hand, even a small asymmetry between the neutrino and antineutrino damping rates strongly changes this picture and can even enable flavor instabilities in otherwise stable systems.

hep-ph↗

arXiv2022

Neutrino Flavor Pendulum Reloaded: The Case of Fast Pairwise Conversion

In core-collapse supernovae or compact binary merger remnants, neutrino-neutrino refraction can spawn fast pair conversion of the type $ν_e \barν_e \leftrightarrow ν_x \barν_x$ (with $x=μ, τ$), governed by the angle-dependent density matrices of flavor lepton number. In a homogeneous and axially symmetric two-flavor system, all angle modes evolve coherently, and we show that the nonlinear equations of motion are formally equivalent to those of a gyroscopic pendulum. Within this analogy, our main innovation is to identify the elusive characteristic of the lepton-number angle distribution that determines the depth of conversion with the "pendulum spin." The latter is given by the real part of the eigenfrequency resulting from the linear normal-mode analysis of the neutrino system. This simple analogy allows one to predict the depth of flavor conversion without solving the nonlinear evolution equations. Our approach provides a novel diagnostic tool to explore the physics of nonlinear systems.

astro-ph.HE↗

arXiv2022

Snowmass 2021 topical group report: Neutrinos from Natural Sources

This is the final report from the Snowmass 2021 Neutrino Frontier Topical Group on Neutrinos from Natural Sources. It covers a broad range of neutrino sources, from low-energy neutrinos from the early universe to ultra high-energy sources. We divide this report by source, and discuss the motivations for pursuing searches in each case, the current state of the field, and the prospects for future theoretical and experimental developments. We consider neutrinos produced in the early universe; solar neutrinos; geoneutrinos; supernova neutrinos, including the diffuse supernova neutrino background (DSNB); neutrinos produced in the atmosphere; and high-energy astrophysical neutrinos.

hep-ph↗

arXiv2022

Neutrino Emission from Luminous Fast Blue Optical Transients

Mounting evidence suggests that Luminous Fast Blue Optical Transients (LFBOTs) are powered by a compact object, launching an asymmetric and fast outflow responsible for the radiation observed in the ultraviolet, optical, infrared, radio, and X-ray bands. Proposed scenarios aiming to explain the electromagnetic emission include an inflated cocoon, surrounding a jet choked in the extended stellar envelope. In alternative, the observed radiation may arise from the disk formed by the delayed merger of a black hole with a Wolf-Rayet star. We explore the neutrino production in these scenarios, i.e. internal shocks in a choked jet and interaction between the outflow and the circumstellar medium (CSM). If observed on-axis, the choked jet provides the dominant contribution to the neutrino fluence. Intriguingly, the IceCube upper limit on the neutrino emission inferred from the closest LFBOT, AT2018cow, excludes a region of the parameter space otherwise allowed by electromagnetic observations. After correcting for the Eddington bias on the observation of cosmic neutrinos, we conclude that the emission from an on-axis choked jet and CSM interaction is compatible with the detection of two track-like neutrino events observed by the IceCube Neutrino Observatory in coincidence with AT2018cow, and otherwise considered to be of atmospheric origin. While the neutrino emission from LFBOTs does not constitute the bulk of the diffuse background of neutrinos observed by IceCube, detection prospects of nearby LFBOTs with IceCube and the upcoming IceCube-Gen2 are encouraging. Follow-up neutrino searches will be crucial for unravelling the mechanism powering this emergent transient class.

astro-ph.HE↗

arXiv2022

High energy particles from young supernovae: gamma-ray and neutrino connections

Young core-collapse supernovae (YSNe) are factories of high-energy neutrinos and gamma-rays as the shock accelerated protons efficiently interact with the protons in the dense circumstellar medium. We explore the detection prospects of secondary particles from YSNe of Type IIn, II-P, IIb/II-L, and Ib/c. Type IIn YSNe are found to produce the largest flux of neutrinos and gamma-rays, followed by II-P YSNe. Fermi-LAT and the Cherenkov Telescope Array (IceCube-Gen2) have the potential to detect Type IIn YSNe up to $10$~Mpc ($4$~Mpc), with the remaining YSNe Types being detectable closer to Earth. We also find that YSNe may dominate the diffuse neutrino background, especially between $10$~TeV and $10^3$~TeV, while they do not constitute a dominant component to the isotropic gamma-ray background observed by Fermi-LAT. At the same time, the IceCube high-energy starting events and Fermi-LAT data already allow us to exclude a large fraction of the model parameter space of YSNe otherwise inferred from multi-wavelength electromagnetic observations of these transients.

astro-ph.HE↗

arXiv2022

Enhancement or damping of fast neutrino flavor conversions due to collisions

Fast neutrino flavor conversion can occur in core-collapse supernovae or compact binary merger remnants when non-forward collisions are also at play, and neutrinos are not fully decoupled from matter. This work aims to shed light on the conditions under which fast flavor conversion is enhanced or suppressed by collisions. By relying on a neutrino toy model with three angular bins in the absence of spatial inhomogeneities, we consider two angular configurations: The first one with angular distributions of $ν_e$ and $\barν_e$ that are almost isotropic as expected before complete neutrino decoupling and showing little flavor conversion when collisions are absent. The second one with angular distributions of $ν_e$ and $\barν_e$ that are forward peaked as expected in the free-streaming regime and showing significant flavor conversion in the absence of collisions. By including angle-independent, direction-changing collisions, we find that collisions are responsible for an overall enhancement (damping) of flavor conversion in the former (latter) angular configuration. These opposite outcomes are due to the non-trivial interplay between collisions, flavor conversion, and the initial angular distributions of the electron type neutrinos. The enhancement in neutrino flavor conversion is found to be anticorrelated with the magnitude of flavor conversions in the absence of collisions.

astro-ph.HE↗

arXiv2022

Multi-messenger detection prospects of gamma-ray burst afterglows with optical jumps

Some afterglow light curves of gamma-ray bursts (GRBs) exhibit very complex temporal and spectral features, such as a sudden intensity jump about one hour after the prompt emission in the optical band. We assume that this feature is due to the late collision of two relativistic shells and investigate the corresponding high-energy neutrino emission within a multi-messenger framework, while contrasting our findings with the ones from the classic afterglow model. For a constant density circumburst medium, the total number of emitted neutrinos can increase by about an order of magnitude when an optical jump occurs with respect to the self-similar afterglow scenario. By exploring the detection prospects with the IceCube Neutrino Observatory and future radio arrays such as IceCube-Gen2 radio, RNO-G and GRAND200k, as well as the POEMMA spacecraft, we conclude that the detection of neutrinos with IceCube-Gen2 radio could enable us to constrain the fraction of GRB afterglows with a jump as well as the properties of the circumburst medium. We also investigate the neutrino signal expected for the afterglows of GRB 100621A and a GRB 130427A-like burst with an optical jump. The detection of neutrinos from GRB afterglows could be crucial to explore the yet-to-be unveiled mechanism powering the optical jumps.

astro-ph.HE↗

arXiv2022

Non-Universal Stellar Initial Mass Functions: Large Uncertainties in Star Formation Rates at $z\approx 2-4$ and Other Astrophysical Probes

We explore the assumption, widely used in many astrophysical calculations, that the stellar initial mass function (IMF) is universal across all galaxies. By considering both a canonical Salpeter-like IMF and a non-universal IMF, we are able to compare the effect of different IMFs on multiple observables and derived quantities in astrophysics. Specifically, we consider a non-universal IMF which varies as a function of the local star formation rate, and explore the effects on the star formation rate density (SFRD), the extragalactic background light, the supernova (both core-collapse and thermonuclear) rates, and the diffuse supernova neutrino background. Our most interesting result is that our adopted varying IMF leads to much greater uncertainty on the SFRD at $z \approx 2-4$ than is usually assumed. Indeed, we find a SFRD (inferred using observed galaxy luminosity distributions) that is a factor of $\gtrsim 3$ lower than canonical results obtained using a universal Salpeter-like IMF. Secondly, the non-universal IMF we explore implies a reduction in the supernova core-collapse rate of a factor of $\sim2$, compared against a universal IMF. The other potential tracers are only slightly affected by changes to the properties of the IMF. We find that currently available data do not provide a clear preference for universal or non-universal IMF. However, improvements to measurements of the star formation rate and core-collapse supernova rate at redshifts $z \gtrsim 2$ may offer the best prospects for discernment.

astro-ph.GA↗