Abstracts of Interest
Selected by:
Hayden James
Abstract: 2409.16348
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Title:Detecting dark objects with plasma microlensing by their gravitational wakes
View PDF HTML (experimental)Abstract:A moving mass makes a gravitational wake in the partially ionized interstellar medium, which acts as a lens for radio-frequency light. Consequently, plasma microlensing could complement gravitational microlensing in the search for invisible massive objects, such as stellar remnants or compact dark matter. This work explores the spatial structure of the plasma lens associated with a gravitational wake. Far away from the moving mass, the characteristic lensing signal is the steady demagnification or magnification of a radio source as the wake passes in front of it at the speed of sound. Sources can be plasma lensed at a much greater angular distance than they would be gravitationally lensed to the same degree by the same object. However, only the wakes of objects greatly exceeding stellar mass are expected to dominate over the random turbulence in the interstellar medium.
Abstract: 2409.13141
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Title:Radio Emission from Atmosphere-Skimming Cosmic Ray Showers in High-Altitude Balloon-Borne Experiments
View PDF HTML (experimental)Abstract:Atmosphere-skimming air showers are initiated by cosmic rays with incoming directions that allow the cascade to develop entirely within the atmosphere, without reaching the ground. Radio pulses induced by this type of showers have already been observed in balloon-borne experiments such as ANITA, but a detailed characterisation of their properties is lacking. The extreme range of densities in which these cascades can develop gives rise to a wide range of shower profiles, with radio emission characteristics that can differ significantly from those of regular downward-going showers. In this work, we have used the ZHAireS-RASPASS program to characterise the expected radio emission from atmosphere-skimming air showers and its properties. We have studied the interplay between the magnetic field and atmospheric density profile in the expected radio signal, focusing on its detection aboard balloon-borne experiments. The almost horizontal geometry of the events gives rise to a significant \textit{refractive} asymmetry in the spatial distribution of the electric field, due to the propagation of the radio signals across a gradient of index of refraction. In addition, a unique \textit{coherence} asymmetry appears in the intensity of the signals, as a consequence of the cumulative effect of the Earth's magnetic field over the very long distances that these particle cascades traverse. The implications of the peculiar characteristics of the emission are discussed regarding their impact both on the interpretation of collected data and in the exposure of balloon-borne experiments
Abstract: 2409.16232
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Title:Probing the equation of state of neutron stars using neutrino oscillations
View PDF HTML (experimental)Abstract:We study the phenomena of neutrino oscillations and flavour mixing by incorporating the gravitational effects through the Dirac equation in curved spacetime inside a spherically symmetric star. We show that the flavour transition probabilities of the neutrinos depend on the interior spacetime metric as they propagate out of the star. As a consequence, we show that one could distinguish between different possible equation of states of nuclear matter even for an isolated neutron star if one could determine the flavour composition of emitted neutrinos near the stellar surface.
Abstract: 2409.14382
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Title:Layout optimization and Performance of Large Array of imaging atmospheric Cherenkov Telescope (LACT)
View PDF HTML (experimental)Abstract:Large Array of imaging atmospheric Cherenkov Telescope (LACT) is an array of 32 Cherenkov telescopes with 6-meter diameter mirrors to be constructed at the LHAASO site. In this work, we present a study on the layout optimization and performance analysis of LACT. We investigate two observation modes: large zenith angle observations for ultra-high energy events and small zenith angle observations for lower energy thresholds. For large zenith angles (60°), simulations show that an 8-telescope subarray can achieve an effective area of $3 ~\rm km^2$ and excellent angular resolution. For small zenith angles, we optimize the layout of 4-telescope cells and the full 32-telescope array. The threshold of the full array is about $200~\rm GeV$, which is particularly crucial for studying transient phenomena, including gamma-ray bursts (GRBs) and active galactic nuclei (AGNs). This study provides important guidance for the final LACT layout design and performance estimates under different observational conditions, demonstrating LACT's potential for deep observations of ultra-high energy \gray sources and morphological studies of PeVatrons, as well as time-domain \gray astronomy.
Abstract: 2409.14505
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Title:Gravitational waves from cosmological first-order phase transitions with precise hydrodynamics
View PDF HTML (experimental)Abstract:We calculate the gravitational wave spectrum generated by sound waves during a cosmological phase transition, incorporating several advancements beyond the current state-of-the-art. Rather than relying on the bag model or similar approximations, we derive the equation of state directly from the effective potential. This approach enables us to accurately determine the hydrodynamic quantities, which serve as initial conditions in a generalised hybrid simulation. This simulation tracks the fluid evolution after bubble collisions, leading to the generation of gravitational waves. Our work is the first self-consistent numerical calculation of gravitational waves for the real singlet extension of the standard model. Our computational method is adaptable to any particle physics model, offering a fast and reliable way to calculate gravitational waves generated by sound waves. With fewer approximations, our approach provides a robust foundation for precise gravitational wave calculations and allows for the exploration of model-independent features of gravitational waves from phase transitions.
Abstract: 2409.13818
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Title:Plausible constraints and inflationary production for dark photons
View PDF HTML (experimental)Abstract:Generic constraints on dark photons are generally presented assuming they have Stueckelberg masses. These constraints are strengthened if instead the mass is due to the Higgs mechanism and the dark Higgs is light. First, we show that under reasonable assumptions on the origin of kinetic mixing $\epsilon$ and perturbativity, the strengthened constraints on $\epsilon$ cannot be arbitrarily relaxed by making the Higgs heavy. Second, we demonstrate a simple mechanism for generating dark photon dark matter after inflation, where fluctuations of a dark Higgs by stochastic misalignment can produce stable dark photons through $h\to A'A'$ decay. Third, we point out new lower bounds on $\epsilon$ in the case where the dark photon mediates thermal freeze-out of light dark matter by $s$-channel exchange, taking account of generic expectations for the size of $\epsilon$, and astrophysical upper bounds on the self-interaction cross section.
Abstract: 2409.14900
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Title:Big Bang Nucleosynthesis constraints on resonant DM annihilations
View PDF HTML (experimental)Abstract:We perform a systematic study of BBN constraints from photodisintegration for scenarios in which dark-matter annihilations are resonantly-enhanced. To this end, we implement and make available a new class ResonanceModel within an updated version v1.3.0 of ACROPOLIS. While the corresponding implementation is done in a rather model-independent way, we also make available three benchmark models that can be used to calculate constraints for more concrete scenarios. Using this new version of ACROPOLIS, we present for the first time the corresponding constraints on resonantly-enhanced $s$-wave and $p$-wave annihilations. We show that for $s$-wave annihilations the bounds are usually very similar to the ones without a resonance, while for $p$-wave annihilations the bounds can be significantly stronger.
The updated version v1.3.0 of ACROPOLIS can be found at this https URL .
Abstract: 2409.14780
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Title:Using dust to constrain dark matter models
View PDF HTML (experimental)Abstract:In this paper, we use hydrodynamic zoom-in simulations of Milky Way-type haloes to explore using dust as an observational tracer to discriminate between cold and warm dark matter universes. Comparing a cold and 3.5keV warm dark matter particle model, we tune the efficiency of galaxy formation in our simulations using a variable supernova rate to create Milky Way systems with similar satellite galaxy populations while keeping all other simulation parameters the same. Cold dark matter, having more substructure, requires a higher supernova efficiency than warm dark matter to achieve the same satellite galaxy number. These different supernova efficiencies create different dust distributions around their host galaxies, which we generate by post-processing the simulation output with the POWDERDAY codebase. Analysing the resulting dust in each simulation, we find $\sim$4.5 times more dust in our cold dark matter Milky Way halos compared with warm dark matter. The distribution of dust out to R$_{200\text{c}}$ is then explored, revealing that the warm dark matter simulations are noticeably less concentrated than their cold dark matter counterparts, although differences in substructure complicate the comparison. Our results indicate that dust is a possible unique probe to test theories of dark matter.
Abstract: 2409.14477
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Title:Self-sustaining living habitats in extraterrestrial environments
View PDF HTML (experimental)Abstract:Standard definitions of habitability assume that life requires the presence of planetary gravity wells to stabilize liquid water and regulate surface temperature. Here the consequences of relaxing this assumption are evaluated. Temperature, pressure, volatile loss, radiation levels and nutrient availability all appear to be surmountable obstacles to the survival of photosynthetic life in space or on celestial bodies with thin atmospheres. Biologically generated barriers capable of transmitting visible radiation, blocking ultraviolet, and sustaining temperature gradients of 25-100 K and pressure differences of 10 kPa against the vacuum of space can allow habitable conditions between 1 and 5 astronomical units in the solar system. Hence ecosystems capable of generating conditions for their own survival are physically plausible, given the known capabilities of biological materials on Earth. Biogenic habitats for photosynthetic life in extraterrestrial environments would have major benefits for human life support and sustainability in space. Because the evolution of life elsewhere may have followed very different pathways from on Earth, living habitats could also exist outside traditional habitable environments around other stars, where they would have unusual but potentially detectable biosignatures.
Abstract: 2409.13584
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Title:Induced gravitational waves, metastable cosmic strings and primordial black holes in GUTs
View PDF HTML (experimental)Abstract:We explore the cosmological and astrophysical implications of a realistic hybrid inflation model based on flipped $SU(5)$. The model contains superheavy metastable cosmic strings arising from a waterfall field that encounters a limited number of $e$-foldings during the inflationary phase. In addition to the gravitational waves emitted by the metastable strings, there also appear scalar induced gravitational waves linked to the waterfall phase transition. These two independent sources of gravitational waves can yield a combined spectrum that is compatible with the recent PTA measurements, and with additional features that can be probed in future experiments. We also show the appearance of primordial black holes with mass on the order of $10^{26}$ g from the waterfall phase transition, and with an abundance that can be tested in the gravitational lensing experiments.
Abstract: 2409.13399
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Title:The model-independent evidence of cosmic acceleration revisited
View PDF HTML (experimental)Abstract:We investigate the null test of cosmic accelerated expansion by using the Baryon Acoustic Oscillation (BAO) measurements released by the Dark Energy Spectroscopic Instrument, and we find that the latest BAO data alone can provide strong model-independent evidence for the existence of accelerated expansion in the Universe. Using Gaussian Process reconstruction, we derive the deceleration parameter $q(z)$ from the BAO data, revealing that accelerated expansion persisted until $z \lesssim 0.833$. By further incorporating data from Cosmic Chronometers and 6 expansion rate measured by type Ia supernovae, we find that accelerated expansion continued until $z \lesssim 0.417$.
Abstract: 2409.13391
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Title:Prompt and afterglow analysis of the Fermi-LAT detected GRB 230812B
View PDF HTML (experimental)Abstract:Prompt emission of GRB 230812B stands out as one of the most luminous events observed by both the Fermi-GBM and LAT. Prompt emission spectral analysis (both time-integrated and resolved) of this burst supports an additional thermal component together with a non-thermal, indicating the hybrid jet composition. The spectral parameters alpha, Ep, and kT of the best-fit Band+Blackbody model show a tacking behaviour with the intensity. Further, the low energy afterglow emission is consistent with the synchrotron emission from the external forward shock in the ISM medium. LAT detected very high energy emission (VHE) deviating from the synchrotron mechanism, possibly originating from the Lorentz boosting of prompt emission photons by accelerated electrons in the external shock via Inverse Compton (IC) or Synchrotron Self Compton (SSC) emission mechanisms. The comparison of the prompt and afterglow emission properties of this burst revealed that, unlike the bright prompt emission, the afterglow of GRB 230812B is fainter than the other SN-detected bright bursts (GRB 130427A and GRB 171010A) at a similar redshift.
Abstract: 2409.13495
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Title:Composition-asymmetric and sheared relativistic magnetic reconnection
View PDF HTML (experimental)Abstract:Relativistic magnetic reconnection studies have focused on symmetric configurations so far, where the upstream plasma has identical properties on each side of the layer. The boundary layer between a relativistic jet and an accretion flow forming around a supermassive black hole may present an asymmetric configuration in terms of plasma composition, bulk velocity, temperature and magnetization. In this work, we aim to conduct the first study of relativistic magnetic reconnection where the upstream plasma is composed of electron-positron pairs on one side, and electrons and ions on the other. We also investigate the role of a relativistic symmetric shear flow applied along the reconnecting field lines. We simulate magnetic reconnection using two-dimensional particle-in-cell simulations. The initial setup is adapted from a classic Harris layer without guide field, modified to accommodate plasma-composition and shear asymmetries in the upstream medium. For a composition-asymmetric setup, we find that the reconnection dynamics is driven by the electron-ion side, which is the plasma with the lowest magnetization. The energy partition favors accelerating ions at the expense of electrons even more than in a corresponding symmetric setup. With respect to shear, a super-Alfvénic upstream decreases the laboratory-frame reconnection rate, but, unlike in non-relativistic studies, does not shut off reconnection completely. The asymmetries examined in this work diminish the overall efficiency of electron acceleration relative to corresponding symmetric configurations. In the context of a black hole jet-disk boundary, asymmetric reconnection alone is probably not efficient at accelerating electrons to very high energies, but it might facilitate plasma mixing and particle injection for other acceleration channels at the interface.
This page created: Tue Oct 1 12:15:51 ACST 2024 by Hayden James
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