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1.
In this work, we study the photoproduction of ρ $$ \rho $$ mesons considering the proton and the nucleus as the target. Utilizing the dipole picture and the wave functions obtained via AdS/QCD, we were able to describe the HERA γ⁢p $$ \gamma p $$ data and extend the formalism to the nuclear case considering the Glauber–Gribov model. The preliminary results obtained in the nuclear regime are compared to the recent LHC PbPb→ρPbPb $$ PbPb\to \rho PbPb $$ data and suggest the presence of a nuclear effect called shadowing.  相似文献   

2.
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3.
We study the energy distribution of hard gluons traversing a dense quark-gluon plasma by comparing various transverse momentum broadening rates q^⁡(t) $$ \hat{q}(t) $$, using a probabilistic perturbative approach. These results were applied to address the thermalization problem in heavy ion collisions. Within the weak coupling model, thermalization follows a “bottom-up” process: early-formed high-energy partons emit low-energy gluons, leading to their equilibrium formation, creating a thermal bath that facilitates equilibrium in the high-energy sector. Under this scenario, we model the time dependencies of as a power-law , and assess the impact of on the distribution of hard gluons passing through the medium.  相似文献   

4.
A study of double-charmed meson production in high-energy proton–proton collisions at the Large Hadron Collider is presented. Considering the color dipole formalism developed in the transverse momentum representation along with the double parton scattering mechanism, predictions are made for the transverse momentum differential cross section for different pairs of D $$ D $$-mesons. The theoretical results cover the center-of-mass energy and forward rapidities available by the LHCb experiment. The proton–proton results considering different unintegrated gluon distributions are compared to the respective data collected at the LHC.  相似文献   

5.
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6.
Chisel marks on a stone uncovered in Rupinpiccolo protohistoric hill fort from north-eastern Italy were suggested to be a representation of the night sky (Bernardini et al. 2022 Documenta Praehistorica XLIX). The patterns of the 29 marks are analyzed here to establish if they reproduce popular stellar asterisms. Nine marks are found to match the Tail of Scorpius and five the Orion's Belt, together with Rigel and Betelgeuse. Nine marks are found in the approximate position of the Pleiades showing some match with the cluster members. On the back side, 5 marks possibly reproduce Cassiopeia. One mark slightly North of Orion cannot be identified. The 28 marks show a Pearson correlation coefficient (28) with stellar positions higher than 0.99 with a probability of a wrong correlation lower than 0.001. Departures are about one degree, or about 7 mm, as the mean diameter of the marks, which suggests a manufacturing limitation in the charting. The fort dates 1800–400 BCE when Scorpius and Orion showed about the same orientation at the heliacal rising. The unidentified mark challenges the whole picture. We suggest it could have been the progenitor of a failed supernova, thus offering also the possibility of a verification.  相似文献   

7.
The investigation of supernova remnants (SNRs) across the electromagnetic spectrum from radio up to very high energy gamma-rays can serve as a test of the particle acceleration and touches on one of the unresolved problems of modern astrophysics, namely the origin of cosmic rays and the Galaxy's contribution to the overall cosmic ray spectrum. The multiwavelength observations of Cas A SNR demonstrated that structure and spectral features have clear signs of young SNRs and its overall properties make this object the best target to test a hypothesis of cosmic ray origin in SNRs. Studies of Cas A at very high energies by SHALON telescope showed the location of TeV gamma-ray emission region relative to the position of reveres shock. Also, the spectral energy distribution was obtained at high and very high energies. To describe the spectral and structural features of this SNR viewed in non-thermal emission, two approaches involving reverse and also both reverse and forward shocks to the mechanism of diffusive shock acceleration of cosmic rays in Cas A were applied. It is demonstrated that the observational properties of Cas A are well reproduced by the hadronic model with significant contribution of both the forward and reverse shocks in the generation of broadband emission. Calculation results suggest that the very high efficiency of particle acceleration in Cas A, which value is up to 25% of the supernova explosion energy with energy of accelerated particles not exceeding of eV. Whereas, the forward shock model predicts the spectral characteristics of the TeV-gamma-emission corresponding to ones detected at 800 GeV–40 TeV that are the evidence of acceleration of the hadronic cosmic rays in shells of SNRs up to eV  相似文献   

8.
There are many rotating spheroids in the universe, and many astronomers and physicists have used theoretical methods to study the characteristics of stellar gravity since Newton's time. This paper derives the solutions of eight scattering states ( ϕ ( 0 ) , χ ( 0 ) , ϕ ( 1 ) , χ ( 1 ) , ϕ ( 2 ) $$ \Big({\phi}^{(0)},{\chi}^{(0)},{\phi}^{(1)},{\chi}^{(1)},{\phi}^{(2)} $$ , χ ( 2 ) , ϕ ( 3 ) $$ {\chi}^{(2)},{\phi}^{(3)} $$ , and χ ( 3 ) ) $$ {\chi}^{(3)}\Big) $$ for the Dirac equation with positive-energy E = im $$ E= im $$ , and establishes the relationship between the differential scattering cross section σ i ( p , θ , φ ) $$ {\sigma}_i\left(p,\theta, \varphi \right) $$ and the stellar density μ $$ \mu $$ . It is found that: (1) For the eight scattering states, their average scattering cross-sections σ i ‾ $$ \overline{\sigma_i} $$ are proportional to μ 2 $$ {\mu}^2 $$ , and depend on the star's radius, and the higher the stellar density μ $$ \mu $$ , the greater the sensitivity of σ i ‾ $$ \overline{\sigma i} $$ to the change of μ $$ \mu $$ ; (2) For the four scattering states χ ( i ) , i = 0 , 1 , 2 , 3 $$ {\chi}^{(i)},i=0,1,2,3 $$ , their average scattering amplitudes f ‾ ( p , θ ) $$ \overline{f}\left(p,\theta \right) $$ and σ ‾ ( p , θ ) $$ \overline{\sigma}\left(p,\theta \right) $$ depend on the mass m $$ m $$ of the particles; while for the other four scattering states ϕ ( i ) $$ {\phi}^{(i)} $$ , i = 0 , 1 , 2 , 3 $$ i=0,1,2,3 $$ , then f ‾ $$ \overline{f} $$ and σ ‾ $$ \overline{\sigma} $$ are independent of m $$ m $$ . This study links the gravitational characteristics of stars with the scattering cross section, creating a new method for studying the gravitational characteristics, which helps to reveal the mystery of the gravity of rotating ellipsoidal stars.  相似文献   

9.
Located at less than two pc away, Luhman 16 AB (WISE J104915.57-531906.1) is the closest pair of brown dwarfs and the third closest “stellar” system to Earth. An exoplanet candidate in the Luhman 16 binary system was reported in 2017 based on a weak astrometric signature in the analysis of 12 HST epochs. An additional epoch collected in 2018 and re-analysis of the data with more advanced methods further increased the significance level of the candidate, consistent with a Neptune-mass exoplanet orbiting one of the Luhman 16 brown dwarf components. We report the joint analysis of these previous data together with two new astrometric HST epochs we obtained to confirm or disprove this astrometric signature. Our new analysis rules out the presence of a planet orbiting one component of the Luhman 16 AB system for masses ℳ $$ \mathrm{\mathcal{M}} $$ ≳ $$ \gtrsim $$ 1.5 M♆ (Neptune masses) and periods between 400 and 5000 days. However, the presence of third bodies with masses ℳ $$ \mathrm{\mathcal{M}} $$ ≲ $$ \lesssim $$ 3 M♆ and periods between 2 and 400 days ( ∼ $$ \sim $$ 1.1 years) cannot be excluded. Our measurements make significant improvements to the characterization of this sub-stellar binary, including its mass-ratio 0.8305 ± 0.0006 $$ \pm 0.0006 $$ , individual component masses 35.4 ± $$ \pm $$ 0.2 MꝜ and 29.4 ± $$ \pm $$ 0.2 MꝜ (Jupiter masses), and parallax distance 1.9960 pc ± $$ \pm $$ 50 AU. Comparison of the masses and luminosities of Luhman 16 AB to several evolutionary models shows persistent discrepancies in the ages of the two components, but strengthens the case that this system is a member of the 510 ± $$ \pm $$ 95 Myr Oceanus Moving Group.  相似文献   

10.
The first JWST observations of hot Jupiters showed an unexpected detection of SO 2 $$ {}_2 $$ in their hydrogen-rich atmospheres. We investigate how much sulfur can be expected in the atmospheres of rocky exoplanets and which sulfur molecules can be expected to be most abundant and detectable by transmission spectroscopy. We run thermochemical equilibrium models at the crust–atmosphere interface, considering surface temperatures 500–5000 K, surface pressures 1–100 bar, and various sets of element abundances based on common rock compositions. Between 1000 and 2000 K, we find gaseous sulfur concentrations of up to 25% above the rock in our models. SO 2 $$ {}_2 $$ , SO, H 2 $$ {}_2 $$ S, and S 2 $$ {}_2 $$ are by far the most abundant sulfur molecules. SO 2 $$ {}_2 $$ shows potentially detectable features in transmission spectra at about 4 μ $$ \mu $$ m, between 7 and 8 μ $$ \mu $$ m, and beyond 15 μ $$ \mu $$ m. In contrast, the sometimes abundant H 2 $$ {}_2 $$ S molecule is difficult to detect in these spectra, which are mostly dominated by H 2 $$ {}_2 $$ O and CO 2 $$ {}_2 $$ . Although the molecule PS only occurs with concentrations < 300 $$ <300 $$ ppm, it can cause a strong absorption feature between 0.3 and 0.65 μ $$ \mu $$ m in some of our models for high surface pressures. The detection of sulfur molecules would enable a better characterization of the planetary surface.  相似文献   

11.
In this work, the entanglement entropy is examined within the context of deep inelastic scattering in e p $$ ep $$ collisions. The calculation is based on a formalism where the partonic state at small- x $$ x $$ is maximally entangled, consisting of a large number of micro-states occurring with equal probabilities. Analytical expressions for the number of gluons, N gluon $$ {N}_{\mathrm{gluon}} $$ , are considered, derived from gluon saturation models for dipole-target amplitudes within the framework of the Quantum Chromodynamics (QCD) color dipole picture. A comparison of the entanglement entropy with thermodynamic entropy measured in p p $$ pp $$ and e p $$ ep $$ collisions at high energies is done.  相似文献   

12.
Neutron stars may experience differential rotation on short, dynamical timescales following extreme astrophysical events like binary neutron star mergers. In this work, the masses and radii of differentially rotating neutron star models are computed. We employ a set of equations of states for dense hypernuclear and Δ $$ \Delta $$ -admixed-hypernuclear matter obtained within the framework of CDF theory in the relativistic Hartree-Fock (RHF) approximation. Results are shown for varying meson- Δ $$ \Delta $$ couplings, or equivalently the Δ $$ \Delta $$ -potential in nuclear matter. A comparison of our results with those obtained for nonrotating stars shows that the maximum mass difference between differentially rotating and static stars is independent of the underlying particle composition of the star. We further find that the decrease in the radii and increase in the maximum masses of stellar models when Δ $$ \Delta $$ -isobars are added to hyperonuclear matter (as initially observed for static and uniformly rotating stars) persist also in the case of differentially rotating neutron stars.  相似文献   

13.
Circumstellar disk (CD) around the first generation of stars have been numerically investigated here to see if the cooling regimes also play a role in the formation and evolution of the disk associated with the most massive protostars (MMPS). Also, an emphasis is given to exploring the effect of the initial turbulent motion of the metal-free gas on the resulting morphology of the CD. For this, a systematic range of Mach number ℳ = 0 . 1 − 1 . 0 $$ \mathcal{M}=0.1-1.0 $$ has been examined. It has been found that the disk-to-star mass ratio M disk $$ {M}_{\mathrm{disk}} $$ / M star $$ {M}_{\mathrm{star}} $$ is larger when the model evolution is based on the first H 2 $$ {}_2 $$ line cooling followed by subsequent cooling via collision-induced emission than in the model where only H 2 $$ {}_2 $$ line cooling remains operative. Also, irrespective of the initial turbulence in the cloud, the former type of model yields a CD as massive as 7.66 M ⊙ $$ {}_{\odot } $$ while the latter type produces a disk as massive as 1.29 M ⊙ $$ {}_{\odot } $$ . Moreover, the inner part of the CD is found dominated by higher subsonic turbulent motions in the case of the former type of models than in the latter type. CDs around MMPS in both types of models show stable disk structures.  相似文献   

14.
In this work, we study how to improve well-known techniques for detecting progenitors/descendants of galaxies, such as the NDpredict program, when applied to galaxies in clusters. The improvement of this particular method is based on the use of the red sequence of galaxies in those environments. Objects close to the red sequence in the color and magnitude diagram are more likely to belong to the cluster. This defines a probability scale which is then combined with the one generated by NDpredict. This procedure is optimized for the study of galaxies in clusters over different epochs. Our main result is that, for a sample composed of 120 $$ 120 $$ clusters, with masses greater than 10 13.25 M ⊙ $$ {10}^{13.25}{M}_{\odot } $$ , selected from the IllustrisTNG simulations (namely, the TNG100 runs). In 99 % $$ 99\% $$ of the cases (i.e., 119 $$ 119 $$ systems), we obtain better performance with the red sequence method in comparison to the original NDpredict, and the average gain obtained is 28 % $$ 28\% $$ in the identification of descendants for this sample of cluster galaxies.  相似文献   

15.
We evaluate the feasibility of Bose–Einstein condensate stars (BECS) as models for the interior of neutron stars (NSs). BECS are compact objects composed of bosons, formed through the spin-parallel pairing of neutrons. Here, we utilize the astronomical data from GW170817, XMMU J173203.3-344518 (the lightest NS known), and a novel lower limit on NS core heat capacity to scrutinize the compatibility of BECS with these recent observations of NSs. Our specific focus is to constrain the values of the scattering length a $$ a $$ , parameter determining the strength of particle interactions in the model. Our analysis suggests that if the stars involved in GW170817 were BECSs, the scattering length of their constituent bosons should fall within the 4 $$ 4 $$ to 10 $$ 10 $$ fm range. Additionally, at a scattering length of a ∼ 3.1 − 4 $$ a\sim 3.1-4 $$ fm, stars with mass and radius characteristics akin to XMMU J173203.3-344518 are identified. Moreover, we find that the heat capacity depends on the mass and temperature of BECS, and surpasses the established lower bound for NS cores when a > 2 − 5 $$ a>2-5 $$ fm. In summary, our results endorse BECS models with a ∼ 4 $$ a\sim 4 $$ fm, providing NS observables in agreement with diverse observations and contributing to the understanding of NS interiors.  相似文献   

16.
The effects of a minimal length on the Kerr metric are studied within the pseudo-complex General Relativity (pcGR), which has a minimal length parameter and also depends on a r $$ r $$ -dependent metric, allowing for the accumulation of dark energy around a star. The relevant parameters are the rotational Kerr parameter a $$ a $$ , the mass of a black hole, and a parameter measuring the amount of dark energy accumulated. It is found that the metric is modified by a factor, depending on r $$ r $$ , resulting in a maximal acceleration. This factor shows several singularities. For small black holes, the corresponding effective potentials exhibit potential barriers, avoiding the increase of the black hole's mass. It is found that the effects of a minimal length are only of importance for very small mass black holes and vanish for macroscopic black holes.  相似文献   

17.
The pulsar magnetic inclination angle is a key parameter for pulsar physics. It influences the observable properties of pulsars, such as the pulse beam width, braking index, polarization, and emission geometry. In this study, we give a brief overview of the current state of knowledge and research on this parameter and its implications for the internal physics of pulsars. We use the observed pulsar data of magnetic inclination angle and braking index to constrain the star's number of precession cycles, ξ $$ \xi $$ , which reflects the interaction between superfluid neutrons and other particles inside a neutron star (NS). We apply the method proposed by Cheng et al. (Cheng, Q., Zhang, S. N., Zheng, X. P., & Fan, X. L., 2019, Phys. Rev. D, 99, 083011) to analyze the data of PSR J2013 + 3845 and obtain the constraints for ξ $$ \xi $$ ranging from 2 . 393 × 1 0 5 $$ 2.393\times 1{0}^5 $$ to 1 . 268 × 1 0 6 $$ 1.268\times 1{0}^6 $$ . And further analysis suggests that the internal magnetic field structure of PSR J2013 + 3845 is likely dominated by toroidal components. This study may help us understand the process of internal viscous dissipation and the related evolution of the inclination angles of pulsars, and may have important implications for the study of continuous gravitational wave emissions from NS.  相似文献   

18.
We present relative astrometric and photometric measurements of visual double stars made in 2013–2015, with PISCO2 installed at the 76-cm refractor of Côte d'Azur Observatory in Nice (France). Our observing list contains orbital couples as well as double stars whose motion is still uncertain. Most of the observations were done in 2015, but some other observations of wide couples were done in 2013–2014 (0.3% of the total of the observations). Three different techniques were used for obtaining measurements: lucky imaging, speckle interferometry and the direct vector autocorrelation method. From our observations of 2837 multiple stars, we obtained 5182 new measurements with angular separations in the range of 0 ″ $$ {}^{{\prime\prime} } $$ .1–32 ″ $$ {}^{{\prime\prime} } $$ and an average accuracy of 0 ″ . 018 $$ {0}^{{\prime\prime} }.018 $$ . The mean error on the position angles is 0°.8. Most of the position angles were determined without the usual 180° ambiguity with the application of the direct vector autocorrelation technique and/or by inspection of the Lucky images or the long integration files. We managed to routinely monitor faint systems ( m V ≈ 9 − 11 $$ {m}_V\approx 9-11 $$ ) with large magnitude difference (up to Δ m V ≈ 4 . 5 $$ \Delta {m}_V\approx 4.5 $$ ). We have thus been able to measure 21 systems containing red dwarf stars that had been poorly monitored since their discovery, from which we estimated the stellar masses thanks to Gaia measurements. We also measured the magnitude difference of the two components of 1079 double stars with an estimated error of 0.2 mag. Except for a few objects that are discussed, our measurements are in good agreement with the ephemerides computed with published orbital elements, even for the double stars whose separation is smaller than the diffraction limit. Thanks to good seeing images and with the use of high-contrast numerical filters, we have also been able to obtain 196 measurements with an angular separation smaller than the diffraction limit of our instrumentation, and consistent with those obtained with larger telescopes. We also report measurements of the 164 new double stars that we found in the files obtained during the observations. Finally, from a study of the DR3 Gaia release, it is shown that all the objects of the Tycho Double Star Catalog that we did not resolve in 2015 are probably false detections by Tycho.  相似文献   

19.
Pulsar electrodynamics could be relevant to the physics of stellar surface, which remains poorly understood for more than half a centenary and is difficult to probe due to the absence of direct and clear observational evidence. Nevertheless, highly sensitive telescopes (e.g., China's Five-hundred-meter Aperture Spherical radio Telescope, FAST) may play an essential role to solve the problem since the predicted surface condition would have quite different characteristics in some models of pulsar structure, especially after the establishment of the standard model of particle physics. For instance, small hills (or “zits”) may exist on solid strangeon star surface with rigidity, preferential discharge, that is, gap sparking, may occur around the hills in the polar cap region. In this work, with the 110-min polarization observation of PSR B0950 08 targeted by FAST, we report that the gap sparking is significantly non-symmetrical to the meridian plane on which the rotational and magnetic axes lie. It is then speculated that this asymmetry could be the result of preferential sparking around zits which might rise randomly on pulsar surface. Some polarization features of both single pulses and the mean pulse, as well as the cross-correlation function of different emission regions, have also been presented.  相似文献   

20.
This article focuses on the implications of the recently developed commutative formulation based on branch-cutting cosmology, the Wheeler–DeWitt equation, and Hořava–Lifshitz quantum gravity. Assuming a mini-superspace of variables, we explore the impact of an inflaton-type scalar field ϕ ( t ) $$ \phi (t) $$ on the dynamical equations that describe the trajectories evolution of the scale factor of the Universe, characterized by the dimensionless helix-like function ln − 1 [ β ( t ) ] $$ {\ln}^{-1}\left[\beta (t)\right] $$ . This scale factor characterizes a Riemannian foliated spacetime that topologically overcomes the big bang and big crunch singularities. Taking the Hořava–Lifshitz action as our starting point, which depends on the scalar curvature of the branched Universe and its derivatives, with running coupling constants denoted as g i $$ {g}_i $$ , the commutative quantum gravity approach preserves the diffeomorphism property of General Relativity, maintaining compatibility with the Arnowitt–Deser–Misner formalism. We investigate both chaotic and nonchaotic inflationary scenarios, demonstrating the sensitivity of the branch-cut Universe's dynamics to initial conditions and parameterizations of primordial matter content. The results suggest a continuous connection of Riemann surfaces, overcoming primordial singularities and exhibiting diverse evolutionary behaviors, from big crunch to moderate acceleration.  相似文献   

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