Large Impact Parameters Research Articles

More on heavy-light bootstrap up to double-stress-tensor

We investigate the heavy-light four-point function up to double-stress-tensor, supplementing 1910.06357. By using the OPE coefficients of lowest-twist double-stress- tensor in the literature, we find the Regge behavior for lowest-twist double-stress-tensor in general even dimension within the large impact parameter regime. In the next, we perform the Lorentzian inversion formula to obtain both the OPE coefficients and anomalous dimensions of double-twist operators [ mathcal{O} H mathcal{O} L]n,J with finite spin J in d = 4. We also extract the anomalous dimensions of double-twist operators with finite spin in general dimension, which allows us to address the cases that ∆L is specified to the poles in lowest-twist double-stress-tensors where certain double-trace operators [ mathcal{O} L mathcal{O} L]n,J mix with lowest-twist double-stress-tensors. In particular, we verify and discuss the Residue relation that deter- mines the product of the mixed anomalous dimension and the mixed OPE. We also present the double-trace and mixed OPE coefficients associated with ∆L poles in d = 6, 8. In the end, we turn to discuss CFT2, we verify the uniqueness of double-stress-tensor that is consistent with Virasoso symmetry.

Predictions for the angular dependence of gas mass flow rate and metallicity in the circumgalactic medium

ABSTRACT We use cosmological hydrodynamical simulations to examine the physical properties of the gas in the circumgalactic media (CGM) of star-forming galaxies as a function of angular orientation. We utilize TNG50 of the IllustrisTNG project, as well as the EAGLE simulation to show that observable properties of CGM gas correlate with azimuthal angle, defined as the galiocentric angle with respect to the central galaxy. Both simulations are in remarkable agreement in predicting a strong modulation of flow rate direction with azimuthal angle: inflow is more substantial along the galaxy major axis, while outflow is strongest along the minor axis. The absolute rates are noticeably larger for higher ($\log {(M_\star / \rm {M}_\odot)} \sim 10.5$) stellar mass galaxies, up to an order of magnitude compared to $\dot{M} \lesssim 1$ M⊙ yr−1 sr−1 for $\log {(M_\star / \rm {M}_\odot)}\sim 9.5$ objects. Notwithstanding the different numerical and physical models, both TNG50 and EAGLE predict that the average metallicity of the CGM is higher along the minor versus major axes of galaxies. The angular signal is robust across a wide range of galaxy stellar mass $8.5 \lt \log {(M_\star / \rm {M}_\odot)} \lt 10.5$ at z < 1. This azimuthal dependence is particularly clear at larger impact parameters b ≥ 100 kpc. Our results present a global picture, whereby despite the numerous mixing processes, there is a clear angular dependence of the CGM metallicity. We make forecasts for future large survey programmes that will be able to compare against these expectations. Indeed, characterizing the kinematics, spatial distribution and metal content of CGM gas is key to a full understanding of the exchange of mass, metals, and energy between galaxies and their surrounding environments.

Search for long-lived, massive particles in events with a displaced vertex and a muon with large impact parameter in pp collisions at s=13 TeV with the ATLAS detector

A search for long-lived particles decaying into hadrons and at least one muon is presented. The analysis selects events that pass a muon or missing-transverse-momentum trigger and contain a displaced muon track and a displaced vertex. The analyzed dataset of proton-proton collisions at s=13 TeV was collected with the ATLAS detector and corresponds to 136 fb−1. The search employs dedicated reconstruction techniques that significantly increase the sensitivity to long-lived particle decays that occur in the ATLAS inner detector. Background estimates for Standard Model processes and instrumental effects are extracted from data. The observed event yields are compatible with those expected from background processes. The results are presented as limits at 95% confidence level on model-independent cross sections for processes beyond the Standard Model, and interpreted as exclusion limits in scenarios with pair production of long-lived top squarks that decay via a small R-parity-violating coupling into a quark and a muon. Top squarks with masses up to 1.7 TeV are excluded for a lifetime of 0.1 ns, and masses below 1.3 TeV are excluded for lifetimes between 0.01 ns and 30 ns.1 MoreReceived 27 March 2020Accepted 1 July 2020DOI:https://doi.org/10.1103/PhysRevD.102.032006Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI. Funded by SCOAP3.© 2020 CERN, for the ATLAS CollaborationPhysics Subject Headings (PhySH)Research AreasSupersymmetric modelsParticles & Fields

Perturbative deflection angle for signal with finite distance and general velocities

We propose a perturbative method to compute the deflection angle of both null and massive particles for source and detector at finite distance. This method applies universally to the motion of particles with general velocity in the equatorial plane of stationary axisymmetric spacetimes or static spherical symmetric spacetimes that are asymptotically flat. The resultant deflection angle automatically arranges into a quasi-inverse series form of the impact parameter, with coefficients depending on the metric functions, the signal velocity and the source and detector locations through the apparent angles. In the large impact parameter limit, the series coefficients are reduced to rational functions of sine/cosine functions of the zeroth order apparent angle.

Massive Warm/Hot Galaxy Coronae. II. Isentropic Model

Abstract We construct a new analytic phenomenological model for the extended circumgalactic material (CGM) of L* galaxies. Our model reproduces the O vii/O viii absorption observations of the Milky Way (MW) and the O vi measurements reported by the COS-Halos and eCGM surveys. The warm/hot gas is in hydrostatic equilibrium in an MW gravitational potential, and we adopt a barotropic equation of state, resulting in a temperature variation as a function of radius. A pressure component with an adiabatic index of is included to approximate the effects of a magnetic field and cosmic rays. We introduce a metallicity gradient motivated by the enrichment of the inner CGM by the Galaxy. We then present our fiducial model for the corona, tuned to reproduce the observed O vi–O viii column densities and with a total mass of inside . The gas densities in the CGM are low ( cm−3), and its collisional ionization state is modified by the metagalactic radiation field. We show that for O vi-bearing warm/hot gas with typical observed column densities cm−2 at large ( kpc) impact parameters from the central galaxies, the ratio of the cooling to dynamical times, / , has a model-independent upper limit of . In our model, / at large radii is . We present predictions for a wide range of future observations of the warm/hot CGM, from UV/X-ray absorption and emission spectroscopy to dispersion measure and Sunyaev–Zel’dovich cosmic microwave background measurements. We provide the model outputs in machine-readable data files for easy comparison and analysis.

High spin temperatures at large impact parameters: Ionisation in the outskirts of galaxies

By including the most recent observations of H I 21-cm absorption through nearby galactic discs, we confirm our previous assertion that there is an anti-correlation between the abundance of cool neutral atomic gas and impact parameter. In comparing the measured neutral hydrogen column densities of the sample with the absorption strength, we find a peak in the mean spin temperature of ⟨Tspin/f ⟩ ≈ 2310 K at an impact parameter of ρ ≈ 14 kpc, with ⟨Tspin/f ⟩≳1000 K in the remainder of the disc. This is significantly different to the spin temperature distribution in the Milky Way, which exhibits a constant ≈250 − 400 K over ρ = 8 − 25 kpc. The measured column densities may, however, suffer from beam dilution, which we show appears to be the case for the observations of H I 21-cm emission in which the beam subtends radii of ≳10 kpc. We therefore applied the column density profile of the Milky Way, in addition to the mean of the sample, observed at sufficiently high resolution, and the mean profile for the nearby ∼1012 M⊙ galaxies in the IllustrisTNG simulations. All of the models yield a peak in the mean spin temperature at similar impact parameters (r ≈ 10 − 15 kpc) as the measured column densities. These radii are similar to those of the spiral arms where H II regions are often concentrated. We therefore suggest that the elevated spin temperatures trace the H II regions observed in the outer disc of many spiral galaxies.

New probe to study the symmetry energy at low nuclear density with the deuteron breakup reaction

The reactions of nucleon and polarized deuteron scattered off a heavy target at large impact parameter with intermediate energies have been investigated by using the improved quantum molecular dynamics model. It is found that, due to the difference effect of isovector potential on proton and neutron, there is a significant difference between the angle distribution of elastic scattering protons and neutrons. To overcome the lack of monochromatic neutron beam, the reaction of polarized deuteron peripherally scattered off the heavy target is used to replace the reaction of individual proton and neutron scattered off heavy target to study the isospin effect. It is found that the distributions of elastic scattering angle of proton and neutron originating from the breakup of deuteron are very similar to the results of the individual proton- and neutron-induced reaction. A new probe more effective and more clean, namely the difference between elastic scattering angle of proton and neutron originating from the breakup of polarized deuteron, is promoted to constrain the symmetry energy at subsaturation density.

Probing long-lived particles at Higgs factories

We study displaced vertex signatures of long-lived particles (LLPs) from exotic Higgs decays in the context of a Higgs-portal model and a neutral-naturalness model at the circular electron positron collider (CEPC) and future circular collider ${e}^{+}\text{ }{e}^{\ensuremath{-}}$ (FCC-ee). Such two models feature two representative mass ranges for LLPs, which show very different behavior in their decay signatures. The Higgs-portal model contains a very light sub-GeV scalar boson stemming from a singlet scalar field appended to the Standard Model. Such a light scalar LLP decays into a pair of muons or pions, giving rise to a distinctive signature of collimated muon-jet or pion-jet, thanks to the sub-GeV mass. On the other hand, the neutral-naturalness model, e.g., folded supersymmetry, predicts the lightest mirror glueball of mass $O(10)\text{ }\text{ }\mathrm{GeV}$, giving rise to long decays with a large transverse impact parameter because of the relatively large mass. Utilizing such distinct characteristics to remove the background, we estimate the sensitivities of searches for light scalar bosons and mirror glueballs at the CEPC and FCC-ee. We find either complementary or stronger coverage compared to the previous results in the similar contexts.

Large impact parameter behavior in the CGC/saturation approach: A new nonlinear equation

In this paper we propose a solution to the long standing problem in the CGC/saturation approach: the power-like fall off of the scattering amplitudes at large $b$. We propose a new non-linear equation, which takes into account random walks both in transverse momenta of the produced gluons and in their impact parameters. We demonstrate, that this equation is in accord with previous attempts to include the diffusion in impact parameters in the BFKL evolution equation. We show in the paper, that the solution to a new equation results in the exponential decrease of the scattering amplitude at large impact parameter, and in the restoration of the Froissart theorem.

Proton transfer dynamics modified by CH-stretching excitation.

Gaining insight how specific rovibrational states influence reaction kinetics and dynamics is a fundamental goal of physical chemistry. Purely statistical approaches often fail to predict the influence of a specific state on the reaction outcome, evident in a great number of both experimental and theoretical studies. Most detailed insight in atomistic reaction mechanisms is achieved using accurate collision experiments and high level dynamics calculations. For ion-molecule reactions such experiments are scarce. Here we show the influence of symmetric CH-stretching vibration on the rate and dynamics of proton transfer in the reaction of F- + CH3I. We find a pronounced shift in the reaction dynamics for excited reactions from indirect to preferred direct dynamics at higher collision energy. Moreover, excited reactions occur at larger impact parameters. Finally, we compare vibrational excitation with collision energy and find that vibration is overall more efficient in promoting reactivity, which agrees with recent theoretical calculations.

Unexpected Indirect Dynamics in Base-Induced Elimination.

Base-induced elimination (E2) and bimolecular nucleophilic substitution (SN2) are two of the most versatile reactions that are important in preparative organic chemistry. These stereospecific reactions are often found in direct competition with each other. Elimination can proceed via two distinct transition states, referred to as anti and syn, of which anti is commonly energetically favored. To investigate the intrinsic dynamics of base-induced elimination, reactions under single-collision conditions are required. Here, we present reactive scattering results on the prototype reaction of the fluoride anion with tert-butyl halides. The observed mechanistic fingerprints are associated with the E2 reaction, because steric hindrance at the α-carbon suppresses the SN2 reaction [Carrascosa, E.; Meyer, J.; Zhang, J.; Stei, M.; Michaelsen, T.; Hase, W. L.; Yang, L.; Wester, R. Nat. Commun. 2017, 8, 25]. The reaction coordinate shows energetically submerged transition states, with anti favored over syn, and we found a very shallow prereaction well for anti. We predominantly found indirect dynamics for a range of collision energies, which can be separated into three remarkably different mechanisms. At low collision energies, the first is a large impact parameter indirect mechanism which leads to a forward-backward symmetric scattering signature. The second mechanism is attributed to low-impact parameter reactions with a near-statistical partitioning of the total available energy. The majority of events are associated with widespread isotropic scattering. Unexpectedly, the product ion kinetic energy distributions are independent of collision energy. We associate this with dynamic trapping in a prereaction well supported by a large centrifugal potential. These measured fingerprints support that atomistic reaction dynamics cannot be predicted based on stationary arguments alone.

BFKL equation in the next-to-leading order: solution at large impact parameters

In this paper, we show (1) that the NLO corrections do not change the power-like decrease of the scattering amplitude at large impact parameter (b^2 ,>,r^2 exp ( 2{bar{alpha }}_Seta (1 + 4 {bar{alpha }}_S) ), where r denotes the size of scattering dipole and eta = ln (1/x_{Bj} ) for DIS), and, therefore, they do not resolve the inconsistency with unitarity; and (2) they lead to an oscillating behaviour of the scattering amplitude at large b, in direct contradiction with the unitarity constraints. However, from the more practical point of view, the NLO estimates give a faster decrease of the scattering amplitude as a function of b, and could be very useful for description of the experimental data. It turns out, that in a limited range of b, the NLO corrections generates the fast decrease of the scattering amplitude with b, which can be parameterized as N, propto ,exp ( -,mu ,b ) with mu , propto ,1/r in accord with the numerical estimates in Cepila et al. (Phys Rev D 99(5):051502, https://doi.org/10.1103/PhysRevD.99.051502, arXiv:1812.02548 [hep-ph], 2019).

Subleading eikonal, AdS/CFT and double stress tensors

The eikonal phase which determines the Regge limit of the gravitational scat- tering amplitude of a light particle off a heavy one in Minkowski spacetimes admits an expansion in the ratio of the Schwarzschild radius of the heavy particle to the impact parameter. Such an eikonal phase in AdS spacetimes of any dimensionality has been com- puted to all orders and reduces to the corresponding Minkowski result when both the impact parameter and the Schwarzschild radius are much smaller than the AdS radius. The leading term in the AdS eikonal phase can be reproduced in the dual CFT by a single stress tensor conformal block, but the subleading term is a result of an infinite sum of the double stress tensor contributions. We provide a closed form expression for the OPE coef- ficients of the leading twist double stress tensors in four spacetime dimensions and perform the sum to compute the corresponding lightcone behavior of a heavy-heavy-light-light CFT correlator. The resulting compact expression passes a few nontrivial independent checks. In particular, it agrees with the subleading eikonal phase at large impact parameter.

A Parameter Space Exploration of Galaxy Cluster Mergers. II. Effects of Magnetic Fields

Abstract The hot intracluster plasma in clusters of galaxies is weakly magnetized. Mergers between clusters produce gas compression and motions that can increase the magnetic field strength. In this work, we perform high-resolution nonradiative magnetohydrodynamics simulations of binary galaxy cluster mergers with magnetic fields, to examine the effects of these motions on the magnetic field configuration and strength, as well as the effect of the field on the gas itself. Our simulations sample a parameter space of initial mass ratios and impact parameters. During the first core passage of mergers, the magnetic energy increases via gas compression. After this, shear flows produce temporary, megaparsec-scale, strong-field “filament” structures. Lastly, magnetic fields grow stronger by turbulence. Field amplification is most effective for low-mass ratio mergers, but mergers with a large impact parameter can increase the magnetic energy more via shearing motions. The amplification of the magnetic field is most effective in between the first two core passages of each cluster merger. After the second core passage, the magnetic energy in this region gradually decreases. In general, the transfer of energy from gas motions to the magnetic field is not significant enough to have a substantial effect on gas mixing and the subsequent increase in entropy, which occurs in cluster cores as a result. In the absence of radiative cooling, this results in an overall decrease of the magnetic field strength in cluster cores. In these regions, the final magnetic field is isotropic, while it can be significantly tangential at larger radii.

Solution to the Balitsky-Kovchegov equation with the collinearly improved kernel including impact-parameter dependence

The solution to the impact-parameter dependent Balitsky-Kovchegov equation with the collinearly improved kernel is studied in detail. The solution does not present the phenomenon of Coulomb tails at large impact parameters that have affected previous studies. The origin of this behaviour is explored numerically. It is found to be linked to the fact that this kernel suppresses large daughter dipoles. Solutions based on a physics motivated form of the initial condition are used to compute predictions for structure functions of the proton and the exclusive photo- and electroproduction of vector mesons. A reasonable agreement is found when comparing to HERA and LHC data.

Entanglement in Regge scattering using the AdS/CFT correspondence

The eikonalized parton-parton scattering amplitude at large $\sqrt{s}$ and large impact parameter, is dominated by the exchange of a hyperbolic surface in walled AdS. Its analytical continuation yields a world sheet instanton that is at the origin of the Reggeization of the amplitude and a thermallike quantum entropy ${\mathcal{S}}_{T}$. We explicitly construct the entangled density matrix following from the exchanged surface, and show that its von-Neumann entanglement entropy ${\mathcal{S}}_{E}$ coincides with the thermallike entropy, i.e., ${\mathcal{S}}_{T}={\mathcal{S}}_{E}$. The ratio of the entanglement entropy to the transverse growth of the exchanged surface is similar to the Bekenstein entropy ratio for a black hole, with a natural definition of saturation and the on-set of chaos in high energy collisions. The largest eigenvalues of the entangled density matrix obey a cascade equation in rapidity, reminiscent of nonlinear QCD evolution of wee-dipoles at low-x and weak coupling. We suggest that the largest eigenvalues describe the probability distributions of wee-quanta at low-x and strong coupling that maybe measurable at present and future pp and ep colliders.

Seeking for sterile neutrinos with displaced leptons at the LHC

We study the signal of long-lived sterile neutrino at the LHC produced through the decay of the W boson. It decays into charged lepton and jets. The characteristic signature is a hard prompt lepton and a lepton from the displaced decay of the sterile neutrino, which leads to a bundle of displaced tracks with large transverse impact parameter. Different from other studies, we neither reconstruct the displaced vertex nor place requirement on its invariant mass to maintain sensitivity for low sterile neutrino masses. Instead, we focus on the displaced track from the lepton. A difficulty for low mass sterile neutrino study is that the displaced lepton is usually non-isolated. Therefore, leptons from heavy flavor quark is the major source of background. We closely follow a search for displaced electron plus muon search at CMS and study their control regions, which is related to our signal regions, in great detail to develop a robust estimation of the background for our signals. After further optimization on the signal limiting the number of jets, low HT and large lepton displacement d0 to suppress SM background, we reach an exclusion sensitivity of about 10−8 (10−5) for the mixing angle square at 10 (2) GeV sterile neutrino mass respectively. The strategy we propose can cover the light sterile masses complimentary to beam dump and forward detector experiments.

Linking gas and galaxies at high redshift: MUSE surveys the environments of six damped Lyα systems at z ≈ 3

ABSTRACT We present results from a survey of galaxies in the fields of six z ≥ 3 damped Lyman α (Lyα) systems (DLAs) using the Multi Unit Spectroscopic Explorer (MUSE) at the Very Large Telescope (VLT). We report a high detection rate of up to ${\approx } 80{{\ \rm per\ cent}}$ of galaxies within 1000 km s−1 from DLAs and with impact parameters between 25 and 280 kpc. In particular, we discovered five high-confidence Lyα emitters associated with three DLAs, plus up to nine additional detections across five of the six fields. The majority of the detections are at relatively large impact parameters (>50 kpc) with two detections being plausible host galaxies. Among our detections, we report four galaxies associated with the most metal-poor DLA in our sample (Z/Z⊙ = −2.33 ± 0.22), which trace an overdense structure resembling a filament. By comparing our detections with predictions from the Evolution and Assembly of GaLaxies and their Environments (EAGLE) cosmological simulations and a semi-analytic model designed to reproduce the observed bias of DLAs at z > 2, we conclude that our observations are consistent with a scenario in which a significant fraction of DLAs trace the neutral regions within haloes with a characteristic mass of $M_{\rm h} \approx 10^{11}-10^{12}~\rm M_\odot$, in agreement with the inference made from the large-scale clustering of DLAs. We finally show how larger surveys targeting ≈25 absorbers have the potential of constraining the characteristic masses of haloes hosting high-redshift DLAs with sufficient accuracy to discriminate between different models.

Non-monotonic viscous dissipation of bouncing droplets undergoing off-center collision

The off-center collision of binary bouncing droplets of equal size was studied numerically by a volume-of-fluid method with two marker functions, which has been justified and validated by comparing with available experimental results. A nonmonotonic kinetic energy (KE) recovery with varying impact parameters was discovered. This can be explained by the prolonged entanglement time and the enhanced internal-flow-induced viscous dissipation for bouncing droplets at intermediate impact parameters, compared with those at smaller or larger impact parameters. The distribution of the local viscous dissipation rate (VDR) in the droplet interior shows two major concentration areas, and the competition between these two concentration areas accounts for the nonmonotonic viscous dissipation with varying impact parameters. The nonmonotonic KE recovery with varying impact parameters can also be attributed to the competition between the VDR induced by normal strains and shear strains. The nonmonotonicity was further numerically verified for wider ranges of parameters, and a practically useful formula was proposed to correlate the KE dissipation factor with the impact parameter for various Weber numbers and Ohnesorge numbers.

Soft gravitational radiation from ultra-relativistic collisions at sub- and sub-sub-leading order

Using soft-graviton theorems a well-known zero-frequency limit (ZFL) for the gravitational radiation flux dEGW/dω is re-derived and extended to order mathcal{O}left(omega right) and mathcal{O}left({omega}^2right) for arbitrary massless multi-particle collisions. The (angle-integrated, unpolarized) mathcal{O}left(omega right) correction to the flux turns out to be absent in the case of two-particle elastic collisions. The mathcal{O}left({omega}^2right) correction is instead non-vanishing and takes a simple general expression which is then applied to bremsstrahlung from two-particle elastic collisions. For a tree-level process the outcome is finite and consistent with expectations. Instead, if the tree-level form of the soft theorems is used at sub-sub-leading order even when the elastic amplitude needs an all-loop (eikonal) resummation, an unphysical infrared singularity occurs. Its origin can be traced to the infinite Coulomb phase of gravitational scattering in four dimensions. We briefly discuss how to get rid, in principle, of the unwanted divergences and indicate -without carrying out- a possible procedure to find the proper correction to the naive soft theorems. Nevertheless, if a simple recipe recently proposed for handling these divergences is adopted, we find surprisingly good agreement with results obtained independently via the eikonal approach to transplanckian-energy scattering at large (small) impact parameter (deflection angle), where such Coulomb divergences explicitly cancel out.