arXiv subjects

Ye Li

Publications and source records attributed to Ye Li.

At least 217 records · Page 12Linked to original sources

arXiv2017

A further study of $t_{\rm burst}$ of GRBs: rest frame properties, external plateau contributions and multiple parameter analysis

[Zhang 2014] propose to redefine the true GRB central engine activity duration, $t_{\rm burst}$, by considering the contributions from the prompt $γ$-ray emission, X-ray flare and internal plateau features. With a comprehensive study on a large sample of Swift GRBs, it is shown that the $t_{\rm burst}$ distribution in the observer frame consists of a bimodal feature, suggesting the existence of a new population of ultra-long GRBs. In this work, we make a series of further studies on $t_{\rm burst}$: we update the Swift GRB sample up to June 2016; we investigate the properties of $t_{\rm burst}$ distribution in the rest frame; we redefine $t_{\rm burst}$ by involving external plateau contributions; we make a multiple parameter analysis to investigate whether the bursts within the ultra-long population being statistically different in sense of other features besides the duration distribution. We find that for all situations, the distribution of $t_{\rm burst}$ requires two normal distributions in logarithmic space to provide a good fit, both in observer frame and rest frame. Considering the observational gap effect would not completely erase the bimodal distribution feature. However the bursts within the ultra-long population may have no statistically different in sense of other features besides the duration term. We thus suggest that if the ultra-long population of GRBs indeed exists, their central engine mechanism and radiation mechanism should be similar to the normal population, but they have longer central engine activity timescale.

astro-ph.HE↗

arXiv2016

Resummation of Jet Veto Logarithms at partial N$^3$LL + NNLO for $W^+W^-$ Production at the LHC

We compute the resummed on-shell $W^+ W^-$ production cross section under a jet-veto at the LHC to partial N$^3$LL order matched to the fixed order NNLO result. Differential NNLO cross sections are obtained from an implementation of $q_T$ subtraction in Sherpa. The two-loop virtual corrections to the $q \bar q \rightarrow W^+ W^-$ amplitude, used in both fixed order and resummation predictions, are extracted from the public code {\tt qqvvamp}. We perform resummation using soft collinear effective theory (SCET), with approximate beam functions where only the logarithmic terms are included at two-loop. In addition to scale uncertainties from the hard matching scale and the factorization scale, rapidity scale variations are obtained within the analytic regulator approach. Our resummation results show a decrease in the jet-veto cross-section compared to NNLO fixed order predictions, with reduced scale uncertainties compared to NNLL+NLO resummed predictions. We include the loop-induced $gg$ contribution with jet veto resummation to NLL+LO. The prediction shows good agreement with recent LHC measurements.

hep-ph↗

arXiv2016

A Comparative Study of Long and Short GRBs. I. Overlapping Properties

Gamma ray bursts (GRBs) are classified into long and short categories based on their durations. Broad band studies suggest that these two categories of objects roughly correspond to two different classes of progenitor systems, i.e. compact star mergers (Type I) vs. massive star core collapse (Type II). However, the duration criterion sometimes leads to mis-identification of the progenitor systems. We perform a comprehensive multi-wavelength comparative study between duration-defined long GRBs and short GRBs as well as the so-called "consensus" long GRBs and short GRBs (which are believed to be more closely related to the two types of progenitor systems). The parameters we study include two parts: the prompt emission properties including duration ($T_{90}$), spectral peak energy ($E_{\rm p}$), low energy photon index ($α$), isotropic $γ$-ray energy ($E_{\rm γ, iso}$), isotropic peak luminosity ($L_{\rm p,iso}$), and the amplitude parameters ($f$ and $f_{\rm eff}$); and the host galaxy properties including stellar mass ($M_*$), star formation rate (SFR), metallicity ([X/H]), half light radius ($R_{50}$), angular and physical ($R_{\rm off}$) offset of the afterglow from the center of the host galaxy, the normalized offset ($r_{\rm off}=R_{\rm off}/R_{50}$), and the brightness fraction $F_{\rm light}$. For most parameters, we find interesting overlapping properties between the two populations in both 1D and 2D distribution plots. The three best parameters for the classification purpose are $T_{90}$, $f_{\rm eff}$, and $F_{\rm light}$. However, no single parameter alone is good enough to place a particular burst into the right physical category, suggesting a need of multiple criteria for physical classification.

astro-ph.HE↗

arXiv2016

Detectable MeV neutrinos from black hole neutrino-dominated accretion flows

Neutrino-dominated accretion flows (NDAFs) around rotating stellar-mass black holes (BHs) have been theorized as the central engine of relativistic jets launched in massive star core collapse events or compact star mergers. In this work, we calculate the electron neutrino/anti-neutrino spectra of NDAFs by fully taking into account the general relativistic effects, and investigate the effects of viewing angle, BH spin, and mass accretion rate on the results. We show that even though a typical NDAF has a neutrino luminosity lower than that of a typical supernova (SN), it can reach $10^{50}-10^{51}~{\rm erg~s^{-1}}$ peaking at $\sim 10$ MeV, making them potentially detectable with the upcoming sensitive MeV neutrino detectors if they are close enough to Earth. Based on the observed GRB event rate in the local universe and requiring that at least 3 neutrinos are detected to claim a detection, we estimate a detection rate up to $\sim$ (0.10-0.25) per century for GRB-related NDAFs by the Hyper-Kamiokande (Hyper-K) detector if one neglects neutrino oscillation. If one assumes that all Type Ib/c SNe have an engine-driven NDAF, the Hyper-K detection rate would be $\sim$ (1-3) per century. By considering neutrino oscillations, the detection rate may decrease by a factor of 2-3. Detecting one such event would establish the observational evidence of NDAFs in the universe.

astro-ph.HE↗

arXiv2016

On Efficient Decoding and Design of Sparse Random Linear Network Codes

Random linear network coding (RLNC) in theory achieves the max-flow capacity of multicast networks, at the cost of high decoding complexity. To improve the performance-complexity tradeoff, we consider the design of sparse network codes. A generation-based strategy is employed in which source packets are grouped into overlapping subsets called generations. RLNC is performed only amongst packets belonging to the same generation throughout the network so that sparseness can be maintained. In this paper, generation-based network codes with low reception overheads and decoding costs are designed for transmitting of the order of $10^2$-$10^3$ source packets. A low-complexity overhead-optimized decoder is proposed that exploits "overlaps" between generations. The sparseness of the codes is exploited through local processing and multiple rounds of pivoting of the decoding matrix. To demonstrate the efficacy of our approach, codes comprising a binary precode, random overlapping generations, and binary RLNC are designed. The results show that our designs can achieve negligible code overheads at low decoding costs, and outperform existing network codes that use the generation based strategy.

cs.IT↗

arXiv2016

An Exponential Regulator for Rapidity Divergences

Finding an efficient and compelling regularization of soft and collinear degrees of freedom at the same invariant mass scale, but separated in rapidity is a persistent problem in high-energy factorization. In the course of a calculation, one encounters divergences unregulated by dimensional regularization, often called rapidity divergences. Once regulated, a general framework exists for their renormalization, the rapidity renormalization group (RRG), leading to fully resummed calculations of transverse momentum (to the jet axis) sensitive quantities. We examine how this regularization can be implemented via a multi-differential factorization of the soft-collinear phase-space, leading to an (in principle) alternative non-perturbative regularization of rapidity divergences. As an example, we examine the fully-differential factorization of a color singlet's momentum spectrum in a hadron-hadron collision at threshold. We show how this factorization acts as a mother theory to both traditional threshold and transverse momentum resummation, recovering the classical results for both resummations. Examining the refactorization of the transverse momentum beam functions in the threshold region, we show that one can directly calculate the rapidity renormalized function, while shedding light on the structure of joint resummation. Finally, we show how using modern bootstrap techniques, the transverse momentum spectrum is determined by an expansion about the threshold factorization, leading to a viable higher loop scheme for calculating the relevant anomalous dimensions for the transverse momentum spectrum.

hep-ph↗

arXiv2016

Radio transient following FRB 150418: afterglow or coincident AGN flare?

Recently, Keane et al. reported the discovery of a fading radio transient following FRB 150418, and interpreted it as the afterglow of the FRB. Williams \& Berger, on the other hand, suggested that the radio transient is analogous to a group of variable radio sources, so that it could be a coincident AGN flare in the observational beam of the FRB. A new observation with VLA showed a re-brightening, which is consistent with the AGN picture. Here, using the radio survey data of Ofek et al., we statistically examine the chance coincidence probability to produce an event like the FRB 150418 transient. We find that the probabilities to produce a variable radio transient with at least the same variability amplitude and signal-to-noise ratio as the FRB 150415 transient, without and with the VLA point, are $P_1 \sim 6 \times 10^{-4}$ and $P_1 \sim 2 \times 10^{-3}$, respectively. In addition, the chance probability to have a fading transient detected following a random time (FRB time) is less than $P_2 \sim 10^{-2.9\pm 1.3}$. Putting these together and assuming that the number of radio sources within one Parkes beam is 16, the final chance coincidence of having an FRB 150418-like radio transient to be unrelated to the FRB is $< 10^{-4.9\pm1.3}$ and $< 10^{-4.4\pm1.3}$, respectively, without and with the VLA point. We conclude that the radio transient following FRB 150418 has a low probability being an unrelated AGN flare, and the possibility of being the afterglow of FRB 150418 is not ruled out.

astro-ph.HE↗

arXiv2015

Soft-virtual corrections to Higgs production at N$^3$LO

In this paper, we compute the soft-virtual corrections to Higgs boson production in gluon fusion for infinite top quark mass at next-to-next-to-next-to-leading order in QCD. In addition, we present analogous soft-virtual terms for both Drell-Yan lepton production in QCD and scalar pair production in N = 4 super Yang-Mills theory. The result for Drell-Yan lepton production is derived from the result for Higgs boson production using Casimir scaling arguments together with well-known results available in the literature. For scalar pair production in the N = 4 model, we show by explicit calculation that the result is equal to the part of the Higgs boson soft-virtual term which is of maximal transcendentality weight.

hep-ph↗

arXiv2015

Can life survive Gamma-Ray Bursts in the high-redshift universe?

Nearby Gamma-Ray Bursts (GRBs) have been proposed as a possible cause of mass extinctions on Earth. Due to the higher event rate of GRBs at higher redshifts, it has been speculated that life as we know it may not survive above a certain redshift (e.g. $z>0.5$). We examine the duty cycle of lethal (life-threatening) GRBs in the solar neighborhood, in the Sloan Digital Sky Survey (SDSS) galaxies and GRB host galaxies, with the dependence of the long GRB rate on star formation and metallicity properly taken into account. We find that the number of lethal GRBs attacking Earth within the past 500 Myr ($\sim$ epoch of the Ordovician mass extinction) is $0.93$. The number of lethal GRBs hitting a certain planet increases with redshift, thanks to the increasing star formation rate and decreasing metallicity in high-$z$ galaxies. Taking 1 per 500 Myr as a conservative duty cycle for life to survive, as evidenced by our existence, we find that there are still a good fraction of SDSS galaxies beyond $z=0.5$ where the GRB rate at half-mass radius is lower than this value. We derive the fraction of such benign galaxies as a function of redshift through Monte Carlo simulations, and find that the fraction is $\sim 50\%$ at $z\sim 1.5$ and $\sim 10\%$ even at $z \sim 3$. The mass distribution of benign galaxies is dominated by Milky-Way-like ones, thanks to their commonness, relatively large mass, and low star formation rate. GRB host galaxies are among the most dangerous ones.

astro-ph.HE↗

arXiv2015

Combining parton showers and NNLO matrix elements

In this talk, we discuss recent developments in combining parton showers and fixed-order calculations. We focus on the UNNLOPS method for matching next-to-next-to-leading order computations to the parton shower, and we present results from Sherpa for Drell-Yan lepton-pair and Higgs-boson production at the LHC.

hep-ph↗

arXiv2015

The Millisecond Magnetar Central Engine in short GRBs

One favored progenitor model for short duration gamma-ray bursts (SGRBs) is the coalescence of two neutron stars (NS-NS). One possible outcome of such a merger would be a rapidly spinning, strongly magnetized neutron star (known as a millisecond magnetar). These magnetars may be "supra-massive", implying they would collapse to black holes after losing centrifugal support due to magnetic dipole spindown. By systematically analyzing the BAT-XRT light curves of all short GRBs detected by {\em swift}, we test how well the data are consistent with this central engine model of short GRBs. We find that the so-called "extended emission" observed with BAT in some short GRBs are fundamentally the same component as the "internal X-ray plateau" as observed in many short GRBs, which is defined as a plateau in the lightcurve followed by a very rapid drop. Based on how likely a short GRB hosts a magnetar, we characterize the entire {\em Swift} short GRB sample into three categories: the "internal plateau" sample, the "external plateau" sample, and the "no plateau" sample. The derived magnetar surface magnetic field $B_{\rm p}$ and the initial spin period $P_0$ fall into the reasonable range. No GRBs in the internal plateau sample have the total energy exceeding the maximum energy budget of a millisecond magnetar. Assuming that the rapid fall time at the end of the internal plateau is the collapse time of a supra-massive magnetar to a black hole, and applying the measured mass distribution of NS-NS systems in our Galaxy, we constrain the neutron star equation of state (EOS). The data suggest that the NS equation of state is close to the GM1 model, which has a maximum non-rotating NS mass $M_{\rm TOV} \sim 2.37 M_\odot$.

astro-ph.HE↗

arXiv2014

N$^3$LO Higgs and Drell-Yan production at threshold: the one-loop two-emission contribution

In this paper, we study phenomenologically interesting soft radiation distributions in massless QCD. Specifically, we consider the emission of two soft partons off of a pair of light-like Wilson lines, in either the fundamental or the adjoint representation, at next-to-leading order. Our results are an essential component of the next-to-next-to-next-to-leading order threshold corrections to both Higgs boson production in the gluon fusion channel and Drell-Yan lepton production. Our calculations are consistent with the recently published results for Higgs boson production. As a non-trivial cross-check on our analysis, we rederive a recent prediction for the Drell-Yan threshold cross section using a completely different strategy. Our results are compact, valid to all orders in the dimensional regularization parameter, and expressed in terms of pure functions.

hep-ph↗

arXiv2014

Higgs-boson production through gluon fusion at NNLO QCD with parton showers

We discuss how the UN2LOPS scheme for matching NNLO calculations to parton showers can be applied to processes with large higher-order perturbative QCD corrections. We focus on Higgs-boson production through gluon fusion as an example. We also present an NNLO fixed-order event generator for this reaction.

hep-ph↗

arXiv2014

High precision predictions for exclusive $VH$ production at the LHC

We present a resummation-improved prediction for $VH$ + 0 jets production at the Large Hadron Collider. We focus on highly-boosted final states in the presence of jet veto to suppress the $t{\bar t}$ background. In this case, conventional fixed-order calculations are plagued by the existence of large Sudakov logarithms $α_s^n \log^m (p_T^{veto}/Q)$ for $Q\sim m_V + m_H$ which lead to unreliable predictions as well as large theoretical uncertainties, and thus limit the accuracy when comparing experimental measurements to the Standard Model. In this work, we show that the resummation of Sudakov logarithms beyond the next-to-next-to-leading-log accuracy, combined with the next-to-next-to-leading order calculation, reduces the scale uncertainty and stabilizes the perturbative expansion in the region where the vector bosons carry large transverse momentum. Our result improves the precision with which Higgs properties can be determined from LHC measurements using boosted Higgs techniques.

hep-ph↗

arXiv2014

Jet vetoes for Higgs production at future hadron colliders

We study Higgs boson production in exclusive jet bins at possible future 33 and 100 TeV proton-proton colliders. We compare the cross sections obtained using fixed-order perturbation theory with those obtained by also resuming large logarithms induced by the jet-binning in the gluon-fusion and associated production channels. The central values obtained by the best-available fixed-order predictions differ by $10-20\%$ from those obtained after including resummation over the majority of phase-space regions considered. Additionally, including the resummation dramatically reduces the residual scale variation in these regions, often by a factor of two or more. We further show that in several new kinematic regimes that can be explored at these high-energy machines, the inclusion of resummation improvement is mandatory.

hep-ph↗

arXiv2014

Drell-Yan lepton pair production at NNLO QCD with parton showers

We present a simple approach to combine NNLO QCD calculations and parton showers, based on the UNLOPS technique. We apply the method to the computation of Drell-Yan lepton-pair production at the Large Hadron Collider. We comment on possible improvements and intrinsic uncertainties.

hep-ph↗

arXiv2013

Disentangling radiative corrections using high-mass Drell-Yan at the LHC

We present a detailed numerical study of lepton-pair production via the Drell-Yan process above the Z-peak at the LHC. Our results consistently combine next-to-next-to-leading order QCD corrections and next-to-leading order electroweak effects, and include the leading photon-initiated processes using a recent extraction of the photon distribution function. We focus on the effects of electroweak corrections and of photon-photon scattering contributions, and demonstrate which kinematic distributions exhibit sensitivity to these corrections. We show that a combination of measurements allows them to be disentangled and separately determined.

hep-ph↗

arXiv2013

Single soft gluon emission at two loops

We study the single soft-gluon current at two loops with two energetic partons in massless perturbative QCD, which describes, for example, the soft limit of the two-loop amplitude for $gg\to Hg$. The results are presented as Laurent expansions in $ε$ in $D=4-2ε$ spacetime dimension. We calculate the expansion to order $ε^2$ analytically, which is a necessary ingredient for Higgs production at hadron colliders at next-to-next-to-next-to-leading order in the soft-virtual approximation. We also give two-loop results of the single soft-gluon current in ${\cal N}=4$ Super-Yang-Mills theory, and find that it has uniform transcendentality. By iteration relation of splitting amplitudes, our calculations can determine the three-loop single soft-gluon current to order $ε^0$ in ${\cal N}=4$ Super-Yang-Mills theory in the limit of large $N_c$.

hep-ph↗