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Bo-Qiang Ma

Publications and source records attributed to Bo-Qiang Ma.

At least 73 records · Page 4Linked to original sources
arXiv2021

Reinterpretation of proton strangeness between ATLAS and CMS measurements

We reexamine the shapes of the strange quark parton distribution functions (PDFs) of the proton by means of quantum chromodynamics (QCD) analysis of {\hera} deep inelastic scattering cross section measurement at DESY, and inclusive gauge boson production and $W$ boson production associated with a charm quark from LHC at CERN. We find that there is an overall agreement on the strange quark distributions obtained from CMS $W$ + charm and ATLAS $W/Z$ data at the parton momentum fraction range $x \lesssim 10^{-2}$. Meanwhile, there is also a strong tension between these data towards large $x$. We find that this tension fades away if the ATLAS measurement of $W/Z$ production is analyzed together with the ATLAS $W$ + charm data. The $W/Z$ and $W$ + charm data both from ATLAS and CMS experiments agree that the proton strangeness is enhanced towards small momentum fraction $x$ and is smoothly suppressed at large $x$. Furthermore, a strong $x$ dependence of the strange-to-non-strange parton ratio $R_s(x,Q^2)$ is observed.

hep-ph↗
arXiv2021

Novel pre-burst stage of gamma-ray bursts from machine learning

Gamma-ray bursts (GRBs), as extremely energetic explosions in the universe, are widely believed to consist of two stages: the prompt phase and the subsequent afterglow. Recent studies indicate that some high-energy photons are emitted earlier at source than the prompt phase. Due to the light speed variation, these high-energy photons travel slowly than the low-energy photons, so that they are observed after the prompt low-energy photons at the detector. Based on the data from the Fermi Gamma-ray Space Telescope (FGST), we analyse the photon distribution before the prompt emission in detail and propose the existence of a hitherto unknown pre-burst stage of GRBs by adopting a classification method of machine learning. Analysis on the photons automatically selected by machine learning also produce a light speed variation at $E_{\mathrm{LV}}=\mathrm{3.55\times 10^{17} GeV}$.

astro-ph.HE↗
arXiv2021

Light Speed Variation with Brane/String-Inspired Space-Time Foam

Recently a series of studies on high energy gamma-ray burst~(GRB) photons suggest a light speed variation with linear energy dependence at the Lorentz violation scale of $3.6 \times 10^{17}~\mathrm{GeV}$, with subluminal propagation of high energy photons in cosmological space. We propose stringy space-time foam as a possible interpretation for this light speed variation. In such a string-inspired scenario, bosonic photon open-string travels \textit{in vacuo} at an infraluminal speed with an energy dependence suppressed by a single power of the string mass scale, due to the foamy structure of space-time at small scales, as described by D-brane objects in string theory. We present a derivation of this deformed propagation speed of the photon field in the infrared (IR) regime. We show that the light speed variation, revealed in the previous studies on GRBs time-delay data, can be well described within such a string approach towards space-time foam. We also derive the value of the effective quantum-gravity mass in this framework, and give a qualitative study on the theory-dependent coefficients. We comment that stringent constraints on Lorentz violation in the photon sector from complementary astrophysical observations can also be explained and understood in the space-time foam context.

hep-ph↗
arXiv2021

Threshold anomalies of ultra-high energy cosmic photons due to Lorentz invariance violation

From special relativity, photon annihilation process \HepProcess{{\Pgg}{\Pgg}{\to}{\Pep}{\Pem}} prevents cosmic photons with energies above a threshold to propagate a long distance in cosmic space due to their annihilation with low energy cosmic background photons. However, modifications of the photon dispersion relation from Lorentz invariance violation~(LIV) can cause novel phenomena beyond special relativity to happen. In this paper, we point out that these phenomena include optical transparency, threshold reduction and reappearance of ultra-high energy photons in cosmic space. The recent observation of near and above PeV photon events by the LHAASO Collaboration reveals the necessity to consider the threshold anomalies. Future observations of above threshold photons from extragalactic sources can testify LIV properties of photons.

hep-ph↗
arXiv2021

Ultrahigh-energy photons from LHAASO as probes of Lorentz symmetry violations

The Large High Altitude Air Shower Observatory~(LHAASO) is one of the most sensitive gamma-ray detector arrays currently operating at TeV and PeV energies. Recently the LHAASO experiment detected ultra-high-energy~(UHE; $E_γ\gtrsim 100~\mathrm{TeV}$) photon emissions up to $1.4~\mathrm{PeV}$ from twelve astrophysical gamma-ray sources. We point out that the detection of cosmic photons at such energies can constrain the photon self-decay motivated by superluminal Lorentz symmetry violation~(LV) to a higher level, thus can put strong constraints to certain LV frameworks. Meanwhile, we suggest that the current observation of the PeV-scale photon with LHAASO may provide hints to permit a subluminal type of Lorentz violation in the proximity of the Planckian regime, and may be compatible with the light speed variation at the scale of $3.6\times 10^{17}~\mathrm{GeV}$ recently suggested from gamma-ray burst~(GRB) time delays. We further propose detecting PeV photons coming from extragalactic sources with future experiments, based on LV-induced threshold anomalies of $e^{+}e^{-}$ pair-production, as a crucial test of subluminal Lorentz violation. We comment that these observations are consistent with a D-brane/string-inspired quantum-gravity framework, the space-time foam model.

astro-ph.HE↗
arXiv2021

Light Speed Variation in a String Theory Model for Space-Time Foam

We revisit a supersymmetric string model for space-time foam, in which bosonic open-string states, such as photons, can possess quantum-gravity-induced velocity fluctuations in vacuum. We argue that the suggestion of light speed variation with lower bound from gamma-ray burst photon time delays can serve as a support for this string-inspired framework, through connecting the experimental finding with model predictions. We also derive the value of the effective quantum-gravity mass in this framework, and give a qualitative study on the model-dependent coefficients. Constraints from birefringent effects and/or photon decays, including the novel $γ$-decay constraint obtained here from the latest Tibet AS$γ$ near-PeV photon, are also found to be consistent with predictions in such a quantum-gravity scheme. Future observation that can testify further the theory is suggested.

hep-ph↗
arXiv2021

Pre-burst neutrinos of gamma-ray bursters accompanied by high-energy photons

Previous researches on high-energy neutrino events from gamma-ray bursters (GRBs) suggest a neutrino speed variation $v(E)=c(1\pm E/E^ν_{\mathrm{LV}})$ with ${E}^ν_{\rm LV}=(6.4\pm 1.5)\times10^{17}~{ \rm GeV}$, together with an intrinsic time difference ${Δ{t}_{\rm in}=(-2.8\pm 0.7)\times10^2~{\rm s}}$, which means that high-energy neutrinos come out about 300~s earlier than low-energy photons in the source reference system. Considering the possibility that pre-bursts of neutrinos may be accompanied by high-energy photons, in this work we search for high-energy photon events with earlier emission time from 100 to 1000~s before low-energy photons at source by analyzing Fermi Gamma-ray Space Telescope (FGST) data. We perform the searching of photon events with energies larger than 100~MeV, and find 14 events from 48 GRBs with known redshifts. Combining these events with a $1.07~\rm{TeV}$ photon event observed by the Major Atmospheric Gamma Imaging Cherenkov telescopes (MAGIC), we suggest a pre-burst stage with a long duration period of several minutes of high energy neutrino emissions accompanied by high energy photons at the GRB source.

astro-ph.HE↗
arXiv2021

Probing dipole radiation from binary neutron stars with ground-based laser-interferometer and atom-interferometer gravitational-wave observatories

Atom-interferometer gravitational-wave (GW) observatory, as a new design of ground-based GW detector for the near future, is sensitive at a relatively low frequency for GW observations. Taking the proposed atom interferometer Zhaoshan Long-baseline Atom Interferometer Gravitation Antenna (ZAIGA), and its illustrative upgrade (Z+) as examples, we investigate how the atom interferometer will complement ground-based laser interferometers in testing the gravitational dipole radiation from binary neutron star (BNS) mergers. A test of such kind is important for a better understanding of the strong equivalence principle laying at the heart of Einstein's general relativity. To obtain a statistically sound result, we sample BNS systems according to their merger rate and population, from which we study the expected bounds on the parameterized dipole radiation parameter $B$. Extracting BNS parameters and the dipole radiation from the combination of ground-based laser interferometers and the atom-interferometer ZAIGA/Z+, we are entitled to obtain tighter bounds on $B$ by a few times to a few orders of magnitude, compared to ground-based laser interferometers alone, ultimately reaching the levels of $|B| \lesssim 10^{-9}$ (with ZAIGA) and $|B| \lesssim 10^{-10}$ (with Z+).

gr-qc↗
arXiv2021

Pre-burst events of gamma-ray bursts with light speed variation

Previous researches on high-energy photon events from gamma-ray bursts~(GRBs) suggest a light speed variation $v(E)=c(1-E/E_{\mathrm{LV}})$ with $E_{\mathrm{LV}}=3.6\times10^{17}~\mathrm{ GeV}$, together with a pre-burst scenario that hight-energy photons come out about 10 seconds earlier than low-energy photons at the GRB source. However, in the Lorentz invariance violating scenario with an energy dependent light speed considered here, high-energy photons travel slower than low-energy photons due to the light speed variation, so that they are usually detected after low-energy photons in observed GRB data. Here we find four high-energy photon events which were observed earlier than low-energy photons from Fermi Gamma-ray Space Telescope~(FGST), and analysis on these photon events supports the pre-burst scenario of high energy photons from GRBs and the energy dependence of light speed listed above.

astro-ph.HE↗
arXiv2021

Stringent Tests of Gravity with Highly Relativistic Binary Pulsars in the Era of LISA and SKA

At present, 19 double neutron star (DNS) systems are detected by radio timing and 2 merging DNS systems are detected by kilo-hertz gravitational waves. Because of selection effects, none of them has an orbital period $P_b$ in the range of a few tens of minutes. In this paper we consider a multimessenger strategy proposed by Kyutoku et al. (2019), jointly using the Laser Interferometer Space Antenna (LISA) and the Square Kilometre Array (SKA) to detect and study Galactic pulsar-neutron star (PSR-NS) systems with $P_b \sim$ 10-100 min. We assume that we will detect PSR-NS systems by this strategy. We use standard pulsar timing software to simulate times of arrival of pulse signals from these binary pulsars. We obtain the precision of timing parameters of short-orbital-period PSR-NS systems whose orbital period $P_b \in (8,120)\,$min. We use the simulated uncertainty of the orbital decay, $\dot{P}_{b}$, to predict future tests for a variety of alternative theories of gravity. We show quantitatively that highly relativistic PSR-NS systems will significantly improve the constraint on parameters of specific gravity theories in the strong field regime. We also investigate the orbital periastron advance caused by the Lense-Thirring effect in a PSR-NS system with $P_b = 8\,$min, and show that the Lense-Thirring effect will be detectable to a good precision.

astro-ph.HE↗
arXiv2021

Searching for lepton number violating $Λ$ baryon decays mediated by GeV-scale Majorana neutrino with LHCb

We consider the lepton-number-violating processes in $Λ_b$/$Λ_c$ decays mediated by on-shell GeV-scale sterile neutrino. We calculate the branching ratio for the following processes: $Λ_b^{0} \rightarrow \mathcal{B}^+ μ^{-}μ^- π^+$, where $\mathcal{B}^+$ is $Λ_c^+$ or proton, and $Λ_c^{+} \rightarrow Λμ^{+}μ^+ π^-$, as function of the mass of the sterile neutrino $m_N$ and the heavy-light mixing coefficient of the extended Pontecorvo-Maki-Nakagawa-Sakata (PMNS) matrix $|U_{μN}|^2$. The effect of finite detector size is included in our calculation. After comparing the theoretical effective branching ratio with the expected experimental ability of LHCb, we give the sensitivity upper bounds on $|U_{μN}|^2$ on the ($|U_{μN}|^2$-$m_N$) plane. These channels give comparable results with the bounds given by different search strategies (e.g., at Belle, NuTeV, DELPHI and BEBC) in the mass region $m_N \simeq$ 0.25 GeV - 4.5 GeV, and the limits are stronger in the mass range 2 GeV $<m_N<$ 4.5 GeV.

hep-ph↗
arXiv2020

Light speed variation from active galactic nuclei

Recent studies on the high-energy photons from gamma-ray bursts~(GRBs) suggested a light speed variation $v(E)=c(1-E/E_{\mathrm{LV}})$ with $E_\mathrm{LV}=3.6\times 10^{17}$ GeV. We check this speed variation from previous observations on light curves of three active galactic nuclei (AGNs), namely Markarian 421 (Mrk 421), Markarian 501 (Mrk 501) and PKS 2155-304. We show that several phenomena related to the light curves of these AGNs can serve as the supports for the light speed variation determined from GRBs.

astro-ph.HE↗
arXiv2020

Tests of conservation laws in post-Newtonian gravity with binary pulsars

General relativity is a fully conservative theory, but there exist other possible metric theories of gravity. We consider non-conservative ones with a parameterized post-Newtonian (PPN) parameter, $ζ_2$. A non-zero $ζ_2$ induces a self-acceleration for the center of mass of an eccentric binary pulsar system, which contributes to the second time derivative of the pulsar spin frequency, $\ddotν$. In our work, using the method in Will (1992), we provide an improved analysis with four well-timed, carefully-chosen binary pulsars. In addition, we extend Will's method and derive $ζ_2$'s effect on the third time derivative of the spin frequency, $\dddotν$. For PSR B1913+16, the constraint from $\dddotν$ is even tighter than that from $\ddotν$. We combine multiple pulsars with Bayesian inference, and obtain an upper limit, $\left|ζ_{2}\right|<1.3\times10^{-5}$ at 95% confidence level, assuming a flat prior in $\log_{10} \left| ζ_{2}\right|$. It improves the existing bound by a factor of three. Moreover, we propose an analytical timing formalism for $ζ_2$. Our simulated times of arrival with simplified assumptions show binary pulsars' capability in limiting $ζ_{2}$, and useful clues are extracted for real data analysis in future. In particular, we discover that for PSRs B1913+16 and J0737$-$3039A, $\dddotν$ can yield more constraining limits than $\ddotν$.

gr-qc↗
arXiv2019

Reduced-order surrogate models for scalar-tensor gravity in the strong field and applications to binary pulsars and GW170817

We investigate the scalar-tensor gravity of Damour and Esposito-Farèse (DEF), which predicts non-trivial phenomena in the nonperturbative strong-field regime for neutron stars (NSs). Instead of solving the modified Tolman-Oppenheimer-Volkoff equations, we construct reduced-order surrogate models, coded in the pySTGROM package, to predict the relations of a NS radius, mass, and effective scalar coupling to its central density. Our models are accurate at $\sim1\%$ level and speed up large-scale calculations by two orders of magnitude. As an application, we use pySTGROM and Markov-chain Monte Carlo techniques to constrain parameters in the DEF theory, with five well-timed binary pulsars, the binary NS (BNS) inspiral GW170817, and a hypothetical BNS inspiral in the Advanced LIGO and next-generation GW detectors. In the future, as more binary pulsars and BNS mergers are detected, our surrogate models will be helpful in constraining strong-field gravity with essential speed and accuracy.

gr-qc↗
arXiv2019

A Proof of First Digit Law from Laplace Transform

The first digit law, also known as Benford's law or the significant digit law, is an empirical phenomenon that the leading digit of numbers from real world sources favors small ones in a form $\log(1+{1}/{d})$, where $d=1, 2, ..., 9$. Such a law keeps elusive for over one hundred years because it was obscure whether this law is due to the logical consequence of the number system or some mysterious mechanism of the nature. We provide a simple and elegant proof of this law from the application of the Laplace transform, which is an important tool of mathematical methods in physics. We reveal that the first digit law is originated from the basic property of the number system, thus it should be attributed as a basic mathematical knowledge for wide applications.

stat.OT↗
arXiv2019

Consistent Lorentz violation features from near-TeV IceCube neutrinos

A recent proposal to associate 60~TeV to 2~PeV IceCube neutrino events with gamma-ray bursts~(GRBs) indicates the Lorentz violation of cosmic neutrinos and leads further to the $CPT$ symmetry violation between neutrinos and antineutrinos. Here we find that another 12 northern hemisphere track events possibly correlated with GRBs from three-year IceCube data satisfy the same regularity at a lower energy scale around 1~TeV. The combined fitting indicates a Lorentz violation scale ${E}_{\rm LV}=(6.4\pm 1.5)\times10^{17}~{ \rm GeV}$ and an intrinsic time difference ${Δ{t}_{\rm in}=(-2.8\pm 0.7)\times10^2~{\rm s}}$, from which we find an earlier emission of neutrinos than photons at the GRB source. We also suggest analyzing neutrino events detected a few minutes before the GRB trigger time to test the $CPT$ violation of ultrahigh-energy neutrinos.

hep-ph↗
arXiv2019

Bounding the mass of graviton in a dynamic regime with binary pulsars

In Einstein's general relativity, gravity is mediated by a massless spin-2 metric field, and its extension to include a mass for the graviton has profound implication for gravitation and cosmology. In 2002, Finn and Sutton used the gravitational-wave (GW) back-reaction in binary pulsars, and provided the first bound on the mass of graviton. Here we provide an improved analysis using 9 well-timed binary pulsars with a phenomenological treatment. First, individual mass bounds from each pulsar are obtained in the frequentist approach with the help of an ordering principle. The best upper limit on the graviton mass, $m_{g}<3.5\times10^{-20} \, {\rm eV}/c^{2}$ (90% C.L.), comes from the Hulse-Taylor pulsar PSR B1913+16. Then, we combine individual pulsars using the Bayesian theorem, and get $m_{g}<5.2\times10^{-21} \, {\rm eV}/c^{2}$ (90% C.L.) with a uniform prior for $\ln m_g$. This limit improves the Finn-Sutton limit by a factor of more than 10. Though it is not as tight as those from GWs and the Solar System, it provides an independent and complementary bound from a dynamic regime.

astro-ph.CO↗