arXiv subjects

Qingyu Gan

Publications and source records attributed to Qingyu Gan.

18 recordsLinked to original sources

arXiv2026

The Axion-Photon Mixing and the Extragalactic Magnetic Background: Plateau Regimes, Resonances, and Non-Gaussian Boosts

We present an analytical treatment of Axion-Like-Particle (ALP)--photon mixing with extragalactic background light (EBL) attenuation for constant, Gaussian-stochastic, and non-Gaussian magnetic field configurations--with direct implications for Very High Energy (VHE) gamma-ray observations such as LHAASO, HAWC, and CTA experiments. For constant fields, we derive exact probabilities and identify a perturbative plateau regime where photon survival scales as quartic order of magnetic field, isolating the four-point magnetic correlation as a sensitive probe of non-Gaussianity. For Gaussian stochastic fields, we obtain--for the first time--analytical formulas for non-exponential-decay components in the strong-attenuation regime. Contrary to the widely used domain-like model, photon survival is suppressed by 4-6 orders of magnitude, while both conversion and survival probabilities exhibit distinct multi-peak structures from mass-equal resonance, stochastic resonance, and EBL attenuation. Extending to non-Gaussian fields, we show that non-Gaussianity can enhance photon survival by several orders of magnitude relative to the Gaussian case, potentially explaining the unexpectedly VHE photon event observed by LHAASO. Our results demonstrate that stochastic magnetic fields cannot be reduced to domain-like coherence without losing essential physics, and that VHE gamma-ray spectra encode observable information about both the power spectrum and non-Gaussian structure of intergalactic magnetic fields--critical as next-generation observatories push toward PeV sensitivities.

astro-ph.HE↗

arXiv2026

Exotic PeVatrons as sources of ultra-high-energy gamma rays

We explore novel classes of exotic astrophysical sources capable of producing ultra-high-energy gamma rays extending beyond the PeV scale, motivated by quantum gravity scenarios and dark matter phenomenology. These sources include: ultra-spinning black hole vortex-string systems; exotic compact objects such as boson star, axion star and Q-ball. Such Exotica generate powerful magnetic fields through interactions with millicharged dark matter, enabling particle acceleration mechanisms that surpass the energy limits of conventional astrophysical sources like pulsar wind nebulae and supernova remnants. We demonstrate that such exotic PeVatrons could be distributed throughout our Galaxy and may be detectable by current (LHAASO, HAWC) and next-generation (CTA) gamma-ray observatories.

astro-ph.HE↗

arXiv2025

Gravitational waves in minimal Maxwell $f(R)$ gravity

We discuss the conversion mechanism from scalar field to gravitational waves in magnetic background in $f(R)$ gravity minimal coupled to the Maxwell electrodynamics. Applying the conversion in early universe with primordial magnetic field and the neutron star with strong magnetosphere, the generated gravitational waves, converted from the scalar field, exhibit distinct power spectra which can be potentially probed by future experiments such as DECIGO, BBO, CE and ET.

gr-qc↗

arXiv2025

Excess Radiation from Axion-Photon Conversion

Two notable anomalies in radio observations -- the excess radiation in the Rayleigh-Jeans tail of the cosmic microwave background, revealed by ARCADE2, and the twice-deeper absorption trough of the global 21cm line, identified by EDGES -- remain unresolved. These phenomena may have a shared origin, as the enhancement of the 21cm absorption trough could arise from excess heating. We investigate this scenario through the framework of axion-like particles (ALPs), showing that the resonant conversion of ALPs into photons can produce a photon abundance sufficient to resolve both anomalies simultaneously. Our model naturally explains the observed radio excess between 0.4 and 10GHz while also enhances the 21cm absorption feature at 78MHz. Furthermore, it predicts a novel power-law scaling of the radio spectrum above 0.5GHz and an additional absorption trough below 30MHz, which could be verified through cross-detection in upcoming experiments.

astro-ph.CO↗

arXiv2024

Superoscillations in High Energy Physics and Gravity

We explore superoscillations within the context of classical and quantum field theories, presenting novel solutions to Klein-Gordon's, Dirac's, Maxwell's and Einstein's equations. In particular, we illustrate a procedure of second quantization of fields and how to construct a Fock space which encompasses Superoscillating states. Furthermore, we extend the application of superoscillations to quantum tunnelings, scatterings and mixings of particles, squeezed states and potential advancements in laser interferometry, which could open new avenues for experimental tests of Quantum Gravity effects. By delving into the relationship among superoscillations and phenomena such as Hawking radiation, the Black Hole (BH) information and the Firewall paradox, we propose an alternative mechanism for information transfer across the BH event horizon.

hep-th↗

arXiv2024

Resonant Graviton-Photon Conversion with Stochastic Magnetic Field in the Expanding Universe

We investigate graviton-photon oscillations sourced by cosmological magnetic fields from Gertsenshtein effect. We adopt a robust perturbative approach and we find that the conversion probability from graviton to photon can be resonantly enhanced in monochromatic, multi-chromatic and scale invariant spectrum models of stochastic magnetic field fluctuations. In addition, the expansion of the Universe acts as a decoherence factor, which demands a natural discretization scheme along the line of sight. Including also decoherence from cosmic acceleration, we find that conversion probabilities for stochastic magnetic fields are completely different than results predicted from existing magnetic domain-like models in a wide range of magnetic strengths and coherence lengths. Resonances can be tested by radio telescopes as a probe of high frequency gravitational wave sources and primordial magnetogenesis mechanisms.

gr-qc↗

arXiv2022

Dark Energy and Neutrino Superfluids

We show that the neutrino mass, the dark matter and the dark energy can be explained in a unified framework, postulating a new invisible Born-Infeld field, which we name "non-linear dark photon", undergoing a meV-scale dynamical transmutation and coupled to neutrinos. Dark energy genesis is dynamically explained as a byproduct of the dark photon condensation, inducing the bare massless neutrinos to acquire an effective mass around the meV scale. It is fascinating to contemplate the channel induced by the non-linear dark photon leading to the pairing of the non-relativistic neutrinos, hence generating a cosmological superfluid state. As a consequence, the appearance of a light neutrino composite boson is predicted, providing a good cold dark matter candidate. In particular, if our model is enriched by an extra global Lepton number $U_L(1)$ symmetry, then the neutrino pair can be identified with a composite Majoron field with intriguing phenomenological implications for the neutrinoless-double-beta-decay ($0νββ$). Our model carries interesting phenomenological implications since dark energy, dark matter and the neutrino mass are time-varying dynamical variables, as a consequence of the non-linear Born-Infeld interaction terms. Limits arising from PLANCK+SNe+BAO collaborations data are also discussed. Finally, our model allows for an inverse hierarchy of neutrino masses, with interesting implications for the JUNO experiment.

hep-ph↗

arXiv2022

Induced Gravitational Waves from Multi-Sound Speed Resonances during Cosmological Inflation

We explore the possibility of multi-parametric resonances from time varying sound speed during cosmological inflation. In particular, we fix our set-up to the simpler case beyond a single oscillation model already explored in literature: two sinusoidal harmonics around a constant sound speed equal to one. We find that, within the perturbative regime, except for some certain extreme corners of the parameter space, the primordial density spectrum is characterized by two groups of amplified peaks centered around two critical oscillatory frequencies of the sound speed. As a general result, we show that the energy spectrum of the secondary induced GWs from the inflationary era has a single major broad peak, whereas the one from the radiation dominated phase consists of one/two principle peak-like configuration(s) for relatively small/large ratio of two oscillatory frequencies. The GW relic stochastic backgrounds carry a gravitational memory of the parametric resonances during inflation. GW signals from double sound speed resonances can be tested in complementary channels from Pulsar-timing radio-astronomy, space and terrestrial GW interferometers.

astro-ph.CO↗

arXiv2022

The Large High Altitude Air Shower Observatory (LHAASO) Science Book (2021 Edition)

Since the science white paper of the Large High Altitude Air Shower Observatory (LHAASO) published on arXiv in 2019 [e-Print: 1905.02773 (astro-ph.HE)], LHAASO has completed the transition from a project to an operational gamma-ray astronomical observatory LHAASO is a new generation multi-component facility located in Daocheng, Sichuan province of China, at an altitude of 4410 meters. It aims at measuring with unprecedented sensitivity the spectrum, composition, and anisotropy of cosmic rays in the energy range between 10$^{12}$ and 10$^{18}$~eV, and acting simultaneously as a wide aperture (one stereoradiant) continuously operating gamma-ray telescope in the energy range between 10$^{11}$ and $10^{15}$~eV with the designed sensitivity of 1.3\% of the Crab Unit (CU) above 100 TeV. LHAASO's capability of measuring simultaneously different shower components (electrons, muons, and Cherenkov/fluorescence light), will allow it to investigate the origin, acceleration, and propagation of CR through measurement of the energy spectrum, elemental composition, and anisotropy with unprecedented resolution. The remarkable sensitivity of LHAASO will play a key role in CR physics and gamma-ray astronomy for a general and comprehensive exploration of the high energy universe and will allow important studies of fundamental physics (such as indirect dark matter search, Lorentz invariance violation, quantum gravity) and solar and heliospheric physics. The LHAASO Collaboration organized an editorial working group and finished all editorial work of this science book, to summarize the instrumental features and outline the prospects of scientific researches with the LHAASO experiment.

astro-ph.HE↗

arXiv2021

New Massive JT Multi-Gravity and N-Replica of SYK Models

We study a series of powerful correspondences among new multi-gravity extensions of the Jackiw-Teitelboim model, multi-SYK models and multi-Schwarzian quantum mechanics, in the $\rm{(A)dS_{2}/CFT}$ arena. Deploying a $BF$-like formulation of the model, we discuss the counting of the degrees of freedom for some specific classes of multi-gravity potentials, and unveil connections among a variety of apparently different models. Quantization of multi-gravity models can be then achieved from both the Hartle-Hawking no-boundary proposal, the SYK partition function and the spin-foam approaches. We comment on the SYK quantization procedure, and deepen in the appendix the quantization scheme naturally achieved in the $BF$ framework. The new multi-gravity theory hence recovered presents intriguing applications for analogue gravitational models developed for condensed matter physics, including graphene, endowed with defects and high intensity magnetic fields.

hep-th↗

arXiv2021

Photon Ring and Observational Appearance of a Hairy Black Hole

Recently, the image of a Schwarzschild black hole with an accretion disk has been revisited, and it showed that the "photon ring", defined as highly bent light rays that intersect the disk plane more than twice, is extremely narrow and makes a negligible contribution to the total brightness. In this paper, we investigate the observational appearance of an optically and geometrically thin accretion disk around a hairy black hole in an Einstein-Maxwell-scalar model. Intriguingly, we find that in a certain parameter regime, due to an extra maximum or an "ankle-like" structure in the effective potential for photons, the photon ring can be remarkably wide, thus making a notable contribution to the flux of the observed image. In particular, there appears a wide and bright annulus, which comprises multiple concentric bright thin rings with different luminosity, in the high resolution image.

gr-qc↗

arXiv2021

Photon Spheres and Spherical Accretion Image of a Hairy Black Hole

In this paper, we first consider null geodesics of a class of charged, spherical and asymptotically flat hairy black holes in an Einstein-Maxwell-scalar theory with a non-minimal coupling for the scalar and electromagnetic fields. Remarkably, we show that there are two unstable circular orbits for a photon in a certain parameter regime, corresponding to two unstable photon spheres of different sizes outside the event horizon. To illustrate the optical appearance of photon spheres, we then consider a simple spherical model of optically thin accretion on the hairy black hole, and obtain the accretion image seen by a distant observer. In the single photon sphere case, only one bright ring appears in the image, and is identified as the edge of the black hole shadow. Whereas in the case with two photon spheres, there can be two concentric bright rings of different radii in the image, and the smaller one serves as the boundary of the shadow, whose radius goes to zero at the critical charge.

gr-qc↗

arXiv2020

NANOGrav results and Dark First Order Phase Transitions

The recent NANOGrav evidence of a common-source stochastic background provides a hint to Gravitational Waves (GW) radiation from the Early Universe. We show that this result can be interpreted as a GW spectrum produced from First Order Phase Transitions (FOPTs) around a temperature in the KeV-MeV window. Such a class of FOPTs at temperatures much below the electroweak scale can be naturally envisaged in several Warm Dark Matter models such as Majoron Dark Matter.

hep-ph↗

arXiv2019

Strong cosmic censorship for a scalar field in an Einstein-Maxwell-Gauss-Bonnet-de Sitter black hole

It has been shown that the Christodoulou version of the Strong Cosmic Censorship (SCC) conjecture can be violated for a scalar field in a near-extremal Reissner-Nordstrom-de Sitter black hole. In this paper, we investigate the effects of higher derivative corrections to the Einstein-Hilbert action on the validity of SCC, by considering a neutral massless scalar perturbation in 5- and 6-dimensional Einstein-Maxwell-Gauss-Bonnet-de Sitter black holes. Our numerical results exhibit that the higher derivative term plays a different role in the d = 5 case than it does in the d = 6 case. For d = 5, the SCC violation region increases as the strength of the higher derivative term increases. For d = 6, the SCC violation region first increases and then decreases as the higher derivative correction becomes stronger, and SCC can always be restored for a black hole with a fixed charge ratio when the higher derivative correction is strong enough. Finally, we find that the C2 version of SCC is respected in the d = 6 case, but can be violated in some near-extremal regime in the d = 5 case.

gr-qc↗

arXiv2019

Strong Cosmic Censorship for a Scalar Field in a Logarithmic-de Sitter Black Hole

It has been shown that the quasinormal modes of perturebated fields can be used to investigate the validity of strong cosmic censorship (SCC). Relevant issues for Reissner-Nordstrom-de Sitter (RNdS) black holes and Born-Infeld-de Sitter (BI-dS) black holes have been discussed. In this paper, we investigate SCC in an asymptotic RN-dS black hole with logarithmic nonlinear electromagnetic field perturbed by massless scalar fields. It has been argued that SCC can be violated in a near-extremal RN-dS black hole. However, we find that the NLED effect can rescue SCC for a near-extremal logarithmic-de Sitter black hole. Compared with Born-Infeld model, we find that the NLED effect have similar behavior.

gr-qc↗

arXiv2019

Strong Cosmic Censorship for a Scalar Field in a Born-Infeld-de Sitter Black Hole

It has been shown that the Strong Cosmic Censorship (SCC) can be violated by a scalar field in a near-extremal Reissner-Nordstrom-de Sitter black hole. In this paper, we investigate the Strong Cosmic Censorship in a Born-Infeld-de Sitter black hole by a scalar perturbation field with/without a charge. When the Born-Infeld parameter b becomes small, the nonlinear electrodynamics effect starts to play an important role and tends to rescue SCC. Specifically, we find that the SCC violation region decreases in size with decreasing b. Moreover, for a sufficiently small b, SCC can always be restored in a near-extremal Born-Infeld-de Sitter black hole with a fixed charge ratio.

hep-th↗

arXiv2018

Temperature Dependence of In-plane Resistivity and Inverse Hall Angle in NLED Holographic Model

In the strange metal phase of the high-$T_{c}$ cuprates, it is challenging to explain the linear temperature dependence of the in-plane resistivity and the quadratic temperature dependence of the inverse Hall angle. In this paper, we investigate the temperature dependence of the in-plane resistivity and inverse Hall angle in the nonlinear electrodynamics holographic model developed in our recent work. Maxwell electrodynamics and Born-Infeld electrodynamics are considered. Both cases support a wide spectrum of temperature scalings in parameter space. For Maxwell electrodynamics, the T-linear in-plane resistivity generally dominates at low temperatures and survives into higher temperatures in a narrow strip-like manner. Meanwhile, the T-quadratic inverse Hall angle dominates at high temperatures and extends down to lower temperatures. The overlap between the T-linear in-plane resistivity and the T-quadratic inverse Hall angle, if occurs, would generally present in the intermediate temperate regime. The Born-Infeld case with $a>0$ is quite similar to the Maxwell case. For the Born-Infeld case with $a<0$, there can be a constraint on the charge density and magnetic field. Moreover, the overlap can occur for strong charge density.

hep-th↗

arXiv2016

The modified first laws of thermodynamics of anti-de Sitter and de Sitter space-times

We modify the first laws of thermodynamics of a Reissner-Nordstrom anti-de Sitter black hole and a pure de Sitter space-time by the surface tensions. The corresponding Smarr relations are obeyed. The cosmological constants are first treated as fixed constants, and then as variables associated to the pressures. For the black hole, the law is written as $δE = T δS - σδA$ when the cosmological constant is fixed, where $E$ is the Misner-Sharp mass and $σ$ is the surface tension. Adopting the varied constant, we modify the law as $δE_0 = T δS - σ_{eff}δA +VδP$, where $E_0=M-\frac{Q^2}{2r_+}$ is the enthalpy. The thermodynamical properties are investigated. For the de Sitter space-time, the expressions of the modified laws are different from these of the black hole. The differential way to derive the law is discussed.

hep-th↗