arXiv subjects

H. Lu

Publications and source records attributed to H. Lu.

At least 37 records · Page 2Linked to original sources

arXiv2025

Odd-dimensional Extremal Rotating Black Holes with All Equal Angular Momenta and Small Electric Charges

We consider Einstein-Maxwell gravity in diverse dimensions and construct the small charge perturbation to the extremal rotating black holes with all equal angular momenta in odd $D=2n+1$ dimensions. Exact solutions exist at the next-to-leading order (NLO), and they are analytic, allowing us to obtain the charge corrections to thermodynamic quantities at this order. Irrational exponents in the near-horizon power-series expansion emerge at the next-to-next-to-leading order (NNLO). We show, by numerical computation, that these horizon geometries can indeed be integrated out to asymptotic Minkowski spacetime, thereby proving the existence of the unusual singular horizon behavior of the extremal charged rotating black holes.

hep-th↗

arXiv2025

Black Hole Thermodynamics without Black Hole Solutions

We consider the string-theory inspired Einstein-Maxwell-Maxwell-dilaton theory (EMMD) and show that we can derive the complete set of thermodynamic quantities of charged black holes, without having to solve for the black hole solutions. We argue that the technique can be applied more broadly to string theories, providing an accessible method for determining the thermodynamic properties of large classes of black holes for which exact solutions are typically unavailable.

hep-th↗

arXiv2025

Gravitational Collapse: Generalizing Oppenheimer-Snyder and a Conjecture on Horizon Formation Time

We generalize the Oppenheimer-Snyder model of gravitational collapse by considering a broader class of static, spherically symmetric exterior spacetimes, with an interior geometry described by a Friedmann-Lemaitre-Robertson-Walker (FLRW) geometry. Using Painleve-Gullstrand (PG) coordinates for the spatially flat interior geometry (k=0) and a Novikov-like coordinate system for the spatially closed geometry (k=1), we ensured a smooth transition between the interior and exterior of the collapsing star. By providing general formulas, we analyzed how apparent and event horizons form during the collapse and checked whether the matter satisfies standard energy conditions. For both k=0 and k=1 cases, we studied explicit examples such as Schwarzschild, Schwarzschild-AdS/dS, and Reissner-Nordstrom (RN) black holes, taking into account the effects of the cosmological constant and electric charge. These factors significantly influence the collapse process and can impose constraints on the physical parameters. Our analysis leads to two important results: First, to form a black hole, there is a minimum or critical initial radius for the star to begin collapsing. Second, we propose a conjecture of an inequality regarding the event horizon formation time, starting from the critical radius, namely Delta T_eh <= 19M/6. The upper bound is saturated by the Schwarzschild black hole.

gr-qc↗

arXiv2025

Black Hole Mass/Charge Relation and Weak No-hair Theorem Conjecture

We consider Einstein gravity minimally coupled to two Maxwell fields and one (real) dilaton scalar. We study the electrically-charged spherically-symmetric and static solutions that are asymptotic to Minkowski spacetime. General solutions are described by four independent parameters: mass $M$, two electric charges $(Q_1,Q_2)$ and the scalar charge $Σ$. For black holes, the scalar charge is not independent, but a function of $(M,Q_1,Q_2)$. We provide a set of formulae relating the mass to the charges, which allows us to determine $Σ(M,Q_1,Q_2)$ without having to solve the black hole equations. Our results confirm the weaker version of the no-hair theorem conjecture involving one real scalar: it can be turned on in a black hole, but it does not have a continuous independent hairy parameter.

hep-th↗

arXiv2025

Threshold $J/ψ$ Photoproduction as a Probe of Nuclear Gluon Structure

The nuclear EMC effect is the observation that quark distributions in bound nucleons experience significant modification at large $x$ relative to free nucleons. Despite decades of measurements verifying the presence of this effect in quarks across a wide range of nuclei, behavior of large-$x$ gluons in nuclei remains almost completely unknown. As the nuclear physics community seeks out new observables to try to elucidate the mechanisms behind the EMC effect, it becomes striking that we remain ignorant regarding the impact of nuclear effects on gluonic behavior. Recent photonuclear data using the Hall D photon beam have enabled the first measurement of $J/ψ$ photoproduction from nuclei near and below the energy threshold, with the results highlighted in Physical Review Letters as an Editors' Suggestion. These data have placed the first, and currently only, constraints on the behavior of large-$x$ gluons within bound nucleons. However, compared to the quantity of data which currently informs our knowledge of the quark-sector EMC effect, these data are extremely limited, and remain unable to conclusively observe or exclude large modification of gluon distributions. A high-luminosity photonuclear experiment will enable a precision measurement of incoherent $J/ψ$ photoproduction at and below the threshold region. This data will provide the first stringent constraints on nuclear modification of gluon structure or other exotic effects which could impact the production of $J/ψ$ from nuclei. We request 85 PAC days at Hall D using the GlueX detector with a 12 GeV electron beam energy and a coherent photon peak energy of $8$ GeV, split into 80 days using a $^4$He target and 5 calibration days using a $^2$H target.

nucl-ex↗

arXiv2025

Desclarizing the Wormhole to Black Hole with Negative Mass

We construct new black holes using the curvature-induced scalarization mechanism in Einstein gravity coupled to a massless phantom scalar. We find that the general wormhole solutions with independent scalar charge become descalarized so that the resulting black hole scalar hair becomes secondary and a function of the mass only. The long-range force between the two identical black holes can be attractive, zero or repulsive, depending on the mass/scalar charge relation. Furthermore, the black hole mass can be negative. Our finding suggests that exotic matter responsible for wormholes can also lead to exotic black holes.

gr-qc↗

arXiv2025

Effect of construction steels on PMTs detection efficiency at JUNO

We study the impact of the carbon steel rebars and the steel TT bridge within the JUNO structure on the shielding effect of the coils. Our simulations demonstrate that despite the presence of carbon steel structures of the rebars of the water pool and the TT bridge within the central detector vicinity, the residual magnetic field experienced by the PMTs remains within the acceptable limit established by the JUNO experiment of 10% for CD-PMTs and 20% for Veto-PMTs, compared to the geomagnetic field. The maximum magnetic fields experienced by the CD-PMTs and Veto-PMTs are 9% and 18% of the geomagnetic field strength, respectively. These findings indicate that the residual magnetic field has minimal impacts on the PMTs detection efficiency.

physics.ins-det↗

arXiv2025

Black Hole Entropy Bounded by the Specific Heat

We propose new bounds on black hole entropy in terms of the specific heat at fixed charges. For special spherically-symmetric and static black holes ($g_{tt} g_{rr}=-1$), we prove the bounds with suitable sufficient energy conditions. For more general static and rotating black holes, we test the bounds with a variety of examples. This work extends the previously-known algebraic inequalities of the black hole thermodynamic variables such as the Penrose inequality, to include their derivatives.

gr-qc↗

arXiv2025

Instanton Moduli, Topology and the Bosonic/Heterotic String Origins

We construct new supersymmetric NS(-1)-branes supported by the $SU(2)\times SU(2)$ 't Hooft instantons in ${\cal N}=1$, $D=4$ supergravity. We show that although the magnetic 3-form string flux is invariant under the variation of instanton moduli, the string-frame metric can change topology, giving rise to either $\mathbb R^4$ or the new $\mathbb R\times S^3$ bolt topologies. We uplift the solutions to both heterotic and bosonic strings, where the instanton moduli become parameters of pure geometry. We find that the Killing spinors exist in both theories. The transformation of the Killing spinors from one theory to the other is consistent with the recently proposed bosonic/heterotic string duality. We further construct new BPS solutions in the $D=6$ Salam-Sezgin model, employing the technique developed in the paper.

hep-th↗

arXiv2025

Leading Higher Derivative Corrections to Multipole Moments of Kerr-Newman Black Hole

We study the (leading) 4-derivative corrections, including both parity even and odd terms, to electrically-charged Kerr-Newman black holes. The linear perturbative equations are then solved order by order in terms of two dimensionless rotating and charge parameters. The solution allows us to extract the multipole moments of mass and current from the metric as well as the electric and magnetic multipole moments from the Maxwell field. We find that all the multipole moments are invariant under the field redefinition, indicating they are well-defined physical observables in this effective theory approach to quantum gravity. We also find that parity-odd corrections can turn on the multipole moments that vanish in Einstein theory, which may have significant observational implications.

hep-th↗

arXiv2025

New BPS States from Bosonic/Heterotic Duality

In this paper, we consider the recently proposed bosonic/heterotic duality that relates the heterotic superstrings to the noncritical bosonic string. Although the latter is nonsupersymmetric, it can be viewed as pseudo-supersymmetric in that the theory admits a consistent set of Killing spinor equations whose integrability conditions are satisfied by the equations of motion. We construct two classes of the dual pairs of BPS and pseudo-BPS solutions in the respective heterotic and bosonic strings and obtain their explicit Killing spinors. The existence of such dual pairs lends support to the proposed duality.

hep-th↗

arXiv2025

Weak Cosmic Censorship Conjecture in Gedanken Experiments at All Orders

We present a systematic analysis of the Weak Cosmic Censorship Conjecture (WCCC) through Gedankenexperiments involving black hole perturbations induced by test particles. Our approach allows for the calculation of perturbations to any order for a general class of black holes that admit the zero-temperature extremal limit. We find that the WCCC for extremal and near-extremal black holes is hinged upon the positive sign of only one quantity, namely $W=\left( \frac{\partial S}{\partial T} \right)_{Q_α; T=0}$, which is indeed positive for all the well-known black holes.

gr-qc↗

arXiv2025

Consistent Warped $\mathbb R\times T^{1,1}$ Reduction of Heterotic Supergravity

We find a curious duality between the bosonic sector of heterotic supergravity and the noncritical bosonic string with conformal anomaly. This allows us to map the Mink$_4\times S^3\times S^3$ vacuum of the bosonic string to a new warped $\mathbb R\times (T^{1,1}\times$Mink$_4)$ vacuum of the heterotic theory, which turns out to be supersymmetric, preserving $1/4$ of the supersymmetry. We perform consistent dimensional reduction of the heterotic theory on the warped $\mathbb R\times T^{1,1}$ internal space and obtain ${\cal N}=1$, $D=4$ supergravity, with one complex scalar multiplet and $SU(2)\times SU(2)$ Yang-Mills multiplets, where the gauge symmetry is originated from the isometry group of $T^{1,1}$.

hep-th↗

arXiv2024

Weak Cosmic Censorship Conjecture Cannot be Violated in Gedanken Experiments

We innovate a systematic investigation of the Weak Cosmic Censorship Conjecture (WCCC) using gedanken experiments involving black hole perturbations by test particles. We classify various WCCC violation scenarios proposed in recent decades, including Hubeny, mixed, and the latest Sorce-Wald (SW). We provide general formulae in each case, and resolve contradictions in numerous studies. Following SW type, our analysis reveals that WCCC depends on the sign choice of the parameter $W\equiv \big(\frac{\partial S}{\partial T}\big)_{Q_i; T=0}$ of the extremal black holes. $W > 0$ preserves WCCC and $W < 0$ would indicate potential violation. We show explicitly that $W>0$ for spherically-symmetric and static black holes, and for general case, we argue that it is protected by the black hole no-hair theorem. We also consider asymptotically-(A)dS black holes and argue that there can be no violation either.

gr-qc↗

arXiv2024

Holographic Weyl Anomaly in 8d from General Higher Curvature Gravity

We calculate the holographic central charges for general higher curvature gravity theory dual to eight dimensional CFT. To do this, we first elaborate the general form of Weyl anomaly in 8d CFT and find 11 non-trivial linearly independent curvature combinations, one of which is Euler density and the rest are Weyl invariants, including 7 non-differentiated ones and 3 differentiated ones. The Weyl invariants are constructed as invariant polynomials of curvature tensor and covariant derivatives. We denote $W_{(n)}$ as the Weyl invariant that contains a polynormial term with a minimum of $n$ curvature tensors. Interestingly, since there are a total of 12 Weyl invariants in 8d, our finding means two of them are trivial and expressible as total derivatives. The resulting central charges are expressed in terms of 15 theory-dependent constants. Remarkably, we find that the $W_{(2)}$ invariant corresponds to the $c$-charge that is proportional to $C_T$, while the two $W_{(3)}$'s are related to three-point function parameters of energy-momentum tensor. This suggests a possible connection between the $c$-charges of $W_{(n)}$'s and the $n$-point functions of energy-momentum tensor.

hep-th↗

arXiv2024

Taub-NUT Black Hole in Higher Derivative Gravity and Its Thermodynamics

We construct the first-order perturbative Taub-NUT black hole solutions in Einstein gravity extended with a cubic curvature invariant. The corrected thermodynamic quantities are then obtained by the standard method and the first law and Smarr relation are satisfied. We also study the perturbative correction to thermodynamics using the Reall-Santos (RS) method and verify that the method is still applicable even though the metrics are no longer asymptotic to Minkowski spacetime. We then apply the RS method to obtain the leading correction to the thermodynamics of the complicated Kerr-Taub-NUT black holes.

gr-qc↗

arXiv2024

Charging the Love numbers: Charged scalar response coefficients of Kerr-Newman black holes

We study the electrically-charged massless scalar response to the general Kerr-Newman black hole and obtain the exact (complex) response coefficients, whose real parts are the Love numbers. We find there is a curious discontinuity between the neutral and charged scalar. The Love numbers vanish for the neutral scalar, but are inversely proportional to the electric charge of the scalar in the small charge limit. We study the near-zone of the dynamical equation with non-vanishing frequency $ω$, and show that the system have an $SL(2,\mathbb{R})$ Love-like symmetry. The symmetry selects a special frequency $ω_{\rm cr}$, which vanishes in the neutral case, so that the real part of the response coefficient vanishes identically. We also generalize the results into higher dimensions to some extend.

gr-qc↗

arXiv2024

Giant interfacial Dzyaloshinskii-Moriya Interaction in perovskite La_{0.7}Sr_{0.3}MnO_{3} films

The Dzyaloshinskii-Moriya interaction (DMI) plays a critical role in stabilizing topological spin textures, a key area of growing interest in oxide-based spintronics. While most of reported topological phenomena found in manganites are related to the bulk-like DMI, the understanding of interfacial DMI and its origin in oxide interfaces remain limited. Here we experimentally investigate the interfacial DMI of La_{0.7}Sr_{0.3}MnO_{3} (LSMO) films grown on various substrates by employing spin-wave propagation with drift velocities at room temperature. Our findings reveal a giant interfacial DMI coefficient (\mathit{D} _{s}) of 1.96 pJ/m in LSMO/NdGaO_{3}(110) system, exceeding previously reported values in oxides by one to two orders of magnitude. First-principles calculations further show that with the aid of 6\mathit{s} electrons, the 4\mathit{f} electrons from Nd play a key role in enhancing the spin-orbit coupling of the 3\mathit{d} electrons in Mn, ultimately leading to the observed giant interfacial DMI. This discovery of giant interfacial DMI through engineering the interface of oxides provides valuable insights for advancing functional chiral magnonics and spintronics.

cond-mat.mtrl-sci↗