In this study, we investigate the possibility of enhancing the di-jet resonance searches by tagging the final state radiation (FSR) jet using an event-level deep neural network. It is found that solely relying on the 4-momenta of the leading three jets allows the algorithm to achieve good discriminating power that can identify the hardest FSR jet in the signal while rejecting other soft jets. Once the invariant mass is corrected with the tagged FSR jet, the mass resolution of the signal is greatly enhanced, and the sensitivity of the search is also improved by more than 10%. By crafting the input variables carefully, the algorithm introduces minimal mass sculpting for the background, and its applicability extends to a broad mass range. This work proves that FSR jet tagging can potentially enhance di-jet resonance searches, suiting various stages of the physics programmes at the Large Hadron Collider (LHC) and High-Luminosity LHC (HL-LHC).

China

Bingxuan Liu

Yuxuan Shen

Yuanshunzi Sui

Enhancing di-jet resonance searches via a final-state radiation jet tagging algorithm * Bingxuan Liu is supported by Shenzhen Campus of the Sun Yat-sen University under project 74140-12255011, and by the Young Scientists Fund (C Class) of the National Natural Science Foundation of China (12405122). Both Yuxuan Shen and Yuanshunzi Sui are supported by College Students’ Innovative Entrepreneurial Training Plan Program

This study presents a detailed investigation of the dynamics of massless test particles (photons) to analyze the stability of null circular geodesics around the Kerr–Sen black hole (KSBH) spacetime. KSBH is a new solution arising in the low-energy effective field theory of heterotic string theory. The analysis proceeds by obtaining the radial effective potential, which serves as the foundation for calculating the Lyapunov exponent, a central quantity used to describe the stability or instability of geodesic motion in dynamical systems. The study employs the Lyapunov exponent approach to determine the stability or instability of circular orbits under varying values of the charge parameter $\textit{Q}$ and Kerr parameter $\textit{a}$. Additionally, the analytical expressions for the radius of circular photon orbits and the corresponding impact parameter, defined as the ratio of conserved angular momentum to energy are also derived explicitly. To further analyze the orbital behavior, techniques such as Poincaré maps, the Lyapunov Exponent, and FLI are utilized to distinguish between regular and chaotic trajectories. The sign and magnitude of the Lyapunov exponent provide a rigorous criterion to distinguish between stable and unstable circular orbits. These results contribute to a deeper understanding of the geodesic structure and perturbative stability in string-inspired rotating charged black hole backgrounds. The findings are also compared with those of the KBH case to highlight the impact of the BH charge on the stability of null geodesics. This study provides deeper insights into the dynamical properties of null geodesics in charged rotating BH spacetimes in GR and alternative theory of gravity.

India

Pradeep Singh

Hemwati Nandan

Shubham Kala

Nidhi Handa

Lokesh Joshi

Azerbaijan

G. Mustafa

Probing strong-gravity chaos and stability of circular photon orbits around the Kerr–Sen black hole

<p>Four-derivative heterotic supergravity (without gauge fields) reduced on a <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>p</mi></math>-dimensional torus leads to half-maximal supergravity coupled to <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>p</mi></math> vector multiplets, and it is known that removing the vector multiplets is a consistent truncation of the theory. We find a new consistent truncation of four-derivative heterotic supergravity on a torus that keeps the vector multiplets and precisely reproduces the bosonic action of heterotic supergravity (with heterotic gauge fields). We show that both truncations have an <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>O</mi><mo stretchy="false">(</mo><mi>d</mi><mo>+</mo><mi>p</mi><mo>,</mo><mi>d</mi><mo stretchy="false">)</mo></math> symmetry when reduced on a <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>d</mi></math>-dimensional torus and demonstrate how this embeds in the <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>O</mi><mo stretchy="false">(</mo><mi>d</mi><mo>+</mo><mi>p</mi><mo>,</mo><mi>d</mi><mo>+</mo><mi>p</mi><mo stretchy="false">)</mo></math> symmetry that one gets from reducing on a (<math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><mi>d</mi><mo>+</mo><mi>p</mi></mrow></math>)-dimensional torus without truncation. We then use our new truncation to obtain four-derivative corrections to the Kerr-Sen solution and compute thermodynamic quantities and multipole moments. Finally, we compare the Kerr-Sen solutions of the actions corresponding to the two different choices of truncation with the Kerr solution, the Kerr-Newman solution, and each other, and show that they have distinct four-derivative multipole structures.</p>

Minghao Xia

Liang Ma

Yi Pang

Robert J. Saskowski

Consistent four-derivative heterotic truncations and the Kerr-Sen solution

We obtain the four-derivative corrections to the Kerr-Sen solution in heterotic supergravity, which includes the Gibbons-Maeda-Garfinkle-Horowitz-Strominger solution as a limiting case. In particular, we first embed the Kerr solution into heterotic supergravity and compute the higher-derivative corrections. We then obtain the corrections to the Kerr-Sen solution by performing an $\textit{O}$(1, 2) boost of the Kerr solution, which, in contrast to the two-derivative case, requires field redefinitions to make the $\textit{O}$(1, 2) invariance of the action manifest. Finally, we compute the multipole moments and find that they are distinct from those of the Kerr solution at the four-derivative level. We also find that the multipole moments are distinct from those of the Kerr-Newman solution in Einstein-Maxwell theory at the four-derivative level, even for the most general choice of four-derivative corrections. This gives a way to experimentally distinguish traces of string theory in gravitational wave data.

Peng-Ju Hu

Robert Saskowski

Higher-derivative heterotic Kerr-Sen black holes

The 2HDM+S is the singlet extension of the two-Higgs-doublet model (2HDM). The singlet field and its mixing with the 2HDM Higgs sector lead to new contributions to the electroweak precision observables, in particular, the oblique parameters. In this study, we performed a systematic investigation of the impacts of each mixing angle on the oblique parameters. We adopted the mixing angles and physical Higgs masses as our parameters, which allow a mapping when a specific symmetry structure of the Higgs potential and various theoretical considerations are taken into account. We identified five benchmark cases, where at most one mixing angle was nonzero, and analyzed the 95% C.L. allowed parameter space using the oblique parameters. In the alignment limit of the 2HDM, we find that, other than the usual mass relations of $m_H\sim m_{H^\pm}$ or $m_A\sim m_{H^\pm}$ , electroweak precision measurements also impose an upper limit on the neutral Higgs masses. In the cases with nonzero singlet mixing with the 2HDM Higgses $\textit{H}$ or $\textit{A}$, we find approximate mass relations of $c^2_{\alpha_{HS}} m_{H} + s^2_{\alpha_{HS}}m_{h_S} = m_{H^\pm}$ or $c^2_{\alpha_{AS}} m_{A} + s^2_{\alpha_{AS}}m_{A_S} = m_{H^\pm}$ . These relations are universal to the 2HDM+S models, with or without further symmetry assumption. We also studied the non-alignment limit of the 2HDM+S, which typically has tighter constraints on the masses and mixing angles. Finally, we examined the complementarity between the electroweak precision analyses and the Higgs coupling precision measurements.

Cheng Li

Juxiang Li

Shufang Su

Wei Su

Electroweak precision constraints of the 2HDM+S * Cheng Li, Juxiang Li, and Wei Su are supported by the Natural Science Foundation of China (NSFC) (12305115), Shenzhen Science and Technology Program (202206193000001, 20220816094256002), Guangdong Provincial Key Laboratory of Gamma-Gamma Collider and Its Comprehensive Applications (2024KSYS001), and Guangdong Provincial Key Laboratory of Advanced Particle Detection Technology (2024B1212010005). Juxiang Li is also supported by the Fundamental Research Funds for the Central Universities, and the Sun Yat-sen University Science Foundation. Shufang Su is supported by the Department of Energy (DEFG02-13ER41976/DE-SC0009913)

In the Kerr–Sen black hole, this study investigates the changes in hotspot images before and after the occurrence of magnetic reconnection. After reviewing the Comisso–Asenjo magnetic reconnection process and introducing the hotspot imaging method, we examine the temporal evolution of hotspot intensity, including when energy extraction occurs, when it does not occur, and when the observer’s azimuthal angle is altered. We also discuss the influence of the black hole’s expansion parameter and spin on hotspot imaging. The results indicate that the first flare may serve as a potential signature of ongoing energy extraction; changing the observer’s azimuthal angle may alter the time interval between the first and second flares; a larger expansion parameter makes it more difficult to identify the energy extraction signal, and a higher spin also makes it more challenging to detect the energy extraction signal.

Ke Wang

Xiao-Xiong Zeng

Hotspot images driven by magnetic reconnection in Kerr–Sen black hole

This letter investigates the contribution of the <math altimg='si9.svg'><mrow><msqrt><mrow><mo>&#8722;</mo><mi>g</mi></mrow></msqrt><mi>&#958;</mi><mi>R</mi><msup><mi>&#981;</mi><mn>2</mn></msup></mrow></math> non-minimal interaction to the long range gravitational potential for massive scalar fields, found from the non-relativistic limit of the 2-2 scattering amplitude with graviton exchanges. Such coupling is most naturally motivated from the renormalisation of a scalar field theory with quartic self interaction in a curved spacetime. This is qualitatively different from the minimal ones like <math altimg='si10.svg'><mrow><msqrt><mi>G</mi></msqrt><msup><mi>h</mi><mrow><mi>&#956;</mi><mi>&#957;</mi></mrow></msup><msub><mi>T</mi><mrow><mi>&#956;</mi><mi>&#957;</mi></mrow></msub></mrow></math>, as the vertices corresponding to the former does not explicitly contain any scalar momenta, but instead explicitly contains the momentum carried by graviton line. For the minimal vertex, the long range gravitational potential up to one loop <math altimg='si11.svg'><mrow><mo>(</mo><mi mathvariant='script'>O</mi><mrow><mo>(</mo><mi>G</mi><mo>)</mo></mrow><mo>,</mo><mi mathvariant='script'>O</mi><mrow><mo>(</mo><msup><mi>G</mi><mn>2</mn></msup><mo>)</mo></mrow><mo>)</mo></mrow></math> was obtained earlier from the terms non-analytic in the transfer momentum, <math altimg='si12.svg'><mrow><msup><mi>q</mi><mrow><mo>&#8722;</mo><mn>2</mn></mrow></msup><mo>,</mo><mspace width='0.33em' /><msup><mi>q</mi><mrow><mo>&#8722;</mo><mn>1</mn></mrow></msup><mo>,</mo><mspace width='0.33em' /><mi>ln</mi><msup><mi>q</mi><mn>2</mn></msup></mrow></math>, yielding potentials respectively like <math altimg='si13.svg'><msup><mi>r</mi><mrow><mo>&#8722;</mo><mn>1</mn></mrow></msup></math>, <math altimg='si14.svg'><msup><mi>r</mi><mrow><mo>&#8722;</mo><mn>2</mn></mrow></msup></math>, <math altimg='si15.svg'><msup><mi>r</mi><mrow><mo>&#8722;</mo><mn>3</mn></mrow></msup></math>. However owing to the aforesaid explicit appearance of graviton&#8217;s transfer momentum for the non-minimal vertices, the leading contribution in this case comes at <math altimg='si6.svg'><mrow><mi mathvariant='script'>O</mi><mo>(</mo><mi>&#958;</mi><msup><mi>G</mi><mn>2</mn></msup><mo>)</mo></mrow></math>, and turns out to be subleading compared to even <math altimg='si15.svg'><msup><mi>r</mi><mrow><mo>&#8722;</mo><mn>3</mn></mrow></msup></math>. In order to complement this &#8216;screening&#8217; effect, we consider the three graviton vertex generated by the <math altimg='si16.svg'><mrow><mo>&#8764;</mo><mstyle mathvariant='normal'><mi>&#923;</mi></mstyle><msqrt><mrow><mo>&#8722;</mo><mi>g</mi></mrow></msqrt><mo linebreak='goodbreak'>/</mo><mi>G</mi></mrow></math> term in the action, where &#923; is the cosmological constant. This vertex does not contain any graviton momentum explicitly. With this vertex, and assuming short scale scattering much small compared to the Hubble horizon, we compute the seagull, the vacuum polarisation and the fish diagrams and obtain the 2-2 scattering amplitudes. The leading two body gravitational potential at <math altimg='si17.svg'><mrow><mi mathvariant='script'>O</mi><mo>(</mo><mi>&#958;</mi><mstyle mathvariant='normal'><mi>&#923;</mi></mstyle><msup><mi>G</mi><mn>2</mn></msup><mo>)</mo></mrow></math> behaves like <math altimg='si13.svg'><msup><mi>r</mi><mrow><mo>&#8722;</mo><mn>1</mn></mrow></msup></math>, even though it is much subleading compared to Newton&#8217;s potential due to the appearance of &#923;. We also discuss the scenario where this potential dominates the aforesaid <math altimg='si6.svg'><mrow><mi mathvariant='script'>O</mi><mo>(</mo><mi>&#958;</mi><msup><mi>G</mi><mn>2</mn></msup><mo>)</mo></mrow></math> one.

Avijit Sen Majumder

Sourav Bhattacharya

<italic>&#958;R&#981;</italic> <sup>2</sup> coupling, cosmological constant and quantum gravitational corrections to Newton&#8217;s potential

We analyze quasi-periodic oscillation data from selected X-ray binary systems hosting black holes. To model the spacetime geometry, we resort to the static Sen solution—originally derived in the framework of heterotic string theory—which reduces to the Schwarzschild spacetime for vanishing electric charge. By fitting the observed frequencies within the relativistic precession model, we constrain the mass and charge parameters of the Sen black hole and discuss their astrophysical implications, particularly in distinguishing classical black holes from their string-inspired counterparts.

Kazakhstan

Kuantay Boshkayev

Italy

Marco Muccino

Constraints on the Sen black hole mass and charge from quasi-periodic oscillations

Lepton flavor violation (LFV) offers a powerful probe of physics beyond the Standard Model, particularly in models addressing neutrino masses and the baryon asymmetry of the universe. In this study, we investigate LFV processes within the framework of type II seesaw leptogenesis, where the Standard Model is extended by an $S U(2)_L$ triplet Higgs field. We focus on key LFV processes, including $\mu^+\to e^+\gamma$ , $\mu^+ \to e^+e^-e^+$ , and $\mu \rightarrow e$ conversion in nuclei, deriving stringent constraints on the parameter space from current experimental data. We scan the 3$\textit{σ}$ range of neutrino oscillation parameters and identify the most conservative bounds consistent with existing measurements. Our results reveal that the MEG experiment currently provides the most stringent constraints in the normal ordering (NO) scenario, while the SINDRUM experiment offers comparable sensitivity in the inverted ordering (IO) case. Future experiments, such as MEG II, Mu3e, Mu2e, and COMET, are predicted to significantly improve the sensitivity, testing larger regions of the parameter space.

Chengcheng Han

Yijun Han

Sihui Huang

Zhanhong Lei

Probing type II seesaw leptogenesis through lepton flavor violation * Chengcheng Han acknowledges supports from the National Key R&D Program of China (2023YFA1606100), the Sun Yat-Sen University Science Foundation, the Fundamental Research Funds for the Central Universities at Sun Yat-sen University (24qnpy117) and the Key Laboratory of Particle Astrophysics and Cosmology (MOE) of Shanghai Jiao Tong University

The deflection of light in the gravitational field of a massive body can be analyzed through diverse theoretical approaches. The null geodesic approach is commonly employed to calculate light deflection within strong and weak field limits. Alternatively, several studies have explored the gravitational deflection of light using the material medium approach. For a static, non-rotating spherical mass, the deflection in a Schwarzschild field can be determined by expressing the metric in an isotropic form and evaluating the refractive index to trace the light ray’s trajectory. In this study, we extend the above-mentioned approach to the Kerr–Sen black hole spacetime in heterotic string theory, a solution representing a rotating, charged solution in heterotic string theory. The frame-dragging effects inherent to the Kerr–Sen geometry are incorporated to compute the velocity of light rays, enabling the derivation of the refractive index in this field. Considering the far-field approximation, we calculate the deflection of light in the Kerr–Sen spacetime and compare our results with those obtained for the Kerr and Schwarzschild black hole solution in GR.

Saswati Roy

Atanu Singha

South Africa

Asoke Sen

Deflection of light due to Kerr Sen black hole in heterotic string theory using material medium approach