Markarian 501, a BL Lac object well-known as a high energy gamma-ray source, has exhibited several epochs of very high energy (VHE) gamma-ray flaring events when its synchrotron peak frequency shifted above $$10^{17}$$ Hz, a signature of extreme behavior. From July 16 to July 31, 2014 such flaring events were observed for 15 days by various telescopes. On July 19 (MJD 56857.98), the X-ray outburst from the source was at its highest and on the same day an intriguing narrow peak-like feature around 3 TeV was observed by the MAGIC telescopes, a feature inconsistent with standard interpretations. Using the well-known two-zone photohadronic model, we study these VHE gamma-ray spectra on a day-by-day basis and offer explanation. Our two-zone photohadronic scenario shows that, on MJD 56857.98, the peak-like feature appears at a cutoff energy of $$E^c_{\gamma }=3.18$$ TeV. Below this energy the VHE spectrum increases slowly and is in high emission state. However, for $$E^c_{\gamma }\, > 3.18$$ TeV, the spectrum falls faster, resulting in a mild peak-like feature, not prominent enough as claimed by the MAGIC collaboration.

Mexico

Sarira Sahu

A. Oliveros

D. Páez-Sánchez

G. Sánchez-Colón

United States

Subhash Rajpoot

Spain

M. Martínez

Jose Carmenate

P. Córdoba

Italy

Gaetano Lambiase

Temporary EHBL-like behavior of Markarian 501 during July 2014 VHE flaring

We investigate the effects of dark scalar- and vector-mediated interactions on dark matter admixed neutron stars, employing the two-fluid formalism. We adopt three different nuclear equations of state—BSk22, MPA1 and APR4—to describe the baryonic sector, while the dark component consists of fermionic particles within a relativistic mean field framework. We consider both linear and quadratic scalar interactions with the dark fermion, including a quartic self-interaction in the latter case. The parameters of the dark matter (DM) models are inferred via a Bayesian analysis that incorporates data from NICER observations and binary neutron star merger detections. The neutron star configurations obtained from the selected model parameters develop dark matter cores, leading to more compact objects with smaller masses and radii. Our findings suggest that scalar interactions generally have a weaker impact on the stellar structure compared to vector-mediated ones, though quantitative differences arise. In particular, quadratic scalar couplings suppress the net attractive interaction, allowing for larger dark matter fractions to be accreted. We also compute the sound speed of DM, finding that the scalar and quadratic interactions modify the stiffness of the dark equation of state while respecting causality: vector repulsion enhances the sound speed, whereas scalar attraction tends to soften it. We compare our results with GW1708017, GW190425 and NICER data and constrain DM couplings and mass.

Francesco Grippa

United Kingdom

Tanmay Kumar Poddar

Scalar and vector dark matter admixed neutron stars with linear and quadratic couplings

We investigate the potential for current and future gravitational-wave detectors to observe imprints of explicit diffeomorphism violation in primordial signals. Starting from a simple model with known effects, we derive the strain amplitude and power spectrum for primordial gravitational waves, both of which are affected by the symmetry breaking. Through this, we directly find predictions for the tensor spectral index and tensor-to-scalar which are different from general relativity. By considering the known sensitivity curves for NANOGrav, SKA, THEIA, <italic>&#956;</italic>-ARES, ASTROD-GW, LISA, BBO, DECIGO, CE, AION-km, AEDGE, ET, and aLIGO, we place observability limits on the parameters controlling the diffeomorphism violation. For instance, we find that aLIGO could observe signals for <math altimg='si119.svg'><mrow><msub><mi>s</mi><mn>00</mn></msub><mo>&#8818;</mo><mo>&#8722;</mo><mn>0.1</mn></mrow></math>, while more sensitive future detectors like LISA and DECIGO could probe violations as small as <math altimg='si120.svg'><mrow><msub><mi>s</mi><mn>00</mn></msub><mo>&#8776;</mo><mo>&#8722;</mo><mn>5</mn><mo linebreak='goodbreak'>&#215;</mo><msup><mn>10</mn><mrow><mo>&#8722;</mo><mn>4</mn></mrow></msup></mrow></math> and <math altimg='si121.svg'><mrow><mo>&#8722;</mo><mn>3</mn><mo linebreak='goodbreak'>&#215;</mo><msup><mn>10</mn><mrow><mo>&#8722;</mo><mn>3</mn></mrow></msup></mrow></math>, respectively. Finally, we consider the existing constraints on the number of relativistic degrees of freedom &#916; <italic>N</italic> <inf>eff</inf> which is tightly constrained by Big-Bang Nucleosynthesis, where we find that &#916; <italic>N</italic> <inf>eff</inf> only weakly depends on the symmetry breaking but places a lower bound on the coefficients which is consistent with available bounds from the speed of gravitational waves.

Azerbaijan

Iran

Mohsen Khodadi

South Korea

France

Nils A. Nilsson

Javad T. Firouzjaee

Primordial observables of explicit diffeomorphism violation in gravity

We assess the effect of the cosmic neutrino background (<math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><mi mathvariant="normal">C</mi><mi>ν</mi><mi mathvariant="normal">B</mi></mrow></math>) on superradiant instabilities caused by an ultralight scalar field around spinning black holes (BHs). When the scalar couples to neutrinos via a Yukawa interaction, thermal corrections from the <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><mi mathvariant="normal">C</mi><mi>ν</mi><mi mathvariant="normal">B</mi></mrow></math> induce a quartic self-interaction and an effective mass term for the scalar. We show that, for Yukawa couplings as small as <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msub><mi>y</mi><mrow><mi>ϕ</mi><mi>ν</mi></mrow></msub><mo>∼</mo><msup><mn>10</mn><mrow><mo>−</mo><mn>16</mn></mrow></msup></math> (for astrophysical BHs) or <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msup><mn>10</mn><mrow><mo>−</mo><mn>20</mn></mrow></msup></math> (for supermassive BHs), the quartic term can quench the instability and set observable bounds, even if the scalar does not constitute dark matter. We assess the robustness of these constraints against several sources of uncertainty, including gravitational focusing of relic neutrinos, galactic clustering, and nonlinear backreaction. An enhanced local neutrino density weakens the bounds by up to an order of magnitude compared to a uniform background, yet the induced self-interaction remains strong enough to significantly affect the superradiant dynamics. Our results open a new observational window on neutrino-coupled scalars via BH superradiance.

Luca Visinelli

Impact of the cosmic neutrino background on black hole superradiance

We study the effect of Spontaneous Lorentz Symmetry Breaking (SLSB) on Primordial Gravitational Waves (PGWs) generated during inflation. The SLSB is induced by a time-like Bumblebee vector field which is non-minimally coupled to the Ricci tensor in the Friedmann-Lemaître-Robertson-Walker background. The power spectrum and GW amplitude are computed to investigate how Lorentz violation leaves observable imprints. We calculate the GW strain amplitude over frequencies <math altimg='si1.svg'><mo stretchy='false'>(</mo><msup><mrow><mn>10</mn></mrow><mrow><mo linebreak='badbreak' linebreakstyle='after'>&#8722;</mo><mn>10</mn></mrow></msup><mspace width='0.25em' /><mrow><mi mathvariant='normal'>Hz</mi></mrow><mo>,</mo><msup><mrow><mn>10</mn></mrow><mrow><mn>4</mn></mrow></msup><mspace width='0.25em' /><mrow><mi mathvariant='normal'>Hz</mi></mrow><mo stretchy='false'>)</mo></math>, for a range of the dimensionless Lorentz-violating parameter, <math altimg='si2.svg'><mo linebreak='badbreak' linebreakstyle='after'>&#8722;</mo><msup><mrow><mn>10</mn></mrow><mrow><mo linebreak='badbreak' linebreakstyle='after'>&#8722;</mo><mn>3</mn></mrow></msup><mo>&#8804;</mo><mi>l</mi><mo>&#8804;</mo><msup><mrow><mn>10</mn></mrow><mrow><mo linebreak='badbreak' linebreakstyle='after'>&#8722;</mo><mn>4</mn></mrow></msup></math>, which essentially comes from a slight sensitivity to the equation of state for dark energy. For positive <italic>l</italic> values, the amplitude of GW shows a mild suppression compared to the standard cosmological scenario ( <math altimg='si3.svg'><mi>l</mi><mo linebreak='goodbreak' linebreakstyle='after'>=</mo><mn>0</mn></math>). This effect could be observable with detectors like SKA, <italic>&#956;</italic>-Ares, and BBO. Conversely, negative <italic>l</italic> values amplify the GW amplitude, enhancing detectability by both SKA, <italic>&#956;</italic>-Ares, and BBO, as well as by THEIA and DECIGO. Notably, the GW strain amplitude increases by an order of magnitude as <italic>l</italic> moves from 0 to <math altimg='si4.svg'><mo linebreak='badbreak' linebreakstyle='after'>&#8722;</mo><msup><mrow><mn>10</mn></mrow><mrow><mo linebreak='badbreak' linebreakstyle='after'>&#8722;</mo><mn>3</mn></mrow></msup></math>, improving prospects for detection in high-sensitivity detectors like THEIA and DECIGO.

Leonardo Mastrototaro

Primordial gravitational waves from spontaneous Lorentz symmetry breaking

An ultralight electrophilic scalar field can produce a long-range Yukawa-like spatial profile around a rotating, magnetized star when coupled to the constant number density of electrons in either the magnetosphere or the star itself. This long-range scalar field generates an effective scalar charge in the star or its magnetosphere, leading to a long-range force between two compact stars in a binary system. The electrophilic scalar can also radiate from isolated pulsars or double pulsar binary systems. Using the Crab pulsar and PSR J0737-3039A/B as test cases, we derive constraints on the scalar-electron coupling by analyzing observations of long-range force, orbital period decay in binary systems, and pulsar spin-down rates. Among these, the most stringent limits on the coupling are obtained from the orbital period decay. However, these constraints can be significantly reduced if the scalar interacts with the pervasive cosmic neutrino background. Enhancing experimental sensitivity and studying compact objects with stronger magnetic fields and higher angular velocities could further strengthen these bounds.

Constraints on an electrophilic scalar coupling from rotating magnetized stars and effects of the cosmic neutrino background

Coherence, which represents the superposition of orthogonal states, is a fundamental concept in quantum mechanics and can also be precisely defined within quantum resource theory. Thus exploring quantum coherence in neutrino oscillations can not only help in examining the intrinsic quantum nature but can also explore their potential applications in quantum information technologies. Previous studies on quantum coherence have focused on neutrino flavor oscillations (FO). However, FO imply that neutrinos have mass, and this can lead to the generation of a tiny but finite magnetic dipole moment of neutrinos through quantum loop diagrams at higher orders of perturbative expansion of the interaction. This electromagnetic property of neutrinos can induce spin flavor oscillations (SFO) in the presence of an external magnetic field and hence is expected to enrich the study of coherence. In this work, we investigate quantum coherence in neutrino SFO with three flavor mixing within the interstellar as well as intergalactic magnetic fields, quantified by the <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msub><mi>l</mi><mn>1</mn></msub></math> norm and the relative entropy of coherence, and express these measures in terms of neutrino SFO probabilities. For FO, coherence measures can sustain higher values (say, within 50% of the maximum) over distances of several kilometers, which are relevant for terrestrial experiments like reactor and accelerator neutrinos. However, for SFO, we find that the coherence scale can extend to astrophysical distances, spanning from kiloparsecs to gigaparsecs.

India

Ashutosh Kumar Alok

Trambak Jyoti Chall

Neetu Raj Singh Chundawat

Shireen Gangal

Quantum coherence in neutrino spin-flavor oscillations

The origin of tiny neutrino mass is an unsolved puzzle leading to a variety of phenomenological aspects beyond the Standard Model (BSM). We consider U(1) gauge extension of the Standard Model (SM) where so-called seesaw mechanism is incarnated with the help of thee generations of Majorana type right-handed neutrinos followed by the breaking of U(1) and electroweak gauge symmetries providing anomaly free structure. In this framework, a neutral BSM gauge boson $$Z^\prime $$ <math> <msup> <mi>Z</mi> <mo>′</mo> </msup> </math> is evolved. To explore the properties of its interactions we consider chiral (flavored) frameworks where $$Z^\prime $$ <math> <msup> <mi>Z</mi> <mo>′</mo> </msup> </math> interactions depend on the handedness (generations) of the fermions. In this paper we focus on $$Z^\prime $$ <math> <msup> <mi>Z</mi> <mo>′</mo> </msup> </math> -neutrino interactions which could be probed from cosmic explosions. We consider $$\nu \overline{\nu } \rightarrow e^+ e^-$$ <math> <mrow> <mi>ν</mi> <mover> <mi>ν</mi> <mo>¯</mo> </mover> <mo>→</mo> <msup> <mi>e</mi> <mo>+</mo> </msup> <msup> <mi>e</mi> <mo>-</mo> </msup> </mrow> </math> process which can energize gamma-ray burst (GRB221009A, so far the highest energy) through energy deposition. Hence estimating these rates we constrain U(1) gauge coupling $$(g_X)$$ <math> <mrow> <mo>(</mo> <msub> <mi>g</mi> <mi>X</mi> </msub> <mo>)</mo> </mrow> </math> and $$Z^\prime $$ <math> <msup> <mi>Z</mi> <mo>′</mo> </msup> </math> mass $$(M_{Z^\prime })$$ <math> <mrow> <mo>(</mo> <msub> <mi>M</mi> <msup> <mi>Z</mi> <mo>′</mo> </msup> </msub> <mo>)</mo> </mrow> </math> under Schwarzchild (Sc) and Hartle-Thorne (HT) scenarios. We also study $$\nu $$ <math> <mi>ν</mi> </math> -DM scattering through $$Z^\prime $$ <math> <msup> <mi>Z</mi> <mo>′</mo> </msup> </math> to constrain $$g_X-M_{Z^\prime }$$ <math> <mrow> <msub> <mi>g</mi> <mi>X</mi> </msub> <mo>-</mo> <msub> <mi>M</mi> <msup> <mi>Z</mi> <mo>′</mo> </msup> </msub> </mrow> </math> plane using IceCube data considering high energy neutrinos from cosmic blazar (TXS0506+056), active galaxy (NGC1068), the Cosmic Microwave Background (CMB) and the Lyman- $$\alpha $$ <math> <mi>α</mi> </math> data, respectively. Finally highlighting complementarity we compare our results with current and prospective bounds on $$g_X-M_{Z^\prime }$$ <math> <mrow> <msub> <mi>g</mi> <mi>X</mi> </msub> <mo>-</mo> <msub> <mi>M</mi> <msup> <mi>Z</mi> <mo>′</mo> </msup> </msub> </mrow> </math> plane from scattering, beam-dump and $$g-2$$ <math> <mrow> <mi>g</mi> <mo>-</mo> <mn>2</mn> </mrow> </math> experiments. [ PICS code ].

Japan

K. ShivaSankar

Arindam Das

China

Takaaki Nomura

Czechia

Yuta Orikasa

Probing chiral and flavored $$Z^\prime $$ <math> <msup> <mi>Z</mi> <mo>′</mo> </msup> </math> from cosmic bursts through neutrino interactions

In this paper, we obtain a new spherically symmetric black hole surrounded by the pseudo-isothermal dark matter halo. Furthermore, to explore the effects of the pseudo-isothermal halo profile on a rotating black hole at the M87 galactic center, we derive a rotating black hole solution encompassed by the pseudo-isothermal halo by using the Newman-Janis method. Our investigation focuses on the impact of the pseudo-isothermal halo on the black hole event horizon, time-like and null orbits, as well as the black hole shadow. We find that as the spin parameter a increases, the interval between the inner event horizon and the outer event horizon of the rotating black hole surrounded by the pseudo-isothermal halo in M87 diminishes. This leads to the formation of an extreme black hole. The presence of dark matter, however, has minimal effect on the event horizon. Moreover, in the M87 as the spin parameter a increases, the black hole shadow deviates increasingly from a standard circle, with larger spin parameters causing more pronounced distortion relative to the standard circle. Surprisingly, we observe that the dark matter density has very little influence on the shadow of the black hole surrounded by the pseudo-isothermal halo in the M87. This study contributes to a deeper understanding of black hole structures and the role of dark matter in the universe.

Yi Yang

Dong Liu

Türkiye

Ali Övgün

Zheng-Wen Long

Black hole surrounded by the pseudo-isothermal dark matter halo

We investigate the non-relativistic limit of the Klein–Gordon equation for mixed scalar particles and show that, in this regime, one unavoidably arrives at redefining the particle’s inertial mass. This happens because, in contrast to the case when mixing is absent, the antiparticle sector contribution cannot be neglected for particles with definite flavor. To clearly demonstrate this feature, we adopt the Feshbach–Villars formalism for Klein–Gordon particles. Furthermore, within the same framework, we also demonstrate that, in the presence of a weak gravitational field, the mass parameter that couples to gravity (gravitational mass) does not match the effective inertial mass. This, in turn, implies a violation of the weak equivalence principle. Finally, we prove that the Bargmann’s superselection rule, which prohibits oscillating particles on the basis of the Galilean transformation, is incompatible with the non-relativistic limit of the Lorentz transformation and hence does not collide with the results obtained.