We present a pragmatic approach to lower down the mass scale of right-handed neutrinos in leptogenesis by introducing a scalar decaying to right-handed neutrinos. The key point of our proposal is that the out-of-equilibrium decays of the scalar provide an additional source for right-handed neutrinos and hence the lepton asymmetry. This mechanism works well at low temperatures when the washout of the generated lepton asymmetry is suppressed. Thus, the lepton asymmetry can be effectively produced despite the washout effect is strong or not. Through a comprehensive analysis, we demonstrate that such a scalar-assisted leptogenesis can typically decrease the viable right-handed neutrino mass scale by one to three orders of magnitude.

China

Jun-Yu Tong

Zhao-Huan Yu

Hong-Hao Zhang

Leptogenesis assisted by scalar decays

<p>We study the dynamics of domain walls formed through the spontaneous breaking of an approximate <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msub><mi mathvariant="double-struck">Z</mi><mn>2</mn></msub></math> symmetry in a scalar field, focusing on their collapse under the influence of quantum and thermal corrections induced by a <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msub><mi mathvariant="double-struck">Z</mi><mn>2</mn></msub></math>-violating Yukawa coupling to Dirac fermions in the thermal bath. The thermal effects make the potential bias between the true and false vacua dependent on the temperature and may lead to notable variations in the annihilation temperature of domain walls, in addition to the shift caused by temperature-independent quantum corrections. These modifications could substantially alter the gravitational wave spectrum produced by collapsing domain walls, potentially providing observable signatures for future gravitational wave detection experiments.</p>

Qing-Quan Zeng

Xi He

Jiaming Zheng

Collapsing domain walls with <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msub><mi mathvariant="double-struck">Z</mi><mn>2</mn></msub></math>-violating coupling to thermalized fermions and their impact on gravitational wave detections

We study the transverse momentum ( $p_T$ ) differential anisotropic flow and flow fluctuation in Pb+Pb collisions at $\sqrt{s_{_{NN}}}$ =5.02 TeV at the LHC. A (3+1)-dimensional CLVisc hydrodynamics framework with fluctuating TRENTO (or AMPT) initial conditions is utilized to simulate the space-time evolution of the quark-gluon plasma (QGP) medium. The effects of shear viscosity and the sub-nucleon structure on anisotropic flow and flow fluctuation are analyzed. Our result shows that shear viscosity tends to suppress both flow coefficients ( ${v_2\{2}\}$ , ${v_2\{4\}}$ , and ${\langle v_2\rangle}$ ) and flow fluctuation ( ${\sigma_{v_2}}$ ) owing to its smearing effect on local density fluctuation. The flow coefficients appear to be insensitive to the sub-nucleon structure, whereas the flow fluctuation ${\sigma_{v_2}}$ tends to be suppressed by the sub-nucleon structure in central collisions but enhanced in peripheral collisions. After taking into account the sub-nucleon structure effect, our numerical result can qualitatively describe the relative flow fluctuations ( ${v_2\{4\}/v_2\{2\}}$ , $F({v_2})$ ) measured by the ALICE Collaboration at the LHC. We further investigate the effects of shear viscosity, sub-nucleon structure, and initial condition model on the flow angle and flow magnitude decorrelations ( ${A_2^f}$ , ${M_2^f}$ ) using the four-particle correlation method. We find that the flow decorrelation effect is typically stronger in central collisions than in peripheral collisions. The flow angle decorrelation is found to be insensitive to the shear viscosity and sub-nucleon structure, whereas the flow magnitude decorrelation shows quite different behaviors when using the TRENTO and AMPT initial condition models. Our study sheds light on the anisotropic flow, transport properties, and initial structure of the QGP created in high-energy nuclear collisions.

Germany

Jie Zhu

Canada

Xiang-Yu Wu

Guang-You Qin

Anisotropic flow, flow fluctuation, and flow decorrelation in relativistic heavy-ion collisions: the roles of sub-nucleon structure and shear viscosity * Supported in part by the Natural Science Foundation of China (12225503, 11890710, 11890711, 11935007). Zhu Jie is supported in part by the China Scholarship Council (202306770009). Wu Xiang-Yu is supported in part by the National Science Foundation within the framework of the JETSCAPE collaboration (OAC-2004571) and in part by the Natural Sciences and Engineering Research Council of Canada. Some of the calculations were performed in the Nuclear Science Computing Center at Central China Normal University (NSC$^{3}$), Wuhan, Hubei, China.

Motivated by the work of Cardoso et al. (2022) <cross-ref refid='br0150' id='crf0030'>[15]</cross-ref> on black holes in galaxies, we derive a new black hole solution surrounded by a Dekel-Zhao (DZ) dark matter profile. The derived metric, influenced by DZ profile parameters, exhibits two distinct regimes: for <math altimg='si1.svg'><mi>r</mi><mo>&#8810;</mo><msub><mrow><mi>r</mi></mrow><mrow><mi mathvariant='normal'>c</mi></mrow></msub></math> ( <math altimg='si2.svg'><msub><mrow><mi>r</mi></mrow><mrow><mi mathvariant='normal'>c</mi></mrow></msub></math> is a characteristic radius), exponential corrections dominate, producing significant deviations from the Schwarzschild solution near dense cores, while for <math altimg='si3.svg'><mi>r</mi><mo>&#8811;</mo><msub><mrow><mi>r</mi></mrow><mrow><mi mathvariant='normal'>c</mi></mrow></msub></math>, these corrections vanish, restoring the Schwarzschild metric at large distances. These findings ensure consistency with general relativity in vacuum. The black hole shadow and deflection angle are analyzed, demonstrating that the shadow radius increases with black hole mass ( <math altimg='si4.svg'><msub><mrow><mi>M</mi></mrow><mrow><mi mathvariant='normal'>BH</mi></mrow></msub></math>), while higher central densities ( <math altimg='si5.svg'><msub><mrow><mi>&#961;</mi></mrow><mrow><mi mathvariant='normal'>ch</mi></mrow></msub></math>) result in smaller shadows, reflecting the environmental impact of dense dark matter halos. Photon dynamics reveal how DZ profiles modify critical impact parameters and effective potentials, with gravitational lensing effects highly sensitive to the characteristic radius ( <math altimg='si2.svg'><msub><mrow><mi>r</mi></mrow><mrow><mi mathvariant='normal'>c</mi></mrow></msub></math>). Smaller <math altimg='si2.svg'><msub><mrow><mi>r</mi></mrow><mrow><mi mathvariant='normal'>c</mi></mrow></msub></math> values lead to larger deflection angles due to stronger gravitational effects near compact cores. This work highlights the significance dark matter profiles in shaping black hole observables, providing a theoretical foundation for future observational studies and advancing the understanding of dark matter-black hole interactions in astrophysical and cosmological contexts.

Türkiye

Ali Övgün

Philippines

Reggie C. Pantig

Black hole in the Dekel-Zhao dark matter profile

We investigate fermionic dark matter interactions with standard model particles from an additional   $ {{U}}(1)_{{X}} $   gauge symmetry, assuming kinetic mixing between the   $ {{U}}(1)_{{X}} $   and   $ {{U}}(1)_{{X}} $   gauge fields as well as a nonzero   $ {{U}}(1)_{{X}} $   charge of the Higgs doublet. To ensure gauge-invariant Yukawa interactions and the cancellation of gauge anomalies, standard model fermions are assigned Y-sequential   $ {{U}}(1)_{{X}} $   charges proportional to the Higgs charge. Although the Higgs charge should be small owing to collider constraints, it is useful to decrease the effective cross section of dark matter scattering off nucleons by two orders of magnitude to easily evade direct detection bounds. After performing numerical scans in the parameter space, we find that the introduction of the Higgs charge can also enhance the dark matter relic density by at least two orders of magnitude. In the case where the resonance effect is important for dark matter freeze-out, when the observed relic density and direct detection constraints are tangled, the Higgs charge can expand physical windows to some extent by relieving the tension between the relic density and direct detection.

Lianyou Shan

Dark matter interactions from an extra (1) gauge symmetry with kinetic mixing and Higgs charge  

Evidence for a stochastic gravitational wave background in the nHz frequency band is recently reported by four pulsar timing array collaborations NANOGrav, EPTA, CPTA, and PPTA. It can be interpreted by gravitational waves from collapsing domain walls in the early universe. We assume such domain walls arising from the spontaneous breaking of a <math><msub><mi>Z</mi><mn>2</mn></msub></math> symmetry in a scalar field theory, where a tiny <math><msub><mi>Z</mi><mn>2</mn></msub></math>-violating potential is required to make domain walls unstable. We propose that this <math><msub><mi>Z</mi><mn>2</mn></msub></math>-violating potential is radiatively induced by a feeble Yukawa coupling between the scalar field and a fermion field, which is also responsible for dark matter production via the freeze-in mechanism. Combining the pulsar timing array data and the observed dark matter relic density, we find that the model parameters can be narrowed down to small ranges.

Zhao Zhang

Chengfeng Cai

Yu-Hang Su

Shiyu Wang

Nano-Hertz gravitational waves from collapsing domain walls associated with freeze-in dark matter in light of pulsar timing array observations

We study stochastic gravitational waves from cosmic strings generated in an ultraviolet-complete model for pseudo-Nambu-Goldstone dark matter with a hidden   ${U(1)}$   gauge symmetry. The dark matter candidate in this model can naturally evade direct detection bounds and easily satisfy other phenomenological constraints. The bound on the dark matter lifetime implies an ultraviolet scale higher than   ${U(1)}$  . The spontaneous   ${U(1)}$   symmetry breaking at such a high scale would induce cosmic strings with high tension, resulting in a stochastic gravitational wave background with a high energy density. We investigate the constraints from current gravitational wave experiments as well as the future sensitivity. We find that most viable parameter points can be well studied in future gravitational wave experiments.

Ze-Yu Qiu

Gravitational waves from cosmic strings associated with pseudo-Nambu-Goldstone dark matter  

We propose an ultraviolet completion model for pseudo-Nambu-Goldstone dark matter with a hidden U(1) gauge symmetry. Compared to previous studies, this setup is simpler, introducing less interactions. Dark matter scattering off nucleons is highly suppressed by the ultraviolet scale and direct detection constraints can be easily evaded. The kinetic mixing between the hidden U(1) and the U(1)Y gauge fields would lead to dark matter decays. We find that the current bound on the dark matter lifetime implies that the ultraviolet scale should be higher than 1010 GeV. The phenomenological constraints from the 125 GeV Higgs measurements, the dark matter relic density, and indirect detection of dark matter annihilation are also investigated.

Dan-Yang Liu

Xue-Min Jiang

Ultraviolet completion of pseudo-Nambu-Goldstone dark matter with a hidden U(1) gauge symmetry

We enumerate various effective couplings that contribute to the mixings between an exotic vector boson <math><msup><mi>Z</mi><mo>′</mo></msup></math> and the neutral electroweak vector bosons. The miscellaneous mixing patterns can be evaluated perturbatively. The effective oblique parameters <math><msup><mi>S</mi><mo>′</mo></msup></math>, <math><msup><mi>T</mi><mo>′</mo></msup></math>, and <math><msup><mi>U</mi><mo>′</mo></msup></math> are calculated to compare with the electroweak precision test results. With the contributions to the non-negligible <math><msup><mi>U</mi><mo>′</mo></msup></math> parameter from the <math><msub><mi>ε</mi><mrow><mi>B</mi><mo>,</mo><mi>W</mi></mrow></msub></math> parameters and the aid of some other parameters to cancel the negative <math><msup><mi>T</mi><mo>′</mo></msup></math>, the recent CDF <math><mi>W</mi></math>-mass anomaly can therefore be explained.

Dayun Qiu

Yi-Lei Tang

Corrections to electroweak precision observables from mixings of an exotic vector boson in light of the CDF <math><mi>W</mi></math>-mass anomaly

Recently, the CDF collaboration reported a new measurement of the <math><mi>W</mi></math> boson mass <math><msub><mi>M</mi><mi>W</mi></msub><mo>=</mo><mspace></mspace><mn>80.4335</mn><mo>±</mo><mn>0.0094</mn><mtext> </mtext><mtext> </mtext><mi>GeV</mi></math>, which shows a <math><mo>∼</mo><mn>7</mn><mi>σ</mi></math> deviation from the standard model prediction <math><mn>80.3545</mn><mo>±</mo><mn>0.0057</mn><mtext> </mtext><mtext> </mtext><mi>GeV</mi></math> obtained by the electroweak (EW) global fit. This deviation can be explained by new physics generating moderate EW oblique parameters <math><mi>S</mi></math>, <math><mi>T</mi></math>, and <math><mi>U</mi></math>. In this work, we use the loop corrections induced by some extra EW multiplets to explain the CDF <math><msub><mi>M</mi><mi>W</mi></msub></math> anomaly. The lightest neutral particle in the multiplets can also serve as a candidate of cold dark matter (DM). We consider two such models, namely singlet-triplet scalar DM and singlet-doublet fermionic DM models, and perform numerical scans to find the parameter points accounting for the <math><msub><mi>M</mi><mi>W</mi></msub></math> anomaly. The constraints from the correct DM thermal relic density and direct detection are also taken into account. We find the parameter points simultaneously interpreting the <math><msub><mi>M</mi><mi>W</mi></msub></math> anomaly and satisfying the DM requirements in the former model, but do not find such parameter points in the latter model.

Italy

Jin-Wei Wang

Xiao-Jun Bi

Peng-Fei Yin

Electroweak dark matter model accounting for the CDF <math><mi>W</mi></math>-mass anomaly