We investigated the effect of an isospin chemical potential ( $ \mu_{I} $ ) within the quark-meson model, which approximates quantum chromodynamics (QCD) by modeling low-energy phenomena such as chiral symmetry breaking and phase structure under varying conditions of temperature and chemical potential. Using the functional renormalization group (FRG) flow equations, we calculated the phase diagram in the chiral limit within the two-flavor quark-meson model in a finite $ \mu_{I} $ with $\textit{ρ}$ vector meson interactions. Fluctuation effects significantly decrease the critical chemical potential from the mean-field (MF) value $\mu_{I,{\rm MF}} \gt m_\rho$ to a lower value at which the $\textit{ρ}$ vector meson condensates alongside the chiral condensate once the isospin chemical potential exceeds the critical value $ \mu_{I}^{{\rm{crit}}} $ . This $\textit{ρ}$ condensation was investigated numerically for different meson coupling strengths. The $\textit{ρ}$ meson dominated region is delineated from other phases by a second-order phase transition at lower $ \mu_{I} $ and a first-order transition at slightly higher $ \mu_{I} $ .

China

Mohammed Osman

Defu Hou

Wentao Wang

United States

Hui Zhang

Functional renormalization group study of $\textit{ρ}$ meson condensate at a finite isospin chemical potential in the quark meson model * Supported in part by the National Key Research and Development Program of China (2022YFA1604900). This work is also partly supported by the National Natural Science Foundation of China (NSFC) (12435009, 12275104). Hui Zhang acknowledges the financial support from the Guangdong Major Project of Basic and Applied Basic Research (2020B0301030008) and the National Natural Science Foundation of China (12047523, 12105107)

In the phenomenological study of dark photon, its mass origin is usually not of concern. However, in theoretical model construction, its mass is often generated via a dark Higgs mechanism, which leads to the presence of a light (non-decoupled) dark Higgs particle. In this work, we study the impact of such a dark Higgs particle on the collider detection of the dark photon. We focus on the process of final state dark photon radiating dark Higgs, which is called dark final state radiation (FSR). Considering the effects on both the signal cross section and the distribution of the squared missing mass, the invisible dark photon search at BaBar is reanalyzed and a new exclusion limit for invisible dark photon is presented.

Song Li

Jin Yang

Mengchao Zhang

Yang Zhang

Rui Zhu

Unraveling dark Higgs mechanism via dark photon production at an $\textit{e}$

<p>Motivated by the null results of current dark matter searches and the small-scale problems, we study a dark sector charged by a spontaneous broken gauge <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>U</mi><mo stretchy="false">(</mo><mn>1</mn><msup><mo stretchy="false">)</mo><mo>′</mo></msup></math>. To explore the parameter space of this model, in addition to the consideration of the small-scale data, we also consider the theoretical bounds on the dark Higgs mass, with the upper bound coming from the tree-level perturbative unitarity and the lower bound from the one-loop Linde-Weinberg bound. We deeply examine the dependence of the Linde-Weinberg bound on gauge choice and energy scale, and present a Linde-Weinberg bound that is gauge and scale independent. Combining the theoretical and observational constraints, we obtain the following ranges for the parameter space: the dark matter mass is 10–500 GeV, the mediator (dark photon) mass is 0.5–5 MeV, the dark Higgs mass is 0.05–50 MeV, and the dark fine-structure constant is 0.001–0.4. We conclude that the dark Higgs in this model cannot be ignored in the phenomenological study of the dark sector.</p>

Jin Min Yang

Theoretical bounds on dark Higgs mass in a self-interacting dark matter model with <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><mi>U</mi><mo stretchy="false">(</mo><mn>1</mn><msup><mrow><mo stretchy="false">)</mo></mrow><mrow><mo>′</mo></mrow></msup></mrow></math>

The self-interacting dark matter (SIDM) paradigm offers a potential solution to the small-scale structure problems faced by collisionless cold dark matter. This framework incorporates self-interactions among dark matter particles, typically mediated by a particle with a MeV-scale mass. Recent evidences of nano-Hertz gravitational waves from pulsar timing arrays (PTAs) such as NANOGrav, CPTA, EPTA, and PPTA suggest the occurrence of a first-order phase transition (FOPT) at a MeV-scale temperature. Considering the close proximity between these two scales, we propose that the mediator mass in the SIDM model originates from the spontaneous breaking of a <math><mi>U</mi><mo>(</mo><mn>1</mn><msup><mo>)</mo><mo>′</mo></msup></math> symmetry, which is driven by the FOPT indicated by PTA data. Consequently, the alignment of these two scales is believed to be deeply connected by the same underlying physics. By extensively exploring the parameter space, remarkably, we find that the parameter space favored by SIDM just provides an explanation for the PTA data.

Chengcheng Han

Ke-Pan Xie

Self-interacting dark matter implied by nano-Hertz gravitational waves

We explore a scenario of high-scale supersymmetry where all supersymmetric particles except gauginos stay at a high-energy scale <math><msub><mi>M</mi><mi>SUSY</mi></msub></math> that is much larger than the reheating temperature <math><msub><mi>T</mi><mi>RH</mi></msub></math>. The dark matter is dominated by a bino component with mass around the electroweak scale and the observed relic abundance is mainly generated by the freeze-in process during the early Universe. Considering the various constraints, we identify two available scenarios in which the supersymmetric sector at an energy scale below <math><msub><mi>T</mi><mi>RH</mi></msub></math> consists of (a) bino or (b) bino and wino. Typically, for a bino mass around 0.1–1 TeV and a wino mass around 2 TeV, we find that <math><msub><mi>M</mi><mi>SUSY</mi></msub></math> should be around <math><msup><mn>10</mn><mrow><mn>13</mn><mo>−</mo><mn>14</mn></mrow></msup><mtext> </mtext><mtext> </mtext><mi>GeV</mi></math> with <math><msub><mi>T</mi><mi>RH</mi></msub></math> around <math><msup><mn>10</mn><mrow><mn>4</mn><mo>−</mo><mn>6</mn></mrow></msup><mtext> </mtext><mtext> </mtext><mi>GeV</mi></math>.

South Korea

Peiwen Wu

Freeze-in bino dark matter in high-scale supersymmetry

Motivated by the collisionless cold dark matter small scale structure problem, we propose an asymmetric dark matter model with the dark sector charged under a dark <math><mi>U</mi><mo>(</mo><mn>1</mn><msup><mo>)</mo><mo>′</mo></msup></math>. The mediator between dark matter particles is the dark gauge boson, which obtains its mass through the spontaneous breaking of <math><mi>U</mi><mo>(</mo><mn>1</mn><msup><mo>)</mo><mo>′</mo></msup></math>. This model easily avoids the strong limits from cosmic microwave background (CMB) observation, and has a large parameter space to be consistent with small scale structure data. We focus on a special scenario where portals between the dark sector and visible sector are too weak to be detected by traditional methods. We find that this scenario can increase the effective number of neutrinos (<math><mrow><msub><mrow><mi>N</mi></mrow><mrow><mi>eff</mi></mrow></msub></mrow></math>). In addition, the spontaneous <math><mi>U</mi><mo>(</mo><mn>1</mn><msup><mo>)</mo><mo>′</mo></msup></math> symmetry breaking process can generate stochastic gravitational waves with peak frequency around <math><mrow><msup><mrow><mn>10</mn></mrow><mrow><mo>−</mo><mn>6</mn></mrow></msup><mi>–</mi><msup><mrow><mn>10</mn></mrow><mrow><mo>−</mo><mn>7</mn></mrow></msup><mtext> </mtext><mtext> </mtext><mi>Hz</mi></mrow></math>.

Zien Chen

Kairui Ye

Asymmetric dark matter with a spontaneously broken <math><mrow><mi>U</mi><mo>(</mo><mn>1</mn><msup><mrow><mo>)</mo></mrow><mrow><mo>′</mo></mrow></msup></mrow></math>: Self-interaction and gravitational waves

In this work we revisit the existence of a strong first order electroweak phase transition (SFOEWPT) and recent m  W  precision measurement in the Type-I and Type-II 2HDMs. The   <math> <mi>O</mi> </math>  $$ \mathcal{O} $$ (100) GeV new scalars in 2HDMs are favored by SFOEWPT, which is necessary for electroweak baryogenesis, and observed m  W  shift as well. We find that under current constraints, both Type-I and Type-II 2HDM can explain the SFOEWPT, Z-pole, Higgs precision measurements and m  W  precision measurement of CDF-II at same time, and all these precision measurements are sensitive to heavy Higgs mass splitting in 2HDM. The allowed regions are ∆m  A/C  ∈ (−400, 400) GeV, tan β ∈ (1, 50), and ∆m  A/C  ∈ (−200, 300) GeV, tan β ∈ (1, 10) for Type-I and Type-II 2HDM respectively. Furthermore future lepton collider measurements on Higgs and Z boson properties can explore this scenario in more detail or even rule out it.

Huayang Song

Wei Su

Electroweak phase transition in 2HDM under Higgs, Z-pole, and W precision measurements

Axion-like particles (ALPs) appear in various new physics models with spon- taneous global symmetry breaking. When the ALP mass is in the range of MeV to GeV, the cosmology and astrophysics bounds are so far quite weak. In this work, we investi- gate such light ALPs through the ALP-strahlung production processes pp → W  ±  a, Za with the sequential decay a → γγ at the 14 TeV LHC with an integrated luminosity of 3000 fb −1 (HL-LHC). Building on the concept of jet image which uses calorimeter towers as the pixels of the image and measures a jet as an image, we investigate the potential of machine learning techniques based on convolutional neural network (CNN) to identify the highly boosted ALPs which decay to a pair of highly collimated photons. With the CNN tagging algorithm, we demonstrate that our approach can extend current LHC sensitivity and probe the ALP mass range from 0.3 GeV to 5 GeV. The obtained bounds are stronger than the existing limits on the ALP-photon coupling.

Jie Ren

Daohan Wang

Lei Wu

Detecting an axion-like particle with machine learning at the LHC

Axionlike particles (ALPs) are predicted by many extensions of the Standard Model. When ALP mass lies in the range of MeV–GeV, the cosmology and astrophysics will be largely irrelevant. In this work, we investigate such light ALPs through the ALP-strahlung process <math><mi>p</mi><mi>p</mi><mo>→</mo><mi>V</mi><mi>a</mi><mo>(</mo><mo>→</mo><mi>γ</mi><mi>γ</mi><mo>)</mo></math> at the 14 TeV LHC with an integrated luminosity of <math><mrow><mn>3000</mn><mtext> </mtext><mtext> </mtext><msup><mrow><mi>fb</mi></mrow><mrow><mo>−</mo><mn>1</mn></mrow></msup></mrow></math> (high-luminosity LHC). With the photon-jet algorithm, we demonstrate that our approach can probe the mass range of ALPs, which has been inaccessible in previous LHC experiments. The obtained result can surpass the existing limits on ALP-photon coupling in the ALP mass range from 0.3 to 10 GeV.

Photon-jet events as a probe of axionlike particles at the LHC

We propose a model which explains the baryon asymmetry of the universe and dark matter relic density at the same time. In this model, dark matter candidate is the dark baryon composed by dark quarks. A scalar mediator, which couples to the standard model leptons and dark quarks, is introduced to generate the asymmetry of baryon and dark baryon simultaneously. Direct detection and collider detection of this model are studied. We find that current underground direct detection experiments and LHC can hardly detect this model. But future lepton colliders, such as CEPC, have great potential to detect a large portion of the model parameter space, via novel signal “displaced lepton jet”.