High Energy Physics - Phenomenology (hep-ph)

Abstract: With the chiral unitary approach, we evaluate the hidden strange $B_{c}$-like molecular states of $b\bar{c}s\bar{s}$ systems $\bar{B}_{s}\bar{D}_{s}$, $\bar{B}_{s}^{*}\bar{D}_{s}$, $\bar{B}_{s}\bar{D}_{s}^{*}$, and $\bar{B}_{s}^{*}\bar{D}_{s}^{*}$ coupled to the non-strange channels. The $S$-wave scattering amplitudes are calculated based on the vector meson exchange, four pseudoscalar mesons contact interactions, and four vector mesons contact interactions obtained from the extended local hidden gauge approach. We find six states below the threshold of the most relevant channel. The binding energies of these states are around $1-10$ MeV and the widths are around $0.2-0.7$ MeV. Our research is a supplement to the mass spectra of $B_{c}$-like states, which may be useful for the experimental search in the future.

Abstract: In this letter, we propose a new method for measuring the Sachs form factors ratio ($R =\mu_p G_E/G_M$) based on the transfer of polarization from the initial proton to the final electron in the elastic $e \vec p \to \vec e p$ process, in the case when the axes of quantization of spins of the target proton at rest and of the scattered electron are parallel, i.e., when an electron is scattered in the direction of the spin quantization axis of the proton target. To do this, in the kinematics of the SANE collaboration experiment (2020) on measuring double spin asymmetry in the $\vec e\vec p \to e p$ process, using Kelly (2004) and Qattan (2015) parametrizations, a numerical analysis was carried out of the dependence of the longitudinal polarization degree of the scattered electron on the square of the momentum transferred to the proton, as well as on the scattering angles of the electron and proton. It is established that the difference in the longitudinal polarization degree of the final electron in the case of conservation and violation of scaling of the Sachs form factors can reach 70%. This fact can be used to set up polarization experiments of a new type to measure the ratio $R$.

Abstract: We calculate the Debye screening mass in thermal, dense and magnetized QCD matter in the frame of resummed perturbation theory. In the limit of zero temperature, when the Landau energy level and Fermi surface of quarks match each other $\mu_q^2=2n|qB|$, where $q$, $\mu_q$ and $B$ are respectively the quark electric charge, chemical potential and external magnetic field, the screening mass diverges and the system is in the state of weakly interacting parton gas, which is very different from the known result of strongly interacting quark-gluon plasma at high temperature. The divergence disappears in thermal medium, but the screening mass oscillates with clear peaks at the matched magnetic field.

Abstract: In this paper, we explore the possibility of measuring the complete polarizations of cosmic photons $\gamma$ and the polarizations of cosmic electrons $e^{-}$ and positrons $e^{+}$. Our innovative Vector Meson Photo-production induced polarimetry enables people to measure the circular plarization compoent of a $GeV$ $\gamma$ and to improve its linear polarization measurement, and thus enables people to measure the polarization of $GeV$ $e^{+}/e^{-}$ for the first time. We calculate the production process of $\pi^{+}\pi^{-}$ by a generally polarized photon near nucleon's field in a generalized VPD-SDMEs Factorization with the fitted experimental data, so that it's partially model-independent. We also propose the observables and approach to measure their polarizations based on our calculations. Our new polarimetry of high-energy cosmic $\gamma,e^{+},e^{-}$ will open a new window to reveal the mysteries and solve the puzzles of BSM new physics in particle physics and cosmology.

Abstract: Inspired by the recent evidences of nano-Hertz stochastic gravitational waves observed by the pulsar timing array collaborations, we explore their implied supercooled electroweak phase transition in the singlet extension of the Standard Model. Our findings reveal that by adjusting the model parameter at per milli level, the corresponding percolation temperature can be continuously lowered to 1 GeV. With such a low percolation temperature, the singlet dark matter may freeze out before the electroweak phase transition, and, consequently, the entropy generated during the transition can significantly affect the dark matter relic density and other related constraints.

Abstract: A cosmic first-order phase transition (FOPT) occurring at MeV-scale provides an attractive explanation for the nano-Hertz gravitational wave (GW) background indicated by the recent pulsar timing array data from the NANOGrav, CPTA, EPTA and PPTA collaborations. We propose this explanation can be further tested at the colliders if the hidden sector couples to the Standard Model sector via Higgs portal. Through a careful analysis of the thermal history of the hidden sector, we demonstrate that in order to successfully explain the observed GW signal, the portal coupling must be sizable that it can be probed through Higgs invisible decay at the LHC or future lepton colliders such as CEPC, ILC, and FCC-ee. Our research offers a promising avenue to uncover the physical origin of the nano-Hertz GWs through particle physics experiments.

Abstract: We propose a new dark matter contender within the context of the so-called ``dark dimension'', an innovative 5-dimensional construct that has a compact space with characteristic length-scale in the micron range. The new dark matter candidate is the radion, a bulk scalar field whose quintessence-like potential drives an inflationary phase described by a 5-dimensional de Sitter (or approximate) solution of Einstein equations. We show that the radion could be ultralight and thereby serve as a fuzzy dark matter candidate. We advocate a simple cosmological production mechanism bringing into play unstable Kaluza-Klein graviton towers which are fueled by the decay of the inflaton. We demonstrate that the fuzzy radion can accommodate the signal recently observed in pulsar timing arrays.

Abstract: A leptophobic $Z^\prime$ that does not couple with the Standard Model leptons can evade the stringent bounds from the dilepton-resonance searches. In our earlier paper [T. Arun et al., Search for the $Z'$ boson decaying to a right-handed neutrino pair in leptophobic $U(1)$ models, Phys. Rev. D, 106 (2022) 095035; arXiv:2204.02949], we presented two gauge anomaly-free $U(1)$ models where a heavy leptophobic $Z'$ is present along with right-handed neutrinos ($N_R$). We pointed out the interesting possibility of a correlated search for $Z'$ and $N_R$ at the LHC through the $pp\to Z'\to N_R N_R$ channel. This channel can probe a part of the leptophobic $Z'$ parameter space that cannot be otherwise probed using the standard dijet resonance searches. In this paper, we analyse the monolepton final state arising from the decay of the $N_R$ pair. We show that a leptophobic $Z'$ as heavy as $7$ TeV and with a gauge coupling of the order of the electroweak coupling is discoverable through this channel at the high-luminosity LHC.

Abstract: We review the status of the Standard Model theory of neutron beta decay. Particular emphasis is put on the recent developments in the electroweak radiative corrections. Given that some existing approaches give slightly different results, we thoroughly review the origin of discrepancies, and provide our recommended value for the radiative correction to the neutron and nuclear decay rates. The use of dispersion relation, lattice Quantum Chromodynamics and effective field theory framework allows for high-precision theory calculations at the level of $10^{-4}$, turning neutron beta decay into a powerful tool to search for new physics, complementary to high-energy collider experiments. We offer an outlook to the future improvements.

Abstract: The sensitivity to the strong coupling $\alpha_S(M^2_Z)$ is investigated using existing Deep Inelastic Scattering data from HERA in combination with projected future measurements from the Electron Ion Collider (EIC) in a next-to-next-to-leading order QCD analysis. A potentially world-leading level of precision is achievable when combining simulated inclusive neutral current EIC data with inclusive charged and neutral current measurements from HERA, with or without the addition of HERA inclusive jet and dijet data. The result can be obtained with significantly less than one year of projected EIC data at the lower end of the EIC centre-of-mass energy range. Some questions remain over the magnitude of uncertainties due to missing higher orders in the theoretical framework.

Abstract: Heavy Neutral Leptons are popular hypothetical particles, first introduced as a way to explain neutrino oscillations, and since then extensively studied in relation to many other aspects of physics beyond the Standard Model. They also serve as viable targets for direct experimental searches, being effectively described only by HNL mass and mixing with each neutrino flavor. Motivated by this, we study the lower theoretical boundary for mixing with a specified flavor in two and three HNL cases. We find the connection of this limit with the effective neutrino mass appearing in neutrinoless double beta decay (and similar expressions for mixing with muon and tau neutrino). In two HNL case, there is a rather strict relation between mixing of different HNL with the same neutrino flavor. We find that existing exclusion regions and their expected expansions in the near future are all described by a certain limit. We call that limit pseudodegenerate and find its relation to the symmetrical limit, already studied in the literature. We also study pseudodegenerate limit and conditions under which it is achieved in three HNL case.

Abstract: Several pulsar timing arrays have recently reported the observation of a stochastic background of red-tilted gravitational wave spectrum in the nano-Hz frequencies. An inflationary interpretation of this observation is challenging from various aspects. We report that such a signal can arise from Chern-Simons coupling in axion inflation, where a pseudoscalar inflaton couples to (massive) $U(1)$ gauge field, leading to efficient production of a transverse gauge mode. Such tachyonic particle production during inflation exponentially enhances the primordial perturbations and leads to a unique parity-violating gravitational wave spectrum, that remains flat near the CMB scales but becomes red-tilted at smaller scales. We identify the parameter space consistent with various cosmological constraints and show that the resultant gravitational wave signals can explain the observed excess at NANOGrav.

Abstract: In this article we discuss a minimal extension of the Inert Doublet Model (IDM) with an effective $CP$-violating $D=6$ operator, involving the inert Higgs and weak gauge bosons, that can lift it to a fully realistic setup for creating the baryon asymmetry of the Universe (BAU). Avoiding the need to stick to an explicit completion, we investigate the potential of such an operator to give rise to the measured BAU during a multi-step electroweak phase transition (EWPhT) while sustaining a viable DM candidate in agreement with the measured relic abundance. We find that the explored extension of the IDM can account quantitatively for both DM and for baryogenesis and has quite unique virtues, as we will argue. It can thus serve as a benchmark for a minimal realistic extension of the SM that solves some of its shortcomings and could represent the low energy limit of a larger set of viable completions. After discussing the impact of a further class of operators that open the possibility for a larger mass splitting (enhancing the EWPhT) while generating the full relic abundance also for heavy inert-Higgs DM, we ultimately provide a quantitative evaluation of the induced lepton electric dipole moments in the minimal benchmark for the BAU. These arise here at the two-loop level and are therefore less problematic compared to the ones that emerge when inducing $CP$ violation via an operator involving the SM-like Higgs.

Abstract: It is essential to directly investigate the self-couplings of gauge bosons in the Standard Model (SM) due to its non-Abelian nature, as these couplings play a significant role in comprehending the gauge structure of the model. The discrepancies between the Standard Model's expectations and the measured value of gauge boson self-couplings would serve as strong evidence towards the existence of new physics phenomena that extend beyond the Standard Model. Such deviations could provide valuable insights into the nature of new physics and potentially lead to a deeper understanding of fundamental particles and their interactions. In this study, we examine the sensitivities of anomalous couplings associated with dimension-8 operators that affect the $\gamma \gamma \gamma \gamma$ and $Z \gamma \gamma \gamma$ quartic vertices. The study focuses on the process $e^- \gamma \to e^-\gamma\gamma$ with the incoming photon under Weizs\"acker-Williams approximation at the stage-3 scenerio of Compact Linear Collider (CLIC) that is refer to a CoM energy of 3 TeV. Due to the CLIC options, we take into account the both unpolarized and $\mp80\%$ polarized electron beam with the related integrated luminosities of ${\cal L}=5, 4, 1$ $\rm ab^{-1}$ under the systematic uncertainties of $\delta_{sys}=0, 3, 5$. Obtained sensitivities on the anomalous quartic gauge couplings (aQGCs) for the process $e^- \gamma \to e^-\gamma\gamma$ at $\sqrt{s}= 3$ TeV and various polarizations, are improved by a factor of 2-200 times better for the couplings $f_{T,j}/\Lambda^4$ compared with the experimental results.

Abstract: Recent measurements of the Lamb shift of muonic helium-4 ions were used to infer the alpha particle charge radius. The value found is compatible with the radius extracted from the analysis of the electron-helium scattering. Thus, the new spectroscopic data put additional empiric bounds on some free parameters of certain physics theories beyond the Standard Model. In this paper, we analyze the new data in the context of large extra-dimensional theories. Specifically, we calculate the influence of the radion, the scalar degree of freedom of the higher-dimensional gravity, on the energy difference between the 2S and 2P levels of this exotic atom. The radion field is related to fluctuations of the volume of the supplementary space, and, in comparison with the tensorial degrees of freedom, it couples to matter in a different way. Moreover, as some stabilization mechanism acts exclusively on the scalar degree of freedom, the tensor and scalar fields should be treated as phenomenologically independent quantities. Based on the spectroscopic data of muonic helium, we find constraints for the effective energy scale of the radion as a function of the alpha particle radius. Then, we discuss the implications of these new constraints on the proton radius puzzle.

Abstract: In light of the result published by the Fermilab Muon $(g-2)$ experiment, we investigate a simple model that includes particles of fractional electric charges: a colour-singlet fermion and a scalar with charges $2/3e$ and $1/3e$, respectively. The impact of these particles on the muon anomalous magnetic moment are examined, particularly the restrictions on their Yukawa couplings with the light leptons. Given that lepton flavor violation processes impose stringent constraints on certain scenarios beyond the Standard Model, we asses the one-loop contribution of the new particles to $(g-2)$ in order to identify regions in the parameter space consistent with the Fermilab results and compatible with the current and projected limits on the branching ratio $Br(\mu \rightarrow e \gamma)$. Taking into account the current lower bound for the masses of fractionary charged particles, which is around 634 GeV, we show that the mass of the scalar particle with fractional charge must exceed 1 TeV and may be discovered in future collider experiments. Finally, we also study the validity of our model in light of the QCD lattice results on the muon $(g-2)$.