High Energy Physics - Phenomenology (hep-ph)

Abstract: The absorption of fermionic dark matter has recently been studied as a signature for the direct detection of dark matter. We construct the first UV completion of the scalar effective operator associated with this signature. We calculate the constraints on the model and demonstrate there is viable parameter space which can be probed by a next-generation experiment such as XLZD. We also consider the cosmological history of our model and show that the correct relic abundance can be obtained via freeze-out in the dark sector. However, within this minimal model, we find that the absorption signal is highly suppressed in the parameter space that yields the correct relic abundance.

Abstract: Studies related to $\rm{J}/\psi$ meson, a bound state of charm and anti-charm quarks ($c\bar{c}$), in heavy-ion collisions, provide genuine testing grounds for the theory of strong interaction, quantum chromodynamics (QCD). To better understand the underlying production mechanism, cold nuclear matter effects, and influence from the quark-gluon plasma, baseline measurements are also performed in proton-proton ($pp$) and proton-nucleus ($p$--A) collisions. The inclusive $\rm{J}/\psi$ measurement has contributions from both prompt and non-prompt productions. The prompt $\rm{J}/\psi$ is produced directly from the hadronic interactions or via feed-down from directly produced higher charmonium states, whereas non-prompt $\rm{J}/\psi$ comes from the decay of beauty hadrons. In experiments, $\rm{J}/\psi$ is reconstructed through its electromagnetic decays to lepton pairs, in either $e^{+}+e^{-}$ or $\mu^{+}+\mu^{-}$ decay channels. In this work, for the first time, machine learning techniques are implemented to separate the prompt and non-prompt dimuon pairs from the background to obtain a better identification of the $\rm{J}/\psi$ signal for different production modes. The study has been performed in $pp$ collisions at $\sqrt{s} = 7$ and 13 TeV simulated using PYTHIA8. Machine learning models such as XGBoost and LightGBM are explored. The models could achieve up to 99\% prediction accuracy. The transverse momentum ($p_{\rm T}$) and rapidity ($y$) differential measurements of inclusive, prompt, and non-prompt $\rm{J}/\psi$, its multiplicity dependence, and the $p_{\rm T}$ dependence of fraction of non-prompt $\rm{J}/\psi$ ($f_{\rm B}$) are shown. These results are compared to experimental findings wherever possible.

Abstract: We study an extension of the Standard Model (SM) with two candidates for dark matter (DM) which includes a Dirac fermion and a Vector Dark Matter (VDM) under new $U(1)$ gauge group in the hidden sector. The model is classically scale invariant and the electroweak symmetry breaks because of the loop effects. We investigate the model parameter space allowed by current experimental constraints and phenomenological bounds. It is shown that the model can be satisfied for the large part of parameter space of VDM mass and fermion dark matter mass, i.e., $400< M_V<3000$ GeV and $M_{\psi}<400$ GeV.The electroweak phase transition have been discussed and shown that there is region in the parameter space of the model consistent with DM relic density, direct detection and collider constraints, while at the same time can lead to first order electroweak phase transition. The gravitational waves produced during the phase transition could be probed by future space-based interferometers such as LISA and BBO.

Abstract: We study the exclusive diffractive $c \bar c$ photoproduction in ultraperipheral $pA$ collisions. The formalism makes use of off-diagonal generalizations of the unintegrated gluon distribution, the so-called generalized transverse momentum dependent distributions (GTMDs). We present two different formulations. The first one is based directly on gluon GTMD parametrizations in momentum space. Another option is the calculation of the GTMD as a Fourier transform of the dipole-nucleon scattering amplitude $N(Y,\vec{r}_{\perp},\vec{b}_{\perp})$. The latter approach requires some extra regularization discussed in the paper. Different dipole amplitudes from the literature are used. Compared to previous calculations in the literature, we integrate over the full phase space and therefore cross sections for realistic conditions are obtained. We present distributions in rapidity of $c$ or $\bar c$, transverse momentum of the $c \bar c$ pair, four-momentum transfer squared as well as the azimuthal correlation between a sum and a difference of the $c$ and $\bar c$ transverse momenta. The azimuthal correlations are partially due to the so-called elliptic gluon Wigner distribution. Different models lead to different modulations in the azimuthal angle. The modulations are generally smaller than 5%. They depend on the range of transverse momentum selected for the calculation.

Abstract: With four different type of neutrino-induced interactions, we considered to investigate and reanalyse the KNO scaling in modified multiplicity distributions from a different perspective. In an attempt of first of its kind, we propose alternate fitting function to parameterise the distribution than the most widely adopted Slattery's function and compare it with yet another form. We propose the shifted Gompertz and Weibull functions as the fitting functions and compare their potency for the most conventional form of Slattery's function. In addition the analysis of the data by evaluating the central moments and factorial moments, we show the dependence of moments on the target size.

Abstract: We show that warm inflation can be successfully realized in the high temperature regime through dissipative interactions between the inflaton and a single fermionic degree of freedom, provided that the latter's mass is an oscillatory function of the inflaton field value. We demonstrate, in particular, that despite the consequent large amplitude oscillations of the eta slow-roll parameter, their effect is, on average, sufficiently suppressed to allow for a slow-roll trajectory. In addition, we demonstrate that, even though this also induces a parametric resonance that amplifies inflaton perturbations, this has a negligible effect on CMB scales in the relevant parametric range. Hence, the "Warm Little Inflaton" scenario can be realized with one less fermionic degree of freedom and no need of imposing an additional discrete interchange symmetry.

Abstract: The measurements on a few pentaquarks states $P_c(4440)$, $P_c(4457)$ and $P_{cs}(4459)$ excite our new interests about their structures. Since the masses of $P_c(4440)$ and $P_c(4457)$ are close to the threshold of $\Sigma_c\bar D^*$, in the earlier works, they were regarded as molecular states of $\Sigma_c\bar D^*$ with quantum numbers $I(J^P)=\frac{1}{2}(\frac{1}{2}^-)$ and $\frac{1}{2}(\frac{3}{2}^-)$, respectively. In a similar way $P_{cs}(4459)$ is naturally considered as a $\Xi_c\bar D^*$ bound state with $I=0$. Within the Bethe-Salpeter (B-S) framework we systematically study the possible bound states of $\Lambda_c\bar D^*$, $\Sigma\bar D^*$, $\Xi_c\bar D^*$ and $\Xi_c'\bar D^*$. Our results indicate that $\Sigma_c\bar D^*$ can form a bound state with $I(J^P)=\frac{1}{2}(\frac{1}{2}^-)$, which corresponds to $P_c(4440)$. However for the $I(J^P)=\frac{1}{2}(\frac{3}{2}^-)$ system the attraction between $\Sigma$ and $\bar D^*$ is too weak to constitute a molecule, so $P_{c}(4457)$ may not be a bound state of $\Sigma\bar D^*$ with $I(J^P)=\frac{1}{2}(\frac{3}{2}^-)$. As $\Xi_c\bar D^*$ and $\Xi_c'\bar D^*$ systems we take into account of the mixing between $\Xi_c$ and $\Xi'_c$ and the eigenstets should include two normal bound states $\Xi_c\bar D^*$ and $\Xi_c'\bar D^*$ with $I(J^P)=\frac{1}{2}(\frac{1}{2}^-)$ and a loosely bound state $\Xi_c\bar D^*$ with $I(J^P)=\frac{1}{2}(\frac{3}{2}^-)$. The conclusion that two $\Xi_c\bar D^*$ bound states exist, supports the suggestion that the observed peak of $P_{cs}(4459)$ may hide two states $P_{cs}(4455)$ and $P_{cs}(4468)$. Based on the computations we predict a bound state $\Xi_c'\bar D^*$ with $I(J^P)=\frac{1}{2}(\frac{1}{2}^-)$ but not that with $I(J^P)=\frac{1}{2}(\frac{3}{2}^-)$. Further more accurate experiments will test our approach and results.

Abstract: The current observational properties of neutron stars have not definitively ruled out the possibility of dark matter. In this study, we primarily focus on exploring correlations between the dark matter model parameters and different neutron star properties using a rich set of EOSs. We adopt a two-fluid approach to calculate the properties of neutron stars. For the nuclear matter EOS, we employ several realistic EOS derived from the relativistic mean field model (RMF), each exhibiting varying stiffness and composition. In parallel, we look into the dark matter EOS, considering fermionic matter with repulsive interaction described by a relativistic mean field Lagrangian. A reasonable range of parameters is sampled meticulously. Interestingly, our results reveal a promising correlation between the dark matter model parameters and stellar properties, particularly when we ignore the uncertainties in the nuclear matter EOS. However, when introducing uncertainties in the nuclear sector, the correlation weakens, suggesting that the task of conclusively constraining any particular dark matter model might be challenging using global properties alone, such as mass, radius, and tidal deformability. Notably, we find that dark-matter admixed stars tend to have higher central baryonic density, potentially allowing for non-nucleonic degrees of freedom or direct Urca processes in stars with lower masses. There is also a tantalizing hint regarding the detection of stars with the same mass but different surface temperatures, which may indicate the presence of dark matter. With our robust and extensive dataset, we delve deeper and demonstrate that even in the presence of dark matter, the semi-universal C-Love relation remains intact.