High Energy Physics - Phenomenology (hep-ph)

Abstract: The relic density of Dark Matter (DM) in the freeze-in scenario is highly dependent on the evolution history of the universe and changes significantly in a non-standard (NS) cosmological framework prior to Big Bang Nucleosynthesis (BBN). In this scenario, an additional species dominates the energy budget of the universe at early times (before BBN), resulting in a larger cosmological expansion rate at a given temperature compared to the standard radiation-dominated (RD) universe. To investigate the production of DM in the freeze-in scenario, we consider both standard RD and NS cosmological picture before BBN and perform a comparative analysis. We extend the Standard Model (SM) particle content with a SM singlet DM particle $\chi $ and an axion-like particle (ALP) $a$. The interactions between ALP, SM particles, and DM are generated by higher dimensional effective operators. This setup allows the production of DM $\chi$ from SM bath through the mediation of ALP, via ALP-portal processes. These interactions involve non-renormalizable operators, leading to ultraviolet (UV) freeze-in, which depends on the reheating temperature ($T_{RH}$) of the early universe. In the NS cosmological scenario, the faster expansion rate suppresses the DM production processes, allowing for enhanced effective couplings between the visible and dark sectors to satisfy the observed DM abundance compared to RD scenario. This improved coupling increases the detection prospects for freeze-in DM via the ALP-portal, which is otherwise challenging to detect in RD universe due to small couplings involved. Using an effective field theory set-up, we show that various ALP searches such as in FASER, DUNE, and SHiP, etc. will be able to probe significant parameter space depending on the different model parameters.

Abstract: Coherent elastic neutrino-nucleon scattering, challenged by the low nucleus recoil energy of a few tens of keV, has been observed by the COHERENT experiment using targets CsI and Ar. We study the contribution of a light $Z'$ mediator in a gauged $U(1)_{L_\mu-L_\tau}$ symmetry. In contrast to the mechanism from the kinetic mixing between $U(1)_{\rm em}$ and $U(1)_{L_\mu-L_\tau}$, we adopt a dynamical symmetry breaking of the $U(1)_{L_\mu-L_\tau}$ by employing an extra Higgs doublet. As a result, the weak charge mediated by $Z'$ only depends on the mass of light gauge boson. Since two Goldstone bosons are required to serve as the longitudinal components of $Z$ and $Z'$, the model does not contain a physical CP-odd scalar. Using the introduced Higgs doublet carrying the $U(1)_{\mu-\tau}$ charge, new Higgs decay channels $h\to Z_1 Z_1/Z_1 Z_2$ with percent-level branching fractions become accessible. The $W$-mass anomaly observed by CDF II can be resolved by enhancing the oblique parameter $T$. With the flavored gauge symmetry, the Yukawa couplings to fermion flavors are strictly limited. By utilizing the characteristic and introducing a scalar leptoquark $S^{\frac{1}{3}}=(3,1,2/3)$ that uniquely couples to the $\tau$ lepton, the excesses of $R(D)$ and $R(D^*)$ can be explained. Moreover, $\tau \to \mu (Z_1\to ) e^- e^+$ via the resonant light gauge boson decay can reach the sensitivity of Belle II at an integrated luminosity of 50 ab$^{-1}$.

Abstract: We construct an $S_4$ flavour symmetric minimal inverse seesaw model where the standard model is extended by adding two right-handed and two standard model gauge singlets neutrinos to explain the origin of tiny neutrino masses. The resulting model describes the lepton mass spectra and flavour mixing quite well for the case of the normal hierarchy of neutrino masses. The prediction of the model on the Dirac CP-violating phase is centered around $370.087^\circ$. Furthermore, using the allowed region for the model parameters, we have calculated the value of the effective Majorana neutrino mass, $\lvert\langle m_{ee}\rangle\rvert$, which characterizes neutrinoless double beta decay.

Abstract: We calculate soliton solutions to the scalar field equation of motion that arises for the 4th-order extended Lagrangian (\(\phi^{4}\) theory) in quantum field theory using the extended hyperbolic tangent and the sine-cosine methods. Using the former technique, ten complex soliton waves are obtained; we graphically represent three of these profiles using density plots. In the latter case, two real soliton solutions are obtained, of which, we demonstrate the wave profile for the positive case. Using the multiplier method, we calculate conservation laws in \((1 + 1)\)-, \((2 + 1)\)-, and \((3 + 1)\)-dimensions producing three, six, and ten conservation laws respectively. Lastly, we reflect on the application of conservation laws in particle physics and phenomenology.

Abstract: The widths of the decays $\tau \to K^- K^+ K^- \nu_\tau$ and $\tau \to K^- K^0 \bar{K}^0 \nu_\tau$ are calculated in the $U(3)\times U(3)$ chiral quark NJL model. Four channels are considered: contact, axial vector, vector and pseudoscalar channels. It is shown that the dominant contribution is given by the axial vector channel with an intermediate $\phi$ meson. The obtained results are in satisfactory agreement with the experimental data.

Abstract: We extend the discussion of the recently discovered 'anomaly poles' in QCD Compton scattering. We perform the complete one-loop calculation of the Compton amplitude using momentum transfer $t$ as the regulator of collinear divergences. In the gluon channel, we confirm the presence of poles $1/t$ in both the real and imaginary parts of the amplitude. In the quark channel, we find unexpected infrared single $1/\epsilon$ and double $1/\epsilon^2$ poles. We then perform the one-loop calculation of the leading-twist quark generalized parton distributions (GPDs) with the same regulators and find that all these singular terms can be systematically absorbed into the GPDs, showing that QCD factorization is restored to this order. Having established this, we discuss the fate of the $1/t$ poles. We argue that they become the nonperturbative building blocks of GPDs that encode the chiral and trace anomalies of QCD, in a way consistent with the known constraints these anomalies impose on the nucleon axial and gravitational form factors. The scope of research on GPDs can therefore be expanded to address the manifestation and implications of quantum anomalies in high-energy exclusive processes.

Abstract: Inspired by recent observations of $T_{c\bar{s}0}(2900)^0$ in the $D_s^+ \pi^-$ invariant mass distribution of $B^0 \to \bar{D}^0 D_s^+ \pi^-$ decay and $T_{c\bar{s}0}(2900)^{++}$ in the $D_s^+ \pi^+$ invariant mass distribution of $B^+ \to D^- D_s^+ \pi^+$ decay, we investigate the $T_{c\bar{s}0}(2900)^{++}$ contribution to the $B^+ \to K^+ D^+ D^-$ decay in a molecular scenario, where we consider $T_{c\bar{s}0}(2900)r^{++}$ as a $D^{\ast +} K^{\ast+}$ molecular state. Our estimations indicate that the fit fraction of $T_{c\bar{s}0}(2900)^{++}$ in the $B^+ \to K^+ D^+ D^-$ is about $12.5\%$, and its signal is visible in the $D^+ K^+$ invariant mass distribution. With the involvement of $T_{c\bar{s}0}(2900)^{++}$, the fit fractions of $\chi_{c0}(3915)$ and $\chi_{c2}(3930)$ may be much different with the ones obtained by the present amplitude analysis [Phys. Rev. D \textbf{102}, 112003 (2020)], which may shed light on the long standing puzzle of $\chi_{c0}(3915)$ as the conventional charmonium.

Abstract: Flavour-violating axions appear in models where the Peccei-Quinn(PQ) charges are generation non-universal. Consequently, this charge arrangement will also generate flavour violation in the UV sector. The typical way of implementing such an axion in a UV completion is with a DFSZ model, containing 2 Higgs doublets. In this talk we will present how to parameterize the flavour violation in the UV such that we can find a direct correlation with the flavour violation of the axion. Finally, we show in an example how this connection can help in giving information about the UV completion if an axion is found in a flavour-violating channel.

Abstract: We show the absence of an instability of homogeneous (chiral) condensates against spatially inhomogeneous perturbations for various 2+1-dimensional four-fermion and Yukawa models. All models are studied at non-zero baryon chemical potential, while some of them are also subjected to chiral and isospin chemical potential. The considered theories contain up to 16 Lorentz-(pseudo)scalar fermionic interaction channels. We prove the stability of homogeneous condensates by analyzing the bosonic two-point function, which can be expressed in a purely analytical form at zero temperature. Our analysis is presented in a general manner for all of the different discussed models. We argue that the absence of an inhomogeneous chiral phase (where the chiral condensate is spatially non-uniform) follows from this lack of instability. Furthermore, the existence of a moat regime, where the bosonic wave function renormalization is negative, in these models is ruled out.

Abstract: We consider a minimal extension of the Standard Model in warped extra dimensions, with fields propagating in the bulk including a bulk SM-like Higgs doublet. We show that the Higgs can acquire a non-trivial oscillatory VEV, strongly localized towards the TeV brane, but such that its value at that brane could be highly suppressed due to its oscillatory behaviour. Within the minimal Randall-Sundrum metric background, this oscillatory VEV can alleviate the bounds coming from oblique precision electroweak parameters, such that the KK gluon mass can be around 3 TeV (instead of about 8 TeV for the usual non-oscillatory bulk Higgs). We also discuss the stability of the configuration as well as the naturalness of the model parameters.

Abstract: Electroweak effects in the $e^+e^- \to t \bar{t}$ annihilation process are described with taking into account polarization of the initial and final particles. We investigate the effects of complete one-loop electroweak radiative corrections and higher-order radiative effects to the total cross section and analyze different types of asymmetries for polarized initial and final states for typical energies and degrees of polarization of the ILC and CLIC projects. Numerical results are obtained with the help of Monte Carlo tools: the ReneSANCe event generator and the MCSANC integrator.