High Energy Physics - Phenomenology

Domingo, Florian;Günther, Julian;Kim, Jong Soo;Wang, Zeren Simon

doi: 10.48550/arxiv.2308.07371pmid: N/A

Abstract:A series of far-detector programs have been proposed for operation at various interaction points of the Large Hadron Collider during the upcoming runs. Investigating the potential and complementarity of these experiments for new-physics searches goes through the estimation of their sensitivity to specific long-lived particle models. Here, we present an integrated numerical tool written in the C++ language and called Displaced Decay Counter, which we have created to this end and which can be used in association with MadGraph5, Pythia8, or any other state-of-the-art Monte-Carlo collider simulation tool. Several far-detector models have been implemented within the program, accounting for the geometry and integrated luminosity of projected detectors. Additional or more accurate designs can be easily constructed through a dedicated interface. The functionality of this tool is exemplified through the discussion of three benchmark scenarios, which we consider for the validation of the implemented detector models.

Puyam, Victoria;Singh, N. Nimai

doi: 10.48550/arxiv.2308.05944pmid: N/A

Abstract:A neutrino mass model that can satisfy the exact golden ratio mixing is constructed using $A_{5}$ discrete symmetry group. The deviation from the golden ratio mixing is studied by considering the contribution from the charged lepton sector in a linear seesaw framework. A definite pattern of charged lepton mass matrix predicted by the model controls the leptonic mixing angles. By taking the observed $\theta_{13}$ as the input value, we can obtain the values of all the mixing angles and Dirac CP-violating phase within the current experimental bounds. The model predicts that only the normal neutrino mass ordering is consistent with the current oscillation data. We also study the charged lepton flavor violation (cLFV) process such as $\mu \rightarrow e +\gamma$ and $\tau \rightarrow e +\gamma$ and neutrinoless double beta decay parameter $m_{\beta \beta}$. The present neutrino mass model can explain the current and future sensitivity of the cLFV processes and the present sensitivity of neutrinoless double beta decay parameter when the masses of quasi-Dirac neutrinos are in the TeV range.

Consoli, Maurizio;Rupp, George

doi: 10.48550/arxiv.2308.01429pmid: N/A

Abstract:Perturbative calculations predict that the Standard Model (SM) effective potential should have a new minimum, well beyond the Planck scale, much deeper than the electroweak vacuum. As it is not obvious that gravitational effects can get so strong to stabilize the potential, most authors have accepted the metastability scenario in a cosmological perspective. This perspective is needed to explain why the theory remains trapped into our electroweak vacuum, but requires to control the properties of matter in the extreme conditions of the early universe. Alternatively, one can consider the completely different idea of a non-perturbative effective potential which, as at the beginning of the SM, is restricted to the pure $\Phi^4$ sector yet consistent with the now existing analytical and numerical studies. In this approach, where the electroweak vacuum is the lowest-energy state, besides the resonance of mass $m_h=125$ GeV defined by the quadratic shape of the potential at its minimum, the Higgs field should exhibit a second resonance with mass $690\pm10({\rm stat})\pm20({\rm sys})$ GeV associated with the zero-point energy determining the potential depth. Despite its large mass, this would couple to longitudinal $W$s with the same typical strength as the low-mass state at 125 GeV and represent a relatively narrow resonance of width $\Gamma_H=30÷38$ GeV, mainly produced at LHC by gluon-gluon fusion. So it is interesting that, in the LHC data, one can find various indications for a new resonance in the expected mass range with a non-negligible statistical significance. As this could become an important new discovery by just adding two missing samples of RUN2 data, we outline further refinements of the theoretical predictions that could be obtained by implementing unitarity constraints, in the presence of fermion and gauge fields, with coupled-channel calculations used for meson spectroscopy.

FASER Collaboration

doi: 10.1016/j.physletb.2023.138378pmid: N/A

Abstract:The FASER experiment at the LHC is designed to search for light, weakly-interacting particles produced in proton-proton collisions at the ATLAS interaction point that travel in the far-forward direction. The first results from a search for dark photons decaying to an electron-positron pair, using a dataset corresponding to an integrated luminosity of 27.0 fb$^{-1}$ collected at center-of-mass energy $\sqrt{s} = 13.6$ TeV in 2022 in LHC Run 3, are presented. No events are seen in an almost background-free analysis, yielding world-leading constraints on dark photons with couplings $\epsilon \sim 2 \times 10^{-5} - 1 \times 10^{-4}$ and masses $\sim$ 17 MeV - 70 MeV. The analysis is also used to probe the parameter space of a massive gauge boson from a U(1)$_{B-L}$ model, with couplings $g_{B-L} \sim 5 \times 10^{-6} - 2 \times 10^{-5}$ and masses $\sim$ 15 MeV - 40 MeV excluded for the first time.

Yaouanc, Alain Le;Richard, François

doi: 10.48550/arxiv.2308.12180pmid: N/A

Abstract:Several indications for neutral scalars are observed at the LHC. One of them, a broad resonance peaked at about 650 GeV which we call H(650), was first observed by an outsider combining published histograms from ATLAS and CMS on ZZ -> 4 leptons searches, and this combination shows a local significance close to 4 s.d. Since then, CMS has reported two other indications at the same mass, with similar local significances: H->WW->2leptons+neutrinos and H(650)->bbh(125) where mbb~90 GeV and h(125)->gam gam. ATLAS has completed its analysis of ZZ->4 leptons from which we infer an indication for H(650) with 3.5 s.d. significance. Combining these three results, one gets a global statistical significance above 6 s.d. H(650) has a coupling to WW similar to h(125) and therefore we argue that a sum rule (SR) required by unitarity for W+W- scattering implies that there should be a compensating effect from a doubly charged scalar H++, with a large coupling to W+W+. We therefore predict that this mode should become visible through the vector boson fusion process W+W+->H++, naturally provided by LHC. A recent indication for H++(450)->W+W+ from ATLAS allows a model independent interpretation of this result through the SR constraint which gives BR(H++->W+W+)~10%, implying the occurrence of additional decay modes H+W+ and H+H+ from one or several light H+ with masses below mH++ - mW or MH++/2, that is mH+ < 370 GeV or 225 GeV. A similar analysis is performed for H+(375)->ZW, indicated by ATLAS and CMS. Both channels suggest a scalar field content similar to the Georgi Machacek model with triplets, at variance with the models usually considered. Implications on precision measurements are presented followed by a complete extraction of the GM parameters. An alternate interpretation of the 650 GeV resonance as a tensor is also briefly discussed. Implications for precision measurements are presented.

Ekstedt, Andreas;Gould, Oliver;Hirvonen, Joonas

doi: 10.1007/jhep12(2023)056pmid: N/A

Abstract:We present a Python package, BubbleDet, for computing one-loop functional determinants around spherically symmetric background fields. This gives the next-to-leading order correction to both the vacuum decay rate, at zero temperature, and to the bubble nucleation rate in first-order phase transitions at finite temperature. For predictions of gravitational wave signals from cosmological phase transitions, this is expected to remove one of the leading sources of theoretical uncertainty. BubbleDet is applicable to arbitrary scalar potentials and in any dimension up to seven. It has methods for fluctuations of scalar fields, including Goldstone bosons, and for gauge fields, but is limited to cases where the determinant factorises into a product of separate determinants, one for each field degree of freedom. To our knowledge, BubbleDet is the first package dedicated to calculating functional determinants in spherically symmetric background

Liu, Fangyu;Iminniyaz, Hoernisa

doi: 10.48550/arxiv.2308.12556pmid: N/A

Abstract:We investigate the relic abundance of dark matter from coannihilation in non-standard cosmological scenarios. We explore the effect of coannihilation on the relic density of dark matter and freeze out temperature in quintessence model with kination phase and brane world cosmological scenarios. Since the Hubble expansion rate is enhanced in quintessence and brane world cosmological models, it causes the larger relic density compared to that in the standard one. On the other hand, the relic density of dark matter is decreased due to the coannihilation in the standard cosmological scenario. After including coannihilation in quintessence or brane world cosmological scenarios, we find the decrease of the relic density of dark matter is slightly slower than that in the standard cosmological scenario.

Di Luzio, Luca;Gisbert, Hector;Sørensen, Philip

doi: 10.1007/jhep04(2024)076pmid: N/A

Abstract:It has been recently claimed that the axion coupling to fermions is responsible for an oscillating electric dipole moment (EDM) in the background of axion dark matter. In this work, we re-examine the derivation of this effect. Contrary to previous studies, we point out the physical relevance of an axion boundary term, which is crucial in restoring the axion shift symmetry and drastically affects the EDM phenomenology. To describe the latter, we introduce the notion of a time-averaged effective axion EDM, which encodes the boundary term and whose magnitude depends on the oscillation regime. For slow oscillations, the boundary term washes out the standard oscillating EDM, resulting in an exact cancellation in the static limit. Conversely, during fast oscillations, the boundary term amplifies the effective EDM relatively to the standard EDM contribution. This observable is especially interesting in the case of the electron EDM. For an $\mathcal{O}(1)$ axion-electron coupling, the overall size of the effective EDM in the regime of intermediate or fast oscillations is comparable to the present static EDM limit.

Biondini, Simone;Bollig, Julian;Vogl, Stefan

doi: 10.48550/arxiv.2308.14594pmid: N/A

Abstract:Indirect detection is one of the most powerful methods to search for annihilating dark matter. In this work, we investigate the impact of non-perturbative effects in the indirect detection of dark matter. For this purpose we utilize a minimal model consisting of a fermionic dark matter candidate in the TeV mass range that interacts via scalar- and pseudo-scalar interactions with a massive scalar mediator mixing with the Higgs. The scalar interaction induces an attractive Yukawa potential between dark matter particles, such that annihilations are Sommerfeld enhanced, and bound states can form. These non-perturbative effects are systematically dealt with (potential) non-relativistic effective field theories and we derive the relevant cross sections for dark matter. We discuss their impact on the relic density and indirect detection. Annihilations in dwarf galaxies and the Galactic Center require special care and we derive generalized $J$-factors for these objects that account for the non-trivial velocity dependence of the cross sections in our model. We use limits on the gamma-ray flux based on Fermi-LAT observations and limits on the rate of exotic energy injection from Planck to derive bounds on the parameter space of the model. Finally, we estimate the impact that future limits from the Cherenkov Telescope Array are expected to have on the model.

Fu, Wei-jie;Luo, Xiaofeng;Pawlowski, Jan M.;Rennecke, Fabian;Yin, Shi

doi: 10.48550/arxiv.2308.15508pmid: N/A

Abstract:We investigate the impact of a critical end point (CEP) on the experimentally accessible baryon number fluctuations of different orders. By now, its potential location has been constrained fairly accurately within first principles functional QCD, together with the location of the chiral crossover line and further thermodynamic observables. This information is incorporated in an advanced QCD-assisted low energy effective theory which is used for the computation of baryon number fluctuations at the chemical freeze-out. This computation also takes care of global baryon number conservation at larger density, where the system changes from grand-canonical to canonical statistics. We observe a prominent peak structure, whose amplitude depends on the location of the CEP, while its position is more sensitive to the location of the freeze-out curve. Our results provide guidance for future low energy heavy-ion experiments.