Physics Scenarios Research Articles

Detailed analysis of the curvature bounce: background dynamics and imprints in the CMB

If the spatial sections of the Universe are positively curved, extrapolating the inflationary stage backward in time inevitably leads to a classical bounce. This simple scenario, non-singular and free of exotic physics, deserves to be investigated in details. The background dynamics exhibits interesting features and is shown to be mostly insensitive to initial conditions as long as observational consequences are considered. The primordial scalar power spectrum is explicitly computed, for different inflaton potentials, and the subsequent CMB temperature anisotropies are calculated. The results are compatible with current measurements. Some deviations with respect to the standard paradigm can however appear at large scales and we carefully disentangle what is associated with the vacuum choice with what is more fundamentally due to the bounce itself.

Fusion product measurements by nuclear diagnostics in the Joint European Torus deuterium-tritium 2 campaign (invited).

A new deuterium-tritium experimental, DTE2, campaign has been conducted at the Joint European Torus (JET) between August 2021 and late December 2021. Motivated by significant enhancements in the past decade at JET, such as the ITER-like wall and enhanced auxiliary heating power, the campaign achieved a new fusion energy world record and performed a broad range of fundamental experiments to inform ITER physics scenarios and operations. New capabilities in the area of fusion product measurements by nuclear diagnostics were available as a result of a decade long enhancement program. These have been tested for the first time in DTE2 and a concise overview is provided here. Confined alpha particle measurements by gamma-ray spectroscopy were successfully demonstrated, albeit with limitations at neutron rates higher than some 1017 n/s. High resolution neutron spectroscopy measurements with the magnetic proton recoil instrument were complemented by novel data from a set of synthetic diamond detectors, which enabled studies of the supra-thermal contributions to the neutron emission. In the area of escaping fast ion diagnostics, a lost fast ion detector and a set of Faraday cups made it possible to determine information on the velocity space and poloidal distribution of the lost alpha particles for the first time. This extensive set of data provides unique information for fundamental physics studies and validation of the numerical models, which are key to inform the physics and scenarios of ITER.

Phenomenology analysis of bar{B}^* rightarrow V tau ^-bar{nu }_{tau } decays in and beyond the Standard Model

Motivated by the persistent anomalies reported in the brightarrow c tau bar{nu } data, we investigate the semileptonic decays bar{B}^* rightarrow V tau ^-bar{nu }_{tau } (V=D^*_{u,d,s},J/psi ), within the Standard Model and beyond. The relevant transition form factors, being calculated in the covariant light-front quark model, is the main source of theoretical uncertainties. Using various best-fit solutions for the new operator Wilson coefficients, we report numerical results on various observables related to the processes bar{B}^* rightarrow V tau ^-bar{nu }_{tau }, such as the branching ratios, the ratio of branching fractions, the hadron and lepton polarization asymmetries, the forward–backward asymmetries and the convexity parameter. We also predict the q^2 distribution of these observables both within the Standard Model and in various new physics scenarios. The accessible observables are studied in order to assess their sensitivity to the different new physics scenarios. We can find that some of the new physics scenarios can be differentiated from each other by using these observables and their correlations. We also find that some observables of these decay modes are sizeable and deviate significantly (for new physics coupling parameter S_R especially) from their corresponding standard model values, which are expected to be within the reach of Run III of Large Hadron Collider experiment. And experimental information on these distributions which will be testified in the future can help to disentangle the dynamical origin of the current anomalies.

On the role of chirality flips for the muon magnetic moment and its relation to the muon mass

The muon mass and the anomalous magnetic moment aμ are quantities which require chirality flips, i.e., transitions between left- and right-handed muons. Muon chirality flips are connected to electroweak symmetry breaking and Yukawa couplings. Scenarios for physics beyond the Standard Model motivated by the quest to understand electroweak symmetry breaking and/or the origin of flavour often introduce new sources of chirality flips; they hence provide potentially large contributions to aμ, and the current aμ measurement provides relevant constraints on such scenarios. This connection between aμ, chirality flips, and the muon mass generation mechanism is important and underlies much of the current research on aμ. The present article provides a brief pedagogical introduction to this role of chirality flips and an overview of general relationships. The general statements are illustrated with several concrete models involving e.g., leptoquarks and supersymmetry.

Galaxy Phase-Space Density Data Preclude That Bose–Einstein Condensate Be the Total Dark Matter

Ultralight scalars with a typical mass of the order m∼10−22 eV and light scalars forming a Bose–Einstein condensate (BEC) exhibit a Jeans length in the kpc scale and were therefore proposed as dark matter (DM) candidates. Our treatment here is generic, independent of the particle physics model and applies to all DM BEC, in both in or out of equilibrium situations. Two observed quantities crucially constrain DM in an inescapable way: the average DM density ρDM and the phase-space density Q. The observed values of ρDM and Q in galaxies today constrain both the possibility to form a BEC, and the DM mass m. These two constraints robustly exclude the axion DM that decouples after inflation. Moreover, the value m∼10−22 eV can only be obtained with a number of ultrarelativistic degrees of freedom at decoupling in the trillions, which is impossible for decoupling in the radiation dominated era. In addition, we find for the axion vacuum misalignment scenario that axions are produced strongly out of thermal equilibrium and that the axion mass in such a scenario turns to be 17 orders of magnitude too large to reproduce the observed galactic structures. Moreover, we also consider inhomogenous gravitationally bounded BEC’s supported by the bosonic quantum pressure independently of any particular particle physics scenario. For a typical size R∼ kpc and compact object masses M∼107M⊙ they remarkably lead to the same particle mass m∼10−22 eV as the BEC free-streaming length. However, the phase-space density for the gravitationally bounded BEC’s turns out to be more than sixty orders of magnitude smaller than the galaxy-observed values. We conclude that the BEC cannot be the total DM. The axion can be candidates to be only part of the DM of the universe. Besides, an axion in the mili-eV scale may be a relevant source of dark energy through the zero point cosmological quantum fluctuations.

Search for single production of vectorlike B-quarks at the LHC* *Supported by the Foundation of the Key Research Projects in Universities of Henan (22A140019), the Natural Science Foundation of Henan Province (222300420443) and the Project of Innovation and Entrepreneurship Training for College Students in Henan Province (S202110478024)

New vectorlike quarks have been proposed in many scenarios of new physics beyond the Standard Model, which address the hierarchy problem and may be potentially discovered at the Large Hadron Collider (LHC). Based on a model-independent framework, we propose to search for the vectorlike B-quark (VLQ-B) and focus on resonant production via b-gluon fusion through chromomagnetic interactions. We then explore the possible signals of the VLQ-B through the decay mode at the 14 TeV LHC. After a rapid simulation of signal and background events, the excluded regions and the discovery reach in the parameter plane of are obtained at the LHC with an integrated luminosity of 300 (3000) fbin the dilepton final states.

Slab-driven flow at the base of the mantle beneath the northeastern Pacific Ocean

Flow in the mantle's bottom boundary layer plays an important role in shaping structures and processes in the deep mantle; however, knowledge of lowermost mantle flow patterns remains elusive. In particular, the influence of remnant slabs on lowermost mantle flow is poorly known, although it is likely that slabs play an important role in driving flow and thus in controlling key aspects of lowermost mantle behavior. Measurements of seismic anisotropy can yield relatively direct constraints on slab-induced lowermost mantle flow; however, such observations are challenging to make. We take advantage of the excellent raypath coverage beneath the northeastern Pacific Ocean provided by the USArray deployment in North America to provide detailed sampling of a region that has a long subduction history, with remnant slabs likely impinging on the core-mantle boundary. We present observations of coherent, strong shear wave splitting of SKKS and Sdiff phases across USArray stations and show through global wavefield modeling that the splitting is due to lowermost mantle anisotropy. A stacking approach enables us to make robust estimates of lowermost mantle splitting parameters, which we model by considering realistic mineral physics scenarios. Under the assumption of simple horizontal shear deformation, our observations are consistent with generally north-south flow directions for either a post-perovskite or a bridgmanite mineralogy; ferropericlase cannot explain observations. We speculate that this flow is driven by subducting slab remnants impinging on the core-mantle boundary.

Searching for a vector-like B quark through a tW decay channel at future electron–positron colliders

Vector-like quarks are predicted by several theoretical scenarios of new physics which could solve the hierarchy problem in particular and might be produced through electroweak interactions. In this work, we investigate the prospects for discovering the SU(2) singlet vector-like bottom quark (VLQ-B) in e^{+}e^{-} collisions at the future proposed 3 TeV Compact Linear Collider (CLIC). The analysis is performed within the framework of a simplified model featuring only two free parameters: the VLQ-B mass m_B and the coupling constant g^{*}. We study its single production process e^{+}e^{-}rightarrow B{bar{b}} and perform a detailed analysis in the decay channel Brightarrow tW^{-} at the 3 TeV CLIC. The 2sigma exclusion limit and 5sigma discovery prospects are obtained for the model parameters, respectively. Our results show that the future CLIC will be an ideal hunting ground for such vector-like quarks which have electroweak interactions.

Future Physics Prospects with the CMS Detector at the High-Luminosity LHC

The High-Luminosity Large Hadron Collider is expected to deliver up to 3000 fb^{-1}−1 of proton-proton collisions at 14 TeV center-of-mass energy. We present prospects for selected heavy-ion, Standard Model and Higgs sector measurements with the CMS detector at the HL-LHC, and discuss potential sensitivity to several beyond-Standard Model new physics scenarios.

Comparison of supervised and unsupervised anomaly detection in Belle II pixel detector data

Machine learning has become a popular instrument for the search of undiscovered particles and mechanisms at particle collider experiments. It enables the investigation of large datasets and is therefore suitable to operate directly on minimally-processed data coming from the detector instead of reconstructed objects. Here, we study patterns of raw pixel hits recorded by the Belle II pixel detector, that is operational since 2019 and presently features 4 M pixels and trigger rates up to 5 kHz. In particular, we focus on unsupervised techniques that operate without the need for a theoretical model. These model-agnostic approaches allow for an unbiased exploration of data while filtering out anomalous detector signatures that could hint at new physics scenarios. We present the identification of hypothetical magnetic monopoles against Belle II beam background using self-organizing kohonen maps and autoencoders. These two unsupervised algorithms are compared to a Multilayer Perceptron and a superior signal efficiency of the Autoencoder is found at high background-rejection levels. Our results strengthen the case for using unsupervised machine learning techniques to complement traditional search strategies at particle colliders and pave the way to potential online applications of the algorithms in the near future.

The ALPs from the top: searching for long lived axion-like particles from exotic top decays

We propose a search for long lived axion-like particles (ALPs) in exotic top decays. Flavour-violating ALPs appear as low energy effective theories for various new physics scenarios such as t-channel dark sectors or Froggatt-Nielsen models. In this case the top quark may decay to an ALP and an up- or charm-quark. For masses in the few GeV range, the ALP is long lived across most of the viable parameter space, suggesting a dedicated search. We propose to search for these long lived ALPs in toverline{t} events, using one top quark as a trigger. We focus on ALPs decaying in the hadronic calorimeter, and show that the ratio of energy deposits in the electromagnetic and hadronic calorimeters as well as track vetoes can efficiently suppress Standard Model backgrounds. Our proposed search can probe exotic top branching ratios smaller than 10−4 with a conservative strategy at the upcoming LHC run, and potentially below the 10−7 level with more advanced methods. Finally we also show that measurements of single top production probe these branching ratios in the very short and very long lifetime limit at the 10−3 level.

Consequences of b→sμ+μ− anomalies on B→K(*)νν¯ , Bs→(η,η′)νν¯ and Bs→ϕνν¯ decay observables

The long persistent discrepancies in $b\,\to\,s\, \ell\, \ell$ quark level transitions continue to be the ideal platform for an indirect search of new physics that lies beyond the SM. The measurements of $R_K$, $R_{K^*}$, $P_5^{\prime}$, $\mathcal{B}(B_s\, \to\, \phi\, \mu^+\,\mu^-)$ and $\mathcal{B}(B_s\, \to\, \mu^+\,\mu^-)$ persistently deviate from the standard model expectations. Similarly, the new tests of lepton flavor universality performed using the isospin partners such as $B^0 \, \to \, K_S^{0} \, \ell\,\ell$ and $B^+ \, \to \, K^{+*} \, \ell\,\ell$ exhibit the same pattern of deviation in $R_{K_S^0}$ and $R_{K^{*+}}$ with the existing results. Motivated by these anomalies we search for the patterns of new physics in the family of flavor changing neutral decays with neutral leptons in the final state undergoing $b \, \to \,s\, \nu \, \bar{\nu}$ quark level transitions. There are close relations between $b\,\to\,s\, \ell\, \ell$ and $b \, \to \,s\, \nu \, \bar{\nu}$ transitions not only in standard model but also in various beyond the standard model scenarios. For beyond the standard model physics under the $\rm SU_L(2)$ gauge symmetry one can relate the left handed charged leptons to the neutrinos. Moreover, there are several advantages of studying $b \, \to \,s\, \nu \, \bar{\nu}$ transitions over $b\,\to\,s\, \ell\, \ell$ as they are free from various hadronic uncertainties beyond the form factors such as the non-factorizable corrections and photonic penguin contributions. Hence, we explore the consequences of $b\, \to\, s\, \mu^+\, \mu^-$ anomalies on $B \, \to \, K^{(*)} \,\nu \, \bar{\nu}$, $B_s \to\, (\eta,\eta') \, \nu\,\bar{\nu}$ and $B_s \, \to \, \phi \, \nu \, \bar{\nu}$ decay observables in SMEFT platform within various 1D and 2D new physics scenarios.

Combined analysis of Bc→Ds(*)μ+μ− and Bc→Ds(*)νν¯ decays within Z′ and leptoquark new physics models

We investigate the exclusive rare semileptonic decays $ B_c \to D_{s}^{(*)}\,(\ell \ell, \nu \bar{\nu})$ induced by neutral current transition $b \to s (\ell \ell,\nu \bar{\nu})$ in the presence of non-universal $Z^{\prime}$, scalar and vector leptoquark new physics models. We constrain the new physics parameter space by using the latest experimental measurements of $R_{K^{(*)}}$, $P_5^{\prime}$, $\mathcal{B}(B_s \to \phi \mu^+ \mu^-)$ and $\mathcal{B}(B_s \to \mu^+ \mu^-)$. Throughout the analysis, we choose to work with the particular new physics scenario $C_9 ^{\mu \mu}(NP)=-C_{10} ^{\mu \mu}(NP)$ where both $Z^{\prime}$, $S_{1/3}^3$ and $U_{-2/3}^3$ leptoquarks satisfy the condition. Using these new coupling parameters we scrutinize the several physical observables such as differential branching fraction, the forward backward asymmetry, the lepton polarization asymmetry, the angular observable $P^{\prime}_5$ and the lepton flavor universal sensitive observables including the ratio of branching ratio $R_{D_s^{(*)}}$ and the few $Q$ parameters in the $B_c \to D_s^{(*)}\,\mu ^+ \mu ^-$ and $B_c \to D_s^{(*)}\, \nu \bar{\nu}$ decay processes.

Higgs physics confronts the MW anomaly

The recent high-precision measurement of the W mass by the CDF collaboration is in sharp tension with the Standard Model prediction as obtained by the electroweak fit. If confirmed, this finding can only be explained in terms of new physics effects. In this work, we point out a generic connection between the MW anomaly and Higgs physics observables such as h→γγ,Zγ and the ratio h→ZZ/WW. Moreover, we systematically classify new physics scenarios which can address the MW anomaly via a tree-level contribution to the Tˆ parameter. These include a real scalar triplet, a scalar quadruplet with the same hypercharge of the Higgs doublet, a Z′ boson, a vector triplet with unit hypercharge and a vector boson with the gauge quantum numbers of the Higgs doublet. These solutions to the MW anomaly are characterized by new physics states which are typically too heavy to be discovered in direct searches, but which might leave their imprints in Higgs physics.

Inclusive nonresonant multilepton probes of new phenomena at s=13 TeV

An inclusive search for nonresonant signatures of beyond the standard model (SM) phenomena in events with three or more charged leptons, including hadronically decaying $\tau$ leptons, is presented. The analysis is based on a data sample corresponding to an integrated luminosity of 138 fb$^{-1}$ of proton-proton collisions at $\sqrt{s} =$ 13 TeV, collected by the CMS experiment at the LHC in 2016-2018. Events are categorized based on the lepton and b-tagged jet multiplicities and various kinematic variables. Three scenarios of physics beyond the SM are probed, and signal-specific boosted decision trees are used for enhancing sensitivity. No significant deviations from the background expectations are observed. Lower limits are set at 95% confidence level on the mass of type-III seesaw heavy fermions in the range 845-1065 GeV for various decay branching fraction combinations to SM leptons. Doublet and singlet vector-like $\tau$ lepton extensions of the SM are excluded for masses below 1045 GeV and in the mass range 125-150 GeV, respectively. Scalar leptoquarks decaying exclusively to a top quark and a lepton are excluded below 1.12-1.42 TeV, depending on the lepton flavor. For the type-III seesaw as well as the vector-like doublet model, these constraints are the most stringent to date. For the vector-like singlet model, these are the first constraints from the LHC experiments. Detailed results are also presented to facilitate alternative theoretical interpretations.

Higgs boson decays into a pair of heavy vector quarkonia

Rare Higgs decays into a pair of heavy vector quarkonia, h→VV (V=J/Ψ, ϒ etc.), have been investigated in the standard model. Different from the past literature in which these decays are thought to be only dominated by the longitudinally polarized final states, we also include the transitions, which proceed through h→γ⁎γ⁎/h→Vγ⁎, followed by γ⁎→V. The final vector quarkonia via these ways are dominantly transversely polarized. Our calculation however shows that these transitions could lead to significant contributions to the decay rate, especially for the charmonium final states. The total branching ratios of these processes are predicted to be around 10−10, far below the current experimental upper bounds. Hopefully, experimental studies of these very rare decays in future high-precision experimental facilities might be interesting both to test the standard model and to look for new physics scenarios.

EstrellaNueva: An Open-source Software to Study the Interactions and Detection of Neutrinos Emitted by Supernovae

Supernovae emit large fluxes of neutrinos, which can be detected by detectors on Earth. Future multi-kiloton scale detectors will be sensitive to several neutrino interaction channels, with thousands of events expected if a supernova emerges in the galaxy neighborhood. There are a limited number of tools to study the interaction rates of supernova neutrinos, although a plethora of available supernova models exist. EstrellaNueva is an open-source software to calculate expected rates of supernova neutrinos in detectors using target materials with typical compositions, and additional compositions can be easily added. This software considers the flavor transformation of neutrinos in the supernova through the adiabatic Mikheyev–Smirnov–Wolfenstein effect, and their interaction in detectors through several channels. Most of the interaction cross sections, such as neutrino–electron and neutrino–proton elastic scattering, inverse beta decay, and coherent elastic neutrino–nucleus scattering, have been analytically implemented. This software provides a link between supernova simulations and the expected events in detectors by calculating fluences and event rates in order to ease any comparison between theory and observation. It provides a simple and standalone tool to explore many physics scenarios, offering an option to add analytical cross sections and define any target material.

Learning from radiation at a very high energy lepton collider

We study the potential of lepton collisions with about 10 TeV center of mass energy to probe Electroweak, Higgs and Top short-distance physics at the 100 TeV scale, pointing out the interplay with the long-distance (100 GeV) phenomenon of Electroweak radiation. On one hand, we find that sufficiently accurate theoretical predictions require the resummed inclusion of radiation effects, which we perform at the double logarithmic order. On the other hand, we notice that short-distance physics does influence the emission of Electroweak radiation. Therefore the investigation of the radiation pattern can enhance the sensitivity to new short-distance physical laws. We illustrate these aspects by studying Effective Field Theory contact interactions in di-fermion and di-boson production, and comparing cross-section measurements that require or that exclude the emission of massive Electroweak bosons. The combination of the two types of measurements is found to enhance the sensitivity to the new interactions. Based on these results, we perform sensitivity projections to Higgs and Top Compositeness and to minimal Z′ new physics scenarios at future muon colliders.

Large-energy single hits at JUNO from atmospheric neutrinos and dark matter

Large liquid scintillator detectors, such as JUNO, present a new opportunity to study neutral current events from the low-energy end of the atmospheric neutrinos, and possible new physics signals due to light dark matter. We carefully study the possibility of detecting ``large-energy singles'' (LES), i.e., events with visible scintillation energy $>15\text{ }\text{ }\mathrm{MeV}$, but no other associated tags. For an effective exposure of $20\text{ }\text{ }\mathrm{kton}\ensuremath{-}\mathrm{yr}$ and considering only Standard Model physics, we expect the LES sample to contain $\ensuremath{\sim}40$ events from scattering on free protons and $\ensuremath{\sim}108$ events from interaction with carbon, from neutral-current interactions of atmospheric neutrinos. Backgrounds, largely due to $\ensuremath{\beta}$ decays of cosmogenic isotopes, are shown to be significant only below 15 MeV visible energy. The LES sample at JUNO can competitively probe a variety of new physics scenarios, such as boosted dark matter and annihilation of galactic dark matter to sterile neutrinos.

Cosmological constraints on light but massive relics

Many scenarios of physics beyond the standard model predict new light, weakly coupled degrees of freedom, populated in the early universe and remaining as cosmic relics today. Due to their high abundances, these relics can significantly affect the evolution of the universe. For instance, massless relics produce a shift $\Delta N_{\rm eff}$ to the cosmic expectation of the effective number of active neutrinos. Massive relics, on the other hand, additionally become part of the cosmological dark matter in the later universe, though their light nature allows them to freely stream out of potential wells. This produces novel signatures in the large-scale structure (LSS) of the universe, suppressing matter fluctuations at small scales. We present the first general search for such light (but massive) relics (LiMRs) with cosmic microwave background (CMB) and LSS data, scanning the 2D parameter space of their masses $m_X$ and temperatures $T_X^{(0)}$ today. In the conservative minimum-temperature ($T_X^{(0)}=0.91$ K) scenario, we rule out Weyl (and higher-spin) fermions -- such as the gravitino -- with $m_X\geq 2.26$ eV at 95% C.L., and set analogous limits of $m_X\leq 11.2, 1.06, 1.56$ eV for scalar, vector, and Dirac-fermion relics. This is the first search for LiMRs with joint CMB, weak-lensing, and full-shape galaxy data; we demonstrate that weak-lensing data is critical for breaking parameter degeneracies, while full-shape information presents a significant boost in constraining power relative to analyses with only baryon acoustic oscillation parameters. Under the combined strength of these datasets, our constraints are the tightest and most comprehensive to date.