Probe Of New Physics Research Articles

Impact of B→Kνν¯ measurements on beyond the Standard Model theories

Semileptonic flavor changing neutral current transitions with a pair of neutrinos in the final state are very accurately determined in the standard model (SM) and thus provide an accurate and sensitive probe for physics beyond the SM. Until recently, the poor tagging efficiency for the $B\to K^{(*)}\nu \bar{\nu}$ modes made them less advantageous as a probe of new physics (NP) compared to the charged lepton counterparts. The most recent Belle II result on $B\to K \nu \bar{\nu}$ uses an innovative inclusive tagging technique resulting in a higher tagging efficiency; this together with previous BaBar and Belle results indicates a possible enhancement in the branching fraction of $B^+\to K^+ \nu \bar{\nu}$. A reanalysis of the full Belle dataset together with upcoming Belle II dataset is expected to result in a much more precise measurement of this mode. If the branching ratio is indeed found to be enhanced with improved measurements, this would provide an unambiguous signal of NP without uncertainties due to long-distance non-factorizable effects or power corrections (in contrast to $B\to K^{(*)} \ell \ell$). We have explored the possibilities of such an enhancement as a signal of NP within several scenarios, which can also explain some of the other tensions observed in neutral as well as charged current $B$-decays. In an effective field theory approach, with the most general dimension-six Hamiltonian including light right-handed neutrinos, we explore the viability of all scalar and vector leptoquarks as well as the parameter space possible with a generic vector gauge boson $Z^\prime$ model assuming minimal new particle content. While being consistent with all data, correlations between the observed intriguing discrepancies in $B$-decays are also obtained, which will discriminate between the various NP scenarios.

On measurement of photon polarization in radiative penguin B decays to baryons

A measurement of the photon polarization in radiative penguin B decays provides a test of the Standard Model and a probe for New Physics, that can lead to a deviation from the Standard Model prediction of left-handed photons in brightarrow s gamma . We propose a new method to measure the photon polarization using the baryonic decay B^- rightarrow Lambda bar{p} gamma . The P-violating Lambda -hyperon decay allows a measurement of the Lambda helicity to be performed, which can be uniquely related to the photon polarization in a model-independent way. The B^- rightarrow Lambda bar{p} gamma decay was recently measured to have a large branching fraction providing a possibility to get meaningful results with the data already available at LHC and B-factory experiments. An increase of the B-meson sample at high luminosity LHC experiments and Belle II should provide a really stringent test by using this method already in the near future.

Multimessenger Probes for New Physics in Light of A. Sakharov’s Legacy in Cosmoparticle Physics

A.D. Sakharov’s legacy in now standard model of the Universe is not reduced to baryosynthesis but extends to the foundation of cosmoparticle physics, which studies the fundamental relationship of cosmology and particle physics. Development of cosmoparticle physics involves cross-disciplinary physical, astrophysical and cosmological studies of physics Beyond the Standard model (BSM) of elementary particles. To probe physical models for inflation, baryosynthesis and dark matter cosmoparticle physics pays special attention to model dependent messengers of the corresponding models, making their tests possible. Positive evidence for such exotic phenomena as nuclear interacting dark atoms, primordial black holes or antimatter globular cluster in our galaxy would provide the selection of viable BSM models determination of their parameters.

Gravitational wave physics and astronomy in the nascent era

Abstract The detections of gravitational waves (GW) by the LIGO/Virgo collaborations provide various possibilities for both physics and astronomy. We are quite sure that GW observations will develop a lot, both in precision and in number, thanks to the continuous work on the improvement of detectors, including the expected new detector, KAGRA, and the planned detector, LIGO-India. On this occasion, we review the fundamental outcomes and prospects of gravitational wave physics and astronomy. We survey the development, focusing on representative sources of gravitational waves: binary black holes, binary neutron stars, and supernovae. We also summarize the role of gravitational wave observations as a probe of new physics.

CP-Violating Neutrino Nonstandard Interactions in Long-Baseline-Accelerator Data.

Neutrino oscillations in matter provide a unique probe of new physics. Leveraging the advent of neutrino appearance data from NOvA and T2K in recent years, we investigate the presence of CP-violating neutrino nonstandard interactions in the oscillation data. We first show how to very simply approximate the expected NSI parameters to resolve differences between two long-baseline appearance experiments analytically. Then, by combining recent NOvA and T2K data, we find a tantalizing hint of CP-violating NSI preferring a new complex phase that is close to maximal: ϕ_{eμ} or ϕ_{eτ}≈3π/2 with |ε_{eμ}| or |ε_{eτ}|∼0.2. We then compare the results from long-baseline data to constraints from IceCube and COHERENT.

Rare nonleptonic Bs -meson decays as a probe for new physics beyond the standard model

The recent measurements on a number of b → sμ + μ − processes have manifested anomalous results which could be early evidence for the presence of new physics beyond the standard model in b → s transitions. Supposing this to be the case, we entertain the possibility that a heavy Z′ boson is responsible for these anomalies and that it also affects the rare nonleptonic decays of the meson which receive substantial contributions from the so-called penguin diagrams. The majority of these decay modes are not yet discovered, and within the standard model their rates have been estimated to be relatively suppressed. Taking into account various constraints, we find that the Z′ effects can enlarge the rates of a few of the modes, especially , considerably above their standard-model expectations. Consequently this Z′ scenario may be experimentally testable in the near future.

A novel probe of new physics in e+e− → Zγ

A novel probe of new physics in e+e− → Zγ

Consistent QFT description of non-standard neutrino interactions

Neutrino oscillations are precision probes of new physics. Apart from neutrino masses and mixings, they are also sensitive to possible deviations of low-energy interactions between quarks and leptons from the Standard Model predictions. In this paper we develop a systematic description of such non-standard interactions (NSI) in oscillation experiments within the quantum field theory framework. We calculate the event rate and oscillation probability in the presence of general NSI, starting from the effective field theory (EFT) in which new physics modifies the flavor or Lorentz structure of charged-current interactions between leptons and quarks. We also provide the matching between the EFT Wilson coefficients and the widely used simplified quantum-mechanical approach, where new physics is encoded in a set of production and detection NSI parameters. Finally, we discuss the consistency conditions for the standard NSI approach to correctly reproduce the quantum field theory result.

Standard-Model Prediction of ε_{K} with Manifest Quark-Mixing Unitarity.

The parameter ε_{K} describes CP violation in the neutral kaon system and is one of the most sensitive probes of new physics. The large uncertainties related to the charm-quark contribution to ε_{K} have so far prevented a reliable standard-model prediction. We show that Cabibbo-Kobayashi-Maskawa unitarity enforces a unique form of the |ΔS=2| weak effective Lagrangian in which the short-distance theory uncertainty of the imaginary part is dramatically reduced. The uncertainty related to the charm-quark contribution is now at the percent level. We present the updated standard-model prediction ε_{K}=2.16(6)(8)(15)×10^{-3}, where the errors in parentheses correspond to QCD short-distance, long-distance, and parametric uncertainties, respectively.

Direct CP violation in D^+ rightarrow K^0({bar{K}}^0) pi ^+ decays as a probe for new physics

In this paper we investigate CP violation in charged decays of D meson. Particularly, we study the direct CP asymmetry of the Cabibbo favored non-leptonic D^+ rightarrow {bar{K}}^0 pi ^+ and the doubly Cabibbo-suppressed decay mode D^+ rightarrow K^0 pi ^+ within standard model, two Higgs doublet model with generic Yukawa structure and left right symmetric models. In the standard model, we first derive the contributions from box and di-penguin diagrams contributing to their amplitudes which are relevant to the generation of the weak phases essential for non-vanishing direct CP violation. Then, we show that the generated phases are so tiny leading to null direct CP asymmetries of both decay modes. Regarding the two Higgs doublet model with generic Yukawa structure, after taking into account all constraints on the parameter space of the model, we show that the weak phases of the amplitudes can be enhanced compared to the standard model ones. However, the enhancement is still not enough to have sizable direct CP asymmetries. Finally, within left right symmetric models, we find that |A^{SM+LR}_{CP} (D^+ rightarrow {bar{K}}^0 pi ^+)|lesssim mathcal {O}(10^{-3}) after respecting all relevant constraints on the parameter space of the model.

Beyond the Standard Model physics at CLIC

A summary of the recent results from CERN Yellow Report on the CLIC potential for new physics is presented. Greater emphasis is put on the direct search for new physics scenarios motivated by the open issues of the Standard Model as well as on interpretations of Standard Model measurements as probes of new physics in the context of effective field theory extensions of the Standard Model.

Electroweak loops as a probe of new physics in toverline{t} production at the LHC

We calculate the \U0001d4aa(α) weak corrections to top quark pair production at the LHC and include anomalous electroweak interactions from dimension-six operators. The loop calculation and renormalization are consistently done within the Standard Model Effective Field Theory. Sensitivity to the involved operators is exposed through the virtual corrections, which receive enhancement from electroweak Sudakov logarithms. We investigate the prospects of using this feature for probing New Physics at the LHC that so far has only been studied in final states with on-shell sensitivity such as toverline{t} + Z or t → bW. We find that the large toverline{t} production rate and the excellent perturbative control allow compensating the loop suppression and yield remarkably strong constraints that are competitive with those from toverline{t} + Z.

Measuring the top energy asymmetry at the LHC: QCD and SMEFT interpretations

The energy asymmetry in top-antitop-jet production is an observable of the top charge asymmetry designed for the LHC. We perform a realistic analysis in the boosted kinematic regime, including effects of the parton shower, hadronization and expected experimental uncertainties. Our predictions at particle level show that the energy asymmetry in the Standard Model can be measured with a significance of 3σ during Run 3, and with more than 5σ significance at the HL-LHC. Beyond the Standard Model the energy asymmetry is a sensitive probe of new physics with couplings to top quarks. In the framework of the Standard Model Effective Field Theory, we show that the sensitivity of the energy asymmetry to effective four-quark interactions is higher or comparable to other top observables and resolves blind directions in current LHC fits. We suggest to include the energy asymmetry as an important observable in global searches for new physics in the top sector.

Searching for Fossil Fields in the Gravity Sector.

Evidence for the presence of extra fields during inflation may be found in the anisotropies of the scalar and tensor spectra across a vast range of scales. Indeed, beyond the single-field slow-roll paradigm, a long tensor mode modulating the power spectrum can induce a sizable quadrupolar anisotropy. We investigate how these dynamics play out for the tensor two-point correlator. The resulting quadrupole stores information on squeezed tensor non-Gaussianities, including those sourced by extra field content and responsible for the breaking of so-called consistency relations. We underscore the potential of anisotropies as a probe of new physics: testable at cosmic microwave background scales through the detection of B modes, they are accessible at smaller scales via pulsar timing arrays and interferometers. Our findings are particularly relevant in that recent studies show a considerable suppression for tensor non-Gaussianities if all modes are well inside the horizon. Quadrupolar anisotropies instead probe an unsuppressed ultrasqueezed bispectrum where the long mode can be horizon size.

Four-top as probe of light top-philic New Physics

We study the four-top (t overline{t} t overline{t} ) final state at the LHC as a probe for New Physics (NP) effects due to new particles that couple predominantly to the top quark and whose masses are below the top-quark-pair production threshold. We consider simple NP models containing a new particle with either spin 0, spin 1, or spin 2, and find benchmark points compatible with current experimental results. We find that interference effects between NP and QED amplitudes can be large, pointing out the necessity of NLO contributions to be explicitly computed and taken into account when NP is present. We examine kinematic differences between these models and the Standard Model (SM) at the parton level and the reconstructed level. In the latter case, we focus on events selected requiring two same-sign leptons and multiple jets. We investigate how the different Lorentz structure of the light NP affects the kinematic hardness, the polarization, the spin correlations, and the angular distributions of the parton-level and/or final-state particles. We find that spin-2 light NP would be identified by harder kinematics than the SM. We also show that the angular sepa- ration between the same-sign leptons is a sensitive observable for spin-0 NP. The spin-0 and spin-2 NP cases would also yield a signal in t overline{t} γγ with the invariant mass of the photons in- dicating the mass of the new particle. The spin-1 NP would be identified through an excess in four-top signal and slight or not modification in other observables, as for instance the lack of signal in t overline{t} γγ due to the Landau-Yang theorem. We comment on the opportunities that would open from the kinematic reconstruction of some of the top quarks in the t overline{t} t overline{t} state. Our results provide new handles to probe for light top-philic NP as part of the ongoing experimental program of searches for four-top production at the LHC Run 2 and beyond.

Symmetry-Scaling Based Complex Network Approach to Explore Exotic Hadronic States in High-Energy Collision

Conventionally invariant mass or transverse momentum techniques have been used to probe for any formation of some exotic or unusual resonance states in high energy collision. In this work, we have applied symmetry scaling based complex network approach to study exotic resonance/hadronic states utilizing the clustering coefficients and associated scaling parameter extracted with the complex network based technique of Visibility Graph. We have analyzed the data of Pb–Pb collision data sample at 2.76 TeV from ALICE Collaboration and analyzed different patterns of symmetry scaling, scale-freeness, correlation and clustering among the produced particles. This is a chaos-based complex network technique where simple parameters like Average Clustering Coefficient and Power of Scale-freeness of Visibility Graph (PSVG) may hint at formation of some exotic or unusual resonance states without using conventional methods. From this experiment we may infer that highest range of Average clustering coefficient, might be the resonance states/clusters from where the hadronic decay might have occurred and few clusters with highest value of this parameter may indicate that those clusters may be the ancestors of some strange particles. There have also been extensive study of dilepton production since the study of lepton pair generation in Drell–Yan processes is immensely important as these processes enable us to validate the Standard Model-SM predictions for the fundamental particles interaction at the new energy region and also to probe for new physics beyond SM. Hence we have applied the same methodology and extracted the same parameters for p–p collision data at 8 TeV from CMS, to detect possible resonance states eventually generating lepton pairs.

Six top messages of new physics at the LHC

Six top signatures provide a novel probe of new physics. We discuss production of six top quarks as the decay products of a pair of top partners in the setting of a composite Higgs model, and argue that the six top signal may generically provide one of the first final states to show a discrepancy. We construct an analysis based on quantities such as HT and the numbers of jets which are tagged as boosted tops, W s, or containing b-tags, and show that the LHC with 3 ab−1 can discover top partners with masses up to around 2.5 TeV in the six top signature.

Implications of four-top and top-pair studies on triple-top production

Multi-top quark production is a staple program at the LHC. Single-top and tt¯ productions are studied extensively, while current efforts are zooming in on four-top search, where the Standard Model (SM) cross section is at O(10) fb. In contrast, only at the fb level in SM, triple-top production has not been targeted for study so far. But such a small cross section makes it a unique probe for New Physics. Without the usual discrete Z2 symmetry, the general two Higgs doublet model (g2HDM) can naturally raise the triple-top production to pb level. We illustrate how certain signal regions of four-top search can be utilized to constrain triple-top production, but urge a dedicated search. As an aside, we note that the CMS study at 13 TeV of scalar tt¯ resonance interfering with QCD production background indicate some activity at 400 GeV. We comment that this could be explained in principle in g2HDM via the extra top Yukawa coupling.

Angular distribution as an effective probe of new physics in semihadronic three-body meson decays

We analyze, in a fully model-independent manner, the effects of new physics on a few semi-hadronic three-body meson decays of the type $P_i \to P_f f_1 f_2$, where $P_i$, $P_f$ are well chosen pseudo-scalar mesons and $f_{1,2}$ denote fermions out of which at least one gets detected in experiments. We find that the angular distribution of events of these decays can probe many interesting new physics, such as the nature of the intermediate particle that can cause lepton-flavor violation, or presence of heavy sterile neutrino, or new intermediate particles, or new interactions. We also provide angular asymmetries which can quantify the effects of new physics in these decays. We illustrate the effectiveness of our proposed methodology with a few well chosen decay modes showing effects of certain new physics possibilities without any hadronic uncertainties.

Merits of heavy-heavy diatomic molecules for electron electric-dipole-moment searches

The electric dipole moment of the electron (eEDM) and the Scalar-PseudoScalar (S-PS) interaction are probes of new physics beyond the standard model of elementary particles, but experiments to observe them using atoms and molecules are still in progress. Molecules that have a large effective electric field (Eeff), S-PS coefficient (Ws), and permanent electric dipole moment (PDM) are in principle favorable candidates for such experiments, and hence, it is necessary to analyze these properties. In this work, we calculate Eeff, Ws, and PDM for Ra systems; RaF, RaX (X = Cl, Br, I, and At) and RaY (Y = Cu, Ag, and Au) using the Dirac-Fock and the relativistic coupled-cluster methods. We find that RaX and RaY have larger Eeff and Ws,Ra than RaF. We explain this finding by taking into consideration the large s-p mixing for RaX and RaY, similar to what we had done in our previous work using hydrides and fluorides (A. Sunaga et al., Phys. Rev. A 95, 012502 (2017)). We also discuss the suitability of RaX and RaY molecules for eEDM experiments from the viewpoint of their large PDM and small polarizing electric field (Epol).