scholarly journals Challenges for an axion explanation of the muon g − 2 measurement

2021 ◽  
Vol 2021 (9) ◽  
Author(s):  
Manuel A. Buen-Abad ◽  
JiJi Fan ◽  
Matthew Reece ◽  
Chen Sun
Keyword(s):  
Decay Constant ◽  
Standard Model Prediction ◽  
New Physics ◽  
Effective Theory ◽  
General Sense ◽  
Weak Scale ◽  
Initial Application ◽  
The Standard Model ◽  
Axion Decay Constant ◽  
Axion Decay

Abstract The discrepancy between the muon g − 2 measurement and the Standard Model prediction points to new physics around or below the weak scale. It is tantalizing to consider the loop effects of a heavy axion (in the general sense, also known as an axion-like particle) coupling to leptons and photons as an explanation for this discrepancy. We provide an updated analysis of the necessary couplings, including two-loop contributions, and find that the new physics operators point to an axion decay constant on the order of 10s of GeV. This poses major problems for such an explanation, as the axion couplings to leptons and photons must be generated at low scales. We outline some possibilities for how such couplings can arise, and find that these scenarios predict new charged matter at or below the weak scale and new scalars can mix with the Higgs boson, raising numerous phenomenological challenges. These scenarios also all predict additional contributions to the muon g−2 itself, calling the initial application of the axion effective theory into question. We conclude that there is little reason to favor an axion explanation of the muon g – 2 measurement relative to other models postulating new weak-scale matter.

scholarly journals Flavor physics: Precision as an avenue to discovery

2020 ◽  
Vol 35 (01) ◽  
pp. 1930018
Author(s):  
Diego Guadagnoli
Keyword(s):  
Cp Violation ◽  
Standard Model ◽  
Flavor Physics ◽  
Standard Model Prediction ◽  
New Physics ◽  
Effective Theory ◽  
Theory Approach ◽  
Long Distance ◽  
The Standard Model ◽  
The Impact

This paper describes the work pursued in the years 2008–2013 on improving the Standard Model prediction of selected flavor-physics observables. The latter includes: (1) [Formula: see text], that quantifies indirect CP violation in the [Formula: see text] system and (2) the very rare decay [Formula: see text], recently measured at the LHC. Concerning point (1), the paper describes our reappraisal of the long-distance contributions to [Formula: see text],[Formula: see text] that have permitted to unveil a potential tension between CP violation in the [Formula: see text]- and [Formula: see text]-system. Concerning point (2), the paper gives a detailed account of various systematic effects pointed out in Ref. 4 and affecting the Standard Model [Formula: see text] decay rate at the level of 10% — hence large enough to be potentially misinterpreted as nonstandard physics, if not properly included. The paper further describes the multifaceted importance of the [Formula: see text] decays as new physics probes, for instance how they compare with [Formula: see text]-peak observables at LEP, following the effective-theory approach of Ref. 5. Both cases (1) and (2) offer clear examples in which the pursuit of precision in Standard Model predictions offered potential avenues to discovery. Finally, this paper describes the impact of the above results on the literature, and what is the further progress to be expected on these and related observables.

scholarly journals Precision axion physics with running axion couplings

2021 ◽  
Vol 2021 (8) ◽  
Author(s):  
Kiwoon Choi ◽  
Sang Hui Im ◽  
Hee Jung Kim ◽  
Hyeonseok Seong
Keyword(s):  
Top Quark ◽  
Decay Constant ◽  
Higgs Field ◽  
Energy Scale ◽  
Low Energy ◽  
Loop Contribution ◽  
The Standard Model ◽  
Axion Decay Constant ◽  
Axion Decay ◽  
Sizable Difference

Abstract We study the renormalization group running of axion couplings while taking into account that the Standard Model can be extended to its supersymmetric extension at a certain energy scale below the axion decay constant. We then apply our results to three different classes of axion models, i.e. KSVZ-like, DFSZ-like, and string-theoretic axions, and examine if string-theoretic axions can be distinguished from others by having a different pattern of low energy couplings to the photon, nucleons and electron. We find that the low energy couplings of string-theoretic axions have a similar pattern as those of KSVZ-like axions but yet reveal a sizable difference which might be testable in future axion search experiments. We also note that the coupling of KSVZ-like QCD axions to the electron is dominated by a three-loop contribution involving the exotic heavy quark, gluons, top quark and Higgs field.

scholarly journals Axion–Sterile Neutrino Dark Matter

Universe ◽  
2021 ◽  
Vol 7 (10) ◽  
pp. 354
Author(s):  
Alberto Salvio ◽  
Simone Scollo
Keyword(s):  
Dark Matter ◽  
Decay Constant ◽  
Sterile Neutrino ◽  
Topological Defects ◽  
Primordial Black Holes ◽  
Neutrino Production ◽  
The Standard Model ◽  
Axion Decay Constant ◽  
Axion Decay ◽  
Production Mechanisms

Extending the standard model with three right-handed neutrinos and a simple QCD axion sector can account for neutrino oscillations, dark matter and baryon asymmetry; at the same time, it solves the strong CP problem, stabilizes the electroweak vacuum and can implement critical Higgs inflation (satisfying all current observational bounds). We perform here a general analysis of dark matter (DM) in such a model, which we call the aνMSM. Although critical Higgs inflation features a (quasi) inflection point of the inflaton potential, we show that DM cannot receive a contribution from primordial black holes in the aνMSM. This leads to a multicomponent axion–sterile neutrino DM and allows us to relate the axion parameters, such as the axion decay constant, to the neutrino parameters. We include several DM production mechanisms: the axion production via misalignment and decay of topological defects as well as the sterile neutrino production through the resonant and non-resonant mechanisms and in the recently proposed CPT-symmetric universe.

scholarly journals Standard Model prediction of the Bc lifetime

2021 ◽  
Vol 2021 (7) ◽  
Author(s):  
Jason Aebischer ◽  
Benjamín Grinstein
Keyword(s):  
Standard Model ◽  
Model Prediction ◽  
Strange Quark ◽  
Standard Model Prediction ◽  
New Physics ◽  
Operator Product ◽  
Special Focus ◽  
Third Order ◽  
Clear Cut ◽  
The Standard Model

Abstract Applying an operator product expansion approach we update the Standard Model prediction of the Bc lifetime from over 20 years ago. The non-perturbative velocity expansion is carried out up to third order in the relative velocity of the heavy quarks. The scheme dependence is studied using three different mass schemes for the $$ \overline{b} $$ b ¯ and c quarks, resulting in three different values consistent with each other and with experiment. Special focus has been laid on renormalon cancellation in the computation. Uncertainties resulting from scale dependence, neglecting the strange quark mass, non-perturbative matrix elements and parametric uncertainties are discussed in detail. The resulting uncertainties are still rather large compared to the experimental ones, and therefore do not allow for clear-cut conclusions concerning New Physics effects in the Bc decay.

scholarly journals Flavour Anomalies in a U(1) SUSY Extension of the SM

Symmetry ◽  
2021 ◽  
Vol 13 (2) ◽  
pp. 191
Author(s):  
Alexander Bednyakov ◽  
Alfiia Mukhaeva
Keyword(s):  
Standard Model ◽  
Parameter Space ◽  
Gauge Boson ◽  
New Physics ◽  
Low Energy ◽  
Effective Theory ◽  
The Standard Model ◽  
Meson Mixing ◽  
Additional Anomaly ◽  
Lepton Flavour

Flavour anomalies have attracted a lot of attention over recent years as they provide unique hints for possible New Physics. Here, we consider a supersymmetric (SUSY) extension of the Standard Model (SM) with an additional anomaly-free gauge U(1) group. The key feature of our model is the particular choice of non-universal charges to the gauge boson Z′, which not only allows a relaxation of the flavour discrepancies but, contrary to previous studies, can reproduce the SM mixing matrices both in the quark and lepton sectors. We pay special attention to the latter and explicitly enumerate all parameters relevant for our calculation in the low-energy effective theory. We find regions in the parameter space that satisfy experimental constraints on meson mixing and LHC Z′ searches and can alleviate the flavour anomalies. In addition, we also discuss the predictions for lepton-flavour violating decays B+→K+μτ and B+→K+eτ.

scholarly journals Cosmologically allowed regions for the axion decay constant F

2018 ◽  
Vol 782 ◽  
pp. 181-184 ◽  
Author(s):  
Masahiro Kawasaki ◽  
Eisuke Sonomoto ◽  
Tsutomu T. Yanagida
Keyword(s):  
Decay Constant ◽  
Axion Decay Constant ◽  
Axion Decay

scholarly journals Lattice calculation of the hadronic leading order contribution to the muon g − 2

2020 ◽  
Vol 234 ◽  
pp. 01016
Author(s):  
Hartmut Wittig ◽  
Antoine Gérardin ◽  
Marco Cè ◽  
Georg von Hippel ◽  
Ben Hörz ◽  
...  
Keyword(s):  
Standard Model Prediction ◽  
Detailed Comparison ◽  
New Physics ◽  
Current Status ◽  
Leading Order ◽  
Lattice Calculation ◽  
Muon Anomalous Magnetic Moment ◽  
The Standard Model ◽  
Vacuum Polarisation

The persistent discrepancy of about 3.5 standard deviations between the experimental measurement and the Standard Model prediction for the muon anomalous magnetic moment, aµ, is one of the most promising hints for the possible existence of new physics. Here we report on our lattice QCD calculation of the hadronic vacuum polarisation contribution $ a_\mu ^{{\rm{hvp}}} $, based on gauge ensembles with Nf = 2 + 1 flavours of O(a) improved Wilson quarks. We address the conceptual and numerical challenges that one encounters along the way to a sub-percent determination of the hadronic vacuum polarisation contribution. The current status of lattice calculations of $ a_\mu ^{{\rm{hvp}}} $ is presented by performing a detailed comparison with the results from other groups.

scholarly journals Numerical analysis of Coleman–de Luccia tunneling

2016 ◽  
Vol 31 (24) ◽  
pp. 1650131 ◽  
Author(s):  
Yuhei Goto ◽  
Kazumi Okuyama
Keyword(s):  
Decay Constant ◽  
Periodic Potential ◽  
Thin Wall ◽  
False Vacuum ◽  
Vacuum Decay ◽  
Text Type ◽  
Axion Decay Constant ◽  
Axion Decay ◽  
Range Of Values ◽  
Type Potential

In this paper, we study the false vacuum decay of a single scalar field [Formula: see text] coupled to gravity described by the Coleman–de Luccia (CdL) instanton. We show that it is possible to numerically calculate the bounce factor, which is related to the CdL tunneling rate, without using the thin-wall approximation. In this paper, we consider [Formula: see text]- and [Formula: see text]-type potentials as examples, which have cosmological and phenomenological applications. Especially, in the [Formula: see text]-type potential, we show that the range of values in which axion decay constant can take is restricted by the form of the periodic potential if the CdL tunneling occurs.

ON THE SUPERSTRING AXION MINI-STAR

1998 ◽  
Vol 13 (13) ◽  
pp. 1007-1017 ◽  
Author(s):  
M. D. POLLOCK
Keyword(s):  
Gravitational Collapse ◽  
Mass Formula ◽  
Decay Constant ◽  
Gravitational Constant ◽  
Large Magellanic Cloud ◽  
Magellanic Cloud ◽  
Planck Mass ◽  
Upper Limit ◽  
Axion Decay Constant ◽  
Axion Decay

The theory of the pressure-free-boson mini-star of mass M, whose radius r=2GM/v2 is equated via the indeterminacy principle to ℏ/mv, where [Formula: see text] is the Newton gravitational constant, M P being the Planck mass and m the mass of the boson, travelling at velocity v, is applied to the superstring axion. For a bounded object, the upper limit to the axion potential [Formula: see text] constrains the axions to move at non-relativistic velocities [Formula: see text] where [Formula: see text] GeV is the axion decay constant, predicting the existence of an axion mini-star of mass [Formula: see text]. Such objects can in principle form by gravitational collapse below the temperature T≈100 eV, and are tentatively identified with the microlensing objects recently detected in our Galaxy and in the direction of the Large Magellanic Cloud.

scholarly journals Probing new physics scenarios of muon g − 2 via J/ψ decay at BESIII

2020 ◽  
Vol 2020 (10) ◽  
Author(s):  
Gorazd Cvetič ◽  
C. S. Kim ◽  
Donghun Lee ◽  
Dibyakrupa Sahoo
Keyword(s):  
Model Prediction ◽  
Magnetic Moment ◽  
Experimental Measurement ◽  
Anomalous Magnetic Moment ◽  
Numerical Study ◽  
Standard Model Prediction ◽  
Vector Boson ◽  
New Physics ◽  
Muon Anomalous Magnetic Moment ◽  
The Standard Model

Abstract The disagreement between the standard model prediction and the experimental measurement of muon anomalous magnetic moment can be alleviated by invoking an additional particle which is either a vector boson (X1) or a scalar (X0). This new particle, with the mass mX ≲ 2mμ, can be searched for in the decay J/ψ → μ−μ+X, where X is missing. Our numerical study shows that the search is quite feasible at the BESIII experiment in the parameter space allowed by muon g − 2 measurements.

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