Neutrino oscillation experiments and direct bounds on absolute masses constrain neutrino mass differences to fall into the microwave energy range, for most of the allowed parameter space. As a consequence of these recent phenomenological advances, older constraints on radiative neutrino decays based on diffuse background radiations and assuming strongly hierarchical masses in the eV range are now outdated. We thus derive new bounds on the radiative neutrino lifetime using the high precision cosmic microwave background spectral data collected by the Far Infrared Absolute Spectrophotometer instrument on board of Cosmic Background Explorer. The lower bound on the lifetime is between a few x 10^19 s and 5 x 10^20 s, depending on the neutrino mass ordering and on the absolute mass scale. However, due to phase space limitations, the upper bound in terms of the effective magnetic moment mediating the decay is not better than ~ 10^-8 Bohr magnetons. We also comment about possible improvements of these limits, by means of recent diffuse infrared photon background data. We compare these bounds with pre-existing limits coming from laboratory or astrophysical arguments. We emphasize the complementarity of our results with others available in the literature.
It is interesting to investigate the OZI-forbidden radiative orthoquarkonium decays $J/ψ\to γπ^0, γη$ and $γη'$ in perturbative QCD. In this work without the approximations adopted in literature we carry out a full one-loop calculation which involves integrations of 4-point and 5-point loop functions. Our numerical results are in agreement with the present data. We also briefly discuss the decays of $J/ψ\to γ+ρ^0$, as well as $Υ\to π^0γ, ηγ, η'γ$.
We revisit electroweak radiative corrections to Standard Model Effective Field Theory (SMEFT) operators which are relevant for the $B$-meson semileptonic decays. The one-loop matching formulae onto the low-energy effective field theory are provided without imposing any flavor symmetry. The on-shell conditions are applied especially in dealing with quark-flavor mixings. Also, the gauge independence is shown explicitly in the $R_ξ$ gauge.
Triggered by experimentally driven renewed interest in hyperon properties we address the subject of weak radiative hyperon decays (WRHD). We start with the issue of Hara's theorem and briefly discuss the question of its possible evasion. Then, we give a short review of the story of vector-meson-dominance (VMD) approach to WRHD. We stress the shift from the Hara's-theorem-violating to Hara's-theorem-satisfying version of the VMD approach that did occur over time. Finally, spurred by a recent theoretical paper, we discuss the pole model description of WRHD, putting special attention to the issue…
We revisit the calculation of the width for the radiative decay of a $1^{+-}$ heavy $Q \bar Q$ meson via the channel $1^{+-} \to 0^{-+} +γ$ in the covariant light-front quark model. We carry out the reduction of the light-front amplitude in the non-relativistic limit, explicitly computing the leading and next-to-leading order relativistic corrections. This shows the consistency of the light-front approach with the non-relativistic formula for this electric dipole transition. Furthermore, the theoretical uncertainty in the predicted width is studied as a function of the inputs for the heavy qua…
In this paper, we summarize the existing methods of solving the evolution equation of the leading-twist $B$-meson LCDA. Then, in the Mellin space, we derive a factorization formula with next-to-leading-logarithmic (NLL) resummation for the form factors $F_{A,V}$ in the $B \to γ\ellν$ decay at leading power in $Λ/m_b$. Furthermore, we investigate the power suppressed local contributions, factorizable non-local contributions (which are suppressed by $1/E_γ$ and $1/m_b$), and soft contributions to the form factors. In the numerical analysis, which employs the two-loop-level hard function and the …
The ATLAS and CMS experiments at the CERN LHC have collected about 25 inverse femtobarns (fb) of data each at the end of their 8 TeV run, and ruled out a huge swath of parameter space in the context of Minimally Supersymmetric Standard Model (MSSM). Limits on masses of the gluino have been pushed to above 1 TeV. These limits are however extremely model dependent and do not always reflect the level of exclusion. So far the limits on the gluino mass using the simplified model approach only constrained its value using its three-body decays. We show in this work that already existing ATLAS and CMS…
We revisit the calculation of multiple parton scattering of a heavy quark in nuclei within the framework of recently improved high-twist factorization formalism, in which gauge invariance is ensured by a delicate setup of the initial partons' transverse momenta. We derive a new result for medium modified heavy quark fragmentation functions in deeply inelastic scattering. It is consistent with the previous calculation of light quark energy loss in the massless limit, but leads to a new correction term in the heavy quark case, which vanishes in the soft gluon radiation limit. We show numerically…
In the framework of perturbative QCD, the radiative decays $J/ψ\rightarrowγη^{(\prime)}$ are revisited in detail, where the involved one-loop integrals are evaluated analytically with the light quark masses kept. We have found that the sum of loop integrals is insensitive to the light quark masses and the branching ratios $\mathcal{B}(J/ψ\rightarrowγη^{(\prime)})$ barely depend on the shapes of $η^{(\prime)}$ distribution amplitudes. With the parameters of $η-η^{\prime}$ mixing extracted from low energy processes and $J/ψ\rightarrowγη^{(\prime)}$ by means of nonperturbative matrix elements $\l…
Radiative Breaking of Two-Zero Neutrino Mass Minors: Revisiting the $\mathrm{U}(1)_{L_μ-L_τ}$ Model
ICRR, The University of Tokyo（东京大学宇宙射线研究所）；Kavli Institute for the Physics and Mathematics of the Universe (WPI), The University of Tokyo Institutes for Advanced Study, The University of Tokyo（东京大学国际高等研究院 Kavli宇宙物理与数学研究所）
Conflicting values of the hypertriton ($_Λ^{3}$H) lifetime were extracted in recent relativistic heavy-ion collision experiments. The ALICE Collaboration's reported $_Λ^{3}$H lifetime $τ(_Λ^{3}$H) is compatible within measurement uncertainties with the free $Λ$ lifetime $τ_Λ$, as naively expected for a loosely bound $Λ$ hyperon in $_Λ^{3}$H, whereas STAR's reported range of $τ(_Λ^{3}$H) values is considerably shorter: $τ_{\rm STAR}(_Λ^{3}$H)$\sim$(0.4-0.7)$τ_Λ$. This $_Λ^{3}$H lifetime puzzle is revisited theoretically using $_Λ^{3}$H three-body wavefunctions generated in a chiral effective fi…
We examine how a parametrization of neutrino mixing matrix reflecting quark-lepton complementarity can be probed by considering phase-averaged oscillation probabilities, flavor composition of neutrino fluxes coming from atmospheric and astrophysical neutrinos and lepton flavor violating radiative decays. We discuss about some distinct features of the parametrization by comparing with the triminimal parametrization of perturbations to tri-bimaximal neutrino mixing matrix.
QCD theory predicts the existence of glueballs, but so far all experimental endeavors have failed to identify any such states. To remedy this discrepancy between QCD, which has proven to be a successful theory for strong interactions, and the failure of experimental searches for glueballs, one is tempted to accept the promising interpretation that the glueballs mix with regular $q\bar q$ states of the same quantum numbers. The lattice estimate of the masses of pure $0^{++}$ glueballs ranges from 1 to 2 GeV, which is the region of the $f_0$ family. Thus many authors suggest that the $f_0$ meson…
The $P$-wave charmonium decays $h_{c}\rightarrowγη^{(\prime)}$ are revisited by taking into account relativistic corrections. The decay amplitudes are derived in the Bethe-Salpeter formalism, in which the involved one-loop integrals are evaluated analytically. Intriguingly, from both the quark-antiquark content and the gluonic content of $η^{(\prime)}$, the relativistic corrections make significant contributions to the decay rates of $h_{c}\rightarrowγη^{(\prime)}$. By comparison with the leading-order contributions from the quark-antiquark content (one-loop level), the ones from the gluonic c…
It is often the case that scalar fields are produced in the early Universe in the form of coherent oscillation. These scalar fields may have huge abundances and affect the evolution of the Universe. In particular, if the lifetime is long enough, they may cause cosmological disasters. We revisit the issue of coherent oscillation of the scalar field when it couples with another oscillating scalar field, and find a situation that the abundance, or the amplitude of the oscillation, is significantly reduced by a variant type of the adiabatic suppression mechanism. As a concrete example, it is appli…
We study lifetimes of heavy mesons in the 't Hooft model, a large-$N_c$ theory of strong interaction in two-dimensional spacetime. Since this model is solvable, one can evaluate the total decay widths through hadronic amplitudes that are determined unambiguously within the formalism. We investigate quark-hadron duality by numerically comparing the exclusive result and one from the heavy quark expansion, with the contribution of Pauli interference being consistently incorporated. Within certain numerical accuracy, we find that the maximal difference between inclusive and exclusive rates for $τ[…
Revisiting the limits on dark matter annihilation cross-section and decay lifetime in light of electron and positron fluxes
Yokohama National University（横滨国立大学）；RIKEN Center for Interdisciplinary Theoretical and Mathematical Sciences(iTHEMS), RIKEN（理化学研究所交叉理论数学科学中心(iTHEMS)）；National Astronomical Observatory of Japan (NAOJ)（日本国立天文台）；SOKENDAI（综合研究大学院大学）；The University of Tokyo（东京大学）；KEK（高能加速器研究机构）；Kavli IPMU (WPI), UTIAS, The University of Tokyo（东京大学柏校区卡弗里宇宙物理学与数学国际研究中心）；Indian Institute of Technology Hyderabad（印度理工学院海得拉巴分校）
We calculate the radiative corrections of order O(alpha E_e/m_N) as next-to-leading order corrections in the large nucleon mass expansion to Sirlin's radiative corrections of order O(alpha/pi) to the neutron lifetime. The calculation is carried out within a quantum field theoretic model of strong low-energy pion--nucleon interactions described by the linear sigma-model (LsM) with chiral SU(2)xSU(2) symmetry and electroweak hadron-hadron, hadron-lepton and lepton-lepton interactions for the electron-lepton family with SU(2)_L x U(1)_Y symmetry of the Standard Electroweak Model (SEM). Such a qua…
If dark matter decays to electromagnetically-interacting particles, it can inject energy into the baryonic gas and thus affect the processes of recombination and reionization. This leaves an imprint on the cosmic microwave background (CMB): the large-scale polarization is enhanced, and the small-scale temperature fluctuation is damped. We use the WMAP three-year data combined with galaxy surveys to constrain radiatively decaying dark matter. Our new limits to the dark-matter decay width are about ten times stronger than previous limits. For dark-matter lifetimes that exceed the age of the Univ…
Combining neutrino mass generation and a dark matter candidate in a unified model has always been intriguing. We revisit the class of R$ν$MDM models, which incorporate minimal dark matter in radiative neutrino mass models based on the one-loop ultraviolet completions of the Weinberg operator. The possibility of an exact accidental $Z_2$ is completely ruled out in this scenario. We study the phenomenology of one of the models with an approximate $Z_2$ symmetry. In addition to the Standard Model particles, it contains two real scalar quintuplets, one vector- like quadruplet fermion and a fermion…
We propose to search for the neutrino radiative decay by fitting a photon energy spectrum of the cosmic infrared background to a sum of the photon energy spectrum from the neutrino radiative decay and a continuum. By comparing the present cosmic infrared background energy spectrum observed by AKARI and Spitzer to the photon energy spectrum expected from neutrino radiative decay with a maximum likelihood method, we obatined a lifetime lower limit of $3.1 \times 10^{12}$ to $3.8 \times 10^{12}$ years at 95% confidence level for the third generation neutrino $ν_3$ in the $ν_3$ mass range between …
An analysis of radiative decays of the neutrinos $ν_j\to ν_l γ$ is discussed in MSSM extensions with a vector like lepton generation. Specifically we compute neutrino decays arising from the exchange of charginos and charged sleptons where the photon is emitted by the charged particle in the loop. It is shown that while the lifetime of the neutrino decay in the Standard Model is $\sim 10^{43}$ yrs for a neutrino mass of 50 meV, the current lower limit from experiment from the analysis of the Cosmic Infrared Background is $\sim 10^{12}$ yrs and thus beyond the reach of experiment in the foresee…
The scotogenic model is a well motivated scenario that provides both an explanation for neutrino masses and for dark matter. We focus on a real scalar dark matter candidate in this model, produced through standard thermal freeze-out. We analyze the parameter space of the model compatible with the observed dark matter relic abundance, direct and indirect detection searches, limits from lepton flavour violating decays and constraints from the neutrino sector. As the mass differences of the dark matter with the neutral and charged states are found to be small, the new scalars and fermions of the …
Of the the three best-measured electroweak observables, $α$, $G_μ$ and $M_Z$, the first two are extracted from low-energy processes. Both $G_μ$ and $M_Z$ are now known to an accuracy of about 2 parts in $10^5$ and there is a proposal to improve the measurement of the muon lifetime by a factor of 10 in an experiment at Brookhaven. Yet calculations of electroweak radiative corrections currently do no better than a few parts in $10^3$--$10^4$ and therefore cannot exploit to available experimental precision. We report on the calculation of the ${\cal O}(N_fα^2)$ corrections to Thomson scattering a…
The universal radiative corrections common to neutron and super-allowed nuclear beta decays (also known as ``inner'' corrections) are revisited in light of a recent dispersion relation study that found $+2.467(22)\%$, i.e.~about $2.4σ$ larger than the previous evaluation. For comparison, we consider several alternative computational methods. All employ an updated perturbative QCD four-loop Bjorken sum rule (BjSR) defined QCD coupling supplemented with a nucleon form factor based Born amplitude to estimate axial-vector induced hadronic contributions. In addition, we now include hadronic contrib…
We show that a Majorana heavy neutrino with a mass O(100TeV) is a good candidate particle for cold dark matter. It can be responsible for the majority of the cosmological diffuse photon background owing to lifetime of the order of O(10^(25)s), dominantly fixed by the radiative two-body decay. The lifetime is suppressed by two mechanisms: the leptonic GIM cancellation and the see-saw weak coupling suppression. As a fermion cold dark matter particle, a heavy neutrino favours the average mass density of the Universe constrained by the Einstein-Cartan cosmology.
Recently, the O(alpha) and O(alpha^3 ln(alpha)) radiative corrections to the orthopositronium lifetime have been presented in closed analytical form, in terms of basic irrational numbers that can be evaluated numerically to arbitrary precision [Phys. Rev. Lett. 101, 193401 (2008)]. Here, we present the details of this calculation and reveal the nature of these new constants. We also list explicit transformation formulas for generalized polylogarithms of weight four, which may be useful for other applications.
Minimal $SU(5)$ Grand Unified models predict massless neutrinos and struggle to achieve gauge coupling unification compatible with the observed lower limit on the proton lifetime. Both of these issues can be resolved by embedding minimal radiative neutrino mass models into $SU(5)$. We systematically analyze the possible ways to realize radiative neutrino mass generation in $SU(5)$ and provide a list of the minimal models. We find various models that have not been considered in the literature and demonstrate the compatibility of radiative neutrino masses with gauge coupling unification and prot…
We revisit the decoupling effects associated with heavy particles in the renormalization group running of the vacuum energy in a mass-dependent renormalization scheme. We find the running of the vacuum energy stemming from the Higgs condensate in the entire energy range and show that it behaves as expected from the simple dimensional arguments meaning that it exhibits the quadratic sensitivity to the mass of the heavy particles in the infrared regime. The consequence of such a running to the fine-tuning problem with the measured value of the Cosmological Constant is analyzed and the constraint…
