This paper presents results of experimental and numerical investigations of a seesaw energy dissipation system （SEDS） using fluid viscous dampers （FVDs）. To confirm the characteristics of the FVDs used in the test...This paper presents results of experimental and numerical investigations of a seesaw energy dissipation system （SEDS） using fluid viscous dampers （FVDs）. To confirm the characteristics of the FVDs used in the tests, harmonic dynamic loading tests were conducted in advance of the flee vibration tests and the shaking table tests. Shaking table tests were conducted to demonstrate the damping capacity of the SEDS under random excitations such as seismic waves, and the results showed SEDSs have sufficient damping capacity for reducing the seismic response of flames. Free vibration tests were conducted to confirm the reliability of simplified analysis. Time history response analyses were also conducted and the results are in close agreement with shaking table test results.展开更多
Early studies suggested that the Aleutian–Icelandic low seesaw(AIS) features multidecadal variation. In this study, the multidecadal modulation of the AIS and associated surface climate by the Atlantic Multidecadal O...Early studies suggested that the Aleutian–Icelandic low seesaw(AIS) features multidecadal variation. In this study, the multidecadal modulation of the AIS and associated surface climate by the Atlantic Multidecadal Oscillation(AMO) during late winter(February–March) is explored with observational data. It is shown that, in the cold phase of the AMO(AMO|-),a clear AIS is established, while this is not the case in the warm phase of the AMO(AMO|+). The surface climate over Eurasia is significantly influenced by the AMO’s modulation of the Aleutian low(AL). For example, the weak AL in AMO|-displays warmer surface temperatures over the entire Far East and along the Russian Arctic coast and into Northern Europe,but only over the Russian Far East in AMO|+. Similarly, precipitation decreases over central Europe with the weak AL in AMO|-, but decreases over northern Europe and increases over southern Europe in AMO|+.The mechanism underlying the influence of AMO|-on the AIS can be described as follows: AMO|-weakens the upward component of the Eliassen–Palm flux along the polar waveguide by reducing atmospheric blocking occurrence over the Euro–Atlantic sector, and hence drives an enhanced stratospheric polar vortex. With the intensified polar night jet, the wave trains originating over the central North Pacific can propagate horizontally through North America and extend into the North Atlantic, favoring an eastward-extended Pacific–North America–Atlantic pattern, and resulting in a significant AIS at the surface during late winter.展开更多
In this paper,following the Occam’s razor principle,we have put forward a very simple form of the Dirac neutrino mass matrix M_(D) in the minimal seesaw model with the right-handed neutrino mass matrix being diagonal...In this paper,following the Occam’s razor principle,we have put forward a very simple form of the Dirac neutrino mass matrix M_(D) in the minimal seesaw model with the right-handed neutrino mass matrix being diagonal M_(R)=diag(M_(1),M_(2));it has one texture zero and only contains three real parameters,whose values can be determined from the neutrino oscillation experimental results.Such a model leads to a neutrino mass matrix M_(v)≃-M_(D)M_(R)^(-1)M_(D)^(T)that obeys the TM1 and μ-τ reflection symmetries simultaneously.In this way all the lepton flavor mixing parameters except for θ_(13) are predicted;the value of θ_(12) is predicted by the TM1 symmetry,while those of θ_(23),δ,ρ and σ by the μ-τ reflection symmetry.And the neutrino masses are predicted to be of the NO case with m_(1)=0,for which all three light neutrino masses will be pinned down with the help of the experimental results for the neutrino mass squared differences.For these results,the effective Majorana neutrino mass∣(M_(ν))_(ee)∣that controls the rate of the neutrinoless double beta decay is predicted to be 1.6 or 3.8 meV in the case of σ=0 or π/2.We have also studied the implications of the model for leptogenesis.It turns out that only in the two-flavor leptogenesis regime(which holds in the temperature range 10^(9)-10^(12) GeV)can leptogenesis have a chance to be successful.And a successful leptogenesis can be achieved at M_(1)≃1.2×10^(11) GeV in the case of σ=π/2,but not in the case of σ=0.展开更多
In Asaka et al(2021 Phys.Rev.D 103,015014),Asaka,Ishida and Tanaka put forward an interesting possibility that the neutrinoless double beta decay can be hidden in the minimal seesaw model with the two right-handed neu...In Asaka et al(2021 Phys.Rev.D 103,015014),Asaka,Ishida and Tanaka put forward an interesting possibility that the neutrinoless double beta decay can be hidden in the minimal seesaw model with the two right-handed neutrinos having a hierarchical mass structure:the lighter one is lighter enough than the typical Fermi-momentum scale of nuclei while the heavier one is sufficiently heavy to decouple from the neutrinoless double beta decay.Then,in the basis where the mass matrices of the charged leptons and right-handed neutrinos are diagonal,for some particular texture of the Dirac neutrino mass matrix M_(D),the neutrinoless double beta decay can be hidden.In this paper,on top of this specified model,we study the interesting scenario that M_(D)further obeys the TM1 symmetry orμ-τreflection symmetry which are well motivated by the experimental results for the neutrino mixing parameters.展开更多
Lepton flavor violation(LFV)offers a powerful probe of physics beyond the Standard Model,particularly in models addressing neutrino masses and the baryon asymmetry of the universe.In this study,we investigate LFV proc...Lepton flavor violation(LFV)offers a powerful probe of physics beyond the Standard Model,particularly in models addressing neutrino masses and the baryon asymmetry of the universe.In this study,we investigate LFV processes within the framework of type Ⅱ seesaw leptogenesis,where the Standard Model is extended by an SU(2)_(L) triplet Higgs field.We focus on key LFV processes,including μ^(+)→e^(+)γ,e^(+)→e^(-)e^(+),and μ→e conversion in nuclei,deriving stringent constraints on the parameter space from current experimental data.We scan the 3σ range of neutrino oscillation parameters and identify the most conservative bounds consistent with existing measurements.Our results reveal that the MEG experiment currently provides the most stringent constraints in the normal ordering(NO)scenario,while the SINDRUM experiment offers comparable sensitivity in the inverted ordering(IO)case.Future experiments,such as MEGⅡ,Mu3e,Mu2e,and COMET,are predicted to significantly improve the sensitivity,testing larger regions of the parameter space.展开更多
We investigate the process of lepton-number-violating pion decay,which dominates the nuclear neutrinoless double beta decay induced by the short-range operator within the type-Ⅰ seesaw mechanism.The type-Ⅰ seesaw me...We investigate the process of lepton-number-violating pion decay,which dominates the nuclear neutrinoless double beta decay induced by the short-range operator within the type-Ⅰ seesaw mechanism.The type-Ⅰ seesaw mechanism leads to the Dirac and Majorana mass terms of neutrinos by introducing the gauge-singlet righthanded neutrinos,which are often called sterile neutrinos.Applying the chiral perturbation theory,we calculate the transition amplitudes for light and heavy sterile neutrinos up to O(Q^(2)/Λ_(χ)^(2)),where Q is the typical low-energy scale in this process and Λ_(χ) the chiral symmetry breaking scale.We then adopt a naive interpolation formula of mass dependence to obtain the amplitude in the full mass range and briefly discuss its validity.展开更多
Extending across three major plateaus,namely the Qinghai-Tibetan Plateau,the Inner Mongolia-Xinjiang Plateau and the Loess Plateau,Northwest China has the complex terrain and spatio-temporal climate variations,and is ...Extending across three major plateaus,namely the Qinghai-Tibetan Plateau,the Inner Mongolia-Xinjiang Plateau and the Loess Plateau,Northwest China has the complex terrain and spatio-temporal climate variations,and is affected by the interactions among different circulation systems,such as the summer monsoon,the westerlies and the plateau monsoon.The understanding of the climate variability,as well as its characteristics and evolution mechanisms in this area has been limited so far.In this paper,the precipitation characteristics and mechanisms in the eastern and western parts of Northwest China during the flood season are compared and analyzed based on the data from 192 national meteorological observational sites in Northwest China in 1961-2016.The results show that,divided by the northern boundary of the East Asian summer monsoon,there are huge differences in the precipitation variation characteristics between the eastern and western parts.The inter-annual variations,interdecadal variations and total trends in the two parts all show a significant seesaw phenomenon.Moreover,it is found that the seesaw phenomenon of precipitation variation is closely related to the opposite variation between the East Asian summer monsoon index(MI)and the westerly circulation index(WI).In addition,the inverse variations on different time scales are only related to the contributions of precipitation at specific grades.Besides,in the two matching patterns of precipitation in the seesaw phenomenon,the middle and high latitudes are occupied by the"high-low-high"wave trains in the precipitation increases in the east of Northwest China(ENWC)and decreases in the west of Northwest China(WNWC)pattern,meaning precipitation increases in ENWC and decreases in WNWC.Whereas the opposite"low-high-low"wave trains at 500 hPa height are observed in the middle and high latitudes in the WH-EA pattern at 500 hPa height,meaning precipitation increases in WNWC and decreases in ENWC.Thus,the atmosphere circulation situation with two wave train types can support both the precipitation seesaw phenomenon and the opposite variation between MI and WI.Moreover,the seesaw phenomenon is shown to be related to the separate or joint effects of the South Asian High,ENSO and the plateau heating on the common but opposite effect on the summer monsoon and the westerlies,in which the South Asian High probably plays a more critical role.This study could deepen the scientific understanding of precipitation mechanisms and improve the weather forecast technology in Northwest China during the flood season.展开更多
Using the NCEP/NCAR reanalysis and the ENSO indices from the Climate Prediction Center over the period 1978-2014,we have investigated the contemporaneous circulation variations in the Northern and Southern Hemispheres...Using the NCEP/NCAR reanalysis and the ENSO indices from the Climate Prediction Center over the period 1978-2014,we have investigated the contemporaneous circulation variations in the Northern and Southern Hemispheres by performing the singular value decomposition analysis of sea level pressure anomalies（SLPA） after the ENSO signal is regressed out.It is found that there exists a polar-tropical seesaw mode（PTSM） that characterizes with the out of phase fluctuations of SLPA between the polar and tropical regions in the Northern and Southern Hemispheres in boreal winter.This PTSM explains 47.74%of the total covariance of SLPA and is almost independent of ENSO.It demonstrates a long-term trend and oscillation cycles of 2-3 and 4-6 yr.The long-term trend in PTSM indicates that the sea level pressure gradually decreases in the tropics and increases in the polar region with time.This PTSM looks roughly symmetric about the equator besides the seesaw pattern of SLPA between the tropics and polar region in each hemisphere.The disturbances in the geopotential height field in association with the PTSM shows baroclinic features in the tropics whereas equivalent barotropic features in the mid and high latitudes in the troposphere.The anomalous thermal forcing in the tropical region is possibly one of the factors facilitating the formation of this PTSM.Significant global precipitation and temperature anomalies related to the PTSM are observed.In the positive PTSM phase,precipitation and temperature are higher than normal in southern Europe and the Mediterranean and surrounding areas,but lower than normal in northern Europe and Siberia.Precipitation is higher than normal while temperature is lower than normal in Northeast Asia.Significant temperature and precipitation anomalies possibly occur in the regions of western China,northern India,parts of North America,parts of subtropical Africa,Maritime Continent,and Antarctic.These results are helpful for better understanding of the circulation variations and the mechanisms behind the interactions between the Northern and Southern Hemispheres and the related winter climate anomalies over globe.展开更多
The observation of neutrino oscillations requires new physics beyond the standard model （SM）. A SM-like gauge theory with p lepton families can be extended by introducing q heavy right-handed Majorana neutrinos but ...The observation of neutrino oscillations requires new physics beyond the standard model （SM）. A SM-like gauge theory with p lepton families can be extended by introducing q heavy right-handed Majorana neutrinos but preserving its SU（2）L × U（1）Y gauge symmetry. The overall neutrino mass matrix M turns out to be a symmetric （p＋q） × （p＋q） matrix. Given p 〉 q, the rank of M is in general equal to 2q, corresponding to 2q non-zero mass eigenvalues. The existence of （p-q） massless left-handed Majorana neutrinos is an exact consequence of the model, independent of the usual approximation made in deriving the Type-I seesaw relation between the effective p x p light Majorana neutrino mass matrix Mv and the q × q heavy Majorana neutrino mass matrix MR. In other words, the numbers of massive left- and right-handed neutrinos are fairly matched. A good example to illustrate this ＂seesaw fair play rule＂ is the minimal seesaw model with p = 3 and q = 2, in which one massless neutrino sits on the unbalanced seesaw.展开更多
The lepton-number-violating decays of singly-charged Higgs bosons H^± are investigated in the minimal type-（ Ⅰ＋Ⅱ ） seesaw model with one SU（2）L Higgs triplet △ and one heavy Majorana neutrino N1 at the Te...The lepton-number-violating decays of singly-charged Higgs bosons H^± are investigated in the minimal type-（ Ⅰ＋Ⅱ ） seesaw model with one SU（2）L Higgs triplet △ and one heavy Majorana neutrino N1 at the TeV scale. We find that the branching ratios B（H^＋ → 1α^＋υ^-） （for α = e,μ,τ） depend not only on the mass and mixing parameters of three light neutrinos υi （for i = 1, 2, 3） but also on those of N1. Assuming that the mass of N1 lies in the range of 200 GeV to 1 TeV, we figure out the generous interference bands for the contributions of υi and N1 to B（H^＋→ 1α^＋υ^-）. We illustrate some salient features of such interference effects by considering three typical mass patterns of υi, and show that the relevant Majorana CP-violating phases can affect the magnitudes of B（H^＋→ 1α^＋υ^-）） in this parameter region.展开更多
Neutrinos stand out among the elementary particles because of their unusually small masses.Various seesaw mechanisms attempt to explain this fact.In this work,applying insights from matrix theory,we are in a position ...Neutrinos stand out among the elementary particles because of their unusually small masses.Various seesaw mechanisms attempt to explain this fact.In this work,applying insights from matrix theory,we are in a position to treat variants of seesaw mechanisms in a general manner.Specifically,using Weyl's inequalities,we discuss and rigorously prove under which conditions the seesaw framework leads to a mass spectrum with exactly three light neutrinos.We find an estimate of the mass of heavy neutrinos to be the mass obtained by neglecting light neutrinos,shifted at most by the maximal strength of the coupling to the light neutrino sector.We provide analytical conditions allowing one to prescribe that precisely two out of five neutrinos are heavy.For higher-dimensional cases the inverse eigenvalue methods are used.In particular,for the CP-invariant scenarios we show that if the neutrino sector has a valid mass matrix after neglecting the light ones,i.e.if the respective mass submatrix is positive definite,then large masses are provided by matrices with large elements accumulated on the diagonal.Finally,the Davis-Kahan theorem is used to show how masses affect the rotation of light neutrino eigenvectors from the standard Euclidean basis.This general observation concerning neutrino mixing,together with results on the mass spectrum properties,opens directions for further neutrino physics studies using matrix analysis.展开更多
The same-sign tetralepton signature via the mixing of neutral Higgs bosons and their cascade decays to charged Higgs bosons is a unique signal in the type-Ⅱ seesaw model with the mass spectrum M_(A^(0))≈M_(H^(0))>...The same-sign tetralepton signature via the mixing of neutral Higgs bosons and their cascade decays to charged Higgs bosons is a unique signal in the type-Ⅱ seesaw model with the mass spectrum M_(A^(0))≈M_(H^(0))>M_(H^(+))>M_(H^(±±)).In this study,we investigate this signature at future lepton colliders,such as the ILC,CLIC,and MuC.Direct searches for doubly charged scalar H^(±±)at the LHC have excluded MHg+t<350(870) GeV in the H^(±±)+W^(±)W(±)(l^(±)^(±))decay mode.Therefore,we choose M_(A^(0))=400,600,1000,1500 GeV as our benchmark scenarios.Constrained by direct search,H^(±±)+W^(±)W(±)(l^(±)^(±))d=is the only viable decay mode for Mρ=400 GeV at the √s=1 TeV ILC.With an integrated luminosity L=8 ab^(-1),the promising region,with approximately 150 signal events,corresponds to a narrow band in the range of 10^(-4) GeV≤v△≤10^(-2)GeV.Meanwhile,for Mpo=600 GeV at the √s=1.5 TeV CLIC,approximately 10 signal events can be produced with L=2.5 ab^(-1).For heavier triplet scalars M_(A^(0))■870 GeV,although the H^(±±) decay mode is allowed,the cascade decays are suppressed.A maximum event number~16 can be obtained at approximately v△~4×10^(4)GeV and λ_(14)~0.26 for M_(A^(0))=1000 GeV with L=5 ab^(-1) at the √s=3 TeV CLIC.Finally,we find that this signature is not promising for M_(A^(0))= 1500 GeV at the √s=6 TeV MuC.Based on the benchmark scenarios,we also study the observability of this signature.In the H^(±±)+W^(±)W(±)(l^(±)^(±))d mode,one can probe MρS 800(1160) GeV at future lepton colliders.展开更多
Type Ⅱ seesaw leptogenesis simultaneously explains the origin of neutrino masses,the baryon asymmetry of our universe,and inflation.The Large Hadron Collider(LHC)provides an opportunity to directly test type Ⅱ seesa...Type Ⅱ seesaw leptogenesis simultaneously explains the origin of neutrino masses,the baryon asymmetry of our universe,and inflation.The Large Hadron Collider(LHC)provides an opportunity to directly test type Ⅱ seesaw leptogenesis by looking for the predicted triplet Higgs.In this paper,we perform an analysis of the detection prospect for the triplet Higgs at the LHC through multi-electron channels.We find that due to the contribution of the pp→H^(±±)H^(∓) process,the sensitivity of multi-electron channels searching for doubly-charged Higgs pair production can be improved.We also investigate the 3e+E_(T)^(miss) signals to probe pp→H^(±±)H^(∓) production and find that the future high luminosity LHC could probe a triplet Higgs around 1.2 TeV at the 2σlevel.展开更多
We discuss a linear seesaw model with a field content as minimum as possible,introducing a modular S_(4)using gauged U(1)_(B−L) symmetries.Owing to the rank two neutrino mass matrix,we obtain a vanishing neutrino mass...We discuss a linear seesaw model with a field content as minimum as possible,introducing a modular S_(4)using gauged U(1)_(B−L) symmetries.Owing to the rank two neutrino mass matrix,we obtain a vanishing neutrino mass eigenvalue,and only the normal mass hierarchy of neutrinos is favored via the modular S_(4)symmetry.In our numericalΔχ^(2)analysis,we especially determine a relatively sharp prediction on the sum of neutrino masses to be approximately 60 meV,in addition to other predictions.展开更多
文摘This paper presents results of experimental and numerical investigations of a seesaw energy dissipation system （SEDS） using fluid viscous dampers （FVDs）. To confirm the characteristics of the FVDs used in the tests, harmonic dynamic loading tests were conducted in advance of the flee vibration tests and the shaking table tests. Shaking table tests were conducted to demonstrate the damping capacity of the SEDS under random excitations such as seismic waves, and the results showed SEDSs have sufficient damping capacity for reducing the seismic response of flames. Free vibration tests were conducted to confirm the reliability of simplified analysis. Time history response analyses were also conducted and the results are in close agreement with shaking table test results.
基金supported by the Research Council of Norway(Grant Nos.EPOCASA#229774/E10 and SNOWGLACE#244166)the National Natural Science Foundation of China(Grant No.41605059)the Young Talent Support Plan launched by the China Association for Science and Technology(Grant No.2016QNRC001)
文摘Early studies suggested that the Aleutian–Icelandic low seesaw(AIS) features multidecadal variation. In this study, the multidecadal modulation of the AIS and associated surface climate by the Atlantic Multidecadal Oscillation(AMO) during late winter(February–March) is explored with observational data. It is shown that, in the cold phase of the AMO(AMO|-),a clear AIS is established, while this is not the case in the warm phase of the AMO(AMO|+). The surface climate over Eurasia is significantly influenced by the AMO’s modulation of the Aleutian low(AL). For example, the weak AL in AMO|-displays warmer surface temperatures over the entire Far East and along the Russian Arctic coast and into Northern Europe,but only over the Russian Far East in AMO|+. Similarly, precipitation decreases over central Europe with the weak AL in AMO|-, but decreases over northern Europe and increases over southern Europe in AMO|+.The mechanism underlying the influence of AMO|-on the AIS can be described as follows: AMO|-weakens the upward component of the Eliassen–Palm flux along the polar waveguide by reducing atmospheric blocking occurrence over the Euro–Atlantic sector, and hence drives an enhanced stratospheric polar vortex. With the intensified polar night jet, the wave trains originating over the central North Pacific can propagate horizontally through North America and extend into the North Atlantic, favoring an eastward-extended Pacific–North America–Atlantic pattern, and resulting in a significant AIS at the surface during late winter.
基金supported in part by the National Natural Science Foundation of China under Grant Nos.11605081,12142507 and 12147214the Natural Science Foundation of the Liaoning Scientific Committee under Grant No.2022MS-314
文摘In this paper,following the Occam’s razor principle,we have put forward a very simple form of the Dirac neutrino mass matrix M_(D) in the minimal seesaw model with the right-handed neutrino mass matrix being diagonal M_(R)=diag(M_(1),M_(2));it has one texture zero and only contains three real parameters,whose values can be determined from the neutrino oscillation experimental results.Such a model leads to a neutrino mass matrix M_(v)≃-M_(D)M_(R)^(-1)M_(D)^(T)that obeys the TM1 and μ-τ reflection symmetries simultaneously.In this way all the lepton flavor mixing parameters except for θ_(13) are predicted;the value of θ_(12) is predicted by the TM1 symmetry,while those of θ_(23),δ,ρ and σ by the μ-τ reflection symmetry.And the neutrino masses are predicted to be of the NO case with m_(1)=0,for which all three light neutrino masses will be pinned down with the help of the experimental results for the neutrino mass squared differences.For these results,the effective Majorana neutrino mass∣(M_(ν))_(ee)∣that controls the rate of the neutrinoless double beta decay is predicted to be 1.6 or 3.8 meV in the case of σ=0 or π/2.We have also studied the implications of the model for leptogenesis.It turns out that only in the two-flavor leptogenesis regime(which holds in the temperature range 10^(9)-10^(12) GeV)can leptogenesis have a chance to be successful.And a successful leptogenesis can be achieved at M_(1)≃1.2×10^(11) GeV in the case of σ=π/2,but not in the case of σ=0.
基金supported in part by the National Natural Science Foundation of China under Grant Nos.11605081,12142507 and 12147214the Natural Science Foundation of the Liaoning Scientific Committee under grant NO.2022-MS-314。
文摘In Asaka et al(2021 Phys.Rev.D 103,015014),Asaka,Ishida and Tanaka put forward an interesting possibility that the neutrinoless double beta decay can be hidden in the minimal seesaw model with the two right-handed neutrinos having a hierarchical mass structure:the lighter one is lighter enough than the typical Fermi-momentum scale of nuclei while the heavier one is sufficiently heavy to decouple from the neutrinoless double beta decay.Then,in the basis where the mass matrices of the charged leptons and right-handed neutrinos are diagonal,for some particular texture of the Dirac neutrino mass matrix M_(D),the neutrinoless double beta decay can be hidden.In this paper,on top of this specified model,we study the interesting scenario that M_(D)further obeys the TM1 symmetry orμ-τreflection symmetry which are well motivated by the experimental results for the neutrino mixing parameters.
基金Chengcheng Han acknowledges supports from the National Key R&D Program of China(2023YFA1606100)the Sun Yat-Sen University Science Foundation,the Fundamental Research Funds for the Central Universities at Sun Yat-sen University(24qnpy117)the Key Laboratory of Particle Astrophysics and Cosmology(MOE)of Shanghai Jiao Tong University。
文摘Lepton flavor violation(LFV)offers a powerful probe of physics beyond the Standard Model,particularly in models addressing neutrino masses and the baryon asymmetry of the universe.In this study,we investigate LFV processes within the framework of type Ⅱ seesaw leptogenesis,where the Standard Model is extended by an SU(2)_(L) triplet Higgs field.We focus on key LFV processes,including μ^(+)→e^(+)γ,e^(+)→e^(-)e^(+),and μ→e conversion in nuclei,deriving stringent constraints on the parameter space from current experimental data.We scan the 3σ range of neutrino oscillation parameters and identify the most conservative bounds consistent with existing measurements.Our results reveal that the MEG experiment currently provides the most stringent constraints in the normal ordering(NO)scenario,while the SINDRUM experiment offers comparable sensitivity in the inverted ordering(IO)case.Future experiments,such as MEGⅡ,Mu3e,Mu2e,and COMET,are predicted to significantly improve the sensitivity,testing larger regions of the parameter space.
基金Supported by National Key Research and Development Program of China(2021YFA1601300)Young Scientists in Basic Research(YSBR-099)from Chinese Academy of Sciencesthe Postdoctoral Special Foundation of Gansu Province。
文摘We investigate the process of lepton-number-violating pion decay,which dominates the nuclear neutrinoless double beta decay induced by the short-range operator within the type-Ⅰ seesaw mechanism.The type-Ⅰ seesaw mechanism leads to the Dirac and Majorana mass terms of neutrinos by introducing the gauge-singlet righthanded neutrinos,which are often called sterile neutrinos.Applying the chiral perturbation theory,we calculate the transition amplitudes for light and heavy sterile neutrinos up to O(Q^(2)/Λ_(χ)^(2)),where Q is the typical low-energy scale in this process and Λ_(χ) the chiral symmetry breaking scale.We then adopt a naive interpolation formula of mass dependence to obtain the amplitude in the full mass range and briefly discuss its validity.
基金supported by the National Natural Science Foundation of China (Grant Nos. 41630426 & 4170506)the Youth Fund Projects of Science and Technology from Gansu Province (Grant No. 17JR5RA342)
文摘Extending across three major plateaus,namely the Qinghai-Tibetan Plateau,the Inner Mongolia-Xinjiang Plateau and the Loess Plateau,Northwest China has the complex terrain and spatio-temporal climate variations,and is affected by the interactions among different circulation systems,such as the summer monsoon,the westerlies and the plateau monsoon.The understanding of the climate variability,as well as its characteristics and evolution mechanisms in this area has been limited so far.In this paper,the precipitation characteristics and mechanisms in the eastern and western parts of Northwest China during the flood season are compared and analyzed based on the data from 192 national meteorological observational sites in Northwest China in 1961-2016.The results show that,divided by the northern boundary of the East Asian summer monsoon,there are huge differences in the precipitation variation characteristics between the eastern and western parts.The inter-annual variations,interdecadal variations and total trends in the two parts all show a significant seesaw phenomenon.Moreover,it is found that the seesaw phenomenon of precipitation variation is closely related to the opposite variation between the East Asian summer monsoon index(MI)and the westerly circulation index(WI).In addition,the inverse variations on different time scales are only related to the contributions of precipitation at specific grades.Besides,in the two matching patterns of precipitation in the seesaw phenomenon,the middle and high latitudes are occupied by the"high-low-high"wave trains in the precipitation increases in the east of Northwest China(ENWC)and decreases in the west of Northwest China(WNWC)pattern,meaning precipitation increases in ENWC and decreases in WNWC.Whereas the opposite"low-high-low"wave trains at 500 hPa height are observed in the middle and high latitudes in the WH-EA pattern at 500 hPa height,meaning precipitation increases in WNWC and decreases in ENWC.Thus,the atmosphere circulation situation with two wave train types can support both the precipitation seesaw phenomenon and the opposite variation between MI and WI.Moreover,the seesaw phenomenon is shown to be related to the separate or joint effects of the South Asian High,ENSO and the plateau heating on the common but opposite effect on the summer monsoon and the westerlies,in which the South Asian High probably plays a more critical role.This study could deepen the scientific understanding of precipitation mechanisms and improve the weather forecast technology in Northwest China during the flood season.
基金Supported by the National Natural Science Foundation of China(41175062 and 41330425)Science Innovation Program of the State Key Laboratory of Severe Weather,Chinese Academy of Meteorological Sciences(2015LASW-A03)
文摘Using the NCEP/NCAR reanalysis and the ENSO indices from the Climate Prediction Center over the period 1978-2014,we have investigated the contemporaneous circulation variations in the Northern and Southern Hemispheres by performing the singular value decomposition analysis of sea level pressure anomalies（SLPA） after the ENSO signal is regressed out.It is found that there exists a polar-tropical seesaw mode（PTSM） that characterizes with the out of phase fluctuations of SLPA between the polar and tropical regions in the Northern and Southern Hemispheres in boreal winter.This PTSM explains 47.74%of the total covariance of SLPA and is almost independent of ENSO.It demonstrates a long-term trend and oscillation cycles of 2-3 and 4-6 yr.The long-term trend in PTSM indicates that the sea level pressure gradually decreases in the tropics and increases in the polar region with time.This PTSM looks roughly symmetric about the equator besides the seesaw pattern of SLPA between the tropics and polar region in each hemisphere.The disturbances in the geopotential height field in association with the PTSM shows baroclinic features in the tropics whereas equivalent barotropic features in the mid and high latitudes in the troposphere.The anomalous thermal forcing in the tropical region is possibly one of the factors facilitating the formation of this PTSM.Significant global precipitation and temperature anomalies related to the PTSM are observed.In the positive PTSM phase,precipitation and temperature are higher than normal in southern Europe and the Mediterranean and surrounding areas,but lower than normal in northern Europe and Siberia.Precipitation is higher than normal while temperature is lower than normal in Northeast Asia.Significant temperature and precipitation anomalies possibly occur in the regions of western China,northern India,parts of North America,parts of subtropical Africa,Maritime Continent,and Antarctic.These results are helpful for better understanding of the circulation variations and the mechanisms behind the interactions between the Northern and Southern Hemispheres and the related winter climate anomalies over globe.
基金Supported by National Natural Science Foundation of China (10425522)
文摘The observation of neutrino oscillations requires new physics beyond the standard model （SM）. A SM-like gauge theory with p lepton families can be extended by introducing q heavy right-handed Majorana neutrinos but preserving its SU（2）L × U（1）Y gauge symmetry. The overall neutrino mass matrix M turns out to be a symmetric （p＋q） × （p＋q） matrix. Given p 〉 q, the rank of M is in general equal to 2q, corresponding to 2q non-zero mass eigenvalues. The existence of （p-q） massless left-handed Majorana neutrinos is an exact consequence of the model, independent of the usual approximation made in deriving the Type-I seesaw relation between the effective p x p light Majorana neutrino mass matrix Mv and the q × q heavy Majorana neutrino mass matrix MR. In other words, the numbers of massive left- and right-handed neutrinos are fairly matched. A good example to illustrate this ＂seesaw fair play rule＂ is the minimal seesaw model with p = 3 and q = 2, in which one massless neutrino sits on the unbalanced seesaw.
基金Supported by National Natural Science Foundation of China (10425522)
文摘The lepton-number-violating decays of singly-charged Higgs bosons H^± are investigated in the minimal type-（ Ⅰ＋Ⅱ ） seesaw model with one SU（2）L Higgs triplet △ and one heavy Majorana neutrino N1 at the TeV scale. We find that the branching ratios B（H^＋ → 1α^＋υ^-） （for α = e,μ,τ） depend not only on the mass and mixing parameters of three light neutrinos υi （for i = 1, 2, 3） but also on those of N1. Assuming that the mass of N1 lies in the range of 200 GeV to 1 TeV, we figure out the generous interference bands for the contributions of υi and N1 to B（H^＋→ 1α^＋υ^-）. We illustrate some salient features of such interference effects by considering three typical mass patterns of υi, and show that the relevant Majorana CP-violating phases can affect the magnitudes of B（H^＋→ 1α^＋υ^-）） in this parameter region.
基金Supported partly by the Polish National Science Centre(NCN)under the Grant Agreement 2017/25/B/ST2/01987 and the COST(European Cooperation in Science and Technology)Action CA 16201 PARTICLEFACE。
文摘Neutrinos stand out among the elementary particles because of their unusually small masses.Various seesaw mechanisms attempt to explain this fact.In this work,applying insights from matrix theory,we are in a position to treat variants of seesaw mechanisms in a general manner.Specifically,using Weyl's inequalities,we discuss and rigorously prove under which conditions the seesaw framework leads to a mass spectrum with exactly three light neutrinos.We find an estimate of the mass of heavy neutrinos to be the mass obtained by neglecting light neutrinos,shifted at most by the maximal strength of the coupling to the light neutrino sector.We provide analytical conditions allowing one to prescribe that precisely two out of five neutrinos are heavy.For higher-dimensional cases the inverse eigenvalue methods are used.In particular,for the CP-invariant scenarios we show that if the neutrino sector has a valid mass matrix after neglecting the light ones,i.e.if the respective mass submatrix is positive definite,then large masses are provided by matrices with large elements accumulated on the diagonal.Finally,the Davis-Kahan theorem is used to show how masses affect the rotation of light neutrino eigenvectors from the standard Euclidean basis.This general observation concerning neutrino mixing,together with results on the mass spectrum properties,opens directions for further neutrino physics studies using matrix analysis.
基金Supported by the National Natural Science Foundation of China(11605074,11805081)Natural Science Foundation of Shandong Province(ZR2019QA021,ZR2018MA047)Joint Large-Scale Scientific Facility Funds of the NSFC and CAS(U1732263,U2032115)。
文摘The same-sign tetralepton signature via the mixing of neutral Higgs bosons and their cascade decays to charged Higgs bosons is a unique signal in the type-Ⅱ seesaw model with the mass spectrum M_(A^(0))≈M_(H^(0))>M_(H^(+))>M_(H^(±±)).In this study,we investigate this signature at future lepton colliders,such as the ILC,CLIC,and MuC.Direct searches for doubly charged scalar H^(±±)at the LHC have excluded MHg+t<350(870) GeV in the H^(±±)+W^(±)W(±)(l^(±)^(±))decay mode.Therefore,we choose M_(A^(0))=400,600,1000,1500 GeV as our benchmark scenarios.Constrained by direct search,H^(±±)+W^(±)W(±)(l^(±)^(±))d=is the only viable decay mode for Mρ=400 GeV at the √s=1 TeV ILC.With an integrated luminosity L=8 ab^(-1),the promising region,with approximately 150 signal events,corresponds to a narrow band in the range of 10^(-4) GeV≤v△≤10^(-2)GeV.Meanwhile,for Mpo=600 GeV at the √s=1.5 TeV CLIC,approximately 10 signal events can be produced with L=2.5 ab^(-1).For heavier triplet scalars M_(A^(0))■870 GeV,although the H^(±±) decay mode is allowed,the cascade decays are suppressed.A maximum event number~16 can be obtained at approximately v△~4×10^(4)GeV and λ_(14)~0.26 for M_(A^(0))=1000 GeV with L=5 ab^(-1) at the √s=3 TeV CLIC.Finally,we find that this signature is not promising for M_(A^(0))= 1500 GeV at the √s=6 TeV MuC.Based on the benchmark scenarios,we also study the observability of this signature.In the H^(±±)+W^(±)W(±)(l^(±)^(±))d mode,one can probe MρS 800(1160) GeV at future lepton colliders.
基金C.H.is supported by the Sun Yat-Sen University Science Foundation,and the Fundamental Research Funds for the Central Universities,Sun Yat-sen University(23qnpy58)。
文摘Type Ⅱ seesaw leptogenesis simultaneously explains the origin of neutrino masses,the baryon asymmetry of our universe,and inflation.The Large Hadron Collider(LHC)provides an opportunity to directly test type Ⅱ seesaw leptogenesis by looking for the predicted triplet Higgs.In this paper,we perform an analysis of the detection prospect for the triplet Higgs at the LHC through multi-electron channels.We find that due to the contribution of the pp→H^(±±)H^(∓) process,the sensitivity of multi-electron channels searching for doubly-charged Higgs pair production can be improved.We also investigate the 3e+E_(T)^(miss) signals to probe pp→H^(±±)H^(∓) production and find that the future high luminosity LHC could probe a triplet Higgs around 1.2 TeV at the 2σlevel.
基金Supported by an appointment to the JRG Program at the APCTP through the Science and Technology Promotion Fund and Lottery Fund of the Korean Government。
文摘We discuss a linear seesaw model with a field content as minimum as possible,introducing a modular S_(4)using gauged U(1)_(B−L) symmetries.Owing to the rank two neutrino mass matrix,we obtain a vanishing neutrino mass eigenvalue,and only the normal mass hierarchy of neutrinos is favored via the modular S_(4)symmetry.In our numericalΔχ^(2)analysis,we especially determine a relatively sharp prediction on the sum of neutrino masses to be approximately 60 meV,in addition to other predictions.
