CAS Institute of Theoretical Physics

Beijing, China

CAS Institute of Theoretical Physics

Beijing, China
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Huang Q.-G.,CAS Institute of Theoretical Physics
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2015

Imposing that the excursion distance of the inflaton in field space during inflation be less than the Planck scale, we derive an upper bound on the tensor-to-scalar ratio at the cosmic microwave background scales, i.e., r∗,max, in the general canonical single-field slow-roll inflation model, in particular, the model with non-negligible running of the spectral index αs and/or the running of running βs. We find that r∗,max≃7×10-4 for ns=0.9645 without running and running of running, and r∗,max is significantly relaxed to the order of O(10-2∼10-1) in the inflation model with αs and/or βs∼+O(10-2) which are marginally preferred by the Planck 2015 data. © 2015 American Physical Society.

Zhao Z.-H.,CAS Institute of Theoretical Physics
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2012

In this paper, we give a model for understanding flavor physics in the lepton sector mass hierarchy among different generations and neutrino mixing patterns. The model is constructed in the framework of supersymmetry, with a family symmetry S4*U(1). There are two right-handed neutrinos introduced for a seesaw mechanism, while some standard model gauge group singlet fields are included, which transforms nontrivially under family symmetry. In the model, each order of contributions are suppressed by δ∼0.1 compared to the previous one. In order to reproduce the mass hierarchy, m τ and √Δmatm2, and m μ and √Δmsol2 are obtained at leading order and next-to-leading order, respectively, while the electron can only get its mass through next-to-next-to-next-to-leading order contributions. For neutrino mixing angels, θ 12, θ 23, θ 13 are 45°, 45°, 0, i.e., the bimaximal mixing pattern as a first approximation, while higher order contributions can make them consistent with experimental results. As corrections for θ 12 and θ 13 originate from the same contribution, there is a relation predicted for them: sinθ 13=1- tanθ 121+tanθ 12. Besides, the deviation from π4 for θ 23 should have been as large as the deviation from 0 for θ 13; if not, the former is suppressed by a factor of 4 compared to the latter. © 2012 American Physical Society.

Zhou Y.-F.,CAS Institute of Theoretical Physics
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2012

The heavy fourth-generation Majorana neutrino can be stable and contribute to a small fraction of the relic density of dark matter (DM) in the Universe. Because of its strong coupling to the standard model particles, it can be probed by the current direct and indirect DM detection experiments even it is a subdominant component of the whole halo DM. Assuming that it contributes to the same fraction of the local halo DM density as that of the DM relic density in the Universe, we show that the current Xenon100 data constrain the mass of the stable Majorana neutrino to be greater than the mass of the top quark. In the mass range from 200 GeV to a few hundred GeV, the effective spin-independent cross section for the neutrino elastic-scattering off nucleon is insensitive to the neutrino mass and mixing, and is predicted to be ∼1.5×10 -44cm2, which can be reached by the direct DM detection experiments soon. In the same mass region the predicted effective spin-dependent cross section for the heavy neutrino scattering off proton is in the range of 2×10 -40cm2∼2×10 -39cm2, which is within the reach of the ongoing DM indirect search experiments such as IceCube. We demonstrate such properties of the heavy neutrino DM in a fourth-generation model with the stability of the fourth Majorana neutrino protected by an additional generation-dependent U(1) gauge symmetry. © 2012 American Physical Society.

Shu J.,CAS Institute of Theoretical Physics | Zhang Y.,California Institute of Technology
Physical Review Letters | Year: 2013

We observe a generic connection between LHC Higgs data and electroweak baryogenesis: the particle that contributes to the CP-odd hgg or hγγ vertex would provide the CP-violating source during a first-order phase transition. It is illustrated in the two Higgs doublet model that a common complex phase controls the lightest Higgs properties at the LHC, electric dipole moments, and the CP-violating source for electroweak baryogenesis. We perform a general parametrization of Higgs effective couplings and a global fit to the LHC Higgs data. Current LHC measurements prefer a nonzero phase for tana 1 and electric dipole moment constraints still allow an order-one phase for tana β∼1, which gives sufficient room to generate the correct cosmic baryon asymmetry. We also give some prospects in the direct measurements of CP violation in the Higgs sector at the LHC. © 2013 American Physical Society.

Pang Y.,CAS Institute of Theoretical Physics
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2011

In this note, we correct a mistake in the mass formula in which generalizes the Ashtekar-Magnon-Das method to incorporate extended gravities with quadratic curvature terms. The corrected mass formula confirms that the black hole masses for recently discovered critical gravities vanish. © 2011 American Physical Society.

Tang Y.-L.,CAS Institute of Theoretical Physics
Nuclear Physics B | Year: 2015

The see-saw mechanism is usually applied to explain the lightness of neutrinos. The traditional see-saw mechanism introduces at least two right-handed neutrinos for the realistic neutrino spectrum. In the case of supersymmetry, loop corrections can also contribute to neutrino masses, which lead to the possibility to generate the neutrino spectrum by introducing just one right-handed neutrino. To be realistic, MSSM suffers from the μ problem and other phenomenological difficulties, so we extend NMSSM (the MSSM with a singlet S) by introducing one single right-handed neutrino superfield (N) and relevant phenomenology is discussed. © 2014 The Author.

Huang Y.,CAS Institute of Theoretical Physics | Miao R.-X.,Max Planck Institute for Physics
Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics | Year: 2015

It was found by Hung, Myers and Smolkin that there is entropy discrepancy for the CFTs in 6-dimensional space-time, between the field theoretical and the holographic analyses. Recently, two different resolutions to this puzzle have been proposed. One of them suggests to utilize the anomaly-like entropy and the generalized Wald entropy to resolve the HMS puzzle, while the other one initiates the use of the entanglement entropy which arises from total derivative terms in the Weyl anomaly to explain the HMS mismatch. We investigate these two proposals carefully in this note. By studying the CFTs dual to Einstein gravity, we find that the second proposal cannot solve the HMS puzzle. Moreover, the Wald entropy formula is not well-defined on horizon with extrinsic curvatures, in the sense that, in general, it gives different results for equivalent actions. © 2015 Published by Elsevier B.V.

Parry J.K.,CAS Institute of Theoretical Physics
Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics | Year: 2011

We study the new physics (NP) implications of the recently reported 3.2 σ Standard Model (SM) deviation in the like-sign dimuon asymmetry at the Tevatron. Assuming that new physics only enters the Bs mixing amplitude we explore the implications for generic new physics, general supersymmetric (SUSY) models and also SUSY SU(5). In the case of SUSY SU(5) we exploit the GUT scale relationship between slepton and squark soft masses to predict rates for lepton flavour violation (LFV). The predicted rates for τ→μγ are found to be detectable at future Super- B factories. © 2010 Elsevier B.V.

Cai R.-G.,CAS Institute of Theoretical Physics
Journal of High Energy Physics | Year: 2012

In a recent paper [arXiv:1206.4916] by T. Padmanabhan, it was argued that our universe provides an ideal setup to stress the issue that cosmic space is emergent as cosmic time progresses and that the expansion of the universe is due to the difference between the number of degrees of freedom on a holographic surface and the one in the emerged bulk. In this note following this proposal we obtain the Friedmann equation of a higher dimensional Friedmann-Robertson- Walker universe. By properly modifying the volume increase and the number of degrees of freedom on the holographic surface from the entropy formulas of black hole in the Gauss-Bonnet gravity and more general Lovelock gravity, we also get corresponding dynamical equations of the universe in those gravity theories. © SISSA 2012.

Wu Y.-L.,CAS Institute of Theoretical Physics
Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics | Year: 2012

A model for the lepton-flavor mixing and CP violation is proposed based on the SU F(3) gauge family symmetry and the Majorana feature of neutrinos. A consistent prediction for the lepton-flavor mixing and masses is shown to be resulted from the appropriate vacuum structure of SU F(3) gauge symmetry breaking. By choosing the SU F(3) gauge fixing condition to possess a residual Z 2 symmetry and requiring the vacuum structure of spontaneous symmetry breaking to have approximate global U(1) family symmetries, we obtain naturally the tri-bimaximal mixing matrix and largely degenerate neutrino masses in the neutrino sector and the small mixing matrix in the charged-lepton sector. With a simple ansatz that all the smallness due to the approximate global U(1) family symmetries is characterized by a single Wolfenstein parameter λ≃0.22, and the charged-lepton mixing matrix has a similar hierarchy structure as the CKM quark mixing matrix, we arrive at a consistent prediction for the MNSP lepton-flavor mixing with a maximal spontaneous CP violation: δ=π/2, sin2θ13≃12λ2≃0.024 (sin 22θ 13≃0.094), sin2θ12≃13(1-2λ3)≃0.326 and sin2θ23≃12(1-λ2)≃0.48, which agree well with the current experimental data. The CP-violating Jarlskog-invariant is obtained to be JCP≃16λ(1-λ2/2-λ3)sinδ≃0.035, which is detectable in next generation neutrino experiment. The small masses of the neutrinos and charged leptons are simply attributed to the standard seesaw mechanism. The largely degenerate neutrino masses with the normal hierarchy and inverse hierarchy are discussed and found to be at the order mνi≃O(λ2)≃0.04-0.06eV with a total mass ∑m ν~0.15eV, which is testable in future precision astrophysics and cosmology. © 2012.

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