International Journal of Modern Physics A

The author has known Freeman Dyson since they were both at school in Winchester, England. The friendship has continued ever since.

For twenty years the students in my "Science, Technology, and Society" course, where we use Disturbing the Universe as a textbook, have corresponded with Professor Dyson. That someone of Professor Dyson's standing consistently makes a priority of promptly answering the letters of undergraduate students from all academic majors, and does so with grace and kindness, insight and wisdom, offers a personal glimpse into his character and integrity. On behalf of my students, and as a way of publicly thanking Professor Dyson for participating in our course conversations, I am honored to share samples of our correspondence with him over the years, including student reflections on his involvement in their education.

In this paper, a braneworld model with a perfect fluid on brane and a scalar field on bulk has been used to study quark–hadron phase transition. The bulk scalar field has an interaction with brane matter. This interaction comes into nonconservation relation which describes an energy transfer between bulk and brane. Since quark–hadron transition truly depends on the form of evolution equations, modification of energy conservation equation and Friedmann equation gives rise to some interesting results about the time of transition. The evolution of physical quantities relevant to the quantitative of early times namely energy density ρ, temperature T and scale factor a have been considered utilizing two formalism, crossover formalism and first-order phase transition formalism. The results show that the quark–hadron phase transition occurred about a nanosecond after big bang and the general behavior temperature is similar in both of two formalism.

We study quark flavor violation (QFV) in the squark sector of the Minimal Supersymmetric Standard Model (MSSM). We assume mixing between the second and the third squark generations, i.e. mixing. We focus on QFV effects in bosonic squark decays, in particular on the decay into the lightest Higgs boson , where are the lightest up-type squarks. We show that the branching ratio of this QFV decay can be quite large (up to 50%) due to large QFV trilinear couplings, and large and mixing, despite the strong constraints on QFV from B meson data. This can result in characteristic QFV final states with significant rates at LHC (14 TeV), such as and . The QFV bosonic squark decays can have an influence on the squark and gluino searches at LHC.

Using the path integral formalism in (1+1) dimension of the energy–momentum space representation, we calculate the Green function of relativistic spinning particle subjected to the action of combined vector and scalar linear potentials in the framework of deformed Heisenberg algebra which distinguish to the appearance of nonzero minimum position uncertainty given by where β is the deformation parameter of the modified Heisenberg uncertainty relation . We adapt the space–time transformation method to evaluate quantum corrections and this latter are dependent on the α-point discretization interval. The exact bound states spectrum and the corresponding momentum space wave function are obtained.

We present a procedure for application of T-duality transformation on scattering amplitudes of closed bosonic stringy states. These states arise due to compactification of closed string to lower space–time dimensions through dimensional reduction. The amplitude, in the first quantized formalism, is computed by introducing vertex operators. The amplitude is constructed by the standard prescription and the vertex operators are required to respect conformal invariance. Such vertex operators are constructed in the weak field approximation. Therefore, the vertex operators of the stringy states of our interest are to be defined accordingly. We propose a prescription to implement T-duality on the three-point functions and N-point functions. We argue that it is possible to generate new amplitudes through the transformations on a given amplitude just as T-duality transformations can take us to a new set of string vacuum when acted upon an initial set. Explicit examples are given for three-point and four-point functions.

In rare B meson decays B → Kℓ⁺ℓ^-, a possible contribution of ℓ⁺ℓ^- emission via photon from the "spectator" quark q(q = u, d) in the B meson is investigated in addition to the conventional one . If such a contribution is sizable compared with the standard estimation of B → Kℓ⁺ℓ^-, we will observe visible difference between dΓ(B⁰ → K⁰ℓ⁺ℓ^-)/dq² and dΓ(B⁺ → K⁺ℓ⁺ℓ^-)/dq² in q² dependence . Besides, as a result of the interference between the conventional one and a new one, a dip appears in dΓ(B → Kℓ⁺ℓ^-)/dq² at a small region of q². The interference effect in the B⁰ decay will also be observed differently from that in the B⁺ decay. The calculation is done based on a semiclassical approach, a valence quark model. In the present model, the photon emission from the spectator quark q, d → d+γ(u → u+γ) is independent of the b–s transition mechanism, and the characteristic results are due to a straightforward estimate of the quark propagator which cannot be incorporated into the factorization method. The model is not a valence quark "dominant" model, so that, for example, the valence quarks in the final state carry only 24% of the energy–momentum of the kaon.

We discuss the mechanism by which adinkras holographically store the required information for the Spin(1, 3) Clifford Algebra fiber bundle in the cases of three 4D, = 1 representations: the chiral, vector and tensor supermultiplets.

A detailed study of fragmentation of vector mesons at the next-to-leading order (NLO) in QCD is given for e⁺e^- scattering. A model with broken SU(3) symmetry using three input fragmentation functions α(x, Q²), β(x, Q²) and γ(x, Q²) and a strangeness suppression parameter λ describes all the light quark fragmentation functions for the entire vector meson octet. At a starting low energy scale of for three light quarks (u, d, s) along with initial parametrization, the fragmentation functions are evolved through DGLAP evolution equations at NLO and the cross-section is calculated. The heavy quarks contribution are added in appropriate thresholds during evolution. The results obtained are fitted at the momentum scale of for LEP and SLD data. Good-quality fits are obtained for ρ, K*, ω and ϕ mesons, implying the consistency and efficiency of this model. Strangeness suppression in this model is understood both in terms of ratios of quark fragmentation functions alone as well as in terms of observables; the latter yield a suppression through the K*/ρ multiplicity ratio of about 0.23 while the x dependence of this suppression is also parametrized through the cross-section ratios.