Ambresh Shivaji
We show that the most general fermion loop diagram is finite in both soft and collinear regions and therefore, it's IR finite. We use this result to express the IR singular structure of a box scalar integral in terms of the IR singular structure of reduced triangle scalar integrals.
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We propose a framework for a new type of finite field theories based on a hidden duality between an ultra-violet and an infra-red region. Physical quantities do not receive radiative corrections at a fundamental scale or the fixed point of the duality transformation, and this feature is compatible with models possessing a specific fermionic symmetry. Theories can be tested indirectly by relations among parameters, reflecting underlying symmetries.
We examine a Nambu-Goto string trajectory in the neighbourhood of a cusp and determine the extrinsic curvature invariants. These are demonstrated to be finite, in contradiction with naive expectation. Thus the Nambu action is a valid approximation for the motion of a cosmic string vortex even at cusps. This suggests that cusp annihilation is not a feasible mechanism for particle radiation from cosmic strings.
Models explaining dark matter typically include interactions with charged scalar and fermion fields. The Infra-Red (IR) finiteness of thermal field theories of charged fermions (fermionic QED) has been proven to all orders in perturbation theory. Here we reexamine the IR behaviour of charged scalar theories at finite temperature. Using the method of Grammer and Yennie, we identify and factorise the infra-red divergences to all orders in perturbation theory. The inclusion of IR finite pieces arising from the 4-point interaction terms of scalars with photon fields is key to the exponentiation. W…
We discuss the anomalous magnetic moment of fermion in a realistic SU(3) model of gauge-Higgs unification compactified on an orbifold S^1/Z_2 including Z_2-odd bulk mass for fermions. An operator analysis implies that the anomalous magnetic moment should be finite and predictable, even though higher dimensional gauge theories are non-renormalizable. Our main purpose is to clarify the cancellation mechanism of the UV divergences appearing in various types of Feynman diagrams. The cancellation of divergence turns out to take place between the contributions of the "partners" in the Higgs-like mec…
We calculate the 1-loop effective potential in a supersymmetric model in 5D with $S^1/(Z_2\times Z_2)$ orbifold compactification. The procedure of calculation consists of evaluating first the integrals over four-momenta using the dimensional regularization and then the sum over Kaluza-Klein modes using the zeta-regularization. We show that both fermionic and bosonic contributions are separately finite and argue that, supersymmetry is not necessary for the finiteness of the theory at 1-loop. Also, some general arguments on the finiteness of the theory with arbitrary number of extra dimensions a…
These notes, based on work with Herbi Dreiner and Howie Haber, discuss how to do practical calculations of cross sections and decay rates using two-component fermion notation, as appropriate for supersymmetry and other beyond-the-Standard-Model theories. Included are a list of two-component fermion Feynman rules for the Minimal Supersymmetric Standard Model, and some example calculations.
Note on a BCS analogy of Majorana neutrinos
本文通过BCS理论与跷跷板模型的类比，论证从手征费米子构造马约拉纳中微子的传统做法过于简化，需借助Bogoliubov型正则变换从一个有效狄拉克费米子生成两个马约拉纳费米子。
We consider a class of supersymmetric SU(3)\times SU(2)\times U(1) multihiggs models in which R-parity is violated through bilinear Higgs-lepton interactions. The required, due to R-parity violation, higgs-lepton rotations introduce an alternative way to generate the phenomenologically desirable fermion mass matrix structures independently of the equality of Yukawas, possibly imposed by superstring or other unification.
We analyze the possibility of a spontaneous breaking of C-invariance in gauge theories with fermions in vector-like - but otherwise generic - representations of the gauge group. QCD, supersymmetric Yang-Mills theory, and orientifold field theories, all belong to this class. We argue that charge conjugation is not spontaneously broken as long as Lorentz invariance is maintained. Uniqueness of the vacuum state in pure Yang-Mills theory (without fermions) and convergence of the expansion in fermion loops are key ingredients. The fact that C-invariance is conserved has an interesting application t…
In a minimal extension of the Standard Model, in which new neutral fermions have been introduced, we show that the requirement of vanishing anomalies fixes the hypercharges of all fermions uniquely. This naturally leads to electric charge quantization in this minimal scenario which has features similar to the Standard Model: invariance under the gauge group $SU(2)_L\otimes U(1)_Y$, conservation of the total lepton number and masslessness for the ordinary neutrinos. Such minimal models might arise as low-energy realizations of some heterotic superstring models or $SO(10)$ grand unified theories…
We discuss renormalization in a toy model with one fermion field and one real scalar field phi, featuring a spontaneously broken discrete symmetry which forbids a fermion mass term and a phi^3 term in the Lagrangian. We employ a renormalization scheme which uses the MSbar scheme for the Yukawa and quartic scalar couplings and renormalizes the vacuum expectation value of phi by requiring that the one-point function of the shifted field is zero. In this scheme, the tadpole contributions to the fermion and scalar selfenergies are canceled by choice of the renormalization parameter delta_v of the …
In this note we present general expressions at one loop order that can be used to calculate the contributions to the anomalous magnetic moment of fundamental, charged Dirac fermions. In particular, we provide the expressions for charged and neutral scalar and charged and neutral gauge boson contributions with general vector and axial couplings to the fermion of interest. The calculations presented in this note were originally derived for use in the author's letter, hep-ph/0108080. We have chosen to document and make available the results and derivations in the hope that they will also be usefu…
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