Scattering processes could distinguish Majorana from Dirac neutrinos

It is well known that Majorana neutrinos have a pure axial neutral current interaction while Dirac neutrinos have the standard vector-axial interaction. In spite of this crucial difference, usually Dirac neutrino processes differ from Majorana processes by a term proportional to the neutrino mass, resulting in almost unmeasurable observations of this difference. In the present work we show that once the neutrino polarization evolution is considered, there are clear differences between Dirac and Majorana scattering on electrons. The change of polarization can be achieved in astrophysical environments with strong magnetic fields. Furthermore, we show that in the case of unpolarized neutrino scattering onto polarized electrons, this difference can be relevant even for large values of the neutrino energy.Comment: 12 pages, 5 figure

Supersymmetric contribution to B to rho K and B to pi K^* decays in SCET

We analyze the supersymmetric contributions to the direct CP asymmetries of the decays $B \to \pi K^*$ and $B\to\rho K$ within Soft Collinear Effective Theory. We extend the Standard Model analysis of these asymmetries to include the next leading order QCD corrections. We find that, even with QCD correction, the Standard Model predictions can not accommodate the direct CP asymmetries in these decay modes. Using Mass Insertion Approach, we show that non-minimal flavor SUSY contributions mediated by gluino exchange can enhance the CP asymmetries significantly and thus can accommodate the experimental results.Comment: 12 pages, 5 figures, version to appear in PL

Dynamical Symmetry Breaking With a Fourth Generation

Adding a fourth generation to the Standard Model and assuming it to be valid up to some cutoff \Lambda, we show that electroweak symmetry is broken by radiative corrections due to the fourth generation. The effects of the fourth generation are isolated using a Lagrangian with a genuine scalar without self-interactions at the classical level. For masses of the fourth generation consistent with electroweak precision data (including the B \rightarrow K \pi\ CP asymmetries) we obtain a Higgs mass of the order of a few hundreds GeV and a cutoff \Lambda\ around 1-2 TeV. We study the reliability of the perturbative treatment used to obtain these results taking into account the running of the Yukawa couplings of the fourth quark generation with the aid of the Renormalization Group (RG) equations, finding similar allowed values for the Higgs mass but a slightly lower cut-off due to the breaking of the perturbative regime. Such low cut-off means that the effects of new physics needed to describe electroweak interactions at energy above \Lambda\ should be measurable at the LHC. We use the minimal supersymmetric extension of the standard model with four generations as an explicit example of models realizing the dynamical electroweak symmetry breaking by radiative corrections and containing new physics. Here, the cutoff is replaced by the masses of the squarks and electroweak symmetry breaking by radiative corrections requires the squark masses to be of the order of 1 TeV.Comment: 20 pages, 7 figures. New section adde

Is the standard Higgs scalar elementary?

In the standard electroweak model, the measured top quark mass requires a sizeable Yukawa coupling to the fundamental scalar. This large coupling alone might induce a dynamical breaking of the electroweak symmetry as well as non-perturbative effects. If such is the case, even a standard Higgs scalar as light as 80 GeV should have a non-negligible $t \bar{t}$ component induced by the top condensate.Comment: 8 pages, Latex fil

Neutrino Spin Flavor Precession and Leptogenesis

We argue that \Delta L=2 neutrino spin flavor precession, induced by the primordial magnetic fields, could have a significant impact on the leptogenesis process that accounts for the baryon asymmetry of the universe. Although the extra galactic magnetic fields is extremely weak at present time (about 10^{-9} Gauss), the primordial magnetic filed at the electroweak scale could be quite strong (of order 10^{17} Gauss). Therefore, at this scale, the effects of the spin flavor precession are not negligible. We show that the lepton asymmetry may be reduced by 50% due to the spin flavor precession. In addition, the leptogenesis will have different feature from the standard scenario of leptogenesis, where the lepton asymmetry continues to oscillate even after the electroweak phase transition.Comment: 5 pages, one figure. References adde

Annihilation contribution and B→a0π,f0KB\to a_0 \pi, f_0 K decays

We analyze the decays $B^0 \to a^\pm_0 \pi^\mp$ and $B^{-,0} \to f_0 K^{-,0}$ and show that within the factorization approximation a phenomenological consistent picture can be obtained. We show that in this approach the $O_6$ operator provides the dominant contributions to the suppressed channel $B^0 \to a^+_0 \pi^-$. When the $a_0$ is considered a two quark state, evaluation of the annihilation form factor using Perturbative $QCD$ implies that this contribution is not negligible, and furthermore it can interfere constructively or destructively with other penguin contributions. As a consequence of this ambiguity, the positive identification of $B^0 \to \pi^+ a_0^-$ can not distinguish between the two or four quark assignment of the $a_0$. According to our calculation, a best candidate to distinguish the nature of $a_0$ scalar is $Br(B^-\to \pi^0a_0^-)$ since the predictions for a four quark model is one order of magnitude smaller than for the two quark assignment. When the scalars are seen as two quarks states, simple theoretical assumptions based on SU(2) isospin symmetry provide relations between different B decays involving one scalar and one pseudoscalar meson.Comment: 12 pages, 3 figure

XXZ spin chain in transverse field as a regularization of the sine-Gordon model

We consider here XXZ spin chain perturbed by the operator sigma^x (``in transverse field'') which is a lattice regularization of the sine-Gordon model. This can be shown using conformal perturbation theory. We calculated mass ratios of particles which lie in a discrete part of the spectrum and obtained results in accord with the DHN formula and in disagreement with recent calculations in literature based on numerical Bethe Ansatz and infinite momentum frame methods. We also analysed a short distance behavior of this states (UV or conformal limit). Our result for conformal dimension of the second breather state is different from the conjecture in [Klassen and Melzer, Int. J. Mod. Phys. A8, 4131 (1993)] and is consistent with this paper for other states.Comment: 7 pages, REVTeX, 6 figures, to appear in Phys. Rev.