arXiv subjects
Publications and source records attributed to E. A. Paschos.
I demonstrate that the short distance contribution to K --> Pi Pi decays must be supplemented with large distance effects. A hybrid calculation is outlined based on QCD diagrams supplemented by chiral contributions and Pi-Pi phaseshifts.
The usual see-saw formula is modified by the presence of two Higgs triplets in left-right symmetric theories. The contribution from the left-handed Higgs triplet to the see-saw formula can dominate over the conventional one when the neutrino Dirac mass matrix is identified with the charged lepton or down quark mass matrix. In this case an analytic calculation of the lepton asymmetry, generated by the decay of the lightest right-handed Majorana neutrino, is possible. For typical parameters, the out-of-equilibrium condition for the decay is automatically fulfilled. The baryon asymmetry has the correct order of magnitude, as long as the lightest mass eigenstate is not much lighter then 10^{-6} to 10^{-8} eV, depending on the solution of the solar neutrino problem. A sizable signal in neutrinoless double beta decay can be expected, as long as the smallest mass eigenstate is not much lighter than 10^{-3} eV and the Dirac mass matrix is identified with the charged lepton mass matrix.
The masses and mixing of the light left-handed neutrinos can be related to those of the heavy right-handed neutrinos in left-right symmetric theories. Properties of the light neutrinos are measured in terrestrial experiments and the CP-violating decays of their heavy counterparts produce a baryon asymmetry via the well-known leptogenesis mechanism. The left-handed Higgs triplet, present in left-right symmetric theories, modifies the usual see-saw formula. It is possible to relate the lepton asymmetry to the light neutrino parameters when the triplet and the top quark through the usual see-saw mechanism give dominant contribution to the neutrino mass matrix. We find that in this situation the small angle MSW and vacuum solutions produce reasonable asymmetry, whereas the large angle MSW case requires extreme fine-tuning of the three phases in the mixing matrix.
We calculate neutrino induced cross-sections relevant for oscillation experiments, including the $τ$-lepton threshold for quasi-elastic, resonance and deep inelastic scattering. In addition to threshold effects, we include nuclear corrections for heavy targets which are moderate for quasi-elastic and large for single pion production. Nuclear effects for deep inelastic reactions are small. We present cross sections together with their nuclear corrections for various channels which are useful for interpreting the experimental results and for determining parameters of the neutrino sector..
The renormalization group evolution equation for two neutrino mixing is known to exhibit nontrivial fixed point structure corresponding to maximal mixing at the weak scale. The presence of the fixed point provides a natural explanation of the observed maximal mixing of $ν_μ-ν_τ$ if the $ν_μ$ and $ν_τ$ are assumed to be quasi-degenerate at the seesaw scale without constraining on the mixing angles at that scale. In particular, it allows them to be similar to the quark mixings as in generic grand unified theories. We discuss implementation of this program in the case of MSSM and find that the predicted mixing remains stable and close to its maximal value, for all energies below the $O$(TeV) SUSY scale. We also discuss how a particular realization of this idea can be tested in neutrinoless double beta decay experiments.
We calculate single pion production by neutrinos in the resonance region. We consider both charged and neutral current reactions on free protons and neutrons. We present differential and total cross sections which can be compared with experiments. Then we use these results to calculate the spectra of the emerging pions including the Pauli suppression factor and rescattering corrections for reactions in heavy nuclei. Our results will be useful for studying single pion production and for investigating neutrino oscillations in future experiments.
We present a general model-independent and rephase-invariant formalism that cleanly relates CP and CPT noninvariant observables to the fundamental parameters. Different types of CP and CPT violations in the K^0-, B^0-, B_s^0- and D^0-systems are explicitly defined. Their importance for interpreting experimental measurements of CP and CPT violations is emphasized. In particular, we show that the time-dependent measurements allow one to extract a clean signature of CPT violation.
We study the mixing of elementary and composite particles. In quantum field theory the mixing of composite particles originates in the couplings of the constituent quarks and for neutrinos in self-energy diagrams. In the event that the incoming and outgoing neutrinos have different masses, the self-energy diagrams vanish because energy is not conserved but the finite decaying widths make the mixing possible. We can consider the neutrinos to be "fuzzy" states on their mass shell and the mixing is understood as the overlap of two wavefunctions. These considerations restrict the mass difference to be approximately equal to or smaller than the largest of the two widths: abs(M_i - M_j) lessorequal max(Gamma_i, Gamma_j).
We present a recent analysis of epsilon'/epsilon in the 1/N_c expansion. We show that the 1/N_c corrections to the matrix element of Q_6 are large and positive, indicating a Delta I=1/2 enhancement similar to the one of Q_1 and Q_2 which dominate the CP conserving amplitude. This enhances the CP ratio and can bring the standard model prediction close to the measured value for central values of the parameters.
A calculation of the hadronic matrix elements for K\toππincluding π-πrescattering effects in a dispersion integral is presented. I study the dependence of the results on the matching scale μand use them to calculate the CP-parameter (ε\prime/ε). I find improved stability on the matching scale and good agreement with the experimental results.
We present a new analysis of the ratio ε'/εwhich measures the direct CP violation in K\toππdecays. We use the 1/N_c expansion within the framework of the effective chiral lagrangian for pseudoscalar mesons. The 1/N_c corrections to the hadronic matrix elements of all operators are calculated at leading order in the chiral expansion. Numerically, doing a simple scanning of the input parameters we find 1.5 \cdot 10^{-4}\leq ε'/ε\leq 31.6\cdot 10^{-4}. We also investigate, in the chiral limit, the 1/N_c corrections to the operator Q_6 at next-to-leading order in the chiral expansion. We find large positive corrections which can further enhance ε'/εand bring the standard model prediction close to the measured value for central values of the parameters. Our result indicates that a ΔI=1/2 enhancement may be operative for Q_6 similar to the one of Q_1 and Q_2 which dominate the CP conserving amplitude.
Orbiting $γ$-detectors combined with the magnetic field of the Earth or the Sun can work parasitically as cosmic axion telescopes. The relatively short field lengths allow the axion-to-photon conversion to be coherent for $m_{axion} \sim 10^{-4}$ eV, if the axion kinetic energy is above $\sim 500$ keV (Earth's field), or, $\sim 50$ MeV (Sun's field), allowing thus to search for axions from $e^+e^-$ annihilations, from supernova explosions, etc. With a detector angular resolution of $\sim 1^o$, a more efficient sky survey for energetic cosmic axions passing {\it through the Sun} can be performed. Axions or other axion-like particles might be created by the interaction of the cosmic radiation with the Sun, similarly to the axion searches in accelerator beam dump experiments; the enormous cosmic energy combined with the built-in coherent Primakoff effect might provide a sensitive detection scheme, being out of reach with accelerators. The axion signal will be an excess in $γ$-rays coming either from a specific celestial place behind the Sun, e.g. the Galactic Center, or, from any other direction in the sky being associated with a violent astrophysical event, e.g. a supernova. Earth bound detectors are also of potential interest. The axion scenario also applies to other stars or binary systems in the Universe, in particular to those with superstrong magnetic fields.
We calculate long-distance contributions to the amplitudes A(K^0 --> pi pi, I) induced by the gluon and the electroweak penguin operators Q_6 and Q_8, respectively. We use the 1/N_c expansion within the effective chiral lagrangian for pseudoscalar mesons. In addition, we adopt a modified prescription for the identification of meson momenta in the chiral loop corrections in order to achieve a consistent matching to the short-distance part. Our approach leads to an explicit classification of the loop diagrams into non-factorizable and factorizable, the scale dependence of the latter being absorbed in the low-energy coefficients of the effective theory. Along these lines we calculate the one-loop corrections to the O(p^0) term in the chiral expansion of both operators. In the numerical results, we obtain moderate corrections to B_6^(1/2) and a substantial reduction of B_8^(3/2).
The HERA data at large $Q^2$ and small-$x$ investigate large distances on the light-cone. At such large distances the scattered quarks can maintain their colour identity by polarizing the vacuum as they transfer energy to it. We calculate the probability for the creation of quark-antiquark pairs from the polarized QCD vacuum and their contribution to the structure function.
The parton model as developed for semileptonic B decays is applied to the inclusive decay B to J/Psi+X. We calculate the momentum spectrum of the J/Psi using a one-parameter distribution function for the heavy quark, taken from production experiments, and compare our results with recent data from CLEO which fixes the distribution parameter epsilon_p. An analogous calculation is carried out in the ACCMM model where the data determines the Fermi motion parameter p_f. The models give a good description of the data, provided in each of them the parameter in the distribution function is chosen to correspond to a softer b quark momentum distribution than that commonly used in studies of semileptonic B decays. In particular we arrive at epsilon_p = O(0.008) and p_f = O(0.55 GeV), respectively. The latter value (p_f = 0.5 GeV) produces in the ACCMM model 10^2*|V_ub/V_cb|^2=1.03, which removes a former supposed discrepancy with the ISGW model. Finally, the strength of the effective color singlet coefficient is found to be a_2 = O(0.28) in both models.
The QCD corrections for the box diagrams are revisited for the case of a heavy top quark with $\mt = 174 \GeV$. We resolve first a longstanding discrepancy between two methods of calculation by showing that they give the same results when the threshold factors are treated correctly. Using this observation we refine our earlier results and derive formulae valid for the $K$- and $B$-meson systems. Our formulae are given in terms of integrals to be evaluated numerically, as well as approximate analytical formulae. These calculations include the evolution above $\MW$ which has been neglected by other authors.
We study dynamical symmetry breaking in the Standard Model including the next-to-leading order terms. We introduce at a high, but finite, energy scale Lambda a top quark condensate H={t {bar t}} and derive, using path integral methods, the effective potential including quadratic fluctuations in the scalar field H. We neglect the contributions of all components of the massive electroweak gauge bosons. The existence of a non-trivial minimum in the effective potential leads to the condition that the cut-off Lambda is limited from above: Lambda < Lambda_{crit} approx 4.7 m_t^{phys.} (for N_c = 3), and to a new lower bound for the 4-fermion coupling a = (G N_c Lambda^2)/(8 pi^2) > 1.60. Similar results are obtained if we demand, instead, that the next-to-leading order contributions not shift the location z=(m_t^{bare}/Lambda)^2 of the minimum drastically, e.g.~by not more than a factor of 2. The results are reproduced diagrammatically, where the leading plus all the next-to-leading order diagrams in the (1/N_c)-expansion are included. Dominant QCD effects are also included, but their impact on the numerical results is shown to be small.
A field theoretic description for inclusive semileptonic B meson decays is formulated. We argue that large regions of the phase spaces for the decays are dominated by distances near the light cone. The light-cone dominance allows to incorporate nonperturbative QCD effects in a distribution function. A one-to-one correspondence with the heavy quark effective theory is developed, which can estimate the first two moments of the distribution function. These conditions are useful but not restrictive enough to specify the distribution function, which must still be determined from experiment. Several model-independent predictions, such as scaling, sum rules of the hadronic structure functions and relations among them, are made. General formulas for the differential decay rates on several variables are presented, which are used for calculating the electron energy spectra with an Ansatz for the light-cone distribution function.