4,781 research outputs found

### Aspects of symmetry breaking in SO(10) GUTs

I review some recent results on the Higgs sector of minimal SO(10) grand
unified theories both with and without supersymmetry. It is shown that
nonsupersymmetric SO(10) with just one adjoint triggering the first stage of
the symmetry breaking does provide a successful gauge unification when
radiative corrections are taken into account in the scalar potential, while in
the supersymmetric case it is argued that the troubles in achieving a
phenomenologically viable breaking with representations up to the adjoint are
overcome by considering the flipped SO(10) embedding of the hypercharge.Comment: 8 pages, 1 figure; prepared for the proceedings of DISCRETE'10 -
Symposium on Prospects in the Physics of Discrete Symmetrie

### On soft breaking and CP phases in the supersymmetric standard model

We consider a class of N=1 supersymmetric extensions of the Standard Model in
which the soft breaking sector is CP conserving at the GUT scale. We study the
question of whether the presence of explicit CP violation in the Yukawa sector
of the theory induces through renormalization effects CP violating phases in
the soft terms, which could lead to observable effects. A clear pattern appears
in the structure of phases in the soft sector. In particular, the inclusion of
intergenerational mixing induces large phases in the flavour mixing entries of
the trilinear soft breaking terms, whereas the diagonal entries remain real. A
mechanism is proposed for generating through chargino exchange a contribution
to the neutron electric dipole moment which can be a few orders of magnitude
larger that that of the Standard Model, although still out of reach of
experimental tests. We comment on the possible relevance of these phases for
baryogenesis at the weak scale in minimal supersymetric scenarios, recently
considered in the literature.Comment: 12 pages + 1 figure (postscript file available on request), LATEX,
SISSA 173/93/E

### Supersymmetric predictions for the inclusive $b\to s\gamma$ decay

We study the penguin induced transition $b\to s\ \gamma$ in the minimal N=1
supersymmetric extension of the Standard Model with radiative breaking of the
electroweak group. We include the effects of one-loop corrections to the Higgs
potential and scalar masses. We show that the present upper and lower
experimental limits on the inclusive decay sharply constrain the parameter
space of the model in a wide range of $\tan\beta$ values. The implications of
the recently advocated relation $|B|\ge 2$ for the bilinear SUSY soft breaking
parameter in grand unified theories are also analyzed.Comment: 23 pages + 12 figures (hardcopies available on request), LATEX, SISSA
40/94/E

### D3-branes dynamics and black holes

Using the D3-brane as the fundamental tool, we adress two aspects of D-branes
physics. The first regards the interaction between two electromagnetic dual
D-branes in 10 dimensions. In particular, we give a meaning to {\it both} even
and odd spin structure contributions, the latter being non vanishing for non
zero relative velocity $v$ (and encoding the Lorentz-like contribution). The
second aspect regards the D-brane/black holes correspondence. We show how the 4
dimensional configuration corresponding to a {\it single} D3-brane wrapped on
the orbifold T^6/Z_3 represents a regular Reissner-Nordstrom solution of d=4
N=2 supergravityComment: 8 pages, latex, 1 eps figure. Talk presented by M. Bertolini at the
conference "Quantum aspects of gauge theories, supergravity and unification"
in Corfu`; to appear in the proceeding

### Closed string exchanges on $C^2/Z_2$ in a background B-field

In an earlier work it was shown that the IR singularities arising in the
nonplanar one loop two point function of a noncommutative ${\cal N}=2$ gauge
theory can be reproduced exactly from the massless closed string exchanges. The
noncommutative gauge theory is realised on a fractional $D_3$ brane localised
at the fixed point of the $C^2/Z_2$ orbifold. In this paper we identify the
contributions from each of the closed string modes. The sum of these adds upto
the nonplanar two-point function.Comment: 27 page

### Regular R-R and NS-NS BPS black holes

We show in a precise group theoretical fashion how the generating solution of
regular BPS black holes of N=8 supergravity, which is known to be a solution
also of a simpler N=2 STU model truncation, can be characterized as NS-NS or
R-R charged according to the way the corresponding STU model is embedded in the
original N=8 theory. Of particular interest is the class of embeddings which
yield regular BPS black hole solutions carrying only R-R charge and whose
microscopic description can possibly be given in terms of bound states of
D-branes only. The microscopic interpretation of the bosonic fields in this
class of STU models relies on the solvable Lie algebra (SLA) method. In the
present article we improve this mathematical technique in order to provide two
distinct descriptions for type IIA and type IIB theories and an algebraic
characterization of S*T--dual embeddings within the N=8,d=4 theory. This
analysis will be applied to the particular example of a four parameter
(dilatonic) solution of which both the full macroscopic and microscopic
descriptions will be worked out.Comment: latex, 30 pages. Final version to appear on Int.J.Mod.Phy

### Direct CP Violation in B->phi K_s and New Physics

In the presence of large New Physics contributions to loop-induced b->s
transitions, sizable direct CP violation in B-> phi K decays is expected on
general grounds. We compute explicitly CP-violating effects using QCD
factorization and find that, even in the restricted case in which New Physics
has the same penguin structure as the Standard Model, the rate asymmetry can be
of order one. We briefly discuss a more general scenario and comment on the
inclusion of power-suppressed corrections to factorization.Comment: 3 page

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