123 research outputs found
Composite quarks and leptons in higher space-time dimensions
A new approach towards the composite structure of quarks and leptons in the
context of the higher dimensional unified theories is proposed. Owing to the
certain strong dynamics, much like an ordinary QCD, every possible vectorlike
multiplets of composites appear in higher dimensional bulk space-time, however,
through a proper Sherk-Schwarz compactification only chiral set of composite
quarks and leptons survive as the massless states in four dimensions. In this
scenario restrictions related with the 't Hooft's anomaly matching condition
are turned out to be avoided and, as a result, the composite models look rather
simple and economic. We demonstrate our approach by an explicit construction of
model of preons and their composites unified in the supersymmetric SU(5) GUT in
five space-time dimensions. The model predicts exactly three families of the
composite quarks and leptons being the triplets of the chiral horizontal
symmetry SU(3)_h which automatically appears in the composite spectrum when
going to ordinary four dimensions.Comment: 13 pages, tcilatex, no figures, v2 - misprints correcte
Symmetry breaking, conformal geometry and gauge invariance
When the electroweak action is rewritten in terms of SU(2) gauge invariant
variables, the Higgs can be interpreted as a conformal metric factor. We show
that asymptotic flatness of the metric is required to avoid a Gribov problem:
without it, the new variables fail to be nonperturbatively gauge invariant. We
also clarify the relations between this approach and unitary gauge fixing, and
the existence of similar transformations in other gauge theories.Comment: 11 pages. Version 2: typos corrected, discussion of Elitzur's theorem
added. Version to appear in J.Phys.
Emergent Gravity from Noncommutative Gauge Theory
We show that the matrix-model action for noncommutative U(n) gauge theory
actually describes SU(n) gauge theory coupled to gravity. This is elaborated in
the 4-dimensional case. The SU(n) gauge fields as well as additional scalar
fields couple to an effective metric G_{ab}, which is determined by a dynamical
Poisson structure. The emergent gravity is intimately related to
noncommutativity, encoding those degrees of freedom which are usually
interpreted as U(1) gauge fields. This leads to a class of metrics which
contains the physical degrees of freedom of gravitational waves, and allows to
recover e.g. the Newtonian limit with arbitrary mass distribution. It also
suggests a consistent picture of UV/IR mixing in terms of an induced gravity
action. This should provide a suitable framework for quantizing gravity.Comment: 28 pages + 11 pages appendix. V2: references and discussion added.
V3: minor correctio
Dynamical Chiral Symmetry Breaking on a Brane in Reduced QED
Reduced gauge theories are theories in which while gauge fields propagate in
a bulk, fermion fields are localized on a brane. We study dynamical chiral
symmetry breaking on a 2-brane and a 1-brane in reduced QED_{3+1}, and on a
1-brane in reduced QED_{2+1}. Since, unlike higher dimensional gauge theories,
QED_{3+1} and QED_{2+1} are well defined, their reduced versions can serve as a
laboratory for studying dynamics in a higher dimensional brane world. The
analysis of the Schwinger-Dyson (SD) equations in these theories reveals rich
and quite nontrivial dynamics in which the conformal symmetry and its breakdown
play a crucial role. Explicit solutions of the SD equations in the
near-critical regime are obtained and the character of the corresponding phase
transition is described.Comment: PRD versio
Modified F(R) Horava-Lifshitz gravity: a way to accelerating FRW cosmology
We propose a general approach for the construction of modified gravity which
is invariant under foliation-preserving diffeomorphisms. Special attention is
paid to the formulation of modified Ho\v{r}ava-Lifshitz gravity (FRHL),
whose Hamiltonian structure is studied. It is demonstrated that the
spatially-flat FRW equations of FRHL are consistent with the constraint
equations. The analysis of de Sitter solutions for several versions of FRHL
indicates that the unification of the early-time inflation with the late-time
acceleration is possible. It is shown that a special choice of parameters for
FRHL leads to the same spatially-flat FRW equations as in the case of
traditional -gravity. Finally, an essentially most general modified
Ho\v{r}ava-Lifshitz gravity is proposed, motivated by its fully
diffeomorphism-invariant counterpart, with the restriction that the action does
not contain derivatives higher than the second order with respect to the time
coordinate.Comment: LaTeX 11 pages. v4: Some errors have been correcte
Generalized Froggatt-Nielsen Mechanism
In this paper, we propose a Generalized Froggatt-Nielsen mechanism in which
non-renormalizable operators involving a GUT group and non-singlet
Higgs field are introduced. Thus the GUT gauge symmetry breaking and the
generation of hierarchical flavor hierarchy have a common origin in this
mechanism. In this Generalized Froggatt-Nielsen mechanism, we propose
universality conditions for coefficients corresponding to different
contractions in the group productions. We find that the predictions in
Generalized Froggatt-Nielsen mechanism for SU(5) GUT is different to that of
ordinary Froggatt-Nielsen mechanism. Such Generalized Froggatt-Nielsen
mechanism can be used in GUT models when ordinary Froggatt-Nielsen mechanism is
no longer available. We study the application of Generalized Froggatt-Nielsen
mechanism in SO(10) model. We find that realistic standard model mass hierarchy
and mixings can be obtained both in SU(5) and SO(10) GUT models with such
Generalized Froggatt-Nielsen mechanism.Comment: 4 pages, no figure
Neutrino Democracy, Fermion Mass Hierarchies And Proton Decay From 5D SU(5)
The explanation of various observed phenomena such as large angle neutrino
oscillations, hierarchies of charged fermion masses and CKM mixings, and
apparent baryon number conservation may have a common origin. We show how this
could occur in 5D SUSY SU(5) supplemented by a flavor symmetry
and additional matter supermultiplets called 'copies'. In addition, the proton
decays into , with an estimated lifetime of order
yrs. Other decay channels include and with comparable rates. We
also expect that BRBR
Model for fermion mass matrices and the origin of quark-lepton symmetry
Several phenomenological features of fermion masses and mixings can be
accounted for by a simple model for fermion mass matrices, which suggests an
underlying U(2) horizontal symmetry. In this context, it is also proposed how
an approximate quark-lepton symmetry can be achieved without unified gauge
theories.Comment: 12 pages, RevTex. Minor changes, some references adde
Standard Model Higgs from Higher Dimensional Gauge Fields
We consider the possibility that the standard model Higgs fields may
originate from extra components of higher dimensional gauge fields. Theories of
this type considered before have had problems accommodating the standard model
fermion content and Yukawa couplings different from the gauge coupling.
Considering orbifolds based on abelian discrete groups we are lead to a 6
dimensional G_2 gauge theory compactified on T^2/Z_4. This theory can naturally
produce the SM Higgs fields with the right quantum numbers while predicting the
value of the weak mixing angle sin^2 theta_W = 0.25 at the tree-level, close to
the experimentally observed one. The quartic scalar coupling for the Higgs is
generated by the higher dimensional gauge interaction and predicts the
existence of a light Higgs. We point out that one can write a quadratically
divergent counter term for Higgs mass localized to the orbifold fixed point.
However, we calculate these operators and show that higher dimensional gauge
interactions do not generate them at least at one loop. Fermions are introduced
at orbifold fixed points, making it easy to accommodate the standard model
fermion content. Yukawa interactions are generated by Wilson lines. They may be
generated by the exchange of massive bulk fermions, and the fermion mass
hierarchy can be obtained. Around a TeV, the first KK modes would appear as
well as additional fermion modes localized at the fixed point needed to cancel
the quadratic divergences from the Yukawa interactions. The cutoff scale of the
theory could be a few times 10 TeV.Comment: 29 pages, 1 figure, LaTeX. v2: Section on the absence of tadpole at
all order removed. Typos corrected. Refs. added. Final version appeared in
PR
SU(7) Unification of SU(3)_C*SU(4)_W* U(1)_{B-L}
We propose the SUSY SU(7) unification of the SU(3)_C* SU(4)_W* U(1)_{B-L}
model. Such unification scenario has rich symmetry breaking chains in a
five-dimensional orbifold. We study in detail the SUSY SU(7) symmetry breaking
into SU(3)_C* SU(4)_W* U(1)_{B-L} by boundary conditions in a Randall-Sundrum
background and its AdS/CFT interpretation. We find that successful gauge
coupling unification can be achieved in our scenario. Gauge unification favors
low left-right and unification scales with tree-level \sin^2\theta_W=0.15. We
use the AdS/CFT dual of the conformal supersymmetry breaking scenario to break
the remaining N=1 supersymmetry. We employ AdS/CFT to reproduce the NSVZ
formula and obtain the structure of the Seiberg duality in the strong coupling
region for 3/2N_c<N_F<3N_C. We show that supersymmetry is indeed broken in the
conformal supersymmetry breaking scenario with a vanishing singlet vacuum
expectation value.Comment: 25 pages, 1 figure
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