10,990 research outputs found

### Natural Dirac Neutrinos from Warped Extra Dimension

Dirac neutrinos arising from gauged discrete symmetry \`a la Krauss-Wilczek
are implemented in the minimal custodial Randall-Sundrum model. In the case of
a normal hierarchy, all lepton masses and mixing pattern can be naturally
reproduced at the TeV scale set by the electroweak constraints, while
simultanously satisfy bounds from lepton flavour violation. A nonzero neutrino
mixing angle, $\theta_{13}$, is generic in the scenario, as well as the
existence of sub-TeV right-handed Kaluza-Klein neutrinos, which may be searched
for at the LHC.Comment: Talk given at the 2nd Young Researchers Workshop "Physics Challenges
in the LHC Era", Frascati, May 10 and 13, 2010, 6 page

### $U(1)_{B-L}$ extra-natural inflation with Standard Model on a brane

The interrelation between inflationary cosmology and new physics beyond the
Standard Model (SM) is studied in a $U(1)_{B-L}$ extension of the SM embedded
in a (4+1)-dimensional spacetime. In the scenario we study, the inflaton arises
from the Wilson loop of the $U(1)_{B-L}$ gauge group winding an
extra-dimensional cycle. Particular attention is paid to the coupling between
the inflaton and SM particles that are confined on a brane localised in the
extra dimension. We find that the inflaton decay channels are rather restricted
in this scenario and the resulting reheating temperature is relatively low.Comment: 1+14 page

### Phenomenology from a U(1) gauged hidden sector

We consider the phenomenological consequences of a hidden Higgs sector
extending the Standard Model (SM), in which the matter content are uncharged
under the SM gauge groups. We consider a simple case where the hidden sector is
gauged under a U(1) with one Higgs singlet. The only couplings between SM and
the hidden sector are through mixings between the neutral gauge bosons of the
two respective sectors, and between the Higgs bosons. We find signals testable
at the LHC that can reveal the existence and shed light on the nature of such a
hidden sector.Comment: 5 pages, 2 figures. Talk given at the Lake Louise Winter Institute
2007, Feb. 19-24, Alberta, Canad

### Testing Realistic Quark Mass Matrices in the Custodial Randall-Sundrum Model with Flavor Changing Top Decays

We study quark mass matrices in the Randall-Sundrum (RS) model with bulk
symmetry $SU(2)_L \times SU(2)_R \times U(1)_{B-L}$. The Yukawa couplings are
assumed to be within an order of magnitude of each other, and perturbative. We
find that quark mass matrices of the symmetrical form proposed by Koide
\textit{et. al.} [Y. Koide, H. Nishiura, K. Matsuda, T. Kikuchi and T.
Fukuyama, Phys. Rev. D {\bf 66}, 093006 (2002)] can be accommodated in the RS
framework with the assumption of hierarchyless Yukawa couplings, but not the
hermitian Fritzsch-type mass matrices. General asymmetrical mass matrices are
also found which fit well simultaneously with the quark masses and the
Cabibbo-Kobayashi-Maskawa matrix. Both left-handed (LH) and right-handed (RH)
quark rotation matrices are obtained that allow analysis of flavour changing
decay of both LH and RH top quarks. At a warped down scale of 1.65 TeV, the
total branching ratio of t \ra Z + jets can be as high as $\sim 5 \times
10^{-6}$ for symmetrical mass matrices and $\sim 2 \times 10^{-5}$ for
asymmetrical ones. This level of signal is within reach of the LHC.Comment: 30 pages, 6 figures. Reference added, typos corrected, discussions in
Sec. IV B expanded. Version conforms to the published versio

### A Very Narrow Shadow Extra Z-boson at Colliders

We consider the phenomenological consequences of a hidden Higgs sector
extending the Standard Model (SM), in which the ``shadow Higgs'' are uncharged
under the SM gauge groups. We consider a simple U(1) model with one Higgs
singlet. One mechanism which sheds light on the shadow sector is the mixing
between the neutral gauge boson of the SM and the additional U(1) gauge group.
The mixing happens through the usual mass-mixing and also kinetic-mixing, and
is the only way the ``shadow $Z$'' couples to the SM. We study in detail
modifications to the electroweak precision tests (EWPTs) that the presence of
such a shadow sector would bring, which in turn provide constraints on the
kinetic-mixing parameter, $s_\epsilon$, left free in our model. The shadow $Z$
production rate at the LHC and ILC depends on $s_\epsilon$. We find that
observable event rate at both facilities is possible for a reasonable range of
$s_\epsilon$ allowed by EWPTs.Comment: 10 pages, 7 figures. Note and refs. adde

### Twisted Mass Finite Volume Effects

We calculate finite volume effects on the pion masses and decay constant in
twisted mass lattice QCD (tmLQCD) at finite lattice spacing. We show that the
lighter neutral pion in tmLQCD gives rise to finite volume effects that are
exponentially enhanced when compared to those arising from the heavier charged
pions. We demonstrate that the recent two flavour twisted mass lattice data can
be better fitted when twisted mass effects in finite volume corrections are
taken into account.Comment: 17 pages, revte

### Strange quarks in quenched twisted mass lattice QCD

Two twisted doublets, one containing the up and down quarks and the other
containing the strange quark with an SU(2)-flavor partner, are used for studies
in the meson sector. The relevant chiral perturbation theory is presented, and
quenched QCD simulations (where the partner of the strange quark is not active)
are performed. Pseudoscalar meson masses and decay constants are computed; the
vector and scalar mesons are also discussed. A comparison is made to the case
of an untwisted strange quark, and some effects due to quenching,
discretization, and the definition of maximal twist are explored.Comment: 37 pages, 12 figures, accepted for publicatio

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