2,552 research outputs found
Exact Potts Model Partition Functions for Strips of the Honeycomb Lattice
We present exact calculations of the Potts model partition function
for arbitrary and temperature-like variable on -vertex
strip graphs of the honeycomb lattice for a variety of transverse widths
equal to vertices and for arbitrarily great length, with free
longitudinal boundary conditions and free and periodic transverse boundary
conditions. These partition functions have the form
, where
denotes the number of repeated subgraphs in the longitudinal direction. We give
general formulas for for arbitrary . We also present plots of
zeros of the partition function in the plane for various values of and
in the plane for various values of . Explicit results for partition
functions are given in the text for (free) and (cylindrical),
and plots of partition function zeros are given for up to 5 (free) and
(cylindrical). Plots of the internal energy and specific heat per site
for infinite-length strips are also presented.Comment: 39 pages, 34 eps figures, 3 sty file
Little Higgs Models and Precision Electroweak Data
We study the low energy limit of Little Higgs models. The method consists in
eliminating the heavy fields using their classical equations of motion in the
infinite mass limit. After the elimination of the heavy degrees of freedom we
can directly read off deviations from the precision electroweak data. We also
examine the effects on the low energy precision experiments.Comment: Misprint in eps3 for the custodial model corrected and additional
discussion of the triplet higg
Potts model on recursive lattices: some new exact results
We compute the partition function of the Potts model with arbitrary values of
and temperature on some strip lattices. We consider strips of width
, for three different lattices: square, diced and `shortest-path' (to be
defined in the text). We also get the exact solution for strips of the Kagome
lattice for widths . As further examples we consider two lattices
with different type of regular symmetry: a strip with alternating layers of
width and , and a strip with variable width. Finally we make
some remarks on the Fisher zeros for the Kagome lattice and their large
q-limit.Comment: 17 pages, 19 figures. v2 typos corrected, title changed and
references, acknowledgements and two further original examples added. v3 one
further example added. v4 final versio
Singlet Fermionic Dark Matter explains DAMA signal
It has been suggested that, considering channeling effect, the order of a few
GeV dark matters which are elastically scattered from detector nuclei might be
plausible candidates reconciling the DAMA annual modulation signal with the
results of other null experiments. We show that Singlet Fermionic Dark Matter
can be such a dark matter candidate, simultaneously providing the correct
thermal relic density which is consistent with the WMAP data.Comment: 9 pages, 3 figure
Constraint of B_{d,s}-bar{B}_{d,s} mixing on warped extra-dimension model
Recent CDF measurement of the Bs-Bs oscillation frequency, at the Tevatron
imposes significant constraint on various models for new physics. A warped
extra-dimension model with custodial isospin symmetry accommodates the Bd-Bd
mixing at tree level mainly through the Kaluza-Klein gluons. This is due to the
misalignment between the bulk gauge eigenstates and the localized Yukawa
eigenstates of the bulk fermions. We adopt the universal 5D Yukawa coupling
model where all Yukawa couplings are of order one. The SM fermion mass spectra
and mixings are controlled by the bulk Dirac mass parameters. With two versions
of the hadronic parameter values, we investigate the implication of the
observed BB mixings on this model. The CP-violating effects on the Bd system is
shown to provide very strong constraint: The first Kaluza-Klein mass of a gluon
has its lower bound about 3.7 TeV with 1 sigma uncertainty.Comment: published version in JHEP, CP-violating effects include
Mass matrix Ansatz and lepton flavor violation in the THDM-III
Predictive Higgs-fermion couplings can be obtained when a specific texture
for the fermion mass matrices is included in the general two-Higgs doublet
model. We derive the form of these couplings in the charged lepton sector using
a Hermitian mass matrix Ansatz with four-texture zeros. The presence of
unconstrained phases in the vertices phi-li-lj modifies the pattern of
flavor-violating Higgs interactions. Bounds on the model parameters are
obtained from present limits on rare lepton flavor violating processes, which
could be extended further by the search for the decay tau -> mu mu mu and mu-e
conversion at future experiments. The signal from Higgs boson decays phi -> tau
mu could be searched at the large hadron collider (LHC), while e-mu transitions
could produce a detectable signal at a future e mu-collider, through the
reaction e mu -> h0 -> tau tau.Comment: 17 pages, 9 figure
Little Hierarchy, Little Higgses, and a Little Symmetry
Little Higgs theories are an attempt to address the little hierarchy problem,
i.e., the tension between the naturalness of the electroweak scale and the
precision measurements showing no evidence for new physics up to 5-10 TeV. In
little Higgs theories, the Higgs mass-squareds are protected to the one-loop
order from the quadratic divergence. This allows the cutoff to be raised up to
\~10 TeV, beyond the scales probed by the precision data. However, strong
constraints can still arise from the contributions of the new TeV scale
particles and hence re-introduces the fine-tuning problem. In this paper we
show that a new symmetry, denoted as T-parity, under which all heavy gauge
bosons and scalar triplets are odd, can remove all the tree-level contributions
to the electroweak observables and therefore makes the little Higgs theories
completely natural. The T-parity can be manifestly implemented in a majority of
little Higgs models by following the most general construction of the low
energy effective theory a la Callan, Coleman, Wess and Zumino. In particular,
we discuss in detail how to implement the T-parity in the littlest Higgs model
based on SU(5)/SO(5). The symmetry breaking scale f can be even lower than 500
GeV if the contributions from the unknown UV physics at the cutoff are somewhat
small. The existence of -parity has drastic impacts on the phenomenology of
the little Higgs theories. The T-odd particles need to be pair-produced and
will cascade down to the lightest T-odd particle (LTP) which is stable. A
neutral LTP gives rise to missing energy signals at the colliders which can
mimic supersymmetry. It can also serve as a good dark matter candidate.Comment: 20 pages, 2 figures, RevTeX; v2: Yukawa sector in the SU(5)/SO(5)
model slightly modified. Also added comments on the Dirac mass term for the
fermionic doublet partner; v3: clarifying comments on the modified Yukawa
sector. version to appear on JHE
A "Littlest Higgs" Model with Custodial SU(2) Symmetry
In this note, a ``littlest higgs'' model is presented which has an
approximate custodial SU(2) symmetry. The model is based on the coset space
. The light pseudo-goldstone bosons of the theory
include a {\it single} higgs doublet below a TeV and a set of three
triplets and an electroweak singlet in the TeV range. All of these scalars
obtain approximately custodial SU(2) preserving vacuum expectation values. This
model addresses a defect in the earlier moose
model, with the only extra complication being an extended top sector. Some of
the precision electroweak observables are computed and do not deviate
appreciably from Standard Model predictions. In an S-T oblique analysis, the
dominant non-Standard Model contributions are the extended top sector and higgs
doublet contributions. In conclusion, a wide range of higgs masses is allowed
in a large region of parameter space consistent with naturalness, where large
higgs masses requires some mild custodial SU(2) violation from the extended top
sector.Comment: 22 pages + 8 figures; JHEP style, added references and extra
discussion on size of T contributions, as well as some other minor
clarifications. Version to appear in JHE
in NonCommutative Standard Model
We study the top quark decay to b quark and W boson in the NonCommutative
Standard Model (NCSM). The lowest contribution to the decay comes from the
terms quadratic in the matrix describing the noncommutative (NC) effects while
the linear term is seen to identically vanish because of symmetry. The NC
effects are found to be significant only for low values of the NC
characteristic scale.Comment: 11 page Latex file containing 2 eps figures (redrawn). More
discussion included. To appear in PR
A Composite Little Higgs Model
We describe a natural UV complete theory with a composite little Higgs. Below
a TeV we have the minimal Standard Model with a light Higgs, and an extra
neutral scalar. At the TeV scale there are additional scalars, gauge bosons,
and vector-like charge 2/3 quarks, whose couplings to the Higgs greatly reduce
the UV sensitivity of the Higgs potential. Stabilization of the Higgs mass
squared parameter, without finetuning, occurs due to a softly broken shift
symmetry--the Higgs is a pseudo Nambu-Goldstone boson. Above the 10 TeV scale
the theory has new strongly coupled interactions. A perturbatively
renormalizable UV completion, with softly broken supersymmetry at 10 TeV is
explicitly worked out. Our theory contains new particles which are odd under an
exact "dark matter parity", (-1)^{(2S+3B+L)}. We argue that such a parity is
likely to be a feature of many theories of new TeV scale physics. The lightest
parity odd particle, or "LPOP", is most likely a neutral fermion, and may make
a good dark matter candidate, with similar experimental signatures to the
neutralino of the MSSM. We give a general effective field theory analysis of
the calculation of corrections to precision electroweak observables.Comment: 28 page
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