118 research outputs found
Chiral Anomaly and CPT invariance in an implicit momentum space regularization framework
This is the second in a series of two contributions in which we set out to
establish a novel momentum space framework to treat field theoretical
infinities in perturbative calculations when parity-violating objects occur.
Since no analytic continuation on the space-time dimension is effected, this
framework can be particularly useful to treat dimension-specific theories.
Moreover arbitrary local terms stemming from the underlying infinities of the
model can be properly parametrized. We (re)analyse the undeterminacy of the
radiatively generated CPT violating Chern-Simons term within an extended
version of and calculate the Adler-Bardeen-Bell-Jackiw triangle anomaly
to show that our framework is consistent and general to handle the subtleties
involved when a radiative corretion is finite.Comment: 16 pages, LaTeX, version to appear in PR
Lepton flavor violation in the Simplest Little Higgs model
The flavor sector of Little Higgs models based on product groups, notably the
Littlest Higgs with T parity (LHT), has been extensively studied and some
amount of fine tuning was found to be required to meet the experimental
constraints. However, no such attention has been paid to other classes of
models. Here we analyze the phenomenology of flavor mixing in the lepton sector
of a simple group model, the Simplest Little Higgs (SLH). We obtain the Feynman
rules of the SLH in the 't Hooft-Feynman gauge up to the necessary order and
calculate the leading contributions to the rare processes mu -> e gamma, mu ->
eee and mu-e conversion in nuclei. We find results comparable to those of the
LHT model, because in both cases they arise at the one-loop level. These
require the flavor alignment of the Yukawa couplings of light and heavy leptons
at the per cent level or an effective scale of around 10 TeV.Comment: 41 pages, 8 figures; minor changes and one reference added, version
to appear in JHE
Implicit Regularization and Renormalization of QCD
We apply the Implicit Regularization Technique (IR) in a non-abelian gauge
theory. We show that IR preserves gauge symmetry as encoded in relations
between the renormalizations constants required by the Slavnov-Taylor
identities at the one loop level of QCD. Moreover, we show that the technique
handles divergencies in massive and massless QFT on equal footing.Comment: (11 pages, 2 figures
Precise limits from lepton flavour violating processes on the Littlest Higgs model with T-parity
We recalculate the leading one-loop contributions to mu > e gamma and mu ->
eee in the Littlest Higgs model with T-parity, recovering previous results for
the former. When all the Goldstone interactions are taken into account, the
latter is also ultraviolet finite. The present experimental limits on these
processes require a somewhat heavy effective scale ~2.5 TeV, or the flavour
alignment of the Yukawa couplings of light and heavy leptons at the ~10% level,
or the splitting of heavy lepton masses to a similar precision. Present limits
on tau decays set no bounds on the corresponding parameters involving the tau
leptonComment: 41 pages, 11 figures; v3: matches published version in JHE
l W nu production at CLIC: a window to TeV scale non-decoupled neutrinos
We discuss single heavy neutrino production e+ e- -> N nu -> l W nu, l = e,
mu, tau, at a future high energy collider like CLIC, with a centre of mass
energy of 3 TeV. This process could allow to detect heavy neutrinos with masses
of 1-2 TeV if their coupling to the electron V_eN is in the range 0.004-0.01.
We study the dependence of the limits on the heavy neutrino mass and emphasise
the crucial role of lepton flavour in the discovery of a positive signal at
CLIC energy. We present strategies to determine heavy neutrino properties once
they are discovered, namely their Dirac or Majorana character and the size and
chirality of their charged current couplings. Conversely, if no signal is
found, the bound V_eN < 0.002-0.006 would be set for masses of 1-2 TeV,
improving the present limit up to a factor of 30. We also extend previous work
examining in detail the flavour and mass dependence of the corresponding limits
at ILC, as well as the determination of heavy neutrino properties if they are
discovered at this collider.Comment: LaTeX 32 pages. Added comments and references. Matches version to
appear in JHE
Comparing Implicit, Differential, Dimensional and BPHZ Renormalisation
We compare a momentum space implicit regularisation (IR) framework with other
renormalisation methods which may be applied to dimension specific theories,
namely Differential Renormalisation (DfR) and the BPHZ formalism. In
particular, we define what is meant by minimal subtraction in IR in connection
with DfR and dimensional renormalisation (DR) .We illustrate with the
calculation of the gluon self energy a procedure by which a constrained version
of IR automatically ensures gauge invariance at one loop level and handles
infrared divergences in a straightforward fashion. Moreover, using the
theory setting sun diagram as an example and comparing explicitly
with the BPHZ framework, we show that IR directly displays the finite part of
the amplitudes. We then construct a parametrization for the ambiguity in
separating the infinite and finite parts whose parameter serves as
renormalisation group scale for the Callan-Symanzik equation. Finally we argue
that constrained IR, constrained DfR and dimensional reduction are equivalent
within one loop order.Comment: 21 pages, 2 figures, late
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