862 research outputs found
Critical point of QCD at finite T and \mu, lattice results for physical quark masses
A critical point (E) is expected in QCD on the temperature (T) versus
baryonic chemical potential (\mu) plane. Using a recently proposed lattice
method for \mu \neq 0 we study dynamical QCD with n_f=2+1 staggered quarks of
physical masses on L_t=4 lattices. Our result for the critical point is T_E=162
\pm 2 MeV and \mu_E= 360 \pm 40 MeV. For the critical temperature at \mu=0 we
obtained T_c=164 \pm 2 MeV. This work extends our previous study [Z. Fodor and
S.D.Katz, JHEP 0203 (2002) 014] by two means. It decreases the light quark
masses (m_{u,d}) by a factor of three down to their physical values.
Furthermore, in order to approach the thermodynamical limit we increase our
largest volume by a factor of three. As expected, decreasing m_{u,d} decreased
\mu_E. Note, that the continuum extrapolation is still missingComment: 10 pages, 2 figure
The Gaugephobic Higgs
We present a class of models that contains Randall-Sundrum and Higgsless
models as limiting cases. Over a wide range of the parameter space WW
scattering is mainly unitarized by Kaluza-Klein partners of the W and Z, and
the Higgs particle has suppressed couplings to the gauge bosons. Such a
gaugephobic Higgs can be significantly lighter than the 114 GeV LEP bound for a
standard Higgs, or heavier than the theoretical upper bound. These models
predict a suppressed single top production rate and unconventional Higgs
phenomenology at the LHC: the Higgs production rates will be suppressed and the
Higgs branching fractions modified. However, the more difficult the Higgs
search at the LHC is, the easier the search for other light resonances (like
Z', W', t', exotic fermions) will be.Comment: 20 pages, 3 figure
Anomaly Mediation, Fayet-Iliopoulos D-terms and the Renormalisation Group
We address renormalisation group evolution issues that arise in the Anomaly
Mediated Supersymmetry Breaking scenario when the tachyonic slepton problem is
resolved by Fayet-Iliopoulos term contributions. We present typical sparticle
spectra both for the original formulation of this idea and an alternative using
Fayet-Iliopoulos terms for a U(1) compatible with a straightforward GUT
embedding.Comment: 20 pages, 2 figure
Massive Supergravity and Deconstruction
We present a simple superfield Lagrangian for massive supergravity. It
comprises the minimal supergravity Lagrangian with interactions as well as mass
terms for the metric superfield and the chiral compensator. This is the natural
generalization of the Fierz-Pauli Lagrangian for massive gravity which
comprises mass terms for the metric and its trace. We show that the on-shell
bosonic and fermionic fields are degenerate and have the appropriate spins: 2,
3/2, 3/2 and 1. We then study this interacting Lagrangian using goldstone
superfields. We find that a chiral multiplet of goldstones gets a kinetic term
through mixing, just as the scalar goldstone does in the non-supersymmetric
case. This produces Planck scale (Mpl) interactions with matter and all the
discontinuities and unitarity bounds associated with massive gravity. In
particular, the scale of strong coupling is (Mpl m^4)^1/5, where m is the
multiplet's mass. Next, we consider applications of massive supergravity to
deconstruction. We estimate various quantum effects which generate non-local
operators in theory space. As an example, we show that the single massive
supergravity multiplet in a 2-site model can serve the function of an extra
dimension in anomaly mediation.Comment: 24 pages, 2 figures, some color. Typos fixed and refs added in v
The Intermediate Higgs
Two paradigms for the origin of electroweak superconductivity are a weakly
coupled scalar condensate, and a strongly coupled fermion condensate. The
former suffers from a finetuning problem unless there are cancelations to
radiative corrections, while the latter presents potential discrepancies with
precision electroweak physics. Here we present a framework for electroweak
symmetry breaking which interpolates between these two paradigms, and mitigates
their faults. As in Little Higgs theories, the Higgs is a pseudo-Nambu
Goldstone boson, potentially composite. The cutoff sensitivity of the one loop
top quark contribution to the effective potential is canceled by contributions
from additional vector-like quarks, and the cutoff can naturally be higher than
in the minimal Standard Model. Unlike the Little Higgs models, the cutoff
sensitivity from one loop gauge contributions is not canceled. However, such
gauge contributions are naturally small as long as the cutoff is below 6 TeV.
Precision electroweak corrections are suppressed relative to those of
Technicolor or generic Little Higgs theories. In some versions of the
intermediate scenario, the Higgs mass is computable in terms of the masses of
these additional fermions and the Nambu-Goldstone Boson decay constant. In
addition to the Higgs, new scalar and pseudoscalar particles are typically
present at the weak scale
A Simple Explanation for DAMA with Moderate Channeling
We consider the possibility that the DAMA signal arises from channeled events
in simple models where the dark matter interaction with nuclei is suppressed at
small momenta. As with the standard WIMP, these models have two parameters (the
dark matter mass and the size of the cross-section), without the need to
introduce an additional energy threshold type of parameter. We find that they
can be consistent with channeling fractions as low as about ~ 15%, so long as
at least ~70% of the nuclear recoil energy for channeled events is deposited
electronically. Given that there are reasons not to expect very large
channeling fractions, these scenarios make the channeling explanation of DAMA
much more compelling.Comment: 6 pages, 2 figure
Strengthening Web Based Learning through Software Quality Analysis
The Web is changing the way people access & exchange information. Specifically in the teaching & learning environment, we are witnessing that the traditional model of presence based magisterial classes is shifting towards Web Based Learning. This new model draws on remote access systems, knowledge sharing, and student mobility. In this context, pedagogical strategies are also changing, and for instance, Project- Based Learning (PBL) is seen as a potential driver for growth and development in this arena. This study is focused on a PBL oriented course with a Distributed Remote ACcess (DRAC) system. The objective is to analyze how quantitative methods can be leveraged to design and evaluate automatic diagnosis and feedback tools to assist students on quality-related pedagogical issues in DRAC enabled PBL courses. Main conclusions derived from this study are correlation-based and reveal that the development of automatic quality assessment and feedback requires further research
Lattice determination of the critical point of QCD at finite T and \mu
Based on universal arguments it is believed that there is a critical point
(E) in QCD on the temperature (T) versus chemical potential (\mu) plane, which
is of extreme importance for heavy-ion experiments. Using finite size scaling
and a recently proposed lattice method to study QCD at finite \mu we determine
the location of E in QCD with n_f=2+1 dynamical staggered quarks with
semi-realistic masses on lattices. Our result is T_E=160 \pm 3.5 MeV
and \mu_E= 725 \pm 35 MeV. For the critical temperature at \mu=0 we obtained
T_c=172 \pm 3 MeV.Comment: misprints corrected, version to appear in JHE
The Fayet-Iliopoulos D-term and its renormalisation in softly-broken supersymmetric theories
We consider the renormalisation of the Fayet-Iliopoulos D-term in a
softly-broken abelian supersymmetric theory, and calculate the associated
beta-function through three loops. We show that there exists (at least through
three loops) a renormalisation group invariant trajectory for the coefficient
of the D-term, corresponding to the conformal anomaly solution for the soft
masses and couplings.Comment: 30 pages, Revtex, 15 Figures. Minor changes, and inadvertent omission
of author from this abstract correcte
The Fayet-Iliopoulos D-term and its renormalisation in the MSSM
We consider the renormalisation of the Fayet-Iliopoulos D-term in a
softly-broken supersymmetric gauge theory with a non-simple gauge group
containing an abelian factor, and present the associated beta-function through
three loops. We also include in an appendix the result for several abelian
factors. We specialise to the case of the minimal supersymmetric standard model
(MSSM), and investigate the behaviour of the Fayet-Iliopoulos coupling for
various boundary conditions at the unification scale. We focus particularly on
the case of non-standard soft supersymmetry breaking couplings, for which the
Fayet-Iliopoulos coupling evolves significantly between the unification scale
and the weak scale.Comment: 18 pages, Revtex, 2 figures. Expanded version including general
results for gauge groups with several abelian factors. Minor typos correcte
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