Lorentz Center

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## Universe in a Box: LHC, Cosmology and Lattice Field Theory |

Standard Model
and high energy Lorentz violation
We show that
if Lorentz symmetry is violated at high energies, interactions that are usually
non-renormalizable can become renormalizable
by weighted power counting. We present a CPT invariant, Lorentz violating
extension of the Standard Model containing two scalar-two fermion
interactions (which can explain neutrino masses) and four fermion
interactions (which can explain proton decay). The presence of four fermion vertices allows us to argue that the known low
energy physics can be reproduced also if the elementary scalars are suppressed,
in the Nambu--Jona-Lasinio
spirit, avoiding the ambiguities of common non-renormalizable
approaches. Using a large-Nc expansion, we study the
dynamical symmetry breaking in the scalarless model,
and show that the effective potential has a Lorentz invariant minimum and that
the Lorentz violation does not reverberate down to low energies. The mechanism
generates fermion masses, gauge-boson masses and
scalar bound states, to be identified with composite Higgs bosons. Moreover, it
predicts relations among the parameters of the Standard Model.
Exact lattice supersymmetry
I will review
the recent constructions of lattice theories which retain one or more exact supersymmetries at non-zero lattice spacing with particular
emphasis on N=4 super Yang-Mills. Applications to AdSCFT
will be discussed and recent results from numerical simulations presented.
IRFP on the
lattice
I will discuss
the current evidence for IRFP on the lattice, focussing
on the techniques used in numerical simulations and their limitations.
Traces of a
fixed point: Unravelling the phase diagram at large Nf
With a
sufficiently high number of fundamental fermionic flavours present, Yang-Mills theory develops an infrared fixed
point and becomes (quasi-)conformal in nature. The range of flavour
numbers for which this occurs defines the conformal window, the lower limit of
which has yet to be determined. We studied the phase diagram of SU(3) Yang-Mills theory with twelve flavours
of staggered fermions. Here we present evidence for the occurrence of a bulk
transition towards a chirally broken phase and the
existence of a Coulomb phase on the symmetric side of this transition, using
results of measurements of the sign of the beta function along lines of constant
physics. Since such a phase can only occur in the presence of an attractive
fixed point in the renormalization group flow and an associated conformal
phase, this implies the existence of the conformal window and sets a bound on
its lower end.
The Limits of
Custodial Symmetry
I introduce a
toy model implementing the proposal of using a custodial symmetry to protect
the Zbb coupling from large corrections. This
"doublet-extended standard model" adds a weak doublet of fermions
(including a heavy partner of the top quark) to the particle content of the
standard model in order to implement an O(4) x U(1)_X = SU(2)_L x SU(2)_R x
P_{LR} x U(1)_X symmetry that protects the Zbb
coupling. This symmetry is softly broken to the gauged SU(2)_L x U(1)_Y
electroweak symmetry by a Dirac mass M for the new doublet; adjusting the value
of M allows one to explore the range of possibilities between the
O(4)-symmetric (M to 0) and standard-model-like (M to infinity) limits. In this
simple model, I find that the experimental limits on the Zbb
coupling favor smaller M while the presence of a potentially sizable negative
contribution to T strongly favors large M. A fit to all precision electroweak
data shows that the heavy partner of the top quark must be heavier than about
3.4 TeV, making it difficult to search for at LHC.
Higher
Dimensional Models on the Lattice: The case of the Layer Phase
T.b.c.
Condensate
Enhancement in SU(3) Yang-Mills
T.b.c.
Unitarity in Walking Technicolor
We investigate
the longitudinal WW scattering in models of technicolor featuring spin-one vector and
axial-vector resonances and a spin-zero isospin-zero
state. We show how the walking dynamics constrains the interplay of these
states in the unitarization of the scattering
amplitudes"
Technicolor
Dark Matter
Dark Matter
candidates are natural in Technicolor theories. I will discuss signals of
Technicolor Dark Matter at LHC and constraints from earth based experiments
such as CDMS and XENON.
Lattice
epsilon regime and minimal walking technicolor
We discuss how
lattice data with small values of mpi*L can be
described using lattice chiral perturbation theory in
the epsilon regime. Some open questions are highlighted. A comparison to
on-going lattice simulations of minimal walking Technicolor is made.
Monte Carlo
Renormalization Group calculation for many-fermion
models
Monte Carlo
Renormalization Group methods were designed to study critical behavior in
statistical systems and quantum field theories. They are particularly powerful
in determining phase structure and critical indexes. In this talk I outline how
the 2-lattice MCRG matching can be used to determine the bare beta function of
many fermion systems. I will discuss models with fermion numbers 0,4,12 and 16, moving from the clearly QCD
like to conformal models.
Running
coupling measurements in technicolor
models
The
renormalized coupling, and its running, is one of the fundamental properties of
a gauge theory, and plays an important role in potential walking technicolor models. We describe
how to calculate the renormalized coupling non-perturbatively
via lattice simulations, by measuring
Electroweak
phase transition in walking technicolor
First order
temperature-dependent electroweak phase transitions may arise in walking technicolor models. I analyze the
transitions in minimal walking technicolor
and in ultra minimal technicolor by using the
effective potential. In minimal walking technicolor,
the phase transition is sufficiently strong for electroweak baryogenesis
in a significant region of the parameter space. In ultra minimal technicolor the interplay of two
transitions leads to a rich phase diagram with the possibility of a restoration
and an extra breaking of the electroweak symmetry.
Studies of
gauge theories in finite volume and the conformal window
We report new
results on nearly conformal gauge theories with fermions in the fundamental
representation of the SU(3) color gauge group as the number of fermion flavors is varied in the Nf
= 4-16 range. To unambiguously identify the chirally broken
phase below the conformal window we apply a comprehensive lattice tool set
in finite volumes which includes the test of Goldstone pion
dynamics, the spectrum of the fermion Dirac operator,
and eigenvalue distributions of random matrix theory.
We also discuss the theory inside the conformal window and
beyond. The importance of finite volume
zero momentum gauge field dynamics is explained.
Glueball
masses and string tension in SU(2) gauge theory with adjoint fermions
In a recent
work, we have pointed out that a clean signal for the existence of an infrared
fixed point in a gauge theory with fermions can be obtained by looking for
signatures in the gluonic sector. In this talk, we
shall describe the technical details of our calculations and discuss possible
systematic errors. We shall show that, although those measurements are
technically difficult, they can be kept under good control even with a limited
number of configurations.
The PRACE
Project - Applications, Benchmarks and Prototypes
I can give an
overview of PRACE, what it is aiming at, what kind of opportunities /
difficulties there are, what kind of prototype systems, what about access, what
about benchmarking etc.
Conformal
phase transition in QCD and beyond
I describe the
main characteristics of the conformal phase transition. The examples are the phase
transition with respect to the quark flavor number in QCD and the phase
transition with respect to the coupling constant in grapheme like dynamics.
Comparing mesonic and gluonic sectors in SU(2) with two adjoint fermions.
The masses of
the lowest-lying states in the meson and in the gluonic
sector of an SU(2) gauge theory with two Dirac flavors in the adjoint representation are compared on the lattice at a
fixed $\beta = 2.25$ for values of the bare fermion
mass $m_0$ that span a range between the quenched regime and the massless limit. Even for light constituent fermions, the
spectrum shows a well-defined hierarchy: the lightest glueballs
are found to be lighter than the lightest mesons. I will discuss the
implications of these findings, combined with the results presented in the
talks of Pica, Rago and Lucini.
A strategy for discriminating between the (near-)conformal
and the confining scenario is outlined.
Mesonic
spectrum of SU(2) with two Adjoint
Dirac fermions
I will report
on our recent accurate computation of the low-lying mesonic
states of the SU(2) gauge theory with two adjoint fermions. We performed lattice simulations focusing
on the chiral regime of the theory while keeping the
systematic errors under control by using a sequence of lattices of increasing
size. Results for the pseudoscalar and vector meson
masses, the pseudoscalar decay constant and the chiral condensate, obtained on the largest lattices and
smallest quark masses available to date, will be discussed. The relevance of
our findings for the existence of an IR fixed point in the theory will be
clarified.
Investigating
the Scaling of SU(2) with two Adjoint
Fermions
SU(2) with two adjoint
fermions is an interesting candidate theory for Walking Technicolour.
I will present our recent lattice results on the running of the coupling and
the mass anomalous dimension in this theory, using the Schr\"odinger
functional scheme.
Infrared
effective dynamics of SU(2) with adjoint
fermions
In this talk I
will present the result of a recent lattice study of a SU(2)
model with two adjoint fermions. I will focus the
presentation on the infrared behaviour of the theory,
and I will investigate the possibility of comparing the dynamical data to suitabbly choosen quenced simulations.
Infrared fixed
point in SU(2) gauge theory with 2 adjoint
representation fermions
T.b.c.
Minimal Flavor
Constraints for Technicolor
We introduce a
new set of minimal flavor constraints valid for a general class of models of
dynamical electroweak symmetry breaking. We show that these constraints are
important and cannot be neglected.
Phases of
Gauge Theories and QCD Duals
I will present
the state-of-the-art of the phase diagrams for strongly coupled gauge theories
as function of the number of flavors, colors and matter representation for SU,
Sp and SO gauge theories. I will also argue that different nonsupersymmetric
gauge theories can be nontrivially related, in their respective conformal
windows, via an electro-magnetic duality transformation.
Discovering
dark matter
T.b.c.
Cohomology of supersymmetric gauge theories
revisited
Using
Algebraic-Renormalization techniques we study the consistency conditions
pertaining to supersymmetric abelian
gauge theories, finding a new cohomologically
non-trivial solution. This implies that supersymmetry may be anomalous in certain gauge theories. While
a full loop calculation has yet to be done, we examine the implications of some
anomalous supersymmetry Ward identities in a concrete
model.
The
crumpled phase in the dynamical triangulation approach to quantum gravity.
Numerical
simulations in the dynamical triangulation formulation of quantum gravity have
shown the existence of an `elongated phase' and a `crumpled phase', which have
unphysical features for coupling values far from the crtitical
coupling separating these phases. We attempt to give a physical interpretation
of these phenomea, with emphasis on the crumpled
phase for which we present old unpublished results.
Lattice Weak
Matrix Elements & CP Violation: Standard Model Model
and beyond.
T.b.c.
Sextet quarks:
at the sill of the conformal window?
I will present
recent numerical results for the SU(3) gauge theory
with two flavors of sextet quarks that indicate that if it is conformal, it is
barely over the edge into the window. I
will also discuss peculiarities of the Aoki phase.
From
hierarchy problem to unification and dark matter.
The
electroweak hierarchy problem has provided a paradigm for model building for
decades. Technicolor with its various incarnations provides a natural solution.
However, various other model building paradigms can be addressed within technicolor as well. In this talk
I will discuss some concrete examples, like how fourth generation of ordinary
matter may arise, and how simple technicolor model
can also provide unification of the three Standard Model coupling constants and
lead to viable dark matter candidates.
Progress on Calorons
T.b.c.
Black branes in Einstein-Gauss-Bonnet gravity
For his
presentation, click here
Study of the
running coupling constant in 10-flavor QCD with the Schrödinger functional
method
The
electroweak gauge symmetry is allowed to be spontaneously broken by the
strongly interacting vector-like gauge dynamics, especially provided the gauge
coupling runs slowly in a wide range of energy scale. This may open up the
possibility that the origin of all masses may be traced back to the gauge
theory. We use the Schrödinger functional method to study the scale dependence
of the gauge coupling of 10-flavor QCD. Some preliminary results are presented.
Conformal
Higgs, or Techni-dilaton - Composite Higgs at
Conformal Phase Transition
Walking/Conformal
technicolor near the Banks-Zaks conformal fixed point is discussed in terms of conformal
phase transition (CPT) which is characterized by the essential singularity
scaling, breakdown of the Ginzburg-Landau effective
theory, and large anomalous dimension. In terms of the gauged Nambu-Jona-Lasinio model, the CPT takes place as a fusion
of infrared fixed point and ultraviolet fixed point with \gamma_m
=1. As a remnant of conformal symmetry there exists a light scalar, techni-dilaton, in the broken phase, while no light spectra
exist in the symmetric phase (conformal window). The techni-dilaton
may be discovered in LHC. [Back] |