1,505 research outputs found
The quantum mechanics of perfect fluids
We consider the canonical quantization of an ordinary fluid. The resulting
long-distance effective field theory is derivatively coupled, and therefore
strongly coupled in the UV. The system however exhibits a number of
peculiarities, associated with the vortex degrees of freedom. On the one hand,
these have formally a vanishing strong-coupling energy scale, thus suggesting
that the effective theory's regime of validity is vanishingly narrow. On the
other hand, we prove an analog of Coleman's theorem, whereby the semiclassical
vacuum has no quantum counterpart, thus suggesting that the vortex premature
strong-coupling phenomenon stems from a bad identification of the ground state
and of the perturbative degrees of freedom. Finally, vortices break the usual
connection between short distances and high energies, thus potentially
impairing the unitarity of the effective theory.Comment: 35 page
Quantum Gravity in Everyday Life: General Relativity as an Effective Field Theory
This article is meant as a summary and introduction to the ideas of effective
field theory as applied to gravitational systems.
Contents:
1. Introduction
2. Effective Field Theories
3. Low-Energy Quantum Gravity
4. Explicit Quantum Calculations
5. ConclusionsComment: 56 pages, 2 figures, JHEP style, Invited review to appear in Living
Reviews of Relativit
Planck Scale Boundary Conditions and the Higgs Mass
If the LHC does only find a Higgs boson in the low mass region and no other
new physics, then one should reconsider scenarios where the Standard Model with
three right-handed neutrinos is valid up to Planck scale. We assume in this
spirit that the Standard Model couplings are remnants of quantum gravity which
implies certain generic boundary conditions for the Higgs quartic coupling at
Planck scale. This leads to Higgs mass predictions at the electroweak scale via
renormalization group equations. We find that several physically well motivated
conditions yield a range of Higgs masses from 127-142 GeV. We also argue that a
random quartic Higgs coupling at the Planck scale favors M_H > 150 GeV, which
is clearly excluded. We discuss also the prospects for differentiating
different boundary conditions imposed for \lambda(M_{pl}) at the LHC. A
striking example is M_H = 127\pm 5 GeV corresponding to \lambda(M_{pl})=0,
which would imply that the quartic Higgs coupling at the electroweak scale is
entirely radiatively generated.Comment: 12 pages, 5 figures; references added and other minor improvements,
matches version published in JHE
Effective Theory of a Dynamically Broken Electroweak Standard Model at NLO
We consider the Standard Model as an effective theory at the weak scale
of a generic new strong interaction that dynamically breaks electroweak
symmetry at the energy scale (few) TeV. Assuming only the
minimal field content with the Standard Model fermions and gauge bosons, but
without a light Higgs particle, we construct the complete Lagrangian through
next-to-leading order, that is, including terms of order . The
systematics behind this expansion is clarified. Although similar to chiral
perturbation theory, it is not governed by the dimension of operators alone,
but depends in an essential way on the loop expansion. Power-counting formulas
are derived that indicate the classes of operators required at the
next-to-leading order. The complete set of operators at leading and
next-to-leading order is then listed, based on the restrictions implied by the
Standard-Model gauge symmetries. We recover the well-known operators discussed
in the literature in connection with the electroweak chiral Lagrangian and in
similar contexts, but we collect a complete and systematic list of all terms
through order . This includes some operators not discussed in
explicit terms before. We also show that a few of the previously considered
operators can be eliminated via the equations of motion. As another important
result we confirm the known list of dimension-6 operators in the Standard Model
with an elementary Higgs doublet, essentially as a special case of our
scenario.Comment: 35 pages, 1 figure; references adde
Proof Theory and Ordered Groups
Ordering theorems, characterizing when partial orders of a group extend to
total orders, are used to generate hypersequent calculi for varieties of
lattice-ordered groups (l-groups). These calculi are then used to provide new
proofs of theorems arising in the theory of ordered groups. More precisely: an
analytic calculus for abelian l-groups is generated using an ordering theorem
for abelian groups; a calculus is generated for l-groups and new decidability
proofs are obtained for the equational theory of this variety and extending
finite subsets of free groups to right orders; and a calculus for representable
l-groups is generated and a new proof is obtained that free groups are
orderable
Two-Point Functions and S-Parameter in QCD-like Theories
We calculated the vector, axial-vector, scalar and pseudo-scalar two-point
functions up to two-loop level in the low-energy effective field theory for
three different QCD-like theories. In addition we also calculated the
pseudo-scalar decay constant . The QCD-like theories we used are those
with fermions in a complex, real or pseudo-real representation with in general
n flavours. These case correspond to global symmetry breaking pattern of
, or .
We also estimated the S parameter for those different theories.Comment: 29 page
Vanishing Cosmological Constant by Gravitino-Dressed Compactification of 11D Supergravity
We consider compactifications induced by the gravitino field of eleven
dimensional supergravity. Such compactifications are not trivial in the sense
that the gravitino profiles are not related to pure bosonic ones by means of a
supersymmetry transformation. The basic property of such backgrounds is that
they admit -torsion although they have vanishing Riemann tensor. Thus,
these backgrounds may be considered also as solutions of the teleparallel
formulation of supergravity. We construct two classes of solutions, one with
both antisymmetric three-form field, gravity and gravitino and one with only
gravity and gravitino. In these classes of solutions, the internal space is a
parallelized compact manifold, so that it does not inherit any cosmological
constant to the external spacetime. The latter turns out to be flat Minkowski
in the maximally symmetric case. The elimination of the cosmological constant
in the spontaneously compactified supergravity seems to be a generic property
based on the trading of the cosmological constant for parallelizing torsion.Comment: 17 pages, no figure
A Rationale for Long-lived Quarks and Leptons at the LHC: Low Energy Flavour Theory
In the framework of gauged flavour symmetries, new fermions in parity
symmetric representations of the standard model are generically needed for the
compensation of mixed anomalies. The key point is that their masses are also
protected by flavour symmetries and some of them are expected to lie way below
the flavour symmetry breaking scale(s), which has to occur many orders of
magnitude above the electroweak scale to be compatible with the available data
from flavour changing neutral currents and CP violation experiments. We argue
that, actually, some of these fermions would plausibly get masses within the
LHC range. If they are taken to be heavy quarks and leptons, in
(bi)-fundamental representations of the standard model symmetries, their
mixings with the light ones are strongly constrained to be very small by
electroweak precision data. The alternative chosen here is to exactly forbid
such mixings by breaking of flavour symmetries into an exact discrete symmetry,
the so-called proton-hexality, primarily suggested to avoid proton decay. As a
consequence of the large value needed for the flavour breaking scale, those
heavy particles are long-lived and rather appropriate for the current and
future searches at the LHC for quasi-stable hadrons and leptons. In fact, the
LHC experiments have already started to look for them.Comment: 10 pages, 1 figur
Spontaneous Parity Violation in SUSY Strong Gauge Theory
We suggest simple models of spontaneous parity violation in supersymmetric
strong gauge theory. We focus on left-right symmetric model and investigate
vacuum with spontaneous parity violation. Non-perturbative effects are
calculable in supersymmetric gauge theory, and we suggest two new models. The
first model shows confinement, and the second model has a dual description of
the theory. The left-right symmetry breaking and electroweak symmetry breaking
are simultaneously occurred with the suitable energy scale hierarchy. The
second model also induces spontaneous supersymmetry breaking.Comment: 14 page
Vacuum stability, neutrinos, and dark matter
Motivated by the discovery hint of the Standard Model (SM) Higgs mass around
125 GeV at the LHC, we study the vacuum stability and perturbativity bounds on
Higgs scalar of the SM extensions including neutrinos and dark matter (DM).
Guided by the SM gauge symmetry and the minimal changes in the SM Higgs
potential we consider two extensions of neutrino sector (Type-I and Type-III
seesaw mechanisms) and DM sector (a real scalar singlet (darkon) and minimal
dark matter (MDM)) respectively. The darkon contributes positively to the
function of the Higgs quartic coupling and can stabilize the
SM vacuum up to high scale. Similar to the top quark in the SM we find the
cause of instability is sensitive to the size of new Yukawa couplings between
heavy neutrinos and Higgs boson, namely, the scale of seesaw mechanism. MDM and
Type-III seesaw fermion triplet, two nontrivial representations of
group, will bring the additional positive contributions to the gauge coupling
renormalization group (RG) evolution and would also help to stabilize
the electroweak vacuum up to high scale.Comment: 18 pages, 15 figures; published versio
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