64 research outputs found
Flavor in Minimal Conformal Technicolor
We construct a complete, realistic, and natural UV completion of minimal
conformal technicolor that explains the origin of quark and lepton masses and
mixing angles. As in "bosonic technicolor", we embed conformal technicolor in a
supersymmetric theory, with supersymmetry broken at a high scale. The exchange
of heavy scalar doublets generates higher-dimension interactions between
technifermions and quarks and leptons that give rise to quark and lepton masses
at the TeV scale. Obtaining a sufficiently large top quark mass requires strong
dynamics at the supersymmetry breaking scale in both the top and technicolor
sectors. This is natural if the theory above the supersymmetry breaking also
has strong conformal dynamics. We present two models in which the strong top
dynamics is realized in different ways. In both models, constraints from
flavor-changing effects can be easily satisfied. The effective theory below the
supersymmetry breaking scale is minimal conformal technicolor with an
additional light technicolor gaugino. We argue that this light gaugino is a
general consequence of conformal technicolor embedded into a supersymmetric
theory. If the gaugino has mass below the TeV scale it will give rise to an
additional pseudo Nambu-Goldstone boson that is observable at the LHC.Comment: 37 pages; references adde
Entanglement Entropy of 3-d Conformal Gauge Theories with Many Flavors
Three-dimensional conformal field theories (CFTs) of deconfined gauge fields
coupled to gapless flavors of fermionic and bosonic matter describe quantum
critical points of condensed matter systems in two spatial dimensions. An
important characteristic of these CFTs is the finite part of the entanglement
entropy across a circle. The negative of this quantity is equal to the finite
part of the free energy of the Euclidean CFT on the three-sphere, and it has
been proposed to satisfy the so called F-theorem, which states that it
decreases under RG flow and is stationary at RG fixed points. We calculate the
three-sphere free energy of non-supersymmetric gauge theory with a large number
N_F of bosonic and/or fermionic flavors to the first subleading order in 1/N_F.
We also calculate the exact free energies of the analogous chiral and
non-chiral {\cal N} = 2 supersymmetric theories using localization, and find
agreement with the 1/N_F expansion. We analyze some RG flows of supersymmetric
theories, providing further evidence for the F-theorem.Comment: 31 pages, 2 figures; v2 refs added, minor change
Minimal Conformal Technicolor and Precision Electroweak Tests
We study the minimal model of conformal technicolor, an SU(2) gauge theory
near a strongly coupled conformal fixed point, with conformal symmetry softly
broken by technifermion mass terms. Conformal symmetry breaking triggers chiral
symmetry breaking in the pattern SU(4) -> Sp(4), which gives rise to a
pseudo-Nambu-Goldstone boson that can act as a composite Higgs boson. The top
quark is elementary, and the top and electroweak gauge loop contributions to
the Higgs mass are cut off entirely by Higgs compositeness. In particular, the
model requires no top partners and no "little Higgs" mechanism. A nontrivial
vacuum alignment results from the interplay of the top loop and technifermion
mass terms. The composite Higgs mass is completely determined by the top loop,
in the sense that m_h/m_t is independent of the vacuum alignment and is
computable by a strong-coupling calculation. There is an additional composite
pseudoscalar A with mass larger than m_h and suppressed direct production at
LHC. We discuss the electroweak fit in this model in detail. Corrections to Z
-> bb and the T parameter from the top sector are suppressed by the enhanced
Sp(4) custodial symmetry. Even assuming that the strong contribution to the S
parameter is positive and usuppressed, a good electroweak fit can be obtained
for v/f ~ 0.25, where v and f are the electroweak and chiral symmetry breaking
scales respectively. This requires fine tuning at the 10% level.Comment: 34 pages, 4 figures; v2: updated precision electroweak fi
Holography of a Composite Inflaton
We study the time evolution of a brane construction that is holographically
dual to a strongly coupled gauge theory that dynamically breaks a global
symmetry through the generation of an effective composite Higgs vev. The D3/D7
system with a background magnetic field or non-trivial gauge coupling (dilaton)
profile displays the symmetry breaking. We study motion of the D7 brane in the
background of the D3 branes. For small field inflation in the field theory the
effective Higgs vev rolls from zero to the true vacuum value. We study what
phenomenological dilaton profile generates the slow rolling needed, hence
learning how the strongly coupled gauge theory's coupling must run. We note
that evolution of our configuration in the holographic direction, representing
the phyiscs of the strong interactions, can provide additional slowing of the
roll time. Inflation seems to be favoured if the coupling changes by only a
small amount or very gently. We speculate on how such a scenario could be
realized away from N=4 gauge theory, for example, in a walking gauge theory.Comment: 13 pages, 12 figures; v2: Added reference
Scaling laws near the conformal window of many-flavor QCD
We derive universal scaling laws for physical observables such as the
critical temperature, the chiral condensate, and the pion decay constant as a
function of the flavor number near the conformal window of many-flavor QCD in
the chiral limit. We argue on general grounds that the associated critical
exponents are all interrelated and can be determined from the critical exponent
of the running gauge coupling at the Caswell-Banks-Zaks infrared fixed point.
We illustrate our findings with the aid of nonperturbative functional
Renormalization Group (RG) calculations and low-energy QCD models.Comment: 18 pages, 4 figures, references added and discussion expanded
(matches JHEP version
Distinguishing among Technicolor/Warped Scenarios in Dileptons
Models of dynamical electroweak symmetry breaking usually include new spin-1
resonances, whose couplings and masses have to satisfy electroweak precision
tests. We propose to use dilepton searches to probe the underlying structure
responsible for satisfying these. Using the invariant mass spectrum and charge
asymmetry, we can determine the number, parity, and isospin of these
resonances. We pick three models of strong/warped symmetry breaking, and show
that each model produces specific features that reflect this underlying
structure of electroweak symmetry breaking and cancellations.Comment: Added missing referenc
Vectorlike Confinement at the LHC
We argue for the plausibility of a broad class of vectorlike confining gauge
theories at the TeV scale which interact with the Standard Model predominantly
via gauge interactions. These theories have a rich phenomenology at the LHC if
confinement occurs at the TeV scale, while ensuring negligible impact on
precision electroweak and flavor observables. Spin-1 bound states can be
resonantly produced via their mixing with Standard Model gauge bosons. The
resonances promptly decay to pseudo-Goldstone bosons, some of which promptly
decay to a pair of Standard Model gauge bosons, while others are charged and
stable on collider time scales. The diverse set of final states with little
background include multiple photons and leptons, missing energy, massive stable
charged particles and the possibility of highly displaced vertices in dilepton,
leptoquark or diquark decays. Among others, a novel experimental signature of
resonance reconstruction out of massive stable charged particles is
highlighted. Some of the long-lived states also constitute Dark Matter
candidates.Comment: 33 pages, 6 figures. v4: expanded discussion of Z_2 symmetry for
stability, one reference adde
Linear confinement without dilaton in bottom-up holography for walking technicolour
In PRD78(2008)055005 [arXiv:0805.1503 [hep-ph]] and PRD79(2009)075004
[arXiv:0809.1324 [hep-ph]], we constructed a holographic description of walking
technicolour theories using both a hard- and a soft-wall model. Here, we show
that the dilaton field becomes phenomenologically irrelevant for the spectrum
of spin-one resonances once a term is included in the Lagrangian that mixes the
Goldstone bosons and the longitudinal components of the axial vector mesons. We
show how this mixing affects our previous results and we make predictions about
how this description of technicolour can be tested.Comment: 7 pages, no figure
Bounds on 4D Conformal and Superconformal Field Theories
We derive general bounds on operator dimensions, central charges, and OPE
coefficients in 4D conformal and N=1 superconformal field theories. In any CFT
containing a scalar primary phi of dimension d we show that crossing symmetry
of implies a completely general lower bound on the central
charge c >= f_c(d). Similarly, in CFTs containing a complex scalar charged
under global symmetries, we bound a combination of symmetry current two-point
function coefficients tau^{IJ} and flavor charges. We extend these bounds to
N=1 superconformal theories by deriving the superconformal block expansions for
four-point functions of a chiral superfield Phi and its conjugate. In this case
we derive bounds on the OPE coefficients of scalar operators appearing in the
Phi x Phi* OPE, and show that there is an upper bound on the dimension of Phi*
Phi when dim(Phi) is close to 1. We also present even more stringent bounds on
c and tau^{IJ}. In supersymmetric gauge theories believed to flow to
superconformal fixed points one can use anomaly matching to explicitly check
whether these bounds are satisfied.Comment: 47 pages, 9 figures; V2: small corrections and clarification
Determining the conformal window: SU(2) gauge theory with N_f = 4, 6 and 10 fermion flavours
We study the evolution of the coupling in SU(2) gauge field theory with
, 6 and 10 fundamental fermion flavours on the lattice. These values are
chosen close to the expected edges of the conformal window, where the theory
possesses an infrared fixed point. We use improved Wilson-clover action, and
measure the coupling in the Schr\"odinger functional scheme. At four flavours
we observe that the couping grows towards the infrared, implying QCD-like
behaviour, whereas at ten flavours the results are compatible with a Banks-Zaks
type infrared fixed point. The six flavour case remains inconclusive: the
evolution of the coupling is seen to become slower at the infrared, but the
accuracy of the results falls short from fully resolving the fate of the
coupling. We also measure the mass anomalous dimension for the case.Comment: 22 pages, 12 figures. Proof readin
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