2,420 research outputs found
A Multiproject Chip Approach to the Teaching of Analog MOS LSI and VLSI
Multiproject chip implementation has been used in teaching analog MOS circuit design. After having worked with computer simulation and layout aids in homework problems, students designed novel circuits including several high
performance op amps, an A/D converter, a switched capacitor filter, a 1 K dynamic RAM, and a variety of less conventional MOS circuits such as a VII converter, an AC/DC converter, an AM radio receiver, a digitally-controlled
analog signal processor, and on-chip circuitry for measuring transistor capacitances. These circuits were laid out as part of an NMOS multiproject chip. Several of the designs exhibit a considerable degree of innovation;
fabrication pending, computer simulation shows that some may be pushing the state of the art. Several designs are of interest to digital designers; in fact, the course has provided knowledge and technique needed for detailed
digital circuit design at the gate level
One-loop Higgs mass finiteness in supersymmetric Kaluza-Klein theories
We analyze the one-loop ultraviolet sensitivity of the Higgs mass in a
five-dimensional supersymmetric theory compactified on the orbifold S^1/Z_2,
with superpotential localized on a fixed-point brane. Four-dimensional
supersymmetry is broken by Scherk-Schwarz boundary conditions. Kaluza-Klein
interactions are regularized by means of a brane Gaussian distribution along
the extra dimension with length l_s\simeq\Lambda^{-1}_s, where \Lambda_s is the
cutoff of the five-dimensional theory. The coupling of the n-mode, with mass
M^{(n)}, acquires the n-dependent factor exp{-(M^{(n)}/\Lambda_s)^2/2}, which
makes it to decouple for M^{(n)}\gg \Lambda_s. The sensitivity of the Higgs
mass on \Lambda_s is strongly suppressed and quadratic divergences cancel by
supersymmetry. The one-loop correction to the Higgs mass is finite and equals,
for large values of \Lambda_s, the value obtained by the so-called
KK-regularization.Comment: 8 pages, 1 figure. The discussion on the distribution giving rise to
couplings suppressed by exp(-M/Lambda) is revised and the result is finite
and equals that of the Gaussian cas
Non-perturbative Supersymmetry Breaking and Finite Temperature Instabilities in N=4 Superstrings
We obtain the non-perturbative effective potential for the dual
five-dimensional N=4 strings in the context of finite-temperature regarded as a
breaking of supersymmetry into four space-time dimensions. Using the properties
of gauged N=4 supergravity we derive the universal thermal effective potential
describing all possible high-temperature instabilities of the known N=4
superstrings. These strings undergo a high-temperature transition to a new
phase in which five-branes condense. This phase is described in detail, using
both the effective supergravity and non-critical string theory in six
dimensions. In the new phase, supersymmetry is perturbatively restored but
broken at the non-perturbative level.Comment: 21 pages. Proceedings of the Corfu Summer Institute on Elementary
Particle Physics, Corfu, Greece, September 199
Anomalous U(1)s masses in non-supersymmetric open string vacua
Anomalous U(1)s are omnipresent in realizations of the Standard Model using
D-branes. Such models are typically non-supersymmetric, and the anomalous U(1)
masses are potentially relevant for experiment. In this paper, the string
calculation of anomalous U(1) masses (hep-th/0204153) is extended to
non-supersymmetric orientifolds.Comment: 12 pages, Latex2e. (v2) final version to be published in Phys. Lett.
A Class of Non-Supersymmetric Open String Vacua
We analyze non-supersymmetric four dimensional open string models of type IIB
string theory compactified on with Scherk-Schwarz deformation
acting on an of the torus. We find that there are always two
solutions to the tadpole conditions that are shown to be connected via Wilson
lines in an non-trivial way. These models although non-supersymmetric, are free
of R-R and NS-NS tadpoles.Comment: 9 pages, no figues, Latex file (v2
Making Ends Meet: String Unification and Low-Energy Data
A long-standing problem in string phenomenology has been the fact that the
string unification scale disagrees with the GUT scale obtained by extrapolating
low-energy data within the framework of the minimal supersymmetric standard
model (MSSM). In this paper we examine several effects that may modify the
minimal string predictions and thereby bring string-scale unification into
agreement with low-energy data. These include heavy string threshold
corrections, non-standard hypercharge normalizations, light SUSY thresholds,
intermediate gauge structure, and thresholds arising from extra matter beyond
the MSSM. We explicitly evaluate these contributions within a variety of
realistic free-fermionic string models, including the flipped SU(5), SO(6) x
SO(4), and various SU(3) x SU(2) x U(1) models, and find that most of these
sources do not substantially alter the minimal string predictions. Indeed, we
find that the only way to reconcile string unification with low-energy data is
through certain types of extra matter. Remarkably, however, many of the
realistic string models contain precisely this required matter in their
low-energy spectra.Comment: 10 pages, standard LaTeX, 1 figure (Encapsulated PostScript), version
published in Phys. Rev. Lett. 75 (1995) 264
Supersymmetry and Electroweak breaking from extra dimensions at the TeV-scale
We analyze some features of the role that extra dimensions, of radius in
the TeV range, can play in the soft breaking of supersymmetry and the
spontaneous breaking of electroweak symmetry. We use a minimal model where the
gauge and Higgs sector of the MSSM are living in the bulk of five dimensions
and the chiral multiplets in a four-dimensional boundary. Supersymmetry is
broken in the bulk by the Scherk-Schwarz mechanism and transmitted to the
boundary by radiative corrections. The particle spectrum is completely
predicted as a function of a unique -charge. The massless sector corresponds
to the pure Standard Model and electroweak symmetry is radiatively broken with
a light Higgs weighing \simlt 110 GeV. The -problem is solved and
Higgsinos, gauginos and heavy Higgses acquire masses . Chiral
sfermions acquire radiative squared-masses . The effective
potential is explicitly computed in the bulk of extra dimensions and some
cosmological consequences can be immediately drawn from it. Gauge coupling
running and unification is studied in the presence of Scherk-Schwarz
supersymmetry breaking. The unification is similar to that in the
supersymmetric theory.Comment: 27 pages, Latex, 7 figures. Minor change
Moduli Dependence of One--Loop Gauge Couplings in (0,2) Compactifications
We derive the moduli dependence of the one--loop gauge couplings for
non--vanishing gauge background fields in a four--dimensional heterotic (0,2)
string compactification. Remarkably, these functions turn out to have a
representation as modular functions on an auxiliary Riemann surface on
appropriate truncations of the full moduli space. In particular, a certain kind
of one--loop functions is given by the free energy of two--dimensional solitons
on this surface.Comment: 12 pages and 1 figur
Non-linear MSSM
Using the formalism of constrained superfields, we derive the most general
effective action of a light goldstino coupled to the minimal supersymmetric
standard model (MSSM) and study its phenomenological consequences. The
goldstino-induced couplings become important when the (hidden sector) scale of
spontaneous supersymmetry breaking, , is relatively low, of the order
of few TeV. In particular, we compute the Higgs potential and show that the
(tree level) mass of the lightest Higgs scalar can be increased to the LEP
bound for TeV to 7 TeV. Moreover, the effective quartic Higgs
coupling is increased due to additional tree-level contributions proportional
to the ratio of visible to hidden sector supersymmetry breaking scales. This
increase can alleviate the amount of fine tuning of the electroweak scale that
exists in the MSSM. Among the new goldstino couplings, beyond those in MSSM,
the most important ones generate an invisible decay of the Higgs boson into a
goldstino and neutralino (if m_h>m_{\chi_1^0}), with a partial decay rate that
can be comparable to the SM channel h^0-> \gamma\gamma. A similar decay of Z
boson is possible if m_Z>m_{\chi_1^0} and brings a lower bound on
that must be of about 700 GeV. Additional decay modes of the Higgs or Z bosons
into a pair of light goldstinos, while possible, are suppressed by an extra 1/f
factor and have no significant impact on the model.Comment: 25 pages, LaTeX, 8 figures; v3: added reference
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