79 research outputs found
Is "just-so" Higgs splitting needed for t-b-\tau Yukawa unified SUSY GUTs?
Recent renormalization group calculations of the sparticle mass spectrum in
the Minimal Supersymmetric Standard Model (MSSM) show that t-b-\tau Yukawa
coupling unification at M_{\rm GUT} is possible when the mass spectra follow
the pattern of a radiatively induced inverted scalar mass hierarchy. The
calculation is entirely consistent with expectations from SO(10) SUSY GUT
theories, with one exception: it seems to require MSSM Higgs soft term mass
splitting at M_{\rm GUT}, dubbed "just-so Higgs splitting" (HS) in the
literature, which apparently violates the SO(10) gauge symmetry. Here, we
investigate three alternative effects: {\it i}). SO(10) D-term splitting, {\it
ii}). inclusion of right hand neutrino in the RG calculation, and {\it iii}).
first/third generation scalar mass splitting. By combining all three effects
(the DR3 model), we find t-b-\tau Yukawa unification at M_{\rm GUT} can be
achieved at the 2.5% level. In the DR3 case, we expect lighter (and possibly
detectable) third generation and heavy Higgs scalars than in the model with HS.
In addition, the light bottom squark in DR3 should be dominantly a right state,
while in the HS model, it is dominantly a left state.Comment: 21 pages with 11 .eps figures; revised version added two reference
Quantum Hall effect anomaly and collective modes in the magnetic-field-induced spin-density-wave phases of quasi-one-dimensional conductors
We study the collective modes in the magnetic-field-induced spin-density-wave
(FISDW) phases experimentally observed in organic conductors of the Bechgaard
salts family. In phases that exhibit a sign reversal of the quantum Hall effect
(Ribault anomaly), the coexistence of two spin-density waves gives rise to
additional collective modes besides the Goldstone modes due to spontaneous
translation and rotation symmetry breaking. These modes strongly affect the
charge and spin response functions. We discuss some experimental consequences
for the Bechgaard salts.Comment: Final version (LaTex, 8 pages, no figure), to be published in
Europhys. Let
Critical Exponents of the Three Dimensional Random Field Ising Model
The phase transition of the three--dimensional random field Ising model with
a discrete () field distribution is investigated by extensive Monte
Carlo simulations. Values of the critical exponents for the correlation length,
specific heat, susceptibility, disconnected susceptibility and magnetization
are determined simultaneously via finite size scaling. While the exponents for
the magnetization and disconnected susceptibility are consistent with a first
order transition, the specific heat appears to saturate indicating no latent
heat. Sample to sample fluctuations of the susceptibilty are consistent with
the droplet picture for the transition.Comment: Revtex, 10 pages + 4 figures included as Latex files and 1 in
Postscrip
Open String Wavefunctions in Warped Compactifications
We analyze the wavefunctions for open strings in warped compactifications,
and compute the warped Kahler potential for the light modes of a probe D-brane.
This analysis not only applies to the dynamics of D-branes in warped
backgrounds, but also allows to deduce warping corrections to the closed string
Kahler metrics via their couplings to open strings. We consider in particular
the spectrum of D7-branes in warped Calabi-Yau orientifolds, which provide a
string theory realizations of the Randall-Sundrum scenario. We find that
certain background fluxes, necessary in the presence of warping, couple to the
fermionic wavefunctions and qualitatively change their behavior. This modified
dependence of the wavefunctions are needed for consistency with supersymmetry,
though it is present in non-supersymmetric vacua as well. We discuss the
deviations of our setup from the RS scenario and, as an application of our
results, compute the warping corrections to Yukawa couplings in a simple model.
Our analysis is performed both with and without the presence of D-brane
world-volume flux, as well as for the case of backgrounds with varying dilaton.Comment: 52 pages, refs. added, minor correction
Indirect Searches for -like Resonances at the LHC
We explore the possibility of indirectly observing the effects of -like
particles with electroweak strength couplings in the Drell-Yan channel at the
LHC with masses above the resonance direct search reach. We find that, mostly
due to statistical limitations, this is very unlikely in almost all classes of
models independently of the spin of the resonance. Not unexpectedly, the one
possible exception to this general result is the case of degenerate
Kaluza-Klein (KK) excitations of the photon and that occur in some
extra-dimensional models. In this special case, the strong destructive
interference with the Standard Model (SM) exchanges below the resonance mass
leads to a well-known significant suppression of the cross section and thus
increased sensitivity to this particular new physics scenario.Comment: 18 pages, 6 figs, discussion and reference adde
The Higgs intense--coupling regime in constrained SUSY models and its astrophysical implications
We analyze the Higgs intense--coupling regime, in which all Higgs particles
of the Minimal Supersymmetric Standard Model are light with masses of the same
order and the value of \tb the ratio of vacuum expectation values of the two
Higgs fields is large, in the framework of Supergravity scenarios with
non--universal soft Supersymmetry breaking scalar masses in the Higgs sector.
In particular, we calculate the relic density abundance of the lightest
neutralino candidate for cold dark matter and the rates in direct and indirect
detection at present and future experiments. We first show that while in the
mSUGRA model this regime is disfavored by present data, there are regions in
the parameter space of models with non--universal Higgs masses where it can
occur. We then show that because of the large value of and the
relatively low values of the neutral Higgs boson masses, the cross section for
neutralino--nucleon scattering is strongly enhanced in this regime and would
allow for the observation of a signal in direct detection experiments such as
CDMS--Soudan. The expected sensitivity of gamma--ray detectors like GLAST might
be also sufficient to observe the annihilation of neutralinos in such a regime.Comment: 19 pages, 5 figure
Neutralino, axion and axino cold dark matter in minimal, hypercharged and gaugino AMSB
Supersymmetric models based on anomaly-mediated SUSY breaking (AMSB)
generally give rise to a neutral wino as a WIMP cold dark matter (CDM)
candidate, whose thermal abundance is well below measured values. Here, we
investigate four scenarios to reconcile AMSB dark matter with the measured
abundance: 1. non-thermal wino production due to decays of scalar fields ({\it
e.g} moduli), 2. non-thermal wino production due to decays of gravitinos, 3.
non-thermal wino production due to heavy axino decays, and 4. the case of an
axino LSP, where the bulk of CDM is made up of axions and thermally produced
axinos. In cases 1 and 2, we expect wino CDM to constitute the entire measured
DM abundance, and we investigate wino-like WIMP direct and indirect detection
rates. Wino direct detection rates can be large, and more importantly, are
bounded from below, so that ton-scale noble liquid detectors should access all
of parameter space for m_{\tz_1}\alt 500 GeV. Indirect wino detection rates via
neutrino telescopes and space-based cosmic ray detectors can also be large. In
case 3, the DM would consist of an axion plus wino admixture, whose exact
proportions are very model dependent. In this case, it is possible that both an
axion and a wino-like WIMP could be detected experimentally. In case 4., we
calculate the re-heat temperature of the universe after inflation. In this
case, no direct or indirect WIMP signals should be seen, although direct
detection of relic axions may be possible. For each DM scenario, we show
results for the minimal AMSB model, as well as for the hypercharged and gaugino
AMSB models.Comment: 29 pages including 13 figure
Open-closed duality and Double Scaling
Nonperturbative terms in the free energy of Chern-Simons gauge theory play a
key role in its duality to the closed topological string. We show that these
terms are reproduced by performing a double scaling limit near the point where
the perturbation expansion diverges. This leads to a derivation of closed
string theory from this large-N gauge theory along the lines of noncritical
string theories. We comment on the possible relevance of this observation to
the derivation of superpotentials of asymptotically free gauge theories and its
relation to infrared renormalons.Comment: 10 pages, LaTe
Lorentz Violation in Extra Dimensions
In theories with extra dimensions it is well known that the Lorentz
invariance of the -dimensional spacetime is lost due to the compactified
nature of the dimensions leaving invariance only in 4d. In such theories
other sources of Lorentz violation may exist associated with the physics that
initiated the compactification process at high scales. Here we consider the
possibility of capturing some of this physics by analyzing the higher
dimensional analog of the model of Colladay and Kostelecky. In that scenario a
complete set of Lorentz violating operators arising from spontaneous Lorentz
violation, that are not obviously Planck-scale suppressed, are added to the
Standard Model action. Here we consider the influence of the analogous set of
operators which break Lorentz invariance in 5d within the Universal Extra
Dimensions picture. We show that such operators can greatly alter the
anticipated Kaluza-Klein(KK) spectra, induce electroweak symmetry breaking at a
scale related to the inverse compactification radius, yield sources of parity
violation in, e.g., 4d QED/QCD and result in significant violations of
KK-parity conservation produced by fermion Yukawa couplings, thus destabilizing
the lightest KK particle. LV in 6d is briefly discussed.Comment: 26 pages, 2 figures; additional references and discussio
Pseudosmooth Tribrid Inflation
We explore a new class of supersymmetric models of inflation where the
inflaton is realised as a combination of a Higgs field and (gauge non-singlet)
matter fields, using a "tribrid" structure of the superpotential. Inflation is
associated with a phase transition around GUT scale energies. The inflationary
trajectory already preselects the later vacuum after inflation, which has the
advantage of automatically avoiding the production of dangerous topological
defects at the end of inflation. While at first sight the models look similar
to smooth inflation, they feature a waterfall and are therefore only
pseudosmooth. The new class of models offers novel possibilities for realising
inflation in close contact with particle physics, for instance with
supersymmetric GUTs or with supersymmetric flavour models based on family
symmetries.Comment: 16 pages, 5 figures. v2 matches publication in JCA
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