5,014 research outputs found
Implications of the Little Higgs Dark Matter and T-odd Fermions
We study the phenomenology of dark matter in the Littlest Higgs model with
T-parity after the discovery of Higgs boson. We analyze the relic abundance of
dark matter, focusing on the effects of coannihilaitons with T-odd fermions.
After determining the parameter space that predicts the correct relic abundance
measured by WMAP and Planck collaborations, we evaluate the elastic scattering
cross section between dark matter and nucleon. In comparison with experimental
results, we find that the lower mass of dark matter is constrained mildly by
LUX 2013 while the future XENON experiment has potential to explore most of the
parameter space for both T-odd lepton and T-odd quark coannihilation scenarios.
We also study the collider signatures of T-odd fermion pair production at the
LHC. Even though the production cross sections are large, it turns out very
challenging to search for these T-odd fermions directly at the collider because
the visible charged leptons or jets are very soft. Furthermore, we show that,
with an extra hard jet radiated out from the initial state, the T-odd quark
pair production can contribute significantly to mono-jet plus missing energy
search at the LHC
Ward Identities and High-energy Scattering Amplitudes in String Theory
High-energy limit of stringy Ward identities derived from the decoupling of
two types of zero-norm states in the old covariant first quantized (OCFQ)
spectrum of open bosonic string are used to check the consistency of saddle
point calculations of high energy scattering amplitudes of Gross and Mende and
Gross and Manes. Some inconsistencies of their saddle point calculations are
found even for the string-tree scattering amplitudes of the excited string
states. We discuss and calculate the missing terms of the calculation by those
authors to recover the stringy Ward identities. In addition, based on the
tree-level stringy Ward identities, we give the proof of a general formula,
which was proposed previously, of all high energy four-point string-tree
amplitudes of arbitrary particles in the string spectrum. In this formula all
such scattering amplitudes are expressed in terms of those of tachyons as
conjectured by Gross. The formula is extremely simple which manifestly
demonstrates the universal high energy behavior of the interactions among all
string states.Comment: 1 typo, to appear in Nucl. Phys.
Spectral Weights, d-wave Pairing Amplitudes, and Particle-hole Tunneling Asymmetry of a Strongly Correlated Superconductor
The spectral weights (SW's) for adding and removing an electron of the
Gutzwiller projected d-wave superconducting (SC) state of the t-J-type models
are studied numerically on finite lattices. Restrict to the uniform system but
treat exactly the strong correlation between electrons, we show that the
product of weights is equal to the pairing amplitude squared, same as in the
weakly coupled case. In addition, we derive a rigorous relation of SW with
doping in the electron doped system and obtain particle-hole asymmetry of the
conductance-proportional quantity within the SC gap energy and, also, the
anti-correlation between gap sizes and peak heights observed in tunneling
spectroscopy on high Tc cuprates.Comment: 4 Revtex pages and 4 .eps figures. Published versio
Physical Layer Security in Wireless Ad Hoc Networks Under A Hybrid Full-/Half-Duplex Receiver Deployment Strategy
This paper studies physical layer security in a wireless ad hoc network with
numerous legitimate transmitter-receiver pairs and eavesdroppers. A hybrid
full-/half-duplex receiver deployment strategy is proposed to secure legitimate
transmissions, by letting a fraction of legitimate receivers work in the
full-duplex (FD) mode sending jamming signals to confuse eavesdroppers upon
their information receptions, and letting the other receivers work in the
half-duplex mode just receiving their desired signals. The objective of this
paper is to choose properly the fraction of FD receivers for achieving the
optimal network security performance. Both accurate expressions and tractable
approximations for the connection outage probability and the secrecy outage
probability of an arbitrary legitimate link are derived, based on which the
area secure link number, network-wide secrecy throughput and network-wide
secrecy energy efficiency are optimized respectively. Various insights into the
optimal fraction are further developed and its closed-form expressions are also
derived under perfect self-interference cancellation or in a dense network. It
is concluded that the fraction of FD receivers triggers a non-trivial trade-off
between reliability and secrecy, and the proposed strategy can significantly
enhance the network security performance.Comment: Journal paper, double-column 12 pages, 9 figures, accepted by IEEE
Transactions on Wireless Communications, 201
Zero-norm states and stringy symmetries
We identify spacetime symmetry charges of 26D open bosonic string theory from
an infinite number of zero-norm states (ZNS) with arbitrary high spin in the
old covariant first quantized string spectrum. We give various evidences to
support this identification. These include massive sigma-model calculation,
Witten string field theory calculation, 2D string theory calculation and, most
importantly, three methods of high-energy stringy scattering amplitude
calculations. The last calculations explicitly prove Gross's conjectures in
1988 on high energy symmetry of string theory.Comment: 6 pages. Talks presented by Jen-Chi Lee at XXVIII Spanish Relativity
Meeting (ERE2005),"A Century of Relativity Physics",Oviedo,Spain,6-10 Sep
2005 and "4th Meeting on constrained Dynamics and Quantum Gravity",Cala
Gonone,Sardinia,Italy,12-16 Sep 2005. To appear in the Journal of Physics:
Conference Serie
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