arXiv subjects

Ran Ding

Publications and source records attributed to Ran Ding.

68 records · Page 4Linked to original sources

arXiv2015

Towards the Natural Gauge Mediation

The sweet spot supersymmetry (SUSY) solves the mu problem in the Minimal Supersymmetric Standard Model (MSSM) with gauge mediated SUSY breaking (GMSB) via the generalized Giudice-Masiero (GM) mechanism where only the mu-term and soft Higgs masses are generated at the unification scale of the Grand Unified Theory (GUT) due to the approximate PQ symmetry. Because all the other SUSY breaking soft terms are generated via the GMSB below the GUT scale, there exists SUSY electroweak (EW) fine-tuning problem to explain the 125 GeV Higgs boson mass due to small trilinear soft term. Thus, to explain the Higgs boson mass, we propose the GMSB with both the generalized GM mechanism and Higgs-messenger interactions. The renormalization group equations are runnings from the GUT scale down to EW scale. So the EW symmetry breaking can be realized easier. We can keep the gauge coupling unification and solution to the flavor problem in the GMSB, as well as solve the μ/B_μ-problem. Moreover, there are only five free parameters in our model. So we can determine the characteristic low energy spectra and explore its distinct phenomenology. The low-scale fine-tuning measure can be as low as 20 with the light stop mass below 1 TeV and gluino mass below 2 TeV. The gravitino dark matter can come from a thermal production with the correct relic density and be consistent with the thermal leptogenesis. Because gluino and stop can be relatively light in our model, how to search for such GMSB at the upcoming run II of the LHC experiment could be very interesting.

hep-ph↗

arXiv2015

LHC Phenomenology of Type II Seesaw: Nondegenerate Case

In this paper, we thoroughly investigate the LHC phenomenology of the type II seesaw mechanism for neutrino masses in the nondegenerate case where the triplet scalars of various charge ($H^{\pm\pm}, H^\pm, H^0, A^0$) have different masses. Compared with the degenerate case, the cascade decays of scalars lead to many new, interesting signal channels. In the positive scenario where $M_{H^{\pm\pm}} M_{H^\pm}>M_{H^0/A^0}$, the detection of $H^{\pm\pm}$ is more challenging, when the cascade decay $H^{\pm\pm}\to H^{\pm}W^{\pm*}$ is dominant. The most important channel is the associated $H^{\pm}H^0/A^0$ production in the final state $\ell^\pm\cancel{E}_Tb\bar{b}b\bar{b}$, which requires a luminosity of 109/fb for a $5σ$ discovery, while the final state $\ell^\pm\cancel{E}_Tb\bar{b}τ^+τ^-$ is less promising. Moreover, the associated $H^0A^0$ production can give same signals as the standard model Higgs pair production. With a much larger cross section, the $H^0A^0$ production in the final state $b\bar{b}τ^+τ^-$ could reach $3σ$ significance at 14 TeV LHC with a luminosity of 300/fb. In summary, with an integrated luminosity of order 500/fb, the triplet scalars can be fully reconstructed at 14 TeV LHC in the negative scenario.

hep-ph↗

arXiv2014

Experimental demonstration of broadband Lorentz non-reciprocity in an integrable photonic architecture based on Mach-Zehnder modulators

We demonstrate the first active optical isolator and circulator implemented in a linear and reciprocal material platform using commercial Mach-Zehnder modulators. In a proof-of-principle experiment based on single-mode polarization-maintaining fibers, we achieve more than 12.5 dB isolation over an unprecedented 8.7 THz bandwidth at telecommunication wavelengths, with only 9.1 dB total insertion loss. Our architecture provides a practical answer to the challenge of non-reciprocal light routing in photonic integrated circuits.

physics.optics↗

arXiv2014

Phenomenology in Minimal Cascade Seesaw for Neutrino Mass

We make a comprehensive analysis on the phenomenology in the minimal version of cascade seesaw for tiny neutrino mass. The seesaw induces at tree level a neutrino mass operator at dimension nine, by introducing a quadruple scalar $Φ$ of hypercharge unity and a quintuple fermion $Σ$ of hypercharge zero. We work in a framework that handles the complicated Yukawa couplings in a nice way without losing generality. All mixing matrices are essentially expressed in terms of the vacuum expectation value of the quadruple scalar v_Φ, a free complex parameter, and known neutrino parameters. We show that the low-energy lepton flavor violating transitions of the charged leptons set strong constraints on the free parameters. The constraints have a significant impact on collider physics, and are incorporated in our signal analysis at the LHC. We investigate the signatures of new particles by surveying all potentially important channels. We find that the 4j2\ell^\pm signal is most important for the detection of the scalars and the 2\ell^{\pm}2\ell^{\mp}2j, 3\ell^{\pm}\ell^{\mp}2j and 3\ell^{\pm}2\ell^{\mp}+\cancel{E_T} signals are quite promising for the fermions.

hep-ph↗

arXiv2014

Broadband on-chip optical non-reciprocity using phase modulators

Breaking the reciprocity of light propagation in photonic integrated circuits (PIC) - especially in the CMOS-compatible silicon-on-insulator platform - is a topic of intense research. However, a practical solution for monolithic integrating of optical isolators and circulators remains elusive. Here, we propose and analyze a new non-reciprocal photonic architecture operating with standard single-mode waveguides (or optical fibers). Our design exploits cascaded phase modulators separated by optical delay lines and suitably driven by time shifted waveforms. Because it is based on fully balanced interferometers and does not involve resonant structures, our scheme is also intrinsically broadband. Using realistic parameters we calculate an extinction ratio superior to 20 dB and insertion loss below -3 dB.

physics.optics↗

arXiv2014

Neutralino Dark Matter in Gauge Mediation After Run I of LHC and LUX

Neutralino can be the dark matter candidate in the gauge-mediated supersymmetry breaking models if the conformal sequestered mechanism is assumed in the hidden sector. In this paper, we study this mechanism by using the current experimental results after the run I of LHC and LUX. By adding new Yukawa couplings between the messenger fields and Higgs fields, we find that this mechanism can predict a neutralino dark matter with correct relic density and a Higgs boson with mass around 125 GeV. All our survived points have some common features. Firstly, the Higgs sector falls into the decoupling limit. So the properties of the light Higgs boson are similar to the predictions of the Standard Model one. Secondly, the correct EWSB hints a relatively small $μ$-term, which makes the lightest neutralino lighter than the lightest stau. So a bino-higgsino dark matter with correct relic density can be achieved. And the relatively small $μ$-term results in a small fine-tuning. Finally, this bino-higgsino dark matter can pass all current bounds, including both spin-independent and spin-dependent direct searches. The spin-independent cross section of our points can be examined by further experiments.

hep-ph↗

arXiv2014

Focus Point Supersymmetry in Extended Gauge Mediation

We propose a small extenion of the minimal gauge mediation through the combination of extended gauge mediation and conformal sequestering. We show that the focus point supersymmetry can be realized naturally, and the fine-tuning is signifcantly reduced compared to the minimal gauge mediation and extended gauge mediation without focus point. The Higgs boson mass is around 125 GeV, the gauginos remain light, and the gluino is likely to be detected at the next run of the LHC. However, the multi-TeV squarks is out of the reach of the LHC. The numerical calculation for finetuning shows that this model remains natural.

hep-ph↗

arXiv2013

Two Component Higgs-Portal Dark Matter

In this paper, we construct two component dark matter model and revisit fine-tuning, unitarity and vacuum stability problem in this framework. Through Higgs-portal interactions, the additional scalar and vector singlet field can interact with the SM particles. The parameter space of the model are severely constraint by observed relic density and direct detection experiments. We found that, unlike the SM, the fine-tuning problem is relaxed due to the modified Veltman condition. The vacuum stability problem is addressed, the additional contributions from two DM singlets to the $β$ function make the Higgs quartic coupling $λ(μ)$ be positive up to Planck scale in some parameter space.

hep-ph↗

arXiv2013

Singlet-Assisted Supersymmetry Breaking For $Sp(2N)$ Theories

We investigate local supersymmetry-breaking vacua in s-confining theories with gauge group $Sp(2N)$. By adapting the general recipe developed by Shadmi and Shirman, we construct a realistic model based on dynamics of SQCD coupled with singlets which allows a spontaneously broken supersymmetry. Since the chiral superfields in model have R-charges R=0 and R=2 only, the tedious computations of Coleman-Weinberg potential can be greatly alleviated from the lesson of David Shih. We observe that the pseudomoduli fields are stabilized at the origin of moduli space at one-loop order with calculability being preserved.

hep-ph↗

arXiv2013

Supersymmetry Breaking in Anti-de Sitter spacetime

We study the questions of how supersymmetry is spontaneously broken in Anti de-Sitter spacetime. We verify that the would-be R-symmetry in $AdS_4$ plays a central role for the existence of meta-stable supersymmetry breaking. To illustrate, some well-known models such as Poloyni models and O'Raifeartaigh models are investigated in detail. Our calculations are reliable in flat spacetime limit and confirm us that meta-stable vacua are generic even though quantum corrections are taken into account.

hep-ph↗

arXiv2013

Comprehensive Constraints on a Spin-3/2 Singlet Particle as a Dark Matter Candidate

We consider the proposal that dark matter (DM) is composed of a spin-3/2 particle that is a singlet of the standard model (SM). Its leading effective interactions with ordinary matter involve a pair of their fields and a pair of SM fermions, in the form of products of chiral currents. We make a comprehensive analysis on possible phenomenological effects of the interactions in various experiments and observations. These include collider searches for monojet plus missing transverse energy events, direct detections of DM scattering off nuclei, possible impacts on the gamma rays and antiproton-to-proton flux ratio in cosmic rays, and the observed relic density. The current data already set strong constraints on the effective interactions in a complementary manner. The constraint from collider searches is most effective at a relatively low mass of DM, and the antiproton-to-proton flux ratio offers the best bound for a heavy DM, while the spin-independent direct detection is the best in between. For DM mass of order 10 GeV to 1 TeV, the effective interaction scale is constrained to be typically above a few tens TeV.

hep-ph↗

arXiv2012

Spin 3/2 Particle as a Dark Matter Candidate: an Effective Field Theory Approach

There is no indication so far on the spin of dark matter particles. We consider the possibility in this work that a spin-3/2 particle acts as dark matter. Employing the approach of effective field theory, we list all possible 4-fermion effective interactions between a pair of such fields and a pair of ordinary fermion fields. We investigate the implications of the proposal on the relic density, the antiproton to proton flux ratio in cosmic rays, and the elastic scattering off nuclei in direct detection. While the relic density and flux ratio are sensitive to all interactions albeit at different levels, the direct detection is only sensitive to a few of them. Using the observed data and experimental bounds, we set constraints on the relation of couplings and dark particle mass. In particular, we find that some mass ranges can already be excluded by jointly applying the observed relic density on the one side and the measured antiproton to proton flux ratio or the upper bounds from direct detection on the other.

hep-ph↗

arXiv2012

A 25 Gb/s Silicon Photonics Platform

Silicon has attracted attention as an inexpensive and scalable material system for photonic-electronic, system-on-chip development. For this, a platform with both photodetectors and modulators working at high speeds, with excellent cross-wafer uniformity, is needed. We demonstrate an optical-lithography, wafer-scale photonics platform with 25 Gb/s operation. We also demonstrate modulation with an ultra-low drive voltage of 1 Vpp at 25 Gb/s. We demonstrate attractive cross-wafer uniformity, and provide detailed information about the device geometry. Our platform is available to the community as part of a photonics shuttle service.

physics.optics↗

arXiv2010

Sub-Volt Silicon-Organic Electrooptic Modulator

Lowering the operating voltage of electrooptic modulators is desirable for a variety of applications, most notably in analog photonics , and digital data communications . In particular for digital systems such as CPUs, it is desirable to develop modulators that are both temperature-insensitive and compatible with typically sub-2V CMOS electronics ; however, drive voltages in silicon-based MZIs currently exceed 6.5V . Here we show an MZI modulator based on an electrooptic polymer-clad silicon slot waveguide, with a halfwave voltage of only 0.69V, and a bandwidth of 500 MHz. We also show that there are also paths to significantly improve both the bandwidth and drive voltage . Our silicon-organic modulator has an intrinsic power consumption less than 0.66 pJ/bit, nearly an order of magnitude improvement over the previous lowest energy silicon MZI .

physics.optics↗