Search

A renormalizable UV model for Axion-Like Particles (ALPs) or hidden photons, that may explain the dark matter usually involves a dark Higgs field which is a singlet under the standard model (SM) gauge group. The dark sector can couple to the SM particles via the portal coupling between the SM-like Higgs and dark Higgs fields. Through this coupling, the dark sector particles can be produced in either the early universe or the collider experiments. Interestingly, not only the SM-like Higgs boson can decay into the light dark bosons, but also a light dark Higgs boson may be produced and decay into the dark bosons in a collider. In this paper, we perform the first collider search for invisible decays by taking both the Higgs bosons into account. We use a multivariate technique to best discriminate the signal from the background. We find that a large parameter region can be {probed} at the International Linear Collider (ILC) operating at the center-of-mass energy of 250 GeV. In particular, even when the SM-like Higgs invisible decay is a few orders of magnitude below the planned sensitivity reaches of the ILC and the high luminosity LHC (HL-LHC), the scenario can be probed by the invisible decay of the dark Higgs boson produced via a similar diagram. Measuring the dark Higgs boson decay into the dark sector will be a smoking gun signal of the light dark sector. A similar search of the dark sector would be expected in, e.g., Cool Copper Collider (C$^3$), Circular Electron Positron Collider (CEPC), Compact Linear Collider (CLIC) and {Future Circular electron-positron Collider (FCC-ee)., Comment: 44 pages, 10 figures

Axion-Like Particles (ALPs) are pseudo Nambu-Goldstone bosons associated with spontaneously broken global $U(1)$ symmetries. Such particles can have lepton-flavor-violating (LFV) couplings to the SM charged leptons. LFV ALPs provide the possibility to address some of the SM long-lasting problems. We investigate the sensitivity of a future muon collider suggested by the Muon Accelerator Program (MAP) to the production of LFV ALPs in the ALP mass range $m_a\leq1$ MeV. ALPs are assumed to be produced through the LFV decay $\tau\ra\ell a$ ($\ell=e,\mu$) of one of the tau leptons produced in the muon-anti muon annihilation. Performing a realistic detector simulation and deploying a multivariate technique, we constrain the LFV couplings $c_{\tau e}$ and $c_{\tau \mu}$ for both the cases of unpolarized and polarized muon beams. Three different chiral structures are considered for the LFV ALP coupling and the muon collider is assumed to operate at the center-of-mass energies of 126, 350 and 1500 GeV. We present a procedure to search for LFV ALPs at colliders which takes advantage of tau polarization-induced effects. Polarized tau leptons which produce such effects can be produced when the initial muon beams are polarized. Utilizing the properties of polarized tau decays, the main SM background which overwhelms the ALP production in the case of unpolarized muon beams can be significantly suppressed. We present 95$\%$ CL expected limits on the LFV couplings and show that the present analysis can improve current experimental limits on the ALP LFV couplings by roughly one order of magnitude., Comment: 31 pages, 11 figures

Axion-like particles (ALPs) are pseudo Nambu-Goldstone bosons associated with spontaneously broken global symmetries emerging in many extensions of the Standard Model. Assuming the most general effective Lagrangian up to dimension-5 operators for an ALP interacting with the SM fields, we investigate for the first time the sensitivity of the LHC13 to the ALP production in association with a di-jet. This study is focused on light ALPs which appear as invisible particles at the detector. Performing a realistic detector simulation and deploying a multivariate technique to best discriminate the signal from backgrounds, we set expected upper bounds on the ALP coupling to gluons. A comprehensive set of background processes is considered, and it is shown that this process provides significant sensitivity to the ALP-gluon coupling and the resulting bound is more stringent than those already obtained at the LHC. We also present prospects for the HE-LHC27 and FCC-hh100 and show that these future colliders are able to improve the limits from the LHC by roughly one order of magnitude., Comment: 20 pages, 6 figures

In this study, assuming the type-Y (flipped) two-Higgs-doublet model (2HDM) in the Standard-Model- (SM) like scenario as the theoretical framework, observability of the additional heavy neutral Higgs bosons $H$ and $A$ is investigated through the signal process chain ${e}^{\ensuremath{-}}{e}^{+}\ensuremath{\rightarrow}AH\ensuremath{\rightarrow}b\overline{b}b\overline{b}$ at a linear collider operating at the center-of-mass energy of 1.5 TeV. The assumed signal process is highly motivated by the enhancements in the $A/H\ensuremath{\rightarrow}b\overline{b}$ decays at relatively high $\mathrm{tan}\ensuremath{\beta}$ values. Such enhancements result in the dominance of the mentioned decay modes even for Higgs masses above the threshold of the on-shell top quark pair production. Taking advantage of such a unique feature, several benchmark scenarios are studied. Simulating the detector response based on the SiD detector at the ILC, simulated events are analyzed to reconstruct the $H$ and $A$ Higgs bosons. The top quark pair production and $Z/\ensuremath{\gamma}$ production are the main SM background processes and are well under control. Results indicate that, the $H$ and $A$ Higgs bosons are observable with signals exceeding $5\ensuremath{\sigma}$ with possibility of mass measurement in all the tested scenarios. Specifically, the parameter space region enclosed with the mass ranges ${m}_{H}=150--500\text{ }\mathrm{GeV}$ and ${m}_{A}=230--580\text{ }\mathrm{GeV}$ with the $A/H$ mass splitting of 80 GeV is observable at the integrated luminosity of $500\text{ }\text{ }{\mathrm{fb}}^{\ensuremath{-}1}$.

In this study, we investigate observability of the neutral scalar ($H$) and pseudoscalar ($A$) Higgs bosons in the framework of the Type-I 2HDM at SM-like scenario at a linear collider operating at $\sqrt s=$ 500 and 1000 GeV. The signal process chain $e^- e^+ \rightarrow A H \rightarrow ZHH\rightarrow jj b\bar{b}b\bar{b}$ where $jj$ is a di-jet resulting from the $Z$ boson decay and $b\bar{b}$ is a $b$ quark pair, is assumed and several benchmark scenarios with different mass hypotheses are studied. The assumed signal process is mainly motivated by the possible enhancements the decay modes $A\rightarrow ZH$ and $H\rightarrow b\bar{b}$ may receive in the Type-I. Event generation is performed for the assumed scenarios separately and the beamstrahlung effects are taken into account. The detector response is simulated based on the SiD detector at the ILC and the simulated events are analyzed to obtain candidate mass distributions of the Higgs bosons. According to the results, the top quark pair production process has the most contribution to the total background and is, however, well-controlled. Results indicate that, in all of the considered scenarios, both of the Higgs bosons $H$ and $A$ are observable with signals exceeding $5\sigma$ with possibility of mass measurement. To be specific, at $\sqrt s=500$ GeV, the region of parameter space with $m_H=150$ GeV and $200\leq m_A \leq 250$ GeV is observable at the integrated luminosity of 500 $fb^{-1}$. Also, at $\sqrt s=1000$ GeV, the region with $150\leq m_H \leq 250$ GeV and $200\leq m_A \leq 330$ GeV with a mass splitting of 50-100 GeV between the $H$ and $A$ Higgs bosons is observable at the same integrated luminosity., Comment: 13 pages, 4 figures, 8 tables

We theoretically design and study a structure of graphene/intrinsic amorphous-silicon Schottky junction solar cell (Gr/i-a-Si_SJSC) with top core/shell quantum dots (CSQDs). A physical model incorporated with optoelectrical characteristics is developed to optimize the structure’s electrical performance by modifying the graphene work function, temperature, and CSQD radius. Simulations show that the conversion efficiency of Gr/i-a-Si_SJSC is increased by increasing the graphene work function, raising the core radius and shell thickness of CSQD and decreasing the temperature. The results reveal that with an appropriate choice of design parameter in an optimized structure, short-circuit current density of 16.2 m A / c m 2 , open-circuit voltage of 0.8 V, fill factor of 75.06%, and calculated power conversion efficiency of 9.93% are obtained.

In this study, assuming the type-I 2HDM at SM-like scenario, observability of heavy neutral CP-even and CP-odd Higgs bosons $H$ and $A$ at a linear collider operating at $\sqrt{s}=1$ TeV is investigated through the signal process chain $e^- e^+ \rightarrow A H \rightarrow ZHH$ where the $Z$ boson experiences a leptonic ($e^-e^+$ or $\mu^-\mu^+$) decay and the $H$ Higgs boson is assumed to decay into a di-photon. This signal process is motivated especially by the clean signature which leptonic and photonic events can provide at colliders, and also by the enhancement due to the charged Higgs-mediated contribution to $H$ di-photon decay at large $\tan\beta$ values. Simulation is based on four benchmark points according to which the Higgs mass $m_H$ ($m_A$) varies within the range $150$-$300$ ($200$-$400$) GeV. Energy smearing of jets and photons are performed, and momentum smearing is also applied to leptons. Results indicate that, for all of the assumed benchmark points, the Higgs bosons $H$ and $A$ are observable with measurable masses, and with signals exceeding $5\sigma$ at integrated luminosities $111$ and $201\,fb^{-1}$ respectively. Such luminosities are easily accessible to future linear colliders., Comment: 31 pages, 29 figures, 11 tables

We investigate theoretically the effect of two-dimensional photonic crystal (PC) defect waveguide parameters embedded into vertical-cavity surface-emitting lasers (VCSELs) on static operation of PC-VCSEL, including spatial hole burning (SHB) and temperature in the active regions. In structures with larger pitch of PC holes, SHB occurs dramatically and temperature increases in the active region. In large-hole diameter to pitch ratio, SHB has little effect and temperature is decreased in the active regions. We also show that with higher input current, temperature rises and SHB occurs.

In this paper, we present characteristics of one-dimensional ZnO-based random lasers by using a time-domain traveling-wave model. The results reveal that by increasing pump intensity, at first the number of laser modes is increased, and then it gets saturated. Also, output intensity shows that by increasing pump pulse width at a fixed pump intensity, laser modes are made to appear; at first, by raising pump pulse width, more laser modes appear, and then the intensity of the output spectrum is increased. Additionally, we show that by nonuniform pumping, a single-mode laser can be achieved. Through investigation of the nanopowder's average size, we show that the output spectrum has its highest intensity and the sharpest laser modes for average nanopowder sizes less than 100 nm. Moreover, the results show that by decreasing pump area, lasing threshold is inclined.

In this paper, the question of observability of a heavy charged Higgs in the mass range 400 GeV < mH < 1000 GeV, is addressed. The production process is set to pp -> H+ -> tb at 14 TeV LHC. The analysis benefits from top tagging technique which is based on finding a fat jet as a result of the boosted top quark decay in signal events. A detailed hadron level analysis is performed and selection efficiencies are presented with different charged Higgs mass hypotheses. Finally running toy experiments and using pseudo-data, a fit over signal plus background distributions is performed to assess possibility of reconstructing the charged Higgs peak and its invariant mass measurement. It is shown that the charged Higgs mass can well be reconstructed in the mass range 500 GeV to 1 TeV, with a signal significance which depends on tanbeta. Eventually 5sigma discovery and 95% C.L. exclusion contours are also provided., 20 pages, 19 figures and tables, accepted version to appear in JHEP