arXiv subjects

H. Murayama

Publications and source records attributed to H. Murayama.

At least 37 records · Page 2Linked to original sources

arXiv2018

The Hyper Suprime-Cam SSP Survey: Overview and Survey Design

Hyper Suprime-Cam (HSC) is a wide-field imaging camera on the prime focus of the 8.2m Subaru telescope on the summit of Maunakea in Hawaii. A team of scientists from Japan, Taiwan and Princeton University is using HSC to carry out a 300-night multi-band imaging survey of the high-latitude sky. The survey includes three layers: the Wide layer will cover 1400 deg$^2$ in five broad bands ($grizy$), with a $5\,σ$ point-source depth of $r \approx 26$. The Deep layer covers a total of 26~deg$^2$ in four fields, going roughly a magnitude fainter, while the UltraDeep layer goes almost a magnitude fainter still in two pointings of HSC (a total of 3.5 deg$^2$). Here we describe the instrument, the science goals of the survey, and the survey strategy and data processing. This paper serves as an introduction to a special issue of the Publications of the Astronomical Society of Japan, which includes a large number of technical and scientific papers describing results from the early phases of this survey.

astro-ph.IM↗

arXiv2017

Thermodynamic evidence for nematic phase transition at the onset of pseudogap in YBa$_2$Cu$_3$O$_y$

A central issue in the quest to understand the superconductivity in cuprates is the nature and origin of the pseudogap state, which harbours anomalous electronic states such as Fermi arc, charge density wave (CDW), and $d$-wave superconductivity. A fundamentally important, but long-standing controversial problem has been whether the pseudogap state is a distinct thermodynamic phase characterized by broken symmetries below the onset temperature $T^*$. Electronic nematicity, a fourfold ($C_4$) rotational symmetry breaking, has emerged as a key feature inside the pseudogap regime, but the presence or absence of a nematic phase transition and its relationship to the pseudogap remain unresolved. Here we report thermodynamic measurements of magnetic torque in the underdoped regime of orthorhombic YBa$_2$Cu$_3$O$_y$ with a field rotating in the CuO$_2$ plane, which allow us to quantify magnetic anisotropy with exceptionally high precision. Upon entering the pseudogap regime, the in-plane anisotropy of magnetic susceptibility increases after exhibiting a distinct kink at $T^*$. Our doping dependence analysis reveals that this anisotropy is preserved below $T^*$ even in the limit where the effect of orthorhombicity is eliminated. In addition, the excess in-plane anisotropy data show a remarkable scaling behaviour with respect to $T/T^*$ in a wide doping range. These results provide thermodynamic evidence that the pseudogap onset is associated with a second-order nematic phase transition, which is distinct from the CDW transition that accompanies translational symmetry breaking. This suggests that nematic fluctuations near the pseudogap phase boundary have a potential link to the strange metallic behaviour in the normal state, out of which high-$T_c$ superconductivity emerges.

cond-mat.supr-con↗

arXiv2015

7Be Solar Neutrino Measurement with KamLAND

We report a measurement of the neutrino-electron elastic scattering rate of 862 keV 7Be solar neutrinos based on a 165.4 kton-day exposure of KamLAND. The observed rate is 582 +/- 90 (kton-day)^-1, which corresponds to a 862 keV 7Be solar neutrino flux of (3.26 +/- 0.50) x 10^9 cm^-2s^-1, assuming a pure electron flavor flux. Comparing this flux with the standard solar model prediction and further assuming three flavor mixing, a nu_e survival probability of 0.66 +/- 0.14 is determined from the KamLAND data. Utilizing a global three flavor oscillation analysis, we obtain a total 7Be solar neutrino flux of (5.82 +/- 0.98) x 10^9 cm^-2s^-1, which is consistent with the standard solar model predictions.

hep-ex↗

arXiv2015

A compact ultra-clean system for deploying radioactive sources inside the KamLAND detector

We describe a compact, ultra-clean device used to deploy radioactive sources along the vertical axis of the KamLAND liquid-scintillator neutrino detector for purposes of calibration. The device worked by paying out and reeling in precise lengths of a hanging, small-gauge wire rope (cable); an assortment of interchangeable radioactive sources could be attached to a weight at the end of the cable. All components exposed to the radiopure liquid scintillator were made of chemically compatible UHV-cleaned materials, primarily stainless steel, in order to avoid contaminating or degrading the scintillator. To prevent radon intrusion, the apparatus was enclosed in a hermetically sealed housing inside a glove box, and both volumes were regularly flushed with purified nitrogen gas. An infrared camera attached to the side of the housing permitted real-time visual monitoring of the cable's motion, and the system was controlled via a graphical user interface.

physics.ins-det↗

arXiv2011

Measurement of the 8B Solar Neutrino Flux with the KamLAND Liquid Scintillator Detector

We report a measurement of the neutrino-electron elastic scattering rate from 8B solar neutrinos based on a 123 kton-day exposure of KamLAND. The background-subtracted electron recoil rate, above a 5.5 MeV analysis threshold is 1.49+/-0.14(stat)+/-0.17(syst) events per kton-day. Interpreted as due to a pure electron flavor flux with a 8B neutrino spectrum, this corresponds to a spectrum integrated flux of 2.77+/-0.26(stat)+/-0.32(syst) x 10^6 cm^-2s^-1. The analysis threshold is driven by 208Tl present in the liquid scintillator, and the main source of systematic uncertainty is due to background from cosmogenic 11Be. The measured rate is consistent with existing measurements and with Standard Solar Model predictions which include matter enhanced neutrino oscillation.

hep-ex↗

arXiv2009

B -> K pi Puzzle and New Sources of CP Violation in Supersymmetry

The difference between the CP asymmetries of the $B^0 \to K^+ π^-$ and $B^+ \to K^+ π^0$ decays has been recently confirmed with an evidence larger than $5σ$'s. We discuss it as a possible signal of new physics associated with new (large) CP violation in the electroweak penguin contributions. We propose a supersymmetry breaking scheme where such new sources of CP violation occur in the flavor non-universal trilinear scalar couplings.

hep-ph↗

arXiv2007

Quark mass uncertainties revive KSVZ axion dark matter

The Kaplan-Manohar ambiguity in light quark masses allows for a larger uncertainty in the ratio of up to down quark masses than naive estimates from the chiral Lagrangian would indicate. We show that it allows for a relaxation of experimental bounds on the QCD axion, specifically KSVZ axions in the $2-3 μ$eV mass range composing 100% of the galactic dark matter halo can evade the experimental limits placed by the ADMX collaboration.

hep-ph↗

arXiv2006

How can we test seesaw experimentally?

The seesaw mechanism for the small neutrino mass has been a popular paradigm, yet it has been believed that there is no way to test it experimentally. We present a conceivable outcome from future experiments that would convince us of the seesaw mechanism. It would involve a variety of data from LHC, ILC, cosmology, underground, and low-energy flavor violation experiments to establish the case.

hep-ph↗

arXiv2005

Theory of Neutrinos: A White Paper

During 2004, four divisions of the American Physical Society commissioned a study of neutrino physics to take stock of where the field is at the moment and where it is going in the near and far future. Several working groups looked at various aspects of this vast field. The summary was published as a main report entitled ``The Neutrino Matrix'' accompanied by short 50 page versions of the report of each working group. Theoretical research in this field has been quite extensive and touches many areas and the short 50 page report provided only a brief summary and overview of few of the important points. The theory discussion group felt that it may be of value to the community to publish the entire study as a white paper and the result is the current article. After a brief overview of the present knowledge of neutrino masses and mixing and some popular ways to probe the new physics implied by recent data, the white paper summarizes what can be learned about physics beyond the Standard Model from the various proposed neutrino experiments. It also comments on the impact of the experiments on our understanding of the origin of the matter-antimatter asymmetry of the Universe and the basic nature of neutrino interactions as well as the existence of possible additional neutrinos. Extensive references to original literature are provided.

hep-ph↗

arXiv2004

Theory of Neutrinos

After a brief overview of the present knowledge of neutrino masses and mixing, we summarize what can be learned about physics beyond the standard model from the various proposed neutrino experiments. We also comment on the impact of the experiments on our understanding of the origin of the matter-antimatter asymmetry of the Universe as well as what can be learned from some experiments outside the domain of neutrinos.

hep-ph↗

arXiv2003

Gauge Theories on an Interval: Unitarity without a Higgs

We consider extra dimensional gauge theories on an interval. We first review the derivation of the consistent boundary conditions (BC's) from the action principle. These BC's include choices that give rise to breaking of the gauge symmetries. The boundary conditions could be chosen to coincide with those commonly applied in orbifold theories, but there are many more possibilities. To investigate the nature of gauge symmetry breaking via BC's we calculate the elastic scattering amplitudes for longitudinal gauge bosons. We find that using a consistent set of BC's the terms in these amplitudes that explicitly grow with energy always cancel without having to introduce any additional scalar degree of freedom, but rather by the exchange of Kaluza--Klein (KK) gauge bosons. This suggests that perhaps the SM Higgs could be completely eliminated in favor of some KK towers of gauge fields. We show that from the low-energy effective theory perspective this seems to be indeed possible. We display an extra dimensional toy model, where BC's introduce a symmetry breaking pattern and mass spectrum that resembles that in the standard model.

hep-ph↗

arXiv2003

Signatures of Baryogenesis in the MSSM

We revisit the electroweak baryogenesis within the context of the minimal supersymmetric standard model (MSSM), studying its potential collider signatures. We find that this mechanism of baryogenesis does not give a new CP violating signal at the $B$-factories. The first circumstantial evidence may come from enhanced $B_s$ or $B_d$ mixing. If a light right-handed scalar top and Higgs are found as required, a linear collider represents the best possibility for confirming the scenario.

hep-ph↗

arXiv2002

Preheating in Supersymmetric Theories

We examine the particle production via preheating at the end of inflation in supersymmetric theories. The inflaton and matter scalars are now necessarily complex fields, and their relevant interactions are restricted by holomorphy. In general this leads to major changes both in the inflaton dynamics and in the efficiency of the preheating process. In addition, supersymmetric models generically contain multiple isolated vacua, raising the possibility of non-thermal production of dangerous topological defects. Because of these effects, the success of leptogenesis or WIMPZILLA production via preheating depends much more sensitively on the detailed parameters in the inflaton sector than previously thought.

hep-ph↗

arXiv2002

The Lower Bound on the Neutralino-Nucleon Cross Section

We examine if there is a lower bound on the direct detection cross section for the neutralino dark matter in the MSSM. If we impose the minimal supergravity boundary conditions as well as the "naturalness" condition, in particular m_{1/2} < 300 GeV, we show that there is a lower bound of 10^{-46}cm^2 on the cross section for neutralino scattering off of a proton. We also clarify the origin for the lower bound. Relaxing either of the assumptions, however, can lead to much smaller cross sections.

hep-ph↗

arXiv2001

Dial M for Flavor Symmetry Breaking

We introduce a realization of Seiberg duality in MQCD that does not involve moving branes. Using related arguments in M Theory and IIA, we investigate the flavor symmetry breaking via flavored magnetic monopole condensation of hep-th/0005076. We verify our results by considering visualizations of M5 branes corresponding to $\N=2$ vacua which survive soft breaking by an adjoint mass term.

hep-th↗

arXiv2000

Energy Spectra of Reactor Neutrinos at KamLAND

The upcoming reactor neutrino experiment, KamLAND, has the ability to explore the Large Mixing Angle (LMA) solution to the solar neutrino problem. Here, we investigate the precision to which KamLAND should be able to measure these parameters, utilizing the distortion of the energy spectrum of reactor neutrinos. Incomplete knowledge of the fuel composition of the reactors will lead to some error on this measurement. We estimate the size of this effect.

hep-ph↗

arXiv2000

Physics at a Neutrino Factory

In response to the growing interest in building a Neutrino Factory to produce high intensity beams of electron- and muon-neutrinos and antineutrinos, in October 1999 the Fermilab Directorate initiated two six-month studies. The first study, organized by N. Holtkamp and D. Finley, was to investigate the technical feasibility of an intense neutrino source based on a muon storage ring. This design study has produced a report in which the basic conclusion is that a Neutrino Factory is technically feasible, although it requires an aggressive R&D program. The second study, which is the subject of this report, was to explore the physics potential of a Neutrino Factory as a function of the muon beam energy and intensity, and for oscillation physics, the potential as a function of baseline.

hep-ex↗

arXiv1999

The Small Observed Baryon Asymmetry from a Large Lepton Asymmetry

Primordial Big-Bang Nucleosynthesis (BBN) tightly constrains the existence of any additional relativistic degrees of freedom at that epoch. However a large asymmetry in electron neutrino number shifts the chemical equilibrium between the neutron and proton at neutron freeze-out and allows such additional particle species. Moreover, the BBN itself may also prefer such an asymmetry to reconcile predicted element abundances and observations. However, such a large asymmetry appears to be in conflict with the observed small baryon asymmetry if they are in sphaleron mediated equilibrium. In this paper we point out the surprising fact that in the Standard Model, if the asymmetries in the electron number and the muon number are equal (and opposite) and of the size required to reconcile BBN theory with observations, a baryon asymmetry of the Universe of the correct magnitude and sign is automatically generated within a factor of two. This small remaining discrepancy is naturally remedied in the supersymmetric Standard Model.

hep-ph↗