119236332
The leptonic Higgs as a messenger of dark matter
We propose that the leptonic cosmic ray signals seen by PAMELA and ATIC result from the annihilation or decay of dark matter particles via states of a leptonic Higgs doublet to τ leptons, linking cosmic ray signals of dark matter to LHC signals of the Higgs sector. The states of the leptonic Higgs doublet are lighter than about 200 GeV, yielding large τ and ττ event rates at the LHC. Simple models are given for the dark matter particle and its interactions with the leptonic Higgs, for cosmic ray signals arising from both annihilations and decays in the galactic halo. For the case of annihilations, cosmic photon and neutrino signals are on the verge of discovery.
119200117
The Higgs as a probe of supersymmetric extra sectors
A bstractWe present a general method for calculating the leading contributions to h0 → gg and h0 → γγ in models where the Higgs weakly mixes with a nearly supersymmetric extra sector. Such mixing terms can play an important role in raising the Higgs mass relative to the value expected in the MSSM. Our method applies even when the extra sector is strongly coupled, and moreover does not require a microscopic Lagrangian description. Using constraints from holomorphy we fix the leading parametric form of the contributions to these Higgs processes, including the Higgs mixing angle dependence, up to an overall coefficient. Moreover, when the Higgs is the sole source of mass for a superconformal sector, we show that even this coefficient is often calculable. For appropriate mixing angles, the contribution of the extra states to h0 → gg and h0 → γγ can vanish. We also discuss how current experimental limits already lead to non-trivial constraints on such models. Finally, we provide examples of extra sectors which satisfy the requirements necessary to use the holomorphic approximation.
119028722
Origins of hidden sector dark matter I: cosmology
We present a systematic cosmological study of a universe in which the visible sector is coupled, albeit very weakly, to a hidden sector comprised of its own set of particles and interactions. Assuming that dark matter (DM) resides in the hidden sector and is charged under a stabilizing symmetry shared by both sectors, we determine all possible origins of weak-scale DM allowed within this broad framework. We show that DM can arise only through a handful of mechanisms, lending particular focus to Freeze-Out and Decay and Freeze-In, as well as their variations involving late time re-annihilations of DM and DM particle anti-particle asymmetries. Much like standard Freeze-Out, where the abundance of DM depends only on the annihilation cross-section of the DM particle, these mechanisms depend only on a very small subset of physical parameters, many of which may be measured directly at the LHC. In particular, we show that each DM production mechanism is associated with a distinctive window in lifetimes and cross-sections for particles which may be produced in the near future. We evaluate prospects for employing the LHC to definitively reconstruct the origin of DM in a companion paper.
53143827
OPE methods for the holomorphic Higgs portal
A bstractWe develop a systematic and general approach to study the effective Higgs Lagrangian in a supersymmetric framework in which the Higgs fields in the visible sector couple weakly to another sector. The extra sector may be strongly coupled in general. It is assumed to be superconformal in the ultraviolet, but develop a mass-gap with supersymmetry breaking in the infrared. The main technique used in our approach is that of the operator product expansion (OPE). By using OPE methods we are able to compute the parameters in the Higgs Lagrangian to quadratic order and make general statements that are applicable to many classes of models. Not only does this approach allow us to understand the traditional problems plaguing simple models from a different perspective, it also reveals new possibilities for solutions of these problems. The methods and results of our work should be useful in constructing a viable and natural model of physics beyond the Standard Model.
118571038
Unravelling strings at the CERN LHC
We construct LHC signature footprints for four semirealistic string/M theory vacua with a minimal supersymmetric standard model visible sector. We find that they all give rise to limited regions in LHC signature space and are qualitatively different from each other for understandable reasons. We also propose a technique in which correlations of LHC signatures can be effectively used to distinguish among these string theory vacua. We expect the technique to be useful for more general string vacua. We argue that further systematic analysis with this approach will allow LHC data to disfavor or exclude major 'corners' of string/M theory and favor others. The technique can be used with limited integrated luminosity and improved.
55061398
LHC string phenomenology
We argue that it is possible to address the deeper LHC inverse problem, to gain insight into the underlying theory from LHC signatures of new physics. We propose a technique which may allow us to distinguish among, and favor or disfavor, various classes of underlying theoretical constructions using (assumed) new physics signals at the LHC. We think that this can be done with limited data (5–10 fb−1), and improved with more data. This is because of two reasons: (a) it is possible in many cases to reliably go from (semi)realistic microscopic string constructions to the space of experimental observables, say, LHC signatures, and (b) the patterns of signatures at the LHC are sensitive to the structure of the underlying theoretical constructions. We illustrate our approach by analyzing two promising classes of string compactifications along with six other string-motivated constructions. Even though these constructions are not complete, they illustrate the point we want to emphasize. We think that using this technique effectively over time can eventually help us to meaningfully connect experimental data to microscopic theory.
17996907
Tidal Spin-up of Stars in Dense Stellar Cusps around Massive Black Holes
We show that main-sequence stars in dense stellar cusps around massive black holes are likely to rotate at a significant fraction of the centrifugal breakup velocity as a result of spin-up by hyperbolic tidal encounters. We use realistic stellar structure models to calculate analytically the tidal spin-up in soft encounters and extend these results to close and penetrating collisions using smoothed particle hydrodynamics simulations. We find that the spin-up effect falls off only slowly with distance from the black hole because the increased tidal coupling in slower collisions at larger distances compensates for the decrease in the stellar density. We apply our results to the stars near the massive black hole in the Galactic center. Over their lifetime, ~1 M☉ main-sequence stars in the inner 0.3 pc of the Galactic center are spun-up on average to ~10%-30% of the centrifugal breakup limit. Such rotation is ~20-60 times higher than is usual for such stars and may affect their subsequent evolution and their observed properties.
18521155
H I observations of two molecular clouds with extremely large velocity dispersions
We have mapped two molecular clouds at (i, b) = (3.2°, + 0.3°) and (i, b) = (5.4°, - OS) in 21-cm line and continuum emission. These clouds show unusually large velocity dispersions of more than 100 km s -1 (FWHM) which has also been seen in 12CO, 13CO and CS emissions. This dispersion is approximately an order of magnitude larger compared with giant molecular clouds. From our H I observations we estimate that the atomic mass of the cloud at i = 3.2° is about 1.5 x 105 Mo and the mass of the cloud at i = 5.4° is 7 x 104 Mo. The ratio of total molecular mass to atomic mass for these clouds appears to be normal for clouds near the Galactic Centre. The main peculiar feature of these clouds is their abnormally large velocity dispersion; the extent in velocity is from about 0 [local standard of rest (LSR)] to 200 km S-I. These clouds are connected, in the i-v plane, to high-velocity ridges that extend over several degrees of longitude. These properties, we believe, provide important clues to the physical process responsible for their large velocity dispersion.
16795402
Dissipation of a Tide in a Differentially Rotating Star
The orbital period of the binary pulsar PSR J0045-7319, which is located in our neighboring galaxy, the Small Magellanic Cloud (SMC), appears to be decreasing on a timescale of ~5 × 105 yr. This timescale is more than 2 orders of magnitude smaller than what is expected from the standard theory of tidal dissipation. Kumar & Quataert proposed that this rapid evolution could be understood provided that the neutron star's companion, a main-sequence B star, has set up significant differential rotation. The goal of this paper is to evaluate the redistribution of angular momentum in the B star due to meridional circulation and shear stresses and to calculate the evolution of the rotation profile when these two processes act in competition with the deposition of momentum by the tidal wave. We find that although angular momentum redistribution is important, the B star may continue to have sufficient differential rotation so that tidal waves are entirely absorbed as they arrive at the surface. The mechanism proposed by Kumar & Quataert to speed up the orbital evolution of the SMC binary pulsar should therefore work as suggested.
15590758
Fundamental Physical Parameters of Collimated Gamma-Ray Burst Afterglows
We determine the basic physical characteristics of eight gamma-ray bursts (GRBs)—980519, 990123, 990510, 991208, 991216, 000301c, 000926, and 010222—by modeling the broadband emission of their afterglows. We find that the burst kinetic energies after the GRB phase are well clustered around a mean value of 3 × 1050 ergs. In contrast, the energy release in gamma rays, after correcting for a collimated explosion, varies among bursts by more than an order of magnitude. The initial jet apertures are in the 2°-14° range, mildly correlated with the energy, with half of the jets being narrower than ~3°. This implies that, within 100 Mpc, there are about 10 GRB remnants (expanding at ~0.1c) that can be resolved with the Very Long Baseline Array. For all eight afterglows, the total energy in the shock-accelerated electrons is close to the equipartition with protons. However, the slope of the power-law electron distribution is not universal, varying between 1.4 and 2.8. In at least half of the cases, the density structure of the medium is inconsistent with an r-2 profile. A homogeneous medium with density in the 0.1-50 cm-3 range can accommodate the broadband emission of all afterglows, with the exception of 990123, for which we find the density to be less than 10-2 cm-3. If GRBs arise from the core collapse of massive stars, then such low densities indicate the existence of superbubbles created by the supernovae and winds within a cluster of massive stars.
18524522
Steepening of Afterglow Decay for Jets Interacting with Stratified Media
We calculate light curves for gamma-ray burst afterglows when material ejected in the explosion is confined to a jet that propagates in a medium with a power-law density profile. The observed light-curve decay steepens by a factor of Γ2 when an observer sees the edge of the jet. In a uniform density medium, the increase in the power-law index (β) of the light curve as a result of this edge effect is ~0.7 and is completed over one decade in observer time. For a preejected stellar wind (ρ ∝ r-2), β increases by ~0.4 over two decades in time as a result of the edge effect, and the steepening of the light curve as a result of the jet sideways expansion takes about four decades in time. Therefore, a break in the light curve for a jet in a wind model is unlikely to be detected even for a very narrow opening angle of a few degrees or less, a case where the lateral expansion occurs at early times when the afterglow is bright. The light curve for the afterglow of GRB 990510, for which an increase in β of approximately 1.35 was observed on a timescale of 3 days, cannot be explained by only the sideways expansion and the edge effects in a jet in a uniform interstellar medium—the increase in β is too large and too rapid. However, the passage of the cooling or synchrotron peak frequencies through the observing band at about 0.1-1 day together with jet edge effect explains the observed data. The jet opening angle is found to be ~5°, and the energy in the explosion to be about 1051 ergs.