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 Colloquium

 Colloquium

 

Dear all, 
It is a pleasure for me to announce that the speaker of the  next colloquium in Ordibehesht is Dr Mehrdad Mirbabayi of IAS, Princeton. More information can be found in the textbox to the right.



Everybody is welcome to attend.


With kind regards,
Y. Farzan

 

Speaker

Dr Mehrdad Mirbabayi

Affliation

IAS, Princeton, USA
Title of talk

Equivalence principle and baryon acoustic peak
«اصل هم‌ارزی و پژواک باریونی»

Date and time

16th of Ordibehesht (6th of May), 4:30 pm

Place

Farmanieh Seminar Room

Abstract

 

In the non-relativistic regime, pertinent to the large scale structure of the Universe, the leading effect of a long-wavelength perturbation on short distance physics is a uniform acceleration. Typically, this has no effect on statistical averages at equal time since a uniform acceleration results in a uniform translation --- a reasoning that has been formalized as a ``consistency condition'' on the cosmological correlation functions. This naive expectation fails in the presence of the baryon acoustic feature if the wavelength of the matter perturbation is shorter than the BAO scale. As a result, there are interesting observable effects in the sky that are fully fixed by the equivalence principle. 
 

 

+ نوشته شده در  یکشنبه ششم اردیبهشت ۱۳۹۴ساعت 14:41  توسط یاسمن فرزان 

arXiv:1504.04371 [pdf, other]

Title: Evidence for Dark Matter Self-Interactions via Collisionless Shocks in  Cluster Mergers
Comments: 5 pages, 1 figure
Subjects: High Energy Physics - Phenomenology (hep-ph)

While dark matter self-interactions may solve several problems with structure formation, so far only the effects of two-body scatterings of dark matter particles have been considered. We show that, if a subdominant component of dark matter is charged under an unbroken $U(1)$ gauge group, collective dark plasma effects need to be taken into account to understand its dynamics. Plasma instabilities can lead to collisionless dark matter shocks in galaxy cluster mergers which might have been already observed in the Abell 3827 and 520 clusters. As a concrete model we propose a thermally produced dark pair plasma of vectorlike fermions. In this scenario the interacting dark matter component is expected to be separated from the stars and the non-interacting dark matter halos in cluster collisions. In addition, the missing satellite problem is softened, while constraints from all other astrophysical and cosmological observations are avoided.

+ نوشته شده در  دوشنبه سی و یکم فروردین ۱۳۹۴ساعت 9:45  توسط یاسمن فرزان 


من و دکتر جباری هر دو امسال قصد دانشجو گرفتن داریم. اگر می خواهید با ما کار کنید در فرم های انتخاب رشته همان گرایش فیزیک ذرات را انتخاب کنید

 

 

پی نوشت: کد 2916
را انتخاب کنید.

+ نوشته شده در  یکشنبه سی ام فروردین ۱۳۹۴ساعت 19:37  توسط یاسمن فرزان  | 

arXiv:1504.04276 (cross-list from astro-ph.HE) [pdf, other]
AMS-02 antiprotons, at last! Secondary astrophysical component and immediate implications for Dark Matter
Comments: 12 pages, 5 figures
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE); High Energy Physics - Phenomenology (hep-ph)

Using the updated proton and helium fluxes just released by the AMS-02 experiment we reevaluate the secondary astrophysical antiproton to proton ratio and its uncertainties, and compare it with the ratio preliminarly reported by AMS-02. We find no unambiguous evidence for a significant excess with respect to expectations. Yet, some preference for thicker halos and a flatter energy dependence of the diffusion coefficient starts to emerge. Also, we provide an assessment of the room left for exotic components such as Galactic Dark Matter annihilation or decay, deriving new stringent constraints.

+ نوشته شده در  شنبه بیست و نهم فروردین ۱۳۹۴ساعت 9:58  توسط یاسمن فرزان 

arXiv:1504.03388 (cross-list from astro-ph.CO) [pdf, other]

Title: The behaviour of dark matter associated with 4 bright cluster galaxies  in the 10kpc core of Abell 3827
Authors: Richard Massey (Durham),  Liliya Williams (Minnesota),  Renske Smit (Durham),  Mark Swinbank (Durham),  Thomas Kitching (MSSL),  David Harvey (EPFL),  Mathilde Jauzac (Durham),  Holger Israel (Durham),  Douglas Clowe (Ohio),  Alastair Edge (Durham),  Matt Hilton (ACRU),  Eric Jullo (LAM),  Adrienne Leonard (UCL),  Jori Liesenborgs (Hasselt),  Julian Merten (JPL),  Irshad Mohammed (Zurich),  Daisuke Nagai (Yale),  Johan Richard (Lyon),  Andrew Robertson (Durham),  Prasenjit Saha (Zurich),  Rebecca Santana (Ohio),  John Stott (Durham),  Eric Tittley (Edinburgh)
Comments: 15 pages, 9 figures
Subjects: Cosmology and Nongalactic Astrophysics (astro-ph.CO); Astrophysics of Galaxies (astro-ph.GA); High Energy Physics - Phenomenology (hep-ph)

Galaxy cluster Abell 3827 hosts the stellar remnants of four almost equally bright elliptical galaxies within a core of radius 10kpc. Such corrugation of the stellar distribution is very rare, and suggests recent formation by several simultaneous mergers. We map the distribution of associated dark matter, using new Hubble Space Telescope imaging and VLT/MUSE integral field spectroscopy of a gravitationally lensed system threaded through the cluster core. We find that each of the central galaxies retains a dark matter halo, but that (at least) one of these is spatially offset from its stars. The best-constrained offset is 1.62+/-0.48kpc, where the 68% confidence limit includes both statistical error and systematic biases in mass modelling. Such offsets are not seen in field galaxies, but are predicted during the long infall to a cluster, if dark matter self-interactions generate an extra drag force. With such a small physical separation, it is difficult to definitively rule out astrophysical effects operating exclusively in dense cluster core environments - but if interpreted solely as evidence for self-interacting dark matter, this offset implies a cross-section sigma/m=(1.7+/-0.7)x10^{-4}cm^2/g x (t/10^9yrs)^{-2}, where t is the infall duration.

+ نوشته شده در  چهارشنبه بیست و ششم فروردین ۱۳۹۴ساعت 10:49  توسط یاسمن فرزان 


فایل صوتی سخنرانی آقای دکتر زارع در مورد زلزله

اسلاید های سخنرانی

فیلم سخنرانی هم آماده هست. اگر علاقه مند باشید می توانید دی-وی-دی آن را از دفتر پژوهشکده تهیه کنید.

مطلب زیر را من  از سایت "نشنال جیوگرافی" کپی می کنم:

How Your Phone Could Save You From an Impending Earthquake

A new study says cell phones could give you enough time to get to safety.

 

 

The epicenter of a major earthquake is someplace you really don’t want to be. Not only does the shaking tend to be most violent there, but there’s also no time to look for shelter. Even a few seconds of warning can make the difference between life and death. And now, scientists say, there's an app for that.  

Writing in the journal Science Advances, Sarah Minson of the U.S. Geological Survey (USGS) and California Institute of Technology and several colleagues claim that plain old smartphones can detect quakes, pinpoint their location, and calculate when the shaking will arrive.

The USGS is spending tens of millions of dollars developing an early warning system called ShakeAlert that will use texts and emails to alert people that a quake has just let loose.

But some earthquake-prone nations—in Central and South America, for example, or the Caribbean, or south Asia—don’t have tens of millions of dollars to spare, or networks of seismographs. That’s why Minson and the USGS Earthquake Hazards Program are working on a much cheaper alternative. “This is a really clever idea that leverages an existing resource," says Kristine Larson, a University of Colorado aerospace engineer who studies how GPS systems can be useful in the earth sciences. Larson wasn’t involved in this research.

Smartphones could be ideal for rapid earthquake warning, Minson and her colleagues realized, because they have built-in GPS sensors and accelerometers, which detect movement. That's how they know where they are at all times, and when they’re being shaken. Phones closer to the epicenter will start shaking first, followed by phones a little farther away, so the timing and the intensity—which drops off with distance—allows the system to calculate where and how powerful the quake is.

The phones are also part of a pre-existing data network, so it’s trivially easy to program them to send news of a quake to a central location, where the data are merged to form an overall picture of the unfolding disaster. And that same network can blast an alert out to anyone in the danger zone.

The phone signals and processing happen at nearly light speed, but it’s reasonable to wonder if even that is fast enough. If your phone is already shaking, it’s arguably too late to do anything about it.

With even a few seconds of warning, you can get under your desk, or pull your car off the road.

But in fact, says Minson, an earthquake creates two distinct types of waves through the solid earth. “The damaging shaking comes from S waves,” she says, which shake the ground back and forth. A quake also sends out P waves, which simply compress the earth in front of them as they go—and, says Minson, “P waves travel faster, so they get to you first. It’s like the midnight ride of Paul Revere,” she says. “He began riding after the British landed, but he was far enough ahead of them to warn people.”

   

When Seconds Matter

It’s the P waves that earthquake early warning systems pick up on, and while the dangerous S waves can arrive very quickly afterward, that can be enough time to take action. “With even a few seconds of warning,” says Minson, “you can get under your desk, or pull your car off the road. If you’re a surgeon,” she says, alluding to a scenario with particularly gruesome potential, “it’s long enough to retract your scalpel and step away from the patient.” It’s also long enough for subways and other trains to be brought to a halt and elevators to be stopped at, rather than between, floors.

The authors of the new report tested the idea with two simulations—a hypothetical magnitude-7 quake on California’s Hayward Fault, in the Bay Area, and another based on the devastating magnitude-9 quake that struck off the shore of Japan in 2011, triggering a killer tsunami. The simulations show that a system relying on just two-tenths of a percent of smartphone users could pinpoint the strength and location of a quake within just five seconds.

“In an ideal world,” says Minson, “we would test the system with actual phones and actual earthquakes.” And in fact, that’s already in process: A pilot program funded by the U.S. Agency for International Development should be in place within the year to do just that.

There are a few potential pitfalls, observes John Vidale, a seismologist at the University of Washington who wasn’t involved in this project. “A system like this would not necessarily be free of false alarms,” he says, “nor immune to pranksters or worse who wanted to cause turmoil from malicious hoaxes.”  

Still, he says, “The idea is creative and sound, and we could see crude versions of such apps very soon

+ نوشته شده در  یکشنبه بیست و سوم فروردین ۱۳۹۴ساعت 19:9  توسط یاسمن فرزان  | 

در آخر شهریور و اول مهر سال آینده همایش بین المللی دیگری روی موضوع فیزیک نوترینو ماده تاریک و فیزیک-بی در پژوهشکده فیزیک برگزار خواهیم کرد. فرم ثبت نام و اطلاعات بیشتر در این سایت قابل دسترس هست.

سال نو پیشاپیش مبارک باد!

+ نوشته شده در  چهارشنبه بیست و هفتم اسفند ۱۳۹۳ساعت 15:43  توسط یاسمن فرزان 

 

خواستم یادآوری کنم سال آینده من و شاهین دانشجو دکتری می گیریم. دقت کنید که نام پژوهشکده ما "پژوهشکده فیزیک" هست نه چیز دیگر. در انتخاب دقت لازم را مبذول نمایید.  در زیر اطلاعیه رسمی را می بینید:

 

 

پژوهشکده فیزیک در سال تحصیلی 95-94 از طریق آزمون سراسری ورودی دکتری در گرایش‌هایی که پژوهشکده در آن فعال است دانشجو می‌پذیرد. این گرایش‌ها عبارتند از فیزیک ذرات (پدیده‌شناسی و فیزیک انرژی‌های بالا- شاخه نظری)  و فیزیک محاسباتی (فیزیک ماده چگال، ماده نرم و آماری). اطلاعات مربوط به جزئیات سایر مراحل انتخاب و پذیرش دانشجو شامل امتحان و مصاحبه در پژوهشگاه پس از مرحله اول آزمون سراسری متعاقباً اعلام خواهد شد.  لازم به ذکر است متقاضیانی که مطابق ضوابط وزارتی مشمول استفاده از سهمیه استعدادهای درخشان می‌شوند، برای پذیرش باید در امتحان و مصاحبه ورودی پژوهشگاه نیز شرکت نمایند.

+ نوشته شده در  یکشنبه بیست و چهارم اسفند ۱۳۹۳ساعت 12:29  توسط یاسمن فرزان 

 Colloquium

 Colloquium  

Dear all,  It is an honor for me to announce that the speaker of the  next colloquium in Farvardin is Prof. Mehdi Zare of IIEES, Tehran. More information can be found in the textbox to the right.

Everybody is welcome to attend.

Happy new year for you and your family! With kind regards, Y. Farzan

 

Speaker

Prof. Mehdi Zare

Affliation

IIEES, Tehran پژوهشگاه بين المللي زلزله شناسي و مهندسي زلزله

Title of talk

An Overview on Earthquake Risk in Tehran Based on Recent Assessments نگاهي به ريسك زلزله در تهران

Date and time

19 Farvardin 1394 (8th April 2015), 4:30 pm

Place

Farmanieh Seminar Room

Abstract

 

 

The seismicity of the region of Tehran might be described on the reported  and recorded earthquakes during the history in this region. Very  recently, we could find some active trends in the region which their activity relate to eastern part of the region especially the North Tehran, Parchin,  Pishva, Mosha and the Garmsar faults. Also, we observed strong  historical earthquakes in this zone. Historical earthquakes showed that  the east of Tehran is more active than the west.  Released seismic  energy map of the region showed the main active zones with high energy  values for microearhquakes data in the east of the region.

The urbanization of Tehran is concentrated on the active fault zones  specially during the last 50 years; such that actually more that 3  million people are living in such dangerous active zones in the south  and north of Tehran. On the other hand, there is an assessment of 10.5  million people living in Tehran and Karaj and their suburbs (a total of  16.2 million population estimated to live in this region in January 2015)  in higher seismic vulnerable zones. We will keep in mind that there a  seismic gap along the major faults passing the urbanized areas of Tehran at least during the last 3000 years, which might be representative at  least for one major earthquake in the future (i.e. M6.5-M7.5). Such  major event might be a major threat for the security of the Capital of  the country. 

 

+ نوشته شده در  شنبه بیست و سوم اسفند ۱۳۹۳ساعت 15:32  توسط یاسمن فرزان 

arXiv:1503.02183 [pdf, other]
Oscillations of the $^7$Be solar neutrinos inside the Earth
Comments: 14 pages, 6 figures, LaTeX
Subjects: High Energy Physics - Phenomenology (hep-ph)

We explore in detail oscillations of the solar $^7$Be neutrinos in the matter of the Earth. The depth of oscillations is about $(0.1 - 0.2)\%$ and the length $\approx 30$ km. The period of the oscillatory modulations in the energy scale is comparable with the width of the line determined by the temperature in the center of the Sun. The latter means that depending on the length of trajectory (nadir angle) one obtains different degree of averaging of oscillations. Exploring these oscillations it is possible to measure the width of the $^7$Be line and therefore the temperature of the Sun, determine precisely $\Delta m^2_{21}$, perform tomography of the Earth, in particular, measure the deviation of its form from sphere, and detect small structures. Studies of the Be neutrinos open up a possibility to test quantum mechanics of neutrino oscillations and search for the sterile neutrinos. Accuracy of these measurements with future scintillator (or scintillator uploaded) detectors of the $\sim 100$ kton mass scale is estimated.

+ نوشته شده در  سه شنبه نوزدهم اسفند ۱۳۹۳ساعت 11:16  توسط یاسمن فرزان 

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