Can Xbox One pause live TV without a DVR box?

It can if you use the Xbox One TV Tuner that will be released in Europe in October. It is a USB cable with a DVT-T2/DVB-C tuner on the end that plugs into an OTA aerial with a coaxial socket. The XBO will dedicate 4GB of HDD space for pausing/rewinding live TV but it will not record. It costs 24GBP and will only be usable in territories that use DVB which does not include the US.

www.xbox.com/en-gb/xbox-one/accessories/digital-tv-tuner

The Xbox One is just serving as a pass-through device for your video signal. While it may do some minor processing, such as process information related to the One Guide, it does not store the content in any way.

The One works in conjunction with your existing devices, such as the cable box, tuner, etc, to provide you with your video signal. All buffering and storing happens on said devices.

The One uses two modes to pilot your devices. It uses the Kinect's IR Blaster to control your existing devices. So to answer your question, if your device supports a function that the One can pilot by emulating a remote's IR signal, you can use the functionality from your One.

I live in the U.S. and yes, the Xbox One will pause live tv.

I have a Winegard outdoor antenna hooked up to the Xbox One antenna adapter, and I have had this setup for about 2 years now.

I can pause live tv that I get over the antenna, and it let me pause for 30 minutes. You can also fast forward and rewind during the 30 minutes of recorded video. It is NOT a DVR, so you can't keep the recordings, but it will pause, rewind, and fast forward during that period, which is very nice for watching live sports over-the-air.

While antenna and adapter cost a bit up front, I have found this to be the cheapest way to view live sports and local channels without a cable subscription.

At one time Microsoft had promised full DVR features and extended recording time, but I have not heard any news on those in a while.